"If it measures good and sounds bad, it is bad.
If it sounds good and measures bad, you've measured the wrong thing."


view:  full / summary

Coming Next...

Posted by Amine Slimani on December 31, 2014 at 1:55 AM Comments comments (6)

Reviews coming next: Sennheiser HD800 with Whiplash Audio Twau Reference cable, Triangle Antal EX speakers, and Artisan Twin Line Pure Silver USB Cable.

Building a reference system - Part 2: Glenn's headphone amplifier

Posted by Amine Slimani on October 21, 2014 at 2:25 PM Comments comments (2)


The story of Glenn’s OTL headphone amplifier started as that of a relentless endeavor to make the ALO recabled Beyer T1s sound as good as it was possible, and ended up being that of finding the center piece of my system that will probably outlast many other major components.

At the time of the purchase of Glenn’s amplifier, I have had the Beyer T1s for around 4 years and had mixed results with those headphones. While the Beyer T1s granted me, at times, with the best music I had experienced in my system, it also made me, at other times, want to sell them.

After various listening sessions with the amplifiers I had on hand, I came to a surprising result: the amplifier that sounded the most coherent with the Beyer T1s was the entry level and very affordable tubed OTL Little Dot MKIII. Although the LD MKIII amplifier did not have the resolution nor the extension at the frequency extremes of my solid state Audio-gd C2 amplifier for instance, it just opened up the sound of the Beyer T1s and sounded more natural and dynamic. As a result of those comparisons, I knew that I did not want a better version of the Audio-gd C2 amplifier but that I should look for a (preferably much) better version of the LD MKIII.

Given that I did not have a lot of experience tube amplifiers, I started doing some research around to see what type of tube amplifiers would work best with the Beyer T1s (which were my reference headphones at the time). It was one of those rare occasions where everyone seemed to agree that the Beyer T1s paired very well with OTL headphones. I was not much surprised with this finding as OTL headphone amplifiers tend to have higher than usual output impedance and Beyer’s own A1 amplifier also happens to have an output impedance of 100 ohms.

Once I narrowed down my field of research to the OTL configuration, I was still faced with a lot of choices from well respected manufacturers: Woo Audio, Decware, etc. The choice was not easy to make especially that I could not listen to any of those alternatives before buying. It was at that point when I was advised by rosgr63 to get in touch with Glenn R. who makes custom made amplifiers of his own design.

Rosgr63, a respected member of both tweak-fi and head-fi, has a very large collection of headphone amplifiers and headphones. Some of his equipment includes the reference class Eddie Current Balancing Act, amongst other high-end headphone amplifiers. So when rosgr63 told me than Glenn’s amplifier was on the same level as some of his best amplifiers, I was very intrigued. After doing a little bit of research, mainly on head-fi, I quickly realized that Glenn made some very impressive products. So I took the plunge and started discussions with Glenn.


The amplifier:

After discussing a little bit with Glenn, we settled on a flexible configuration. While the amplifier uses a 6SN7 tube as driver and 3DG4 (or similar tubes such as the 5AW4s) as a rectifier, there is much more possibilities in the output side.

His amplifier can use, as output tubes, any of the following configurations:

- Six 6BL7 tubes

- Six 6SN7 tubes

- Two or four 6AS7 tubes

- Two 6336 tubes

The fact that an amplifier is capable of using 2, 4 or 6 output tubes is not something very common. But it was a very interesting feature that I was excited about.


Internals (while being built) of the amplifier :

Review system:

System 1 – Headphone Based (optimized)

Computer source: HP Pavillon DV6 (Core i7, 8GB, SSD), Windows 8.1, Fidelizer, JRiver Media 17

Transports: Audiophilleo 2, Kingrex UD384, Jkeny’s modified Hiface MK1, Audio-gd Digital Interface (w/ Tentlabs upgrade clock), Teralink X2, Musiland Monitor 01 USD, EMU 0404 USB

DACs: Metrum Octave MKII, Audio-gd DAC-19 DSP with DSP1 V5 upgrade, Kingrex UD384

Amplifiers: Glenn’s OTL headphone amplifier, Audio-gd C2, Little Dot MKIII

Headphones: Sennheiser HD800 with Wiplash Audio TWau Reference cable, Beyerdynamic T1 with ALO Chain Mail cable, Sennheiser HD650 with Artisan Silver Dream upgrade cable

Digital interconnects: Hifi Cables Sobek BNC, OyaideDB-510 BNC, Wireworld Ultraviolet USB, Artisan Twinline Pure Silver USB cables

Analog Interconnects: Artisan Ultimate Silver Dream RCA, Norse Audio custom 8 conductor UP-OCC ACSS, Deep Sounds SPS ACSS, Kimber PBJ RCA


Power filtration: Bada LB-5600 Filter, Essential Audio Tools Noise Eater, Essential Audio Tools Pulse Protector, Supra Mains distributor

Power cords: Hifi Cables & Cie PowertransPlus (x2), Hifi Cable & Cie SimpleTrans, Olflex power cords

Vibration Control: Aktyna ARIS decoupling feet, Maple and Acrylic Platforms, E&T rack, Stabren Damping pads, Sandbox, Brass cones, Vibrapod, Yamamoto Ebony footers and Various Herbie’s Audio Labs tweaks


System 2 – Speaker Based (not fully optimized)

Yamaha CD 600/ Audio-gd DAC19DSP --> Kimber PBJ --> Yamaha AS500 / Populse T150 --> Hifi Cables & Cie Maxitrans II --> Triangle Antal EX floorstanding speakers


Reference tracks used for the review

My (usual) reference tracks:

CD Quality:

Mahler - Symphony n 5- Decca - 16/44

Sol Gabetta - Schostakowitsch Cellokonzert Nr. 2/ Cello - 16/44

Vivaldi – Concerto for 2 violins - Carmignola/ Mullova - 16/44

Natalie Dessay - Italian Opera Arias - Emi Classics -16/44

Puccini - La Boheme - Decca - 16/44

Glenn Gould - The Goldberg Variations (1981) - 16/44

The Essential James Bond - City of Prague Philharmonic orchestra - 16/44

The Dave Brubeck Quartet - Take Five - HDCD - 16/44

Diana Krall - Live in Paris - 16/44

Norah Jones - Come Away With Me - 16/44

Patricia Barber -Companion - 16/44

Johnny Cash – The Essential - 16/44

Soundrama - "The Pulse" Test CD - 16/44


High Resolution quality:

Rachmaninoff Dances -HD Tracks - 24/96

Mozart Violin Concertos - Marianne Thorsen - 2L - 24/96

Dunedin Consort -Messiah - Linn Records - 24/88

Glenn Gould – The Goldberg Variations (1955) – HDTracks - 24/96

Keith Jarrett - Paris/ London - Testament - 24/96

Jazz at the Pawnshop- HD Tracks - 24/88

Alison Krauss and Union Station - Paper Airplane - 24/96

Ella Fitzgerald/ Louis Armstrong - Ella & Louis - 24/96

Diana Krall – From this Moment on - 24/88

Diana Krall – The Girl in the Other Room - 24/96

The World's Greatest Audiophile Vocal Recordings - Chesky - 24/96

The Kinks - One for the Road Live - 24/96

The Eagles - Hotel California - HD Tracks - 24/96

Head-fi/Chesky Sampler - Open Your Ears - 24/96



The set-up:

Burn-in and warm-up:

While Glenn’s amplifier sounded fantastic from the beginning, it took a little more than two hundred hours (I did not clock the exact number) of burn-in before its sound finally stabilized. I also believe that Glenn burned-in the amplifier at his place for around 100 hours. Part of that change might be attributed to the burn-in of NOS tubes. For instance, after around 100 hours of burn-in, the noise floor of the Sylvania 6SN7W was reduced so much as to become inaudible with the Beyer T1s and go easily unnoticed with the slightly more sensitive HD800s. The good thing though is that it can be enjoyed straight of the box and any change that comes after that can be considered as a bonus.


Vibration control:

I have used Glenn’s amplifier, with the Aktyna ARIS footers, on both a marble platform and a 4 inch thick mahogany platform (my previous maple platforms were too small for Glenn’s amplifier). While I did prefer subjectively the mahogany platform, it also had a few (objective) advantages in comparison with the marble platform than no one could argue about.

First, it reduced microphonics in all tubes being used in Glenn’s amplifier. While even a gentle tap on the audio rack would be heard loudly on the headphones when using the marble tile, the thick mahogany platform seemed to isolate the amplifier much more effectively from outside vibrations.

Second, and most surprisingly, switching to the mahogany platform also reduced the very audible hum on the right channel of my Sylvania VT-231 6SN7 driver tube into the barely audible realm. Why and how that was possible was beyond my understanding, especially that the mahogany platform was more effective at reducing the hum of the VT-231 tube than Herbie’s Audio Lab RX tube dampers.

Third, I think that it also reduced the noise floor somehow of the Sylvania 6SN7W. However, I cannot be totally sure about this as the noise floor of my 6SN7W seems to vary depending on how long I have left them warm up and how often I have used them (in my experience, the more often and the longer it is used, the less their noise floor is audible).

Finally, I subjectively preferred the sound of the amplifier sitting on the mahogany platform. It was not a night and day difference with the marble platform, but the sound was a little bit more relaxed and a little bit richer sounding. In the subjective realm, the effect of the mahogany platform was smaller in amplitude than that of Herbie’s tube dampers.

In any case, one should take into account the platform support used beneath the amplifier and probably avoid very hard materials (such as marble, granite, etc.).


Tube rolling:

Output tubes:

Before getting into the heart of the review, I should probably first share my experience with tube rolling; indeed, as Glenn’s amplifier is an OTL amplifier, its sound is highly dependent on the output tubes as there is no transformer or buffer of any sort between the output tubes and the headphones.

In this case, moving from the two-6AS7 to the six-6BL7 configuration as output tubes is not a simple change in flavor. The move is rather similar to a complete change of headphone amplifier as the gain, the output impedance, the voltage swing, the drive capability as well as the flavor of the sound all change from one output configuration to the other.

With the two-6AS7 configuration, the sound of the amplifier reminds of a bigger and more complete version of the Little Dot MKIII. It has a very big soundstage with tons of dynamics capabilities. It is also very smooth and warm sounding. If I were to be listening blind and were told that it was a very upscale version of the LD MKIII, I would not be surprised. It is a very appealing sound, simple to like and very much how I imagined a big OTL tube amplifier would be.

Moving to the six-6BL7s, the sound transforms into completely different, as if it were coming from a different amplifier altogether. In comparison with the 6AS7s, the sound becomes more focused, the soundstage feels at first smaller and tighter (while it is, in reality, deeper and better defined than that of the 6AS7s), the resolution goes up a few notches, and the overall presentation becomes much more extended at the frequency extremes yet it remains refined and delicate at the same time. As a result, I have to admit that it took me quite some time to “get” this sound. With the six-6BL7s, the sound was unlike anything I could have imagined, leaning more towards the solid state gear type of sound but showing qualities I had never heard from solid state gear.

While I was very happy to have 2 different amplifiers in one package, I have to admit that I ended up mainly using the six-6BL7 option as it is the much superior option with the Beyer T1s as well as with the HD800s I bought after getting the amplifier. I was told by Glenn that rolling different brands of 6BL7 tubes will not change dramatically the sound of the amplifier. I have had no way to verify or deny that claim but I should be receiving soon a dozen of 6BL7s (6 GEs and a mix of other brands). In any case, the RCA 6BL7s configuration is so transparent and nice sounding that I doubt I will be finding a ground shaking difference with different brands. I will update this review if there is anything significant to report.

It can be noted that, for the remaining of the review, I will describing the sound of the amplifier with the six-6BL7s, unless stated otherwise.


Driver tubes:

While switching from one output configuration to the other totally transformed the sound of the amplifier, changing the driver tubes had a much smaller effect, in comparison, at least with the three 6SN7 tubes I had on hand: a grey glass RCA 6SN7, a Sylvania VT231 6SN7, and a Sylvania 6SN7W.

With the “stock” grey glass RCA 6SN7 that came with the amplifier, the sound is on the neutral side, with perhaps a slight emphasis on the bass, in comparison with the other two. The highs are perhaps a little less extended and have less “sparkle” than what is the case with the other two tubes. However, one can live happily with it.

With the Sylvania VT231 6SN7, the sound is very good: great timber of voices and instruments, great soundstage and excellent resolution but, in the tube I bought, there was an annoying buzzing (or hum) on the right channel that lessened with time but never totally went away. It is the closest sounding to solid state flavor, with perhaps the driest bass register. I would have been using it more often if it were not for that hum on the right channel.

With the short bottle JAN Sylvania 6SN7W, the sound is simply magical: it is much more refined, richer sounding and delicate than the other two. It also has a much higher resolution (and low level details rendition) than the other two despite having an audible noise floor. I first thought that it was a little bit lighter sounding than the other two until I realized that it was much more linear and quicker in the bass than the other two. With the 6SN7W, the sound is both faster and warmer than the other two tubes. But here, the warmth does not come from fuzziness but rather from the richness of the timber and the infinite variations between similar close sounding frequencies.

It can also be noted that, for the remaining of the review, I will be describing the sound of the amplifier with Sylvania 6SN7W, unless stated otherwise.

As an additional note, I have also ordered a (grade A) Sophia 6SN7 tube but I will probably not receive it before finishing this review. I am not expecting it to necessarily best the Sylvania 6SN7W but I was curious to listen to a (well made) new production tube. I will write a short paragraph once I receive if there is anything interesting to tell about it.


Rectifier tubes:

I tried 3 rectifier tubes on Glenn’s amplifier: a Westinghouse 3DG4, a Zenith 3DG4 and an RCA 5AW4.

I personally didn't like much the sound of the 3DG4 tube (both the Westinghouse and the Zenith tubes). The sound was very upfront and powerful but that sensation came at the expense of the soundstage layering, depth and spaciousness. It was a little bit too forward for my taste and the headphones I tried it with.

The RCA 5AW4 worked better in my configuration, especially in the soundstage department. It seems to my ears that the RCA 5AW4 tube offers the most refined presentation of the three tubes. It is also the tube of reference I will be using for the remaining of the review, unless stated otherwise.

Now that I have shared my experience with tube rolling on Glenn’s OTL amplifier, let us move on to the description of the sound, using the most synergetic combination in my system: the Sylvania 6SN7W as a driver, the RCA 5AW4 as a rectifier and the six RCA 6BL7s as output tubes.



The Sound:

Timber & tonal balance:

The amplifier is very well balanced, from top to bottom, with no particular weakness in any part of the spectrum. While that kind of balance is a basic quality one should expect from any decent sounding amplifier, it is not always the case as some amplifiers tend to highlight or favor one or more the spectrum over the rest of it. Glenn’s OTL amplifier is no such device as it treats every part of the frequency spectrum with the same level of attention.

While I am usually no fan of the bass, mids and high segmentation of sound, as it is too restrictive for high end devices and usually there is no really no real change in the measured frequency response, I will do an exception for Glenn’s OTL amplifier as It will better help understanding the tonal shift in comparison with solid state amplifiers.

When I reviewed the ALO recabled Beyer T1s a few years ago, I found it to be overall finely balanced but felt at the same time that it lacked dynamic heft in the bass, especially in some extreme dynamic passages. Given that I did not have any high-end amplifier at the time to further challenge that observation, I could not point out the culprit. However, now that I have tried the Beyer T1s with Glenn’s OTL amplifier, I believe that the feeling I described could be mainly attributed to the lack of power in the amplifiers I was using at the time.

Switching to Glenn’s OTL amplifier, the Beyer T1s seemed to gain in bass foundation, especially at higher volumes.

I suspected for a while that the relative lightness in the bass (in very specific conditions) was simply a matter of impedance mismatch, and that solid state amplifiers exercised too much grip over the Beyer T1s making the bass sound over-damped. That is why I ordered a 100 ohm adapter from ZX Amateur cables for my Beyer T1s. Using that 100 ohm adapter to artificially increase the single digit output impedance of the Audio-gd C2 amplifier made the balance of the Beyer T1s more natural (in those particular extreme passages), with a more generous bass section, but degraded the overall transparency and did not come close to the overall sound of Glenn’s OTL amplifier.

The bass of Glenn’s amplifier is surprisingly both more generous are more controlled than any solid state or tube amplifier I had tried before it. It is rare when you can get a bass section that gains in strength, depth, definition and richness in comparison to all previous references. But that is what Glenn’s OTL amplifier has granted me with.

While the increase in bass power and control was a welcome addition to the Beyer T1s, it was a necessary addition to appreciate the true capabilities of the Sennheiser HD800s.

When I last listened to the Sennheiser HD800s, just prior to ordering the ALO recabled Beyer T1s, it was at a high end store in Paris. I listened to the HD800s then with a 3D Lab high end CD player and my Audio-gd C2 amplifier (and also with one of their solid state headphone amplifiers). I remember that I did not like the HD800S at all, as I found the bass to be very light and unnatural, as if I were listening to some mini-monitors – I very much preferred, in that configuration, the silver cabled HD650s as well as the various Grados that were available at their store.

Fast forward a few years to the Beyer T1s and Glenn’s OTL amplifier combination. Once I knew that Glenn developed his amplifier with the Sennheiser HD800s, I could not help wondering how they would sound in my system. My reasoning was simple: anyone that could build such a wonderfully balanced amplifier could not have done so on a sub-par headphone. I had to check (again) his reference headphone.

Thus, when I first tried the HD800s with Glenn’s amplifier, I was very pleasantly surprised with the outcome. The bass light headphones I had discarded a few years ago morphed into some almost bass heavy headphones. Between the Beyer T1s, the HD650s and the HD800s, it was the latter that were surprisingly the “bassiest” of the lot with Glenn’s OTL amplifier. That bass boost did not come from uncontrolled or overemphasized mid bass, but from a very powerful, controlled and refined low bass register.

Moreover, Glenn’s amplifier has a very rich, open, pure and transparent mids section, as expected from a tube headphone amplifier. This helps instruments and voices to register as “realistic” sounding in our brains. I believe that while our brains have been trained (or forced) to tune out unwanted distortions in the frequency extremities, our ears and brains are very sensitive to the middle frequencies. Here, Glenn’s amplifier does not disappoint at all.

Finally, Glenn’s amplifier cleared out another misconception I had about tube amplifiers performance in the highest notes. Indeed, one of my fears was that a tube amplifier would not improve upon the already satisfying performance of the class A biased solid state audio-gd C2 amplifier. I had the unfounded fear that a tube amplifier would not have the extension, the sharpness nor speed of what I considered to be a good sounding solid state amplifier. It turned out that Glenn’s OTL amplifier was both more extended, illuminated, refined, as well as faster than the Audio-gd C2 in the top end. Switching from one amplifier to the other is similar to taking the dust off a TV or monitor set. While the lack of vividness might not be noticeable before taking the dust off, it can become very obvious just after taking it off.

In addition to its wonderful tonal balance (between the bass, mids and highs), the key strength of Glenn’s OTL amplifier, in my opinion, is its ability to make difficult to reproduce instruments and voices sound both real and beautiful. Regardless of the instrument or the volume it is being played at, Glenn’s amplifier is able to reproduce the harmonic structure of different sounds with great fidelity and little to no “editorialization”.

As I pointed out in my review of the Metrum Octave MKII, we have reached an age where many (decently built) consumer audio equipment surpasses the quality of most commercial recordings. With Glenn’s OTL amplifier, it is very easy to sense the shift in tonal balance from one recording to the other, from one track to the other. Here, the sound can easily shift from warm sounding to dry sounding, from smooth to edgy just by changing the album or the track.

As a result, it takes (a lot of) time to understand the full spectrum capabilities of Glenn’s amplifier. Quick A/ B comparisons are not the way to go as they only reveal a fraction of the sonic subtleties of the amplifier.

In that regard, the two-6AS7 configuration is easier to like in quick listening sessions, it is very pleasing tonally but ultimately colored. The six-6BL7 configuration is something totally different: it is controlled, precise, extended and powerful as you would expect from solid state amplification, and it is also delicate, refined, sophisticated and natural sounding as you would expect from tube amplification.


Soundstage & Imaging:

It seems that a common strength that many tube amplifiers share is the ability to portray a realistic soundstage, at least a superior and more pleasing soundstage than the one painted by solid state amplifiers. Glenn’s OTL amplifier did not disappoint me in this regard with both output configurations.

With the two-6AS7 tubes, Glenn’s amplifier throws a rather large soundstage. Whether listening through the ALO recabled Beyer T1s or the HD800s, the experience is very close to that of listening to speakers. Regardless of the recording, the two-6AS7 configuration is able to project (outside of the head) an holographic and pleasing soundstage. Once again, it makes me think of a bigger and a better version of the LD MKIII. However, the representation is not beyond reproach. While it is rather big in scale by headphone standards, it lacks absolute specificity in depth layering and imaging. When using the two-6AS7s as output tubes, the sound is very pleasing and easy to listen (soundstage-wise). Also, while the size and the construction changes from one recording to the other with the two-6AS7 configuration; it is nowhere near the chameleon act of the six-6BL7 configuration.


Indeed, with the six-6BL7 tubes, Glenn’s amplifier moves onto new territory and into something I had never experienced before with headphone based listening.

One thing that I regret, now, after listening to Glenn’s amplifier with superior headphones such as the Beyer T1s or the HD800s, is that I wrongfully described, in the past, the sound of previous (solid state) systems as 3D like or holographic sounding.

When an amplifier such the Audio-gd C2 is able to paint to some degree a map of the soundstage where you can locate different performers, a tube amplifier of the caliber of Glenn’s amplifier is able to not only paint a soundstage where you can locate performers but also to portray a soundstage where you can feel different performers playing. One has to make considerably less efforts to visualize the soundstage of the recording.

It is not that there is no soundstaging and imaging information on lesser amplifiers, but it is rather that the listener can just sit, relax and enjoy a very holographic scene without requiring any specific effort when listening to Glenn’s amplifier. Once, one gets used to this effortless representation, it is difficult to come back to lesser equipment that require more (brain) effort to visualize the same thing. As a result, I have to assume that there are perhaps amplifiers out there that outperform Glenn’s OTL amplifier in a similar fashion in the soundstage department given that it is the kind of attributes that require superior equipment to understand the flaws and limitations of lesser equipment. For now, though, all I can report is that Glenn’s amplifier make my other amplifiers sound as if they were mere entry-level toys in the soundstaging department.

So, what makes the soundstaging of Glenn’s amplifier so special? For one, it has a “chameleon” like soundstaging characteristic. The size and the nature of is soundstage is not a fixed quantity but it is highly correlated to whatever is stored in the recording.

In fact, I would go as far as to say that, with the help of superior headphones, Glenn’s amplifier is able to literally transport the listener to the recording venue. Thanks to its superior resolution, the amplifier is able to project sounds in front of the listener, outside of the head, as if performers were just “there”. Moreover, the amplifier is able to retain that realistic placement of sound while retaining a sense of depth and pin-point location on stage. Meanwhile, although everything is painted in high resolution, the sounds located in the rear do not get projected into the foreground.

Hence, the imaging is very stable with regards to location on-stage and with regards to the volume level. Every performer seems to have his or her specific bubble on the soundstage.

To sum up this section, I would say that there is no blending of sounds (for closely located performers) and there is no change in location in loud passages as if various performers were grounded to their location. But, at the same time, when a performer moves across the soundstage (such as in operas), it is very easy to follow his or her movements on-stage, as if he or she were a real person moving in front of the listener.

Dynamics & PRAT:

Given the physical weight of the amplifier and the size of its power supply section, I had no doubt that it would be a very powerful sounding amplifier with sufficient drive and dynamics capability. And, after countless hours of listening, my experience with it proved that assumption right.

During my previous round with headphone amplifiers comparison, I was surprised with the dynamics capabilities of the Little Dot MKIII. After a little bit of research, I realized that OTL amplifiers could swing much higher voltages into higher impedance headphones, such as the 300 ohm-Sennheiser HD800s or the 600 ohm-Beyer T1s, than most solid amplifiers are able to do on the same loads. Thus, that could explain (at least in part) what I was hearing.

In this regard, it was apparent from the very few instants I listened to Glenn’s amplifier that it was the kind of amplifiers that is able to throw a big and dynamic wall of sound. However, and contrary to Little Dot MKIII, its dynamics prowess is not limited to macro-dynamics but extends to the micro-dynamics realm.

Indeed, Glenn’s amplifier, especially in the six-6BL7 configuration, is able to track every variation of sound (no matter how big or small it is) with finesse. I believe that it is thanks to the grip its power reserve exerts on connected headphones.

A surprising test with Glenn’s OTL amplifier is to turn off the amplifier while the music is still playing. The amplifier can play (on its reserves) for around 30 seconds before it mutes totally. For the first 10 to 15 seconds, there is barely any drop in sound level and no noticeable distortion. The power supply section is obviously “overbuilt” for headphone applications.

As a result, this huge power reserve translates into extremely fast (and controlled) transients that make different instruments and voices seem very realistic and alive.

Moreover, in the most demanding tracks, where other amplifiers would have already thrown the towel or have had a hard time keeping up, Glenn’s OTL amplifier can still hit the headphones with a clean and dynamic swing if such a variation in sound is recorded. If one were to make a car analogy, Glenn OTL amplifier would be most similar to a big V8 (the 6.2 naturally aspirated AMG engine is the one that comes to mind) that has a ton of power, responsiveness and control.

With that being said, it should be noted that while the six-6BL7 configuration has the edge in micro-dynamics, I felt as if the two-6AS7 configuration had the edge in terms of macro-dynamics slam and “freedom”.

It is something rather difficult to explain as, objectively, the six-6BL7 configuration seems to track every change in sound level in an impressive manner, unheard of in previous amplifiers. But, subjectively, and especially on short term listening, the two-6AS7 configuration can feel as “freer sounding”. Whether the two-6AS7 configuration is truer to the source or just adding some sort of distortion that makes it feel as being more powerful is a question I cannot answer.

The only definitive observation that I can report, after many months of listening, is that all the tracks that I had listened to prior to Glenn’s amplifier seemed to have gained in dynamics, as if a (dynamic) expander was applied. It is even more obvious on modern and highly (dynamically) compressed music that is very enjoyable to listen to through Glenn’s OTL amplifier.

Keep in mind that all my observations were done with the three headphones I own (HD650, T1 and HD800) that happen to be on the high impedance side. I have no idea how the amplifier would sound on lower impedance headphones be it dynamic ones (Grados, AKGs etc.) or Orthodynamic ones (Audeze, Hifiman, etc.). Though, according to Glenn, they are supposed to benefit from the high drive capability of the 6AS7s and 6336s tubes.

Finally, I would have to say that Glenn’s amplifier have excellent PRAT (Pace, Rhythm and Timing) capabilities. Indeed, besides pure dynamics, the amplifier has speed, pace and timing qualities that really make the music fun to listen to and less homogenized from one recording to the other. However, these qualities are more apparent with the HD800s and Beyer T1s than with the HD650s. In fact, this is perhaps the area where the HD650s trail in comparison with the HD800s and to the Beyer T1s. While the HD650 can scale up very well with better equipment in terms of resolution, details, soundstage, imaging and even dynamics, they do however trail in term of PRaT. The other two headphones just seem faster and able to accelerate or slow down much in a much more effortless and controlled manner.

In any case, the three headphones I tried with Glenn’s amplifier showed increase in dynamics and PRaT in comparison with other amplifiers on hand, and were more enjoyable through a wide range of styles of music.


Transparency & Resolution:

This last section is perhaps the area where I was most surprised with Glenn’s OTL amplifier. While I was expecting somehow that a big tube amplifier will have a correct voicing, a big soundstage and a lot of drive capability (that translate into high dynamics), I was not prepared for an amplifier that was as much transparent (to whatever is playing upstream) and as much detailed as Glenn’s OTL amplifier was. It is simply the highest resolution amplifier I have listened to.

So how much resolution one should expect from Glenn’s OTL amplifier?

First of all, Glenn OTL amplifier digs very deep in the recordings to uncover details that can be missed on other equipments. On some familiar Diana Krall tracks that I had listened to on various systems (including some expensive speaker systems), I heard very clearly new low level details that I have not heard previously in the same manner. Here, details are presented in a way that it is easy to understand what is happening and what instrument or background noise is playing. On a classical piece of music from a Chesky sampler disc, it was very easy to hear the traffic noise outside the recording venue. On La Boheme opera from Puccini, it is very easy to hear people moving on the scene as if they were just close by.

This high resolution rendition translates also into a better and greater separation between different recordings, or sometimes different tracks on the same recording. Listening with Glenn’s OTL amplifier, it is a real pleasure to switch from one recording to another, as the ambiance and feel of the recording totally changes from one album to the other.

While I did find the transparency to the quality of recordings very enjoyable and entertaining as it avoids boredom (or the need to swap equipment to get a “fresh feel”;), I found that its sensitivity to the quality of the upstream equipment was less simple to deal with. Every little thing matters in setting up the system upstream, especially when using the HD800s.

It starts with the software side of the equation: using Fidelizer is very audible, moving from JRiver Media Center to Foobar is very audible, and changing the BNC digital cable between the Audiophilleo 2 and the Metrum Octave MKII DAC is also very audible. These variations in jitter (that should not be audible according to some) are very audible when using Glenn’s OTL amplifier. This is not the first time I have heard differences in the parameters listed above, but it is the first time I have heard those differences with that much clarity. Glenn’s OTL amplifier shows clearly key strengths and weaknesses of every configuration.

So did this high resolution capability translate into an overly analytical sound? Not at all, by reading the previous sections, you will probably understand that Glenn’s amplifier is not some kind of forward sounding and fatiguing solid state amplifier for “monitoring” purposes. The astounding high level of detail rendition comes, in this case, from a high resolution device that can fit whatever sound is playing without adding any objectionable artifact or distortion.

As a result, and despite its exceptional transparency to the recordings and equipments upstream, Glenn OTL amplifier makes the listener focus more on the strengths than on the weaknesses of the recordings. In some ways, it reminds of how the Metrum Octave MKII compares with lesser DACs. But here, the difference is perhaps even larger once the upstream.



Glenn’s OTL amplifier was a wonderful revelation. It is an extremely fast, powerful and detailed sounding amplifier yet it is also a warm, delicate and very refined sounding amplifier. Glenn’s OTL, as far as I am concerned do not exhibit any of the limitations usually associated with tubes (such as limited bandwidth or resolution). If it were not for the ability to swap tubes or for the occasional driver tube that has an audible noise floor, one would be hard pressed to guess that it is actually a tube amplifier.

While there are endless possibilities of set-up, I have found that the six-6BL7 configuration with a Sylvania 6SN7W as a driver is the way to go for me. Nonetheless, I am sure that the endless choices in 6SN7 tubes will make the amplifier friendlier to insert in different systems.

The question that has been bothering me for the past few months is whether or not Glenn’s amplifier is cheating somehow? And while I looked hard for an answer to that question, I am still not able to provide the reader with a definitive one. However, the amplifier shows some much difference between recordings, DACs, etc. that if any “coloration” of sound is being done, it must be done in a very subtle and efficient way, making the listener focus more on the quality of the representation than on the quality of the recording. The Metrum Octave MKII DAC happens to share a similar take to presenting the music; however, Glenn’s OTL amplifier does it in a bigger scale.

To conclude, I would say that Glenn’s OTL amplifier biggest strength is to reproduce, with the highest possible fidelity, music and not sounds.


Building a reference system - Part 1: Metrum Octave MKII NOS DAC

Posted by Amine Slimani on October 10, 2014 at 5:10 PM Comments comments (1)

Many audiophiles believe that the source is the most important piece of equipment in an audio chain. Indeed, if information is missing from the source, there is nothing that even great preamplifiers, amplifiers, speakers or headphones can do to recover it and add it back to the chain. Conversely, if there is something inherently wrong with the source (distortion or coloration), there is nothing the rest of the chain can to totally cover it; admittedly, it is possible to carefully choose equipment downstream in order to minimize whatever flaw is present upstream, but by doing so, one is only counterbalancing the flaw partially and is perhaps losing other qualities in the process of doing so.

That is why I personally have always paid a lot of attention to the source in my system, and I would also try to do as much research as possible before getting a source component as it seems to be, in my opinion, the fastest evolving type of audio components (be it USB to SPDIF converters or DACs). Given that I was very satisfied with the performance of my Aqvox powered Audiophilleo 2 USB to SPDIF converter, the first item I decided to upgrade in my system was the DAC: I wanted to have a clean base on which to build upon the rest of the system.

But before getting to the Metrum NOS MKII DAC, I think that it might be relevant to share my experience with DACs in order to allow the reader to better put in perspective where I am coming from and what qualities I am looking for in a DAC.

The first DAC that amazed me with its superior sound quality was the discontinued Audio-gd DAC19MK3. It was an all discrete PCM1704UK based DAC using the great sounding Pacific Mircrosonics PMD100 HDCD digital filter. The DAC19MK3 was not only as much detailed or even more detailed than most reasonably priced DACs and CD Players (i.e. under $3000), it also made many of them sound broken. The DAC19MK3 was the first DAC in my experience that sounded “analog” in a good way. The analog sounding part did not come from false warmth or haziness but rather came from the lack of obvious digital colorations. Non-amplified instruments such as violins and pianos started to sound real for the first time. Since then, I had the opportunity to listen to many DACs, and the R2R PCM1704UK based ones always sounded better, to my ears, than the sigma-delta based competitors. However, given that I haven’t sampled every DAC out there, I am sure that there are excellent sigma-delta based DACs out there.

While trying to improve the sound my audio system, I made the “mistake” of selling the PMD100 based DAC19MK3 and replace it with the newer DAC19DSP which replaced the PMD100 (or DF1704) digital filter with a custom DSP filter from Audio-gd. It took me a while to realize my “mistake” (it can perhaps best be qualified as regret instead of mistake since the DAC19DSP is also an excellent sounding DAC, for its price). While the new DAC was better sounding by objective standards (bandwidth extension, details, soundstage… ), I felt, nonetheless, that after a (very) long term period of listening that something was lost in the subjective realm. Indeed, after months of listening, I started noticing that even though the DAC19DSP was better sounding than many sources I had listened to, it didn’t sound as pleasing as the PMD100 on unamplified instruments such as pianos and violins. How did I know that it was coming from the DAC and not from the rest of my chain? The answer is pretty easy: once I experimented with different upsampling methods, I found that some of the faults that I had noticed, would lessen when upsampling to 96K (Upsampling would have probably yielded better results at higher sample rates, as was the case with Kingrex UD384 DAC I reviewed that unsurprisingly tops at 384K), and that by “relaxing” the customizable DSP filter (to -50db passband instead of -130db passband), the DAC surprisingly sounded better.

Experimenting with upsampling on both the DAC19DSP and Kingrex UD384 made me realize that software based upsamplers (such as JRiver built in upsampler or Foobar’s SoX plug-in) sounded better to my ears than straight feeding 44.1K files into those (oversampling) DACs. The (oversimplified) explanation of that finding is pretty simple: upsampling makes us listen more to the selected software upsampler and less to the stock hardware oversampler built in the DAC chips or their hardware digital filter. Those who think that upsampling cannot have any positive impact on sound and can only degrade data should consider this: most, if not all, sigma-delta based DACs already have oversampling filters which are doing … integer upsampling (8x, 16x… ). So there is already upsampling (called oversampling) and digital filtering going on the DACs whether we like or not. Also, one has to keep in mind that the digital filters that are most difficult to construct are those made for the 44.1K (in comparison with 88.2K and 96K+ frequencies) CD/ Redbook format. Programmers have to arbitrate between frequency domain and time domain performance; that is why we see different types of filters: slow roll-off, fast roll-off, minimum phase, intermediate phase…

As a result, it is not straightforward and easy to construct very good sounding digital filters. Some companies, such as Ayre or Meridian to name a few, have developed some interesting sophisticated digital filters and their products are acclaimed by many audio critics. However, those DACs are relatively expensive and are still based on sigma-delta with built-in oversampling.

After reading a lot about different approaches to building modern DACs, I came to the conclusion that I wanted a DAC that was R2R based (that is the architecture my ears seem to favor) and that was flexible in terms of digital filtering.

Ironically, in my case and according to the criteria I had set for myself, the state of the art DAC for me had to be a NOS (Non-oversampling) R2R based DAC – those technologies were already around in the 1980s. There were quite a few choices out there, from the affordable (often Chinese made) TDA1543 based DACs to some very impressive discrete based DACs (TotalDac for instance). I settled on the Metrum Octave MKII because it seemed like a competently built and reasonably priced DAC. Also, it seemed to be very well reviewed by very different people (although that is no guarantee for sound in one’s system).

Given that the Metrum Octave MKII has been extensively reviewed elsewhere, I won’t go into much detail about its technical specifications. I will jump right ahead to the rest of the review.


Review system:

System 1 – Headphone Based (optimized)

Computer source: HP Pavillon DV6 (Core i7, 8GB), Windows 7 64bits SP1, Fidelizer, JRiver Media 17

Transports: Audiophilleo 2, Kingrex UD384, Jkeny’s modified Hiface MK1, Audio-gd Digital Interface (w/ Tentlabs upgrade clock), Teralink X2, Musiland Monitor 01 USD, EMU 0404 USB

DACs: Metrum Octave MKII, Audio-gd DAC-19 DSP with DSP1 V5 upgrade, Kingrex UD384

Amplifiers: Glenn’s OTL headphone amplifier, Audio-gd C2, Little Dot MKIII

Headphones: Sennheiser HD800 with Wiplash Audio TWau Reference cable, Beyerdynamic T1 with ALO Chain Mail cable, Sennheiser HD650 with Artisan Silver Dream upgrade cable

Digital interconnects: Hifi Cables Sobek BNC, OyaideDB-510 BNC, Wireworld Ultraviolet USB, Artisan Twinline Pure Silver USB cables

Analog Interconnects: Artisan Ultimate Silver Dream RCA, Norse Audio custom 8 conductor UP-OCC ACSS, Deep Sounds SPS ACSS, Kimber PBJ RCA

 Power filtration: Bada LB-5600 Filter, Essential Audio Tools Noise Eater, Essential Audio Tools Pulse Protector, Supra Mains distributor

Power cords: Hifi Cables & Cie PowertransPlus (x2), Hifi Cable & Cie SimpleTrans, Olflex power cords

Vibration Control: Aktyna ARIS decoupling feet, Maple and Acrylic Platforms, E&T rack, Stabren Damping pads, Sandbox, Brass cones, Vibrapod, Yamamoto Ebony footers and Various Herbie’s Audio Labs tweaks


System 2 – Speaker Based (not fully optimized)

Yamaha CD 600/ Audio-gd DAC19DSP --> Kimber PBJ --> Yamaha AS500 / Populse T150 --> Hifi Cables & Cie Maxitrans II --> Triangle Antal EX floorstanding speakers


Reference tracks used for the review:

CD Quality:

Mahler - Symphony n 5- Decca - 16/44

Sol Gabetta - Schostakowitsch Cellokonzert Nr. 2/Cello - 16/44

Vivaldi - Concertofor 2 violins - Carmignola/Mullova - 16/44

Natalie Dessay - Italian Opera Arias - Emi Classics -16/44

Puccini - La Boheme - Decca - 16/44

Glenn Gould - The Goldberg Variations (1981) - 16/44

The Essential James Bond - City of Prague Philharmonic orchestra - 16/44

The Dave Brubeck Quartet - Take Five - HDCD - 16/44

Diana Krall - Live in Paris - 16/44

Norah Jones - Come Away With Me - 16/44

Patricia Barber -Companion - 16/44

Johnny Cash – The Essential - 16/44

Soundrama - "The Pulse" Test CD - 16/44


High Resolution quality:

Rachmaninoff Dances -HD Tracks - 24/96

Mozart Violin Concertos - Marianne Thorsen - 2L - 24/96

Dunedin Consort -Messiah - Linn Records - 24/88

Glenn Gould – The Goldberg Variations (1955) – HDTracks - 24/96

Keith Jarrett - Paris/ London - Testament - 24/96

Jazz at the Pawnshop- HD Tracks - 24/88

Alison Krauss and Union Station - Paper Airplane - 24/96

Ella Fitzgerald /Louis Armstrong - Ella & Louis - 24/96

Diana Krall – From this Moment on - 24/88

Diana Krall – The Girl in the Other Room - 24/96

The World's Greatest Audiophile Vocal Recordings - Chesky - 24/96

The Kinks - One for the Road Live - 24/96

The Eagles - Hotel California - HD Tracks - 24/96

Head-fi/Chesky Sampler - Open Your Ears - 24/96



The set-up:

Burn-in and warm-up:

Regarding burn-in, the Octave MKII sounded very good out of the box. Its sound improved a little bit after a few hundred hours of burn-in but the change was not as dramatic as I had previously experienced with other audio components. As for warm-up, once it is fully burnt-in, it still benefits from being left on for a couple of hours. Given how little heat it generates, one can just leave always on and forget about it to get optimum results – at least that is what I do.



As Metrum offers to get their DAC with or without the USB module, I think that many buyers will wonder whether it is worth to get the USB module or not when they are faced with their buying decision.

I personally got the USB version mainly out of curiosity, in order to see how their module performs against stand alone USB converters. The end result is that while USB built-in modules have come a long ways since the early days of horrific sounding and 16/48 limited USB inputs, they are still a little bit away from competently built standalone USB converters such as the Audiophilleo 2 (AP2).

When running the Octave MKII through its USB input, the sound gets more upfront and in-your face than when using the AP2 as a USB transport. I had the (false) impression of greater details for the first few minutes of listening until I realized that the USB input on the Octave MKII was acting like the dynamic contrast you would find on older TV sets with primitive electronics. By turning up the contrast ratio (vs. the Audiophilleo), some of the finer details and nuances are lost in the process. The difference in sound quality between the two inputs is not huge but is pretty noticeable in a transparent system. Would I have noticed the deficiencies of the USB input without comparing it to a better transport? I probably would have not been able to do so.

So when does it make sense to get the USB version of the Octave MKII? If one does not have a source of the caliber of the AP2, and is not ready to invest in an expensive digital cable, it makes sense to stick with the built-in USB input, as it will do (most of) the job just fine. One has always the possibility to upgrade later, with probably better alternatives than the AP2, as the technology is moving pretty fast in the sector of USB transports. Also, the USB Octave MKII is probably going to beat most variations of a USB transport – digital cable – DAC combination.

If you have a transport of similar performance level or better than that of the AP2, you can skip on the USB module. If not, the built-in USB will probably do a fine job.



After a lot of experimentation, I ended up settling on SoX upsampling (on Foobar) with the following parameters:

Upsampling to: 176.4K (for 44.1K files only)

Quality: Best

Passband: 90%

Allow aliasing: checked

Phase: 25% (i.e. intermediate phase)

In many ways, SoX upsampling (with the parameters chosen above) is the closest thing to no-upsampling. Yet, its contribution to the sound is very recording dependant. Sometimes, SoX can sound more relaxed, bigger and portray a deeper soundstage in particular recordings, especially on heavily processed ones. Other times, it seems to reduce the depth of the soundstage on very well recorded classical music pieces. Overall, in the grand scheme of things, those differences are rather tiny. I can definitely live with either configuration.

One has to note, though, that I have chosen the most “relaxed” setting for SoX. Theoretically, lowering the passband to 90% and allowing aliasing should minimize as much as possible (pre and post) ringing. Indeed, it would be counterproductive to use an upsampler with heavy ringing (because it uses a “brickwall-type” of filter), on a NOS DAC that is supposed to have a perfect impulse response (vs. regular oversampling DACs). As for the phase, I settled on 25% as it sounds somewhere in between linear phase and minimum phase. Keep in mind regardless of the digital filter (or lack of filtering) that is applied in the playback chain, the ringing (and other faults) recorded on the digital file cannot be undone, except perhaps with the help of some sophisticated apodizing filters (as claimed by some manufacturers).

An interesting alternative to Foobar’s SoX upsampler is JRiver Media Center built-in upsampler. It gives the most pleasing, musical and analog like representation I have experienced from a PC based media player. And though it is less detailed than SoX upsampling (in Foobar), it remains the closest thing to the analog flavor of the PMD100 digital filter I have come across. I will probably go into more details on the comparison between media players in a separate article as it is not directly related to the Metrum DAC.


Other tweaks:

Although I have read elsewhere (I think it was hifi critic, from memory, but I did not want to go back to other reviews before finishing mine to give people as fresh of a perspective as possible) that the Metrum Octave (MKI) was very sensitive to external factors such as vibration control, I have to admit that I did not spend much time experimenting around with various tweaks and cables. When I received the Metrum Octave MKII, I did a simple drop-in replacement of the DAC19DSP I was using before. Given that I was very satisfied with the sound of the Octave from the start, I did not bother experimenting with specific tweaks.

As a side note, I used the Metrum Octave MKII with the Hifi Cables & Cie PowertransPlus power cord (my reference for more than five years), the Aktyna ARIS 2 aftermarket feet (my reference for more than 4 years) as well as some maple platforms (my reference for more than 5 years). As for interconnects, I exclusively used my also long trusted Artisan Ultimate Silver Dream RCA cables. Although I am an audiophile that likes tweaking his system, I have kept my surrounding “accessories” inventory relatively stable for the past few years as I am both familiar and satisfied with their effect in my system.


The sound:

Timber and tonal balance:

One of the first things you would notice with Octave MKII is how beautifully balanced it is from top to bottom. One of my fears going the NOS route was to encounter a rolled off or heavily distorted high register. Actually, it turned out the Octave was much more energetic than the darker sounding DAC19DSP in the higher frequencies. Meanwhile, the top end is as pure and diversified as I have ever listened to in a DAC, combining the analog-ness of the PMD100 DAC19MK3, the energy of the DAC19DSP and the sophistication of the Kingrex UD384 (when playing high resolution files).

When directly comparing the Octave MKII against the DAC19DSP and the UD384, one might think at first that the DAC19DSP has the more powerful bass, followed by the Octave MKII and then trailed last by the UD384. However, after some more listening to various kind of recordings (high resolution and 16/44 sample rates, well recorded albums as well as poorly recorded ones…;), it became apparent that the DAC19DSP had a small emphasis on the mid bass that made it appear as more powerful sounding than the Octave MKII and UD384. The difference between the Octave MKII and the UD384 is that the Metrum has some powerful low bass when the recording calls upon it, that is greater that of the DAC19DSP, while the UD384 does not have that same impact on the lowest frequencies.

Nonetheless, dissecting the tonal balance piece by piece does not fully do justice to the Octave MKII as its biggest strength is the way it reproduces voices and instruments, as a whole, from a single cloth, in a realistic manner. This does not mean that everything is blended together, without differentiation between sources of sound playing at the same time. It actually means that every single instrument and voice exists as a single entity and not as discontinued compilation of bass, mid and high frequencies.

Granted the DAC19DSP, and many other DACs, already do that seamless integration of the different frequencies, but the Octave MKII just goes a step further. Given the right conditions (i.e. proper source upstream, as well as transparent amplifiers and headphones downstream), the Octave MKII’s depiction of timber of instruments and voices is absolutely stunning. If you like to listen to classical music or non-heavily processed music, you might find the Octave MKII the right match for your system.

In my personal experience, I have found that when a digital source can render properly and convincingly both pianos and violins, there is a good chance that it can render everything else in a satisfying manner.

So, one might ask, how did the violins get rendered? Did the Octave MKII focus on the wooden resonance of the body or the sheen of the strings? The Octave MKII did both and neither. The violins sounded different from one recording to the other, and if different type of violins were used in the same recording, the Octave MKII lets you hear every nuance of it.

Although, I had already heard differences on the DAC19DSP between the Stradivarius and Guadanigni in the nicely recorded Vivaldi - Concerto for 2 violins - Carmignola/Mullova, the Octave MKII just makes it easier to spot differences between the two superbly rendered violins. Meanwhile, despite that greater ability of separation, everything seems to be more enjoyable to listen to.

It seems that instead of focusing on the flaws of a recording, as many analytical DACs tend to do, the Octave MKII seems to be focusing on revealing the details that are most relevant to enjoying the music.

So, is there any weakness or limitation in the timber or tonal balance of the Octave MKII? I suspect that it is in possible to make the bass even more powerful (with a bigger power supply perhaps), but other than that, and without having access to a truly exceptional reference DAC, I cannot find any objectionable fault with its tonal balance and timber rendering of various instruments and voices.

During my almost one year experience with the Octave MKII, I did notice on occasions that the sound was not perfect, that it sounded sometimes harsh or congested in the midrange or simply that some instruments just sounded off. However, the culprit was usually elsewhere in the chain.

Also, the more transparent my components became downstream, the more I started appreciating how beautiful and realistic the tone and the balance of the Octave MKII was.


Soundstage & Imaging:

I was very impressed from the start with the soundstaging capabilities of the Octave MKII. If I had to make a direct comparison in size, I would say that its soundstage size is noticeably bigger than that of the DAC19DSP and slightly bigger than that of the Kingrex UD384. However, it remains a simplistic way of comparing soundstage sizes as it varies from one recording to another and from one sampling rate to the other. That it is just to tell you that it soundstage is as big as I have listened to in my system but I have not had much experience with (very competent) sigma-delta based DACs, other than the UD384, that are supposed to be champions in soundstaging.

However, what struck me when listening to the Octave MKII was not its ability to portray a big soundstage but, rather, its ability to transport me to the recording venue. On many recordings, you can get a pretty good idea of the size of the recording room not by trying to calculate the size of the room that is being painted in front of you but by measuring the size of the room that you are actually occupying.

While this was not very obvious at first, but still noticeable, when using the audio-gd C2 amplifier and the ALO recabled Beyer T1 combination, it was much more obvious and apparent when ending up with Glenn’s OTL amplifier and the HD800s (with Wiplash TWau Reference cable).

While the soundstage size of the HD800s is not clearly as big as that of the Triangle Antal EX speakers (in a 750 sq. feet room), for instance, it is however more realistic and immersive.

Hence, I can imagine other DACs (and most possibly the Metrum Hex) having a bigger soundstage size than that of the Octave MKII. But on its own, and fed from the Aqvox powered Audiophilleo 2, the Octave MKII gratified me with the best soundstage I have heard from a digital source.

As for the layering and imaging, all I have to say is that the Octave MKII combines image specificity and image body beautifully. While the Octave MKII makes it very easy to pinpoint the location of various performers and instruments in the soundstage, it also retains enough “body” to the sound to make it lifelike.

Actually, the imaging specificity is better than what you get in real life. Or to put it in other words, I have never been in a live event that approached the 3D performance and image specificity of the Octave MKII. There are maybe a few possible explanations. Either we do not listen the same way at home and at various concerts. Another explanation is that using multiple microphones has an impact on the 3D perception, but it has the same surprising and counterintuitive result.



The Dynamics of the Octave MKII are as good as I have listened to in a DAC. In comparison with the DAC19DSP which seems to have a better (at least bigger) power supply section and a dedicated all-discrete output section (vs. direct feed from the DAC on the Octave MKII), the Metrum DAC held up surprising well and had overall the edge in dynamics in my system.

More specifically, and even in comparison with live music, the micro-dynamics are as good as I have ever heard. Every little dynamic variation of a voice or instrument is tracked exceptionally well and makes the listening sessions very engaging.

As for the macro-dynamics, and conversely to the soundstaging and imaging department, where I found that the Octave MKII (as well as other DACs) exceed live concerts, I find that macro-dynamics are not as good as what you might experience in live concerts.

Listening to my “ultimate” tracks such as the Dark Knight OST or Gladiator OST, the Octave MKII can make you go through some terrifying moments. But on other tracks, I felt that perhaps there is still room for improvement. Or maybe, it is just that many recordings are too much (dynamically) compressed for their own sake.

In any case, I am just nitpicking, and in comparison with most DACs and CD players I have listened to, the Octave MKII is able to deliver a very lively and dynamic representation of the music.


Transparency & resolution:

The Metrum Octave MKII has a very high level of transparency to the recording. One of my fears when getting a NOS DAC was to have a “romantic” sounding component that would impose a certain character on every single recording (I had the same fear when getting and OTL tube amplifier and my fear also turned out to be unfounded). However the Octave MKII is the most transparent DAC I have listened to in my system (or elsewhere). On Messiah - Dunedin Consort album, for instance, I was able to hear the performers move as if they were just in front of me.

The nice thing about the Octave MKII is that its added level of transparency does not come at the expense of false or excessive brightness. In comparison with previous sources (either CD players or DACs) I have listened to, the Metrum DAC seems to take the dust of all the recordings I have while making them better to listen to at the same time. So, is the Octave MKII cheating somehow? Maybe it is the case, but there is no way to be sure.

The level of details that this little DAC can render is unbelievable. On a Chesky classical music recording, I was able to hear the traffic noise outside the recording venue. On my reference Jazz at the Pawnshop recording, I was able to hear, better than ever, the background chatting and silverware noises while the music was playing at a high volume. Although, there might still be information to extract from the various recordings I have, I do not believe it is necessary to musical enjoyment.




I believed that we have reached a very interesting age in the Digital reproduction of music. Today, a €1000 DAC buys you equipment that can reveal flaws, or at least the very specific character, of most recordings out there.

So why bother spending this much money or even more on a DAC? The answer is in the subtlety. Even though the Metrum Octave MKII NOS DAC can show flaws on many recordings, it has rewarded me with the best sound I have heard in my system. Contrary to what you will find on analytical DACs that focus on laying bare the recording piece by piece regardless of the music as a whole, the Metrum Octave MKII is able to put all that information into context, in a very musical way. Getting a truly good DAC can have the combined effect of being both more revealing and more enjoyable to listen to at the same time.

The main weakness of the Octave MKII DAC, in my personal opinion, is it high sensitivity to the quality of the source (jitter… ). Its USB input is good but can be bettered by the Audiophilleo 2. Meanwhile, its SPDIF input is sensitive to every little change made at the source (media player, usb transport… ). Whether that is a sign of transparency (of its analog section) or a possible improvement in the digital section, I believe that the truth lies somewhere in the middle as even the mega-buck high performing DACs still seem to benefit from better transports (be it CD players or USB converters).

However, given its price performance ratio, I cannot recommend highly enough the Octave MKII to anyone looking for a single ended DAC in this price range.

This review is the first of a series of articles that I will be posting in the coming weeks. As I have elected the Octave MKII as my reference DAC, the readers can get a better sense on how it sounds in my system by reading the next reviews.


Building a reference system - Introduction

Posted by Amine Slimani on October 9, 2014 at 4:50 PM Comments comments (0)


Those who have visited before might have noticed that I haven’t written any new article for more than two years. How did that happen?

Part of the explanation is that I was busier than usual with non-audio related things but that was not the main reason for this disappearance. The main reason for my taking away a break was that I had reached such a satisfying sound quality level with the Beyer T1, Audio-gd DAC and headphone amplifier combination that I was able to settle for a while with the same system and enjoy listening to music without touching to anything.

Nonetheless, as an audiophile and a long time “tweaker”, I could not help myself from wondering: “What if …?”

At that stage, I had two options: either I could continue (my upgrade path) with the audio-gd equipment and have my Beyer T1 balanced or try something totally new. Indeed, I have had a very good experience with audio-gd equipment in the past, and was very satisfied with the price performance ratio of their line up (especially their PCM1704 based DACs). However, I decided to try something totally new instead of simply getting the top of the line equipment from their company. Buying “bigger” component from the same manufacturer would have guaranteed me a “better” sound, while perhaps keeping the same house sound. Meanwhile, I had started noticing some minor faults with my equipment that prompted me to try a new direction.

Before starting buying new equipment, I read a lot of reviews about different equipment and asked opinions from people whose opinion I trust.

What I have been looking for is a sound that is free from any harshness yet detailed enough, revealing yet enjoyable on a very broad range of recordings, and analytical yet very engaging to listen to. Those might seem as contradictory qualities, but one should be able to find such qualities in a good audio system, or else why bother at all with endlessly upgrading equipment?

The way I ended upgrading my equipment, over the course of a few months, was as follows:

1. The DAC, by getting the Metrum NOS Octave MKII

2. The amplifier, by getting a custom made OTL headphone amplifier made by Glenn R.

3. The headphone, by getting the Sennheiser HD800s

4. The headphone cable, by getting a custom silver/gold upgrade cable for the HD800s

5. The tube dampers, by getting the top of the line RX dampers for all 8 tubes of my headphone amplifier

That it is also the order I will us for publishing my next articles.

Meanwhile, the rest of my equipment remained the same: the USB source (i.e. the Aqvox powered Audiophilleo 2), the other cables (mainly from the French manufacturer Hifi Cables & Cie), the power filter (Bada), the audio rack and various tweaks (E&T spider rack, Aktyna ARIS decoupling feet…;).


Did the sound get transformed switching from the older reference to this newly built one? The answer is both yes and no.

On the one hand, one might consider that the sound did not get transformed given that every single album I listen to remained recognizable. The thing is that the coloration of most good audio systems is far smaller in scale than that of most commercial albums.

On the other hand, one might consider that the quality of the system was totally transformed, especially by audiophile standards. Indeed, the level of refinement went up tremendously, the timber and richness of instruments got closer to the real thing than anything I had listened to previously, the soundstage became more immersive than ever, and most importantly, the enjoyment I started getting from listening to my music reached new levels of greatness. The sound has become so breathtakingly good on so many types of recordings that it feels like a hallucination. In my previous reference system, some of the recordings were exceptional to listen to but many of them were just adequate to listen to. In my current system, I enjoy every single piece of recording I listen to whether it is classical music, piano, jazz or modern popular music. Isn’t that what we are after?


I attribute this high quality of musical enjoyment to every single component in my chain, and to the synergy of the system as a whole. Is it the best headphone system one can build? I am pretty sure it is far from it. However, this system has a set of qualities that I have never personally experienced in another system.

Can this system be improved? It most probably can: there are probably systems with deeper and more powerful bass, bigger soundstage or more low level details. However, after months of listening and comparing to my older equipment (I didn’t sold any of it), I have found that is hard to find annoying faults with this system. Perhaps, the most surprising thing is how musical and wonderful sounding the HD800s ended up to be in this system - I have to say that I did not use to care for the HD800s when I listened to them in other configurations.


In the next series of articles I will go into more details on how I ended up choosing every major component in my system, and how I feel each component sound in my system. I will also try to go into as much detail as possible in describing the sonics of each component in order to help people that are interested in one of the components listed previously.


Preview : Glenn OTL headphone amplifier

Posted by Amine Slimani on November 25, 2013 at 4:25 PM Comments comments (0)

As I was looking to upgrade my headphone amplifier for the ALO recabled Beyer T1s, it was clear that I needed to get a tube OTL amplifier as recommended by many people who have tried that combination.


While I was about to order the Woo Audio WA2 (OTL amp based on 6AS7 / 6080, I was lucky enough that Stavros (rosgr63) pointed me towards Glenn who makes some very interesting tube amplifiers.


After discussing a little bit with Glenn, we settled on the configuration shown below. The amplifier uses a 6SN7 tube as driver and 3DG4 as a rectifier. As for the output tubes, it can use different kinds. Here is what Glenn wrote : "It uses six 6BL7s for outputs or two or four 6AS7s or two 6336."

There is already a discussion started here :

Glenn is expecting to finish the build by mid decembre. So keep tuned ...

Review: Reference Tweaks Miracle Wraps

Posted by Amine Slimani on July 24, 2012 at 9:30 AM Comments comments (1)


When nenno from Reference Tweaks first contacted me about his Miracle Wraps, I was very intrigued to say the least. I did not totally understand how such a “tweak” could have an impact on the sound, but since different cables with different shielding schemes have sounded different in the past, I agreed to do the review out of curiosity. The point that surprised most, besides the fact that the effect of the Wraps on the system was noticeable and unmistakable, was that it affected both unshielded and shielded cables. Hence, there is something very specific about the Miracle Wraps, whether it is a specific shielding or “conditioning”, which seems to elude all the cables I have in my collection.

I have read a few times the description of how the Miracle Wraps are supposed to work but I couldn’t understand the science behind; it is probable that PhDs in quantum physics are in a better position to evaluate the claims made by Reference tweaks. However, regardless of the theory behind it, the Miracle Wraps do work, so that is why I decided to write an article about them.

How does it work?

The Miracle Wraps are very easy to use. As their name suggests, you just have to wrap them around the cable you want to “improve”. In my review set, 4 wraps were included: 2 large ones to use with power cords and 2 small ones to use with a pair of line-level interconnect wires.

Wraps - Redesigned:

Although the set that was sent to me 6 months ago has worked perfectly even though I tend to handle them a lot as a reviewer, nenno informed me that Reference Tweaks redesigned the Wraps for even more durability. Below is an extract from the info I was provided with. As far as I know, the redesign did not impact the sound.

All Miracle Wraps are now made with two layers of Japanese paper and they are extra enforced on the essential points. We have done this out of precaution, so far we did not have to replace one Miracle Wraps from customers. We also redesigned the typography. We now use a bigger font and a dark blue ink.

Review System

Equipment used for the review

In order to get a good understanding of the effect of the Wraps I used them in two very different systems: my reference headphone based one as well as a secondary speaker system that I haven’t had time to fine tune yet.

Both systems are described below.

System 1 – Headphone Based (optimized)

Computer source: HP Pavillon DV6 (Core i7, 8GB), Windows 7 64bits SP1, Fidelizer, JRiver Media 17

Transports: Audiophilleo 2, Kingrex UD384, Jkeny’s modified Hiface MK1, Audio-gd Digital Interface (w/ Tentlabs upgrade clock), Teralink X2, Musiland Monitor 01 USD, EMU 0404 USB

DACs: Audio-gd DAC-19 DSP (with DSP1 V5), Kingrex UD384

Amplifiers: Audio-gd C2, Little Dot MKIII

Headphones: ALO recabled Beyerdynamic T1, Sennheiser HD650 with Artisan Silver Dream upgrade cable

Digital interconnects: Hifi Cables Sobek BNC, OyaideDB-510 BNC, Wireworld Ultraviolet USB

Analog Interconnects: Artisan Ultimate Silver Dream RCA, Norse Audio custom 8 conductor UP-OCC ACSS, Deep Sounds SPS ACSS, Kimber PBJ RCA

Power filtration: Bada LB-5600 Filter, Essential Audio Tools Noise Eater, Essential Audio Tools Pulse Protector, Supra Mains distributor

Power cords: Hifi Cables & Cie PowertransPlus (x2), Hifi Cable & Cie SimpleTrans, Olflex power cords

Vibration Control: Aktyna ARIS decoupling feet, Maple and Acrylic Platforms, E&T rack, Stabren Damping pads, Sandbox, Brass cones, Vibrapod, Yamamoto Ebony footers and Various Herbie’s Audio Labs tweaks

System 2 – Speaker Based (not fully optimized)

Yamaha CD 600 --> Kimber PBJ --> Yamaha AS500 / Populse T150 --> Qed Speaker cable --> Triangle Antal EX speakers 

Reference tracks used for the review

My (usual) reference tracks:

CD Quality

Mahler - Symphony n 5- Decca - 16/44

Sol Gabetta - Schostakowitsch Cellokonzert Nr. 2/Cello - 16/44

Vivaldi - Concertofor 2 violins - Carmignola/Mullova - 16/44

Natalie Dessay - Italian Opera Arias - Emi Classics -16/44

Puccini - La Boheme - Decca - 16/44

Glenn Gould - The Goldberg Variations (1981) - 16/44

The Essential James Bond - City of Prague Philharmonic orchestra - 16/44

The Dave Brubeck Quartet - Take Five - HDCD - 16/44

Diana Krall - Live in Paris - 16/44

Norah Jones - Come Away With Me - 16/44

Patricia Barber -Companion - 16/44

Johnny Cash - TheEssential - 16/44

Soundrama - "ThePulse" Test CD - 16/44

High Resolution quality:

Rachmaninoff Dances -HD Tracks - 24/96

Mozart Violin Concertos - Marianne Thorsen - 2L - 24/96

Dunedin Consort -Messiah - Linn Records - 24/88

Glenn Gould – The Goldberg Variations (1955) – HDTracks - 24/96

Keith Jarrett - Paris/ London - Testament - 24/96

Jazz at the Pawnshop- HD Tracks - 24/88

Alison Krauss and Union Station - Paper Airplane - 24/96

Ella Fitzgerald /Louis Armstrong - Ella & Louis - 24/96

Diana Krall – From this Moment on - 24/88

Diana Krall - TheGirl in the Other Room - 24/96

The World's Greatest Audiophile Vocal Recordings - Chesky - 24/96

The Kinks - One forthe Road Live - 24/96

The Eagles - Hotel California - HD Tracks - 24/96

Head-fi/Chesky Sampler - Open Your Ears - 24/96

The Sound:

As I mentioned in the introduction, the effect of the Miracle Wraps was surprisingly audible and repeatable across different systems. The effects were rather similar when used with different analog cables (interconnects, power cords) and were somehow a little bit different when used with digital cables.

Digital cables:

While none of the wraps that were sent to me were intended to be used with digital cables, I nonetheless did try the small ones with both digital spdif cables and usb cables.

The result was mainly a smoother and more focused side. With my digital cables (Oyaide DB510 and Hifi Cables & Cie Sobek), the effect was too much smoothing out, while the effect on USB cables was much better. Perhaps that the fact the USB cables carry both analog (usb bus power) and digital (usb data) signals explains the better results I have had with the Miracle Wraps on the USB Cables in comparison with “simple” spdif digital cables.

Analog cables:

All analog cables seemed to benefit positively from adding the Wraps around them. Regardless of the type of conductor, geometry used and shielding scheme, the Wraps did always make a improvement into the right direction. The only difference I noticed is that with my Artisan Ultimate Silver Dream, I preferred the Wraps at the source while with my ACSS (current mode) Norse Audio interconnects, I preferred them at the amplifier side. Even though, the positioning did not make a day and night different, it is still worth trying since it does not take involve much effort doing it.

Overall, given the similarity of the effect of the Wraps on the analog cables, I will not make a distinction between the use of Miracle Wraps on power cables and on RCA/ACSS interconnect cables. The effect is cumulative, so I encourage anyone that is open to the idea of trying such a tweak to try a whole set (i.e. interconnects and power cable treatment).

Timber & Tonal Balance:

For whatever reason, I was expecting the Wraps to soften somehow the sound. I thought that they would act as some kind of filter and perhaps smooth the sound by softening the transients. Since it was a passive device, that “could not” add anything, it could only subtract things (edge of transients) in my reasoning. This digression is intended to show that despite having the best intentions of objectivity; one always forms an idea on how a new piece of equipment might sound like.

Surprisingly, the main effect of the Miracle in my system is the transformation of my usual sound into a bolder one. Instead of smoothing the sound as I was expecting, the sound became “rawer”. It is like if the garbage and fuzziness surrounding the harmonics were cleaned up without turning the sound into the aggressive side. The audiophile “veil is lifted” cliché could perhaps be applied here but it would not totally describe what I heard.

The effect of the Wraps is impressive in the way that it adds both directness and naturalness at the same time, as superior components should always but so few components actually do.

When taking each audio band separately, there is no increase in bass or lowering in the highs (i.e. change in the frequency domain). So for those looking for a way to alter or fine tune perhaps their system in the frequency domain, you should probably look elsewhere. What the Wraps do is that they provide you with a closer experience to the true color of real instruments in real life. It is difficult to quantify but it is unmistakable for music lovers and enthusiasts.

Soundstage & Imaging:

Because of that “cleaning” effect around the notes I talked about earlier, the instruments and performers stand with better accuracy and definition in the virtual soundstage. While, I was impressed in the beginning by the increase in the size of the soundstage, I did not pay much attention to the size of the soundstage later on. For those looking to increase the size of the soundstage, switching from a regular copper interconnect, such as the Kimber PBJ, to a pure silver one, such as the Artisan Ultimate Silver Dream, might provide better results in that respect.

The Miracle Wraps allow you to have a slightly better defined, the instruments and performers are better carved in space but, overall, the effect is relatively small in scale.


When I first listened to my system after adding the whole set of Miracle Wraps, I had the impression that the volume was raised a little bit. In fact, I had already experienced that feeling with some equipment and cables, and it is usually due to a greater clarity in the sound.

While the sound felt “louder”, I curiously found myself listening to even higher volume levels than usual. Adding the Wraps to a system is the equivalent to adding a more powerful engine to a car, or putting the same engine into a lighter one. Everything sounded unrestrained and more alive. Some little hardness in the sound that was not obviously audible was released and allowed me to turn the volume higher without feeling any objectionable sounding distortion

With the already ultra-clean sounding ALO Beyer T1s, I could listen to “realistic” levels without any sign of strain or hardness. I had to teach myself to back down a little bit in order not ruin my hearing.

Meanwhile, listening at lower levels than usual was also very enjoyable.

As a result, the Miracle Wraps improved noticeably the perceived dynamics while providing with better enjoyment for both low level and high level listening.

Definition & Transparency:

As a passive component, I initially thought that if the Miracle were to have any real effect on the sound it would necessarily imply a loss of transparency and definition.

The end result is unsurprising if you had read the previous sections.

By cleaning the sound from the “un-musical” information, it actually increases both definition and transparency while retaining an interesting level of musicality.

I did not have any seriously flawed or tipped up system to try it with, so I don’t know if the increase in resolution and transparency can become too much after a certain point. But if I had to guess, I would say that the Wraps would be worth trying even in such systems since it has mostly taken my system in the right direction, regardless of the associated equipment and whether it was used in my optimized headphone system or the speaker system that I am currently setting-up.


To sum up, I would say that I have been extremely pleased with the Miracle Wraps and that I will be keeping the set after the review. In my opinion, and in my particular situation, the Wraps represent an excellent value as they take the sound into the right direction (more realism and more directness) without showing any noticeable drawbacks. While the improvement the Wraps make on my system are not quantifiably big in scale, it is nonetheless difficult to live without it after a while.

So, should everyone jump and buy the Miracle Wraps? I believe that the answer is no. The Miracle Wraps are for those who already own a “decent” system (which does not necessarily mean expensive) and have already experimented with cables and other accessories and understood what type of effect they might induce in their system. The average tweak-fi reader will probably fit that description and will probably benefit greatly from adding the Miracle Wraps into their system.

The Miracle Wraps are a highly recommended tweak. It is easy to try and not ridiculously priced for the type of improvement it provides.

kboe's AKG Journey, Collection and Catalogue.

Posted by kboe on February 9, 2012 at 3:25 PM Comments comments (0)

Just click here to jump to the thread.  Or navagate to the thread by going to "forums", then "Headphones".

Review: Kingrex UD384 USB DAC (32bit/384Khz) & UPower

Posted by Amine Slimani on February 4, 2012 at 1:55 PM Comments comments (4)

Do we really need 32bits/384kHz capability in a DAC? That is the first question I asked myself when Christine from Kingrex asked me if I were interested in reviewing their newly released UD384 usb dac. It is until recently that 24/96 and 24/192 have become more common but there is still a long way to catch up with the choice of material released in the 16/44 RBCD format. So why bother releasing such a DAC? After listening for several weeks to the Kingrex UD384, I think that there is at least two possible explanations. First, there are record companies, such as 2L, that are starting to offer higher resolution files than 24/192 (for instance the 24/352 DXD format, or even the non PCM 1bit DSD format). Second, having a 32/384 capable usb DAC allows you to upsample any file (from mp3 to DSD) into 384 KHz directly in your media player. Whether that is a good or bad thing will be discussed later.


However, besides the 32/384 capability, the UD384 distinguishes itself for most DACs by its optional battery power supply. The UD384 can indeed either be sold with a regular (read non-audiophile) 7.5v SMPS power supply or it can be upgraded with a battery power supply. My review unit came with the optional U Power battery supply. Having previously directly compared a usb powered Hiface with a battery powered Hiface, I was staggered by the kind of improvement an upgraded power supply could provide to a source.


While I have been pretty happy with my dac19dsp, which is limited to 24/96, the 32/384 capability and the battery power supply on the UD384 piqued my interest. The UD384 takes on a rather different route than my reference dac: while the dac19dsp uses old R2R PCM1704uk chips, discrete output stages and is 24/96 limited, the UD384 seems to be using an integrated usb/dac chip and non-discrete (IC) output stages. For the power supply, the dac19dsp is using a big R-Core transformer followed by some decent filtration, while the UD384 goes with the smarter route of battery power supply.


So how does the UD384 sounds like? Read on to find out.


Description of the UD384 and the UPower


The Kingrex UD384 is an async USB DAC and Digital to Digital (USB to Spdif) converter capable of up to 24/384 sample rates (from its USB input).

The Kingrex UD384 can be operated either from a regular 7.5v SMPS or from the UPower, which is the optional battery power supply.


Below are some specs on the UD384 and UPower:




UD384 (32bits/384Khz USB DAC )

Input: USB x 1

Analog output: RCA x 2 (Rx1 Lx1)

Digital output :SPDIF x 1       

Sampling rate support :44.1Khz, 48Khz, 88.2Khz, 96Khz, 176.4Khz, 192Khz, & 384Khz(384Khz for USB DAC only)

Supported bit rate: 16 / 24 /32bit

USB:2.0 high speed

Adaptive Clock Generator for Audio Streaming Synchronization

Asynchronous mode changeable through DFU Tool

Power requirement: 7.5V/250mA

Size: 110x82x24mm

Suggested MSRP : $479/pc



U Power:


Pure DC output battery power supply unit

      I.       Two output :

A.    2.5mm DC jacket: 7.5V DC output

B.     USB A :5V DC output(through linear regulator)

II.       Major component: High quality Sanyo Li-ion battery.

III.  Power volume: 2600mA/hr. Included special design for isolated protect circuitry for two Li-ion batteries.

IV.  Using fully high quality aluminum for styling & cooling.

V.    Low battery indicator design for charging reminding.

VI.  CHG/DC OUT switch. Fully isolated the charging and discharging. It will free the AC noise from the charger.

VII.   Parallel charging- each battery cell could charge to its maximum by the design.

Suggested MSRP: US$189/pc


Review System


Equipment used for the review


Computer source: HP Pavillon DV6 (Core i7, 8GB), Windows 7 64bits SP1, Fidelizer, JRiver Media 17

Transports: Audiophilleo 2, Kingrex UD384, Jkeny’s modified Hiface MK1, Audio-gd Digital Interface (w/ Tentlabs upgrade clock), Teralink X2, Musiland Monitor 01 USD, EMU 0404 USB

DACs: Audio-gd DAC-19 DSP (with DSP1 V5), Kingrex UD384

Amplifiers: Audio-gd C2, Little Dot MKIII

Headphones: ALO recabled Beyerdynamic T1, Sennheiser HD650 with Artisan Silver Dream upgrade cable

Digital interconnects: Hifi Cables Sobek BNC, OyaideDB-510 BNC, Wireworld Ultraviolet USB

Analog Interconnects: Artisan Ultimate Silver Dream RCA, Norse Audio custom 8 conductor UP-OCC ACSS, Deep Sounds SPS ACSS, Kimber PBJ RCA

Power filtration: Bada LB-5600 Filter, Essential Audio Tools Noise Eater, Essential Audio Tools Pulse Protector, Supra Mains distributor

Power cords: Hifi Cables & Cie PowertransPlus (x2), Hifi Cable & Cie SimpleTrans, Olflex power cords

Vibration Control: Aktyna ARIS decoupling feet, Maple and Acrylic Platforms, E&T rack, Stabren Damping pads, Sandbox, Brass cones, Vibrapod, Yamamoto Ebony footers and Various Herbie’s Audio Labs tweaks

Reference tracks used for the review


My (usual) reference tracks:


CD Quality

Mahler - Symphony n 5- Decca - 16/44

Sol Gabetta - Schostakowitsch Cellokonzert Nr. 2/Cello - 16/44

Vivaldi - Concertofor 2 violins - Carmignola/Mullova - 16/44

Natalie Dessay - Italian Opera Arias - Emi Classics -16/44

Puccini - La Boheme - Decca - 16/44

Glenn Gould - The Goldberg Variations (1981) - 16/44

The Essential James Bond - City of Prague Philharmonic orchestra - 16/44

The Dave Brubeck Quartet - Take Five - HDCD - 16/44

Diana Krall - Live in Paris - 16/44

Norah Jones - Come Away With Me - 16/44

Patricia Barber -Companion - 16/44

Johnny Cash - TheEssential - 16/44

Soundrama - "ThePulse" Test CD - 16/44

High Resolution quality:

Rachmaninoff Dances -HD Tracks - 24/96

Mozart Violin Concertos - Marianne Thorsen - 2L - 24/96

Dunedin Consort -Messiah - Linn Records - 24/88

Glenn Gould – The Goldberg Variations (1955) – HDTracks - 24/96

Keith Jarrett - Paris/ London - Testament - 24/96

Jazz at the Pawnshop- HD Tracks - 24/88

Alison Krauss and Union Station - Paper Airplane - 24/96

Ella Fitzgerald /Louis Armstrong - Ella & Louis - 24/96

Diana Krall – From this Moment on - 24/88

Diana Krall - TheGirl in the Other Room - 24/96

The World's Greatest Audiophile Vocal Recordings - Chesky - 24/96

The Kinks - One forthe Road Live - 24/96

The Eagles - Hotel California - HD Tracks - 24/96

Head-fi/Chesky Sampler - Open Your Ears - 24/96


Other reference tracks


I personally think that the best way to evaluate any audio equipment is to use music that one is already familiar with; however, given that the Kingrex is 32/384 capable I downloaded all the files that were available at 2L in order to compare the same music at different sample rates (44.1, 96, 192, DSD, DXD). So a great thanks to 2L recordings for offering for free such high quality samples.






The UD384 is fairly easy to set-up (by audiophile standards). You only need to worry about connecting it to the computer via a usb cable and to your amplifier via rca interconnect cables. In comparison with the Audio-gd solution (Digital Interface + dac19dsp) you save 2 power cords, a digital cable and a lot of space.


However, while it easy to set-up, I find that it is perhaps too small and somewhat cumbersome. I wish that Kingrex released a single unit version with a built-in battery power supply which would avoid having a few cables dangling around between the battery power supply, the UD384 unit and the smps power supply. That is however just nit-picking as the UD384 involves little extra cost to set-up properly contrary to many DACs I have tried so far.


U Power


If you are considering the UD384, you ought to think of the “optional” U-Power as a mandatory piece of equipment. Without the U-Power, the sound can be a little bit congested, bright and lacking naturalness and definition. Given the low price (less than $200) of the U Power and its effect on the sound, it shouldn’t be optional in my opinion.


USB cable


Weirdly enough, the UD384 was more sensitive to the quality of the USB cable than the Audiophilleo 2. Given that the AP2 is usb powered and that the UD384 is externally powered, I was expecting the USB to have little to no effect on the sound UD384. I suspect that somehow the UD384 is not 100% galvanically isolated from the usb power line of the computer.

However, you need not to ruin yourself as the relatively affordable Wireworld Ultraviolet usb cable was more or less as competent as the far pricier Artisan Pure Silver usb cable.


Vibration control


Given the low weight and small size of the UD384, it didn’t seem to be affected much by vibration treatment (contrary to the dac19dsp). For the review, the only “tweak” I used was a Herbie’s Audio Stabilizer on top of the unit, and it was more to add weight than to change the sound. Given the lightness of the UD384, it can be easily moved around by the USB and RCA cables.



The UD384 as a USB to Spdif converter


While I did most of my listening of the UD384 as USB DAC, I also tried the unit as USB to SPDIF converter. I will not go to much detail about the sound but here is what I found out: the UD384 is a very good usb to spdif converter, better than the audio-gd Digital Interface for instance, but not as good as the Audiophilleo 2. If your goal is to use the UD384 solely as a usb to spdif converter, there are better alternatives. The UD384 throws a pretty big soundstage as an spdif converter but lacks the details and low level resolution of the AP2.


So the Spdif out is a nice feature but a prospective buyer should not choose the UD384 for sole spdif transfer. It is probable that something like the Stello U3 or JK MK3 will give similar or better performance for a lower price point. However, the real strength of the UD384 is when it is used as a USB DAC. From hereafter my review will describe the sound of the UD384 as a USB DAC unless stated otherwise.


As a side note, I should perhaps mention that although the UD384 did not equal the performance of the AP2 as USB transport, I was pretty surprised to have the UD384 throw a wider and deeper soundstage (in size) than the AP2. That led to investigate possible “enhancements” to the AP2 which led me to ordering the Aqvox USB power supply. Hopefully, the Aqvox will improve the soundstage size while retaining the other qualities of the AP2 (more on that in a future review).



Sample rates – How high should you go?


Before trying the UD384, I used to believe that anything above 96K was pretty much useless for a DAC. In fact, one of the best DACs I have listened to was limited to 20/48.

It has been well documented that is rather difficult to construct digital filters at 16/44 that will preserve the time domain performance in our hearing range (20 Hz-20 KHz for those who have excellent hearing). While in theory 16/44 is sufficient to cover up to 22 KHz, it involves using complex filters that can have a good behavior in the frequency domain but a poor one on the time domain (impulse response), or vice versa. And even with the use of very sophisticated and heavy calculations, there is always a trade-off to be made between the frequency and time domain performance. Moving the sampling to 24/96 makes it far easier to construct digital filters that are good on all parameters. Some audio experts, such as Dan Lavry, say there is no need to go beyond 24/96. Other people insist that 24/192+ and DSD are necessary to maintain a perfect impulse response, at least one that sounds close to the real thing.


Since there is no real consensus on the theory side, I started listening to the UD384 at different sample rate with an “open” mind. What I realized after listening to the same files at different sample rates on the UD384 is that the Kingrex unit benefits greatly from higher resolution files. Christine from Kingrex insisted on trying DSD files and after listening to them (using JRiver upsampling to 24/384) I can confirm that I found them to be excellent, albeit not superior to 24/192 and 24/352 files.

From my experiments, I found the sweet spot to be on 24/192 files: the Kingrex really starts to sound natural at 24/192 sample rates and higher. So given that most music libraries are composed mainly of 16/44 files and perhaps a few 24/88 and 24/96 files, is there a real benefit in having a DAC that can perform so well at 24/384? The answer is yes if you use a superior upsampling such as the one provided in J River Media Center. Upsampling from 16/44 to 24/384 on J River gives a big improvement in sound. The resulting files are not as good as the native high resolution ones but there is a definite improvement with a good upsampler (SoX on Foobar does not give as good results subjectively for instance as those of JRiver).


Side note: For whatever reason, the UD384 does not seem to support 24/352 files (but supports 24/88 and 24/176). Given that I upsampled everything to 24/384 it was not a real problem, but I thought it was worth mentioning.

The Sound


Timber and Tonal Balance


When I first listened to the UD384 (with little burn-in and 16/44 files) I was a little bit disappointed with the sound. But, as I mentioned in the previous section, after trying high resolution files (24/96 and higher) and upsampling, I felt that the UD384 was definitely better balanced at those higher sample rates; Indeed, the UD384 seems to belong to the class of DACs that can benefit greatly from higher sampling rates. As a counterexample, my reference DAC, which is limited to 96K, has rather the same tonal balance regardless of the sample rate. Given how much of a difference JRiver and upsampling to 384K made to the sound, you should keep in mind that all my comments below are based on that particular set-up. Using Foobar with no upsampling does not give nearly as good results as mentioned here.


The UD384 has an overall well balanced sound. Contrary to many sub $1000 DACs, it doesn’t have a mid-treble brightness to simulate fake resolution or a mid-bass bump to simulate fake warmth. The UD384 is rather coherent from top to bottom with no emphasis on any part of the frequency spectrum. The only deviation I could detect from the “absolute sound” is a small lack of extension at the frequency extremes, especially in the low frequencies. To be more specific, the UD384 does not hit as hard on the bass as the Audiophilleo 2 and DAC19DSP (V5) combination does for instance. Other than that (small) subtractive deviation from the absolute best I have listened to in my personal system, there is not much to criticize about the tonal balance of the UD384.


As for the timber of the UD384, I was pleasantly surprised with its behavior. Up until I tried the UD384, I was rather convinced that it was almost impossible for a sub $2000 sigma delta DAC to render pianos and violins as convincingly as old fashioned R2R DAC seem to do so well.

[Note that I do not know for certain that the UD384 uses a sigma delta design but given that it seems to be using a custom integrated USB DAC chip, it is highly probable that it is a sigma delta design. To the best of my knowledge the PCM1704 is the last R2R audio dac chip still being manufactured.]


Playing The Goldberg variations by Glenn Gould (I have the 1981 performance in 16/44 and the 1955 version in 24/96) was a truly special experience. The sequence of the sound emanating from the piano is fully preserved: you do not only distinctly hear the hammer hit the strings but you also clearly hear the strings and the soundboard resonate afterwards. Some DACs put more emphasis on one part or the other but the UD384 seems to get everything right. But is it perfect? It is very close to the sound of the AP2 and dac19dsp combination, although neither as rich nor as diversified sounding. But overall, there is very little to criticize about the UD384, especially considering its price; indeed, as mentioned earlier in the tonal balance section, the UD384 sins are of omission rather than commission.


On less technically difficult recordings such as Diana Krall Live in Paris (16/44) or the Girl in the Other Room (24/96) the voice of the singer and the accompanying instruments (including the piano) sound wonderful and there are chances that you will hear new details and subtleties with the UD384, regardless of where you are coming from.


Comparing the sound produced by the UD384 against that of the AP2 and Dac19dsp combination is very interesting. While the dac19dsp is dense, “grounded” and slightly dark, the UD384 is airier, livelier and more sophisticated on the top end. The center of gravity of the dac19dsp seems slightly left of perfect (left being the low frequencies), while the center of gravity of the UD384 seems a little bit right of an ideal perfect. However, those are slight deviations from absolute neutrality and there is far more coloration among different recordings than there is between these two DACs.


However, it should be noted that these qualities about the UD384 are only apparent when one is using a good media player (such as JRiver 17), high resolution files or upsampling, a good usb cable and most importantly the outboard battery power supply.

With those pre-requisites, the UD 384 can paint a very interesting and harmonically rich picture.


Speaking of harmonic richness, I should perhaps talk about the perceived “contrast ratio”. While the UD384 sounds “sophisticated” and airy in the top end, it doesn’t have quite the same contrast ratio as that of the AP2 and dac19dsp combination which seems to be able to paint with slightly greater precision the difference in timbers of instruments and voices.

Keep in mind that the AP2 alone costs around the price of the UD384 and its battery power supply.


Unlike many mid-tier converters (and most sigma delta converters), the UD384 does not have a choppy representation of timber of voices and instruments. The UD384 rendition of sounds is a very smooth one, albeit not as sharp and defined as that of the AP2 and the dac19dsp combination.


One might think that the smoothness is an indisputable weakness; however, given how many poor recordings there are, it is sometimes a relief to have an excellent DAC such as the UD384 that is a little bit forgiving on the top end.  

Soundstage and Imaging


From the beginning, I was very impressed with the Soundstage and Imaging of the Kingrex UD384, and I also believe that it might be one of the biggest strengths of the unit.


It was rather apparent from the start that the UD384 was capable of throwing a huge, well layered and hyper defined soundstage. This was especially noticeable when using the angled driver ALO Beyer T1.

As good as my reference set-up, namely the Audiophilleo 2 paired with the Audio-gd DAC19DSP, is in other areas, the UD384 is capable of reproducing a bigger and deeper soundstage. The Audiophilleo/Audio-gd dac19 combination can still have a more holographic soundstage on some tracks, but the ability of the UD384 to draw a very deep and layered soundstage is pretty impressive.

Removing the ultra-low jitter Audiophilleo source from the equation and comparing the Kingrex UD384 against the DAC19DSP (with the Audio-gd DI as a source for instance) gives a far clearer win in this department to the battery powered Kingrex UD384.


I should perhaps mention that I mainly used the UD384 with the excellent Artisan Ultimate Silver Dream interconnects. Trying out different (and lesser) cables causes the excellent soundstage to collapse to different degrees. So in order to “squeeze” that kind of performance from the UD384, the use of high quality RCA interconnects seems to be necessary.


Furthermore, while the sound-staging can be huge at times, it does not come at the expense of the imaging. For instance, when I connect my dac19dsp to my c2 amp through the current mode ACSS/CAST connection, using the (cheap) Sharkwire interconnects, I get a similarly big soundstage to that of the UD384 and Artisan Silver cable combination; however, the resulting soundstage is rather diffused with the Sharkwire interconnects in place. Hence, I am led to conclude that the exceptionally big soundstage of the Sharkwire ACSS is a form of distortion rather than a “true” compliance with what was recorded, as it seems to be the case with the Kingrex UD384 and Artisan Silver Cables combination.

Consequently, it is a true pleasure to listen to the Kingrex UD384 with headphones; indeed, instead of feeling that the sound is somewhat stuck between your ears as many entry and mid-level DACs seem to do, you rather get the impression that the sound is originating from outside of your head, which is a far more natural way to hear things.



To be picky, I would say that what the UD384 lacks against the very best I have listened to is a truly holographic and 3D representation of the sound. If I overly exaggerate, I would describe the UD384 as being 2.5D and the AP2+dac19dsp being 3D. The UD384 USB DAC wins in the 2D size department but looses in the overall 3D impression, probably due to inferior low level detail retrieval. However, in many tracks (especially the non-audiophile ones), I preferred the rendition of the UD384 on headphone based listening.



The dynamics of the UD384 is not what draws your attention when listening for the first times to the unit. If I had to rate the dynamics capabilities of the UD384 after a short listening session, I would have said that it was adequate but not impressive.


However, after listening to the UD384 for several weeks, I can report that the dynamics of the UD384 are actually very impressive. Regardless of what type of music is playing, the UD384 sounds “alive”. While the dac19dsp can have technically better dynamics (better voltage swings?), it takes a very superior transport such as the Audiophilleo 2 to make it sing.


Overall, the UD384 is far from being boring while remaining relatively neutral dynamically throughout the audio-band. I believe that the explanation lies in its excellent handling of micro-dynamics.  

Transparency and Definition


A question that one might ask himself is: does the 32/384 capability really translates into high definition as advertised?

Before answering the question, I think it can be helpful to mention than the best measuring device I own, the EMU 0404 USB, is curiously one of the less defined and also one of the lowest resolution external devices I have tried.

So when it comes to transparency and definition, the “pixel-count” is not a reliable indicator of the outcome.


Since the UD384 uses a battery power supply, it is no surprise that it has a low noise floor (no hiss or anything). Its resolution is on par with its price tag, which means that it is much better than entry level DACs but not as good as the best I have heard.


When listening to the UD384, you get the impression that the sound is coming from a black background and depending on how revealing your downstream is what I will say below might be relevant or superfluous.

Giving the arbitrary number of 100 db as the lowest noise floor I can achieve with the AP2/DAC19 combination, I would say that the UD384 is limited to something like 70 db. It seems like a thick (black) blanket is covering the tiniest low level details that make up the recording ambiance of many recordings. While that might seem as a big difference, keep in mind that you need a pretty transparent audio chain downstream to hear those differences; if you are still using a pair of HD650s with their stock cord, there is no need to worry. However, if you have gotten to the trouble of using “high resolution” cables throughout your system and taken care of all the tweaking to increase the subjective resolution of your system, the UD384 might seem like it is lacking a little bit in absolute resolution.


With that being said, the UD384 will offer more than enough resolution in 95% of the cases. I have listened to far pricier CD players and DACs that do not approach the level of details and transparency of the UD384.


Regarding the transparency, the UD384 is a pretty impressive unit, especially considering the price. The UD384 does not seem to color in any identifiable way the music that it is playing which is an important quality for a source.




Overall, I have been positively surprised by the performance of the UD384 USB DAC when paired with its battery power supply. The unit can throw a very deep soundstage and can play with excellent accuracy and great transparency various types of music.


Considering its overall performance, its sub $700 price (with the U Power option) and the fact that you can stream music directly through USB, without resorting to an additional usb to spdif converter, the UD384 seems like an excellent bargain. In total objectivity, the amount of time and money spent on tweaking the audio-gd dac19dsp is probably not worth the increase in performance over the UD384. For anyone with a $700 budget, I would recommend without hesitation acquiring the UD384 USB DAC and its U Power supply.


Does this mean that the UD384 is as good as it gets in that price bracket? Honestly, I can’t say for sure as there are continuously new DACs being released but the UD384 seems like a safe bet. However, what I would like to see changed in the UD384 is the external casing: I would have much preferred having a one box solution, preferably on the heavy side. Many audiophiles own relatively heavy and/or stiff cables and having something as light as the UD384 might not be very convenient for everyone.



Other than that, I highly recommend the UD384 for anyone wishing to start on the computer as a source and/or willing to experiment with the effect of upsampling.


Review: Cardas Recabled Koss KSC75s

Posted by kboe on January 19, 2012 at 5:10 PM Comments comments (0)

January 2012

(Stock 75's)

Reviewer: Kevin Pope

Source: ALO iPod dock, 160GB iPod Classic loaded with AIFF

Amp: Schiit Asgard

Headphones: Koss KSC75 with stock harness, Koss KSC75 with Cardas upgrade harness

Cables: Power - Cardas Twinlink.  Analog - Cardas Quadlink 5-C

Rack: Maple wood button isolation feet

Power Conditioning: None for this review. KISS.

Sundry Accessories: Woo Audio headphone stand, Sennheiser headphone holders

Review Component Retail: $20.00 for stock and $160.00 shipped with Cardas cable.

How far is too far? As audiophiles we are constantly going too far for the sane minded, and sometimes too far within our own small like-minded circles. For the head-philes among us the camp is already split not only on cables in general, but even more so with headphone recables and much, much more so of the price. Pairing a $500.00 ALO cable on a $1300.00 T1 for the believers is not only sane, but reaps dividends in practice. But what happens when one takes that ratio to an extreme. Rather than the 1:2 ratio with our own Amine’s T1, I’m going the radical route with 7:1.

It’s no secret that I’ve long admired Cardas cables. Bob Prangnells Verumecce designs for power, digital and analog have me kicking Cardas to the side for most of my cables, but Cardas remains my headphone re-cable harness of choice, (hint hint Bob). Taking a recent budget find, the Koss KSC75, I’m having Drew at Moon audio recable a pair with a 5 foot, mini jack terminated Cardas headphone cable. This is the same $200.00 I use on my reference K702's.   I’m no Britteny Spears fan, but somehow “Opps, I did it again” seems appropriate.

(Examples taken from on other extreme recables)

While the Koss 75s play strong iPod direct, to asses the cables impact I’d need a bit more discerning rig and simultaneously not go further overboard with price ratios.  Reasonable context is important to maintain review findings so the test rig is as follows; The iPods analog output is tapped with Ken Ball's of ALO Audio's bamboo dock. This signal is ferried with my trusty Cardas Quadlinks into my secondary amp, Schiit’s entry level Asgard. Power is wall direct for minimal complexity and maximum tonal warmth using Cardas Twinlink’s 1m power cable. Both iPod dock and amp are suspended by the budget conscious maple buttons. Again an insane ratio of a nearly $1000.00 rig, (excluding the iPod) powering a $20.00 pair of clip-ons is extreme even to us believers of "whatever it takes is whatever you do".  So much for sanity, but this is the test bed.  I can already tell you that even before receiving the recabled pair, the stock KSC75s sound superb out of this rig. Just plain fun, and that’s something we could all use more of. 

(The test bed)

If you’ve heard a Cardas cable and you got a good aural lock on it’s sonic signature, then you could easily predict how these would sound. Warm, check. Detailed, check. Dense, colored and moist are all apt descriptors. But this is not, like most if not all recables, a game changer. The Koss clip-ons maintain their most prominent characteristics, which is a good thing. Chief among them their bass impact, more correctly word-smithed as jack booted. I bought these headphones as an upgrade for the five dollar generic throw-a-way ear buds I had been using at work. My job enables me to spend the first half of my day with music so long as I can keep highly mobile. But ear buds don’t do bass, the do anemic lower mid-range well, but that’s the limit for that style of transducer. While the supped up Koss’s don’t compete with my AKG’s for speed or resolution down under, they do trail rather close, and even do visceral subjective impact better. That’s where that jack booted bass comes in. Referencing one of my all time favorite go-to’s, Batman: The Dark Knight, dueling composers Hans Zimmer & James Newton Howard work their magic in what I believe is their best work yet. The infamous “God Moment” in the first track at 3:30 reveals deeper subterranean data wrought from the Koss cans than the AKG’s with similar wiring does.

When it comes to the upper highs, the Koss lose out to the AKGs current flagship. Here the extra dough spent on the 702’s provide substantially more air and definition. Cymbals splash with more metal ring and less haze or fuzz as the Koss reproduce. It’s easy to criticize once you’ve heard better, but for $160.00 shipped I’d not. And while it’s a cop out to use a worn out phrase, it’s true and warranted.

Midrange is typical Cardas, and having been extensively covered before in my reviews here I’ll spare you a repeat offense.

So where does that put us. $20.00 buys you an amazingly good deal. For $160.00 you’ll get a clip on portable headphones that are maximized sonically and plays well in the lower midrange league where it’s new price puts it. Competition from something like Grado’s SR-80 is roughly on the same level. Going from memory the SR-80s gave better highs, a clearer midrange, but held back on grunt and fortitude in the nether regions. Something like Audio-Technica’s ES7 seduce with higher tonal color and richness, but fail to impress with detail as precise as the Koss clips.

Cardas bettered these headphones just as it had with my former HD-650s and my current K-702s. But the victory belongs to the all natural Koss KSC75s. I’m not going to say they don’t deserve to sound as good as they do for $20.00 or $160.00, because I’m glad they do.


Member's Review: Modified Wyred 4 Sound DAC-1 (and the Audiophilleo 2 S/PDIF transport)

Posted by kboe on December 27, 2011 at 12:20 AM Comments comments (8)


NOTE:  This is a review pinned by one of our own talented members who's screen name is "Rdr. Seraphim".  He has worked on this for quite some time and when he asked me to read it we both agreed that it should be posted to the main page of the website.  This is a very talented writer and communicator, and like Amine our site owner, his reviews are clear, precise in wording and leave one with no doubt as to what the product will sound like.  Please enjoy this wonderful review as I have.




The Wyred 4 Sound DAC-1 under review--obtained early during its original release--was a special order unit, the original buyer requested a modified DAC-1 with the 24-bit 192KHz USB option, but due to finances had to back out, a lucky break for me. After a brief audition, I returned the unit to the factory for upgrades bringing the unit to parity with the DAC-2, sharing the DAC-2’s power supply, low ESR “super-caps,” an ultra fast Schottky type bridge rectifier, and 24-bit 192KHz USB input, while retaining the primary inputs (USB, Toslink/COAX) of the DAC-1. Like the DAC-2, the modified DAC-1 "requires" software drivers.


Both the DAC-1 and DAC-2 use the same DAC chip, the Reference ESS9018 in quad-differential mode. Suffice to say that among a handful of DACs on the market, it is considered by some to be the most technologically advanced digital to analogue converter available.

There is considerable discussion about the audibility of jitter on some of the audio blogs. In the ESS9018 “...a patented technique is used to re-create the audio data in a crystal-controlled low phase-noise clock domain completely isolated from the clock domain of the transport medium and so not at all related to the clock domain in which the data was sampled1.

Almost everyone would agree that lower distortion (THD, IM) is a good thing. Our auditory system is sensitive to different types of distortion. We are particularly sensitive to 3rd order harmonic distortion, but 2nd order harmonic distortion is sometimes additive, or euphoric. For example, during soft clipping many single-ended tube amplifiers are perceived to simply get louder, versus its solid state sibling, the typical distortion generated during any clipping grates on our hearing.

From the ESS9018 abstract: “The noise that jitter induces is not easily described: it is not a harmonic distortion but is a noise near the tone of the music that varies with the music: it is a noise that surrounds each frequency present in the audio signal and is proportional to it. Jitter noise is therefore subtle and will not be heard in the silence between audio programs. Experienced listeners will perceive it as a lack of clarity in the sound field or as a faint noise that accompanies the otherwise well defined quieter elements of the audio program.2

It is not the purpose of this article to argue the audibility of jitter related to digital audio, but to simply state that in the opinion of this writer, eliminating jitter is as important as minimizing as many known forms of distortion as possible; and I have taken additional measures to ensure that the W4S DAC is fed with a pristine digital audio data stream3.

So, whether or not the elimination of jitter provided the benefits I hear with the W4S DAC, it is "my opinion" that the DAC-1 is nonetheless a remarkably neutral, transparent, high resolution audio component. Musical instruments have improved truth of timber missing from other designs, a soundstage full of information about the recorded venue, and with many more musical details than was previously experienced. It all adds up to a thoroughly enjoyable listening experience.


Digital devices are sensitive to timing errors due to temperature fluctuations, and like some of the more upscale DAC’s, the power switch on the back of the DAC-1 & 2 is intended to be left on, which leaves the system in a kind of "warm," standby mode. The centered “On” button on the front display is really more of a mute button.


My music system is entirely computer based. I gladly admit my addiction to the nearly instantaneous random access nature of hard disk based music systems, along with the ability to download high resolution media if and when I choose. Computer based music is the future, and dedicated music streaming players like Pure Music are state of the art, equivalent to any dedicated hardware based players:


"When playing 16/44 sources, Pure Music sounds as good to me as the best CD transport anyone can dig up - as long as I'm using a high-quality jitter-immune D/A converter. But I can play my 88.2 kHz, 96 kHz and 192 kHz/24 bit masters and then Pure Music beats any CD source. I love being able to play a collection of my masters using the friendly iTunes interface, but with Pure Music bypassing any sound processing that iTunes performs. Throw in a calibrated, dithered volume control marked in decibels, and I'm in heaven. Mechanically, the Mac Mini is quieter than some CD players!" 4


The physical restrictions and limited availability of high resolution media is—thankfully—becoming a thing of the past. HDTracks, Bravura Records, High Definition Tape Transfers, L2, Reference Recordings, and many others are helping move our hobby to the next phase in audiophile evolution. I don’t foresee myself returning to physical media, especially of the shiny silvery variety. If I ever revert back to disc based playback, it will be of the black, oil-based vinyl variety, primarily for the nostalgic experience.



• AC Outlet: Oyaide SWO Gold-Gold-Bronze Cryo 15A

• Balanced Power: BPT BP 3.5 Signature Plus Balanced Power Ultra-Isolator

• Conditioning: Richard Gray RGPC 400 Pro (X2) with Harmonic Technology AC-9 power cords (serially plugged into the BP 3.5 Signature Plus)

NOTE: All audio and computer components in the music chain are plugged into the BP 3.5 Signature Plus


• Software: Pure Music v1.83


• Computer: BTO (build to order) MacBook PRO 15" 2011 with Mercury Extreme SSD and 8GB memory


• Amplifier: Modified DNA (Donald North Audio) Sonett Headphone Amplifier with 1959 Phillips Miniwatt GZ34 and 1980 DR6H30; the tubes are fitted with Herbies Audio Labs UltraSonic Rx Damping Instruments


• BPT L-9C power cord dedicated to the BPT 3.5 Signature Plus Ultra-Isolator

• Downsize VLR - Veil Lifter Reference AC power cord for the amplifier and DAC

• Harmonic Technology AC-9 (one for each RGPC serially plugged into the BP 3.5 Signature Plus)

• USB Cable: Wireworld Platinum Starlight

• RCA Interconnects: Downsize UR1 - Ultimate Reference One


• Isolation: Marigo Mystery Feet under the DAC-1 and DNA Sonett, each resting on 2" maple cutting boards; the MacBook Pro rests on an air bellows Seismic Sink Platform from Townsend Audio

• Vibration: Mapleshade Micropoint Heavyhats judicially applied to the DAC and amplifier; and some "kewl" (cool) framer's weights to add mass

• Vibration: GZ34 and 6H30 are fitted with Herbies Audio Labs UltraSonic Rx Damping Instruments



• Westone ES3X IEM with the TWag replacement cable



The primary characteristics I listen for in a music system are resolution, balance, and musicality. In fact, music is the only thing I use to listen and assess all of the components of my music reproduction system including power conditioning, cables, source, amplifier, and transducers. Numbers are great when they make sense and correlate with what I’m hearing. Sometimes,I even fall into an objectivist role, i.e., is the power is on? Are the lights on? Is music playing? ;-)


1.) resolution, the ability for a music system to reproduce and reveal every nuance in the recording. I believe this is foundational to establishing the music venue. Closely associated with resolution is texture, or the ability to unravel the inner workings of a sound, regardless of its origin. More on texture later;


2.) balance, or the ability to recreate the spectral presentation of the recording, with special importance--for me--on the midrange, and;


3.) musicality, for the ability to recreate the dynamism of the performance, and which conveys the intent of the composer through their music, its message, and the emotions elicited during the listening session. The ability to reproduce these musical queues are what enable us to say, “What a performance!”

If there is one area I admittedly place more emphasis on than others, it’s the midrange. I love classical music, massed or small choral works, and natural acoustic instrumentation.


Dick Olsher describes my personal preference on the midrange best: “You might wonder why I'm obsessed with the midrange as the cornerstone of musicality. It's really a function of the physics of musical instruments. The average spectrum of the orchestra peaks around 400Hz to 500Hz, and then decreases with increasing frequency. The mean spectral level at 2.5kHz to 3kHz is already about 20dB below the peak. And, of course, the lower midrange is rich in fundamentals and their first overtones. In particular, the range of 262Hz to 330Hz (C4 to E4) is common to all voices. In my book, if a component can't get it right in the midrange, frequency extension, imaging, etc., matter very little. The midrange, to my mind, is literally the heart of the matter.”


Ultimately, if the midrange is missing in action, the rest matters very little.




resolution |ˌrezəˈloō sh ən|


4 the smallest interval measurable by a scientific (esp. optical) instrument; the resolving power.

• the degree of detail visible in a photographic or television image.


The analogy of resolution in music reproduction might translate to something like this:


resolution |ˌrezəˈloō sh ən|


4 the smallest interval perceivable (esp. audible) by the human ear; the resolving power.

• the degree of audible detail from a transducer or amplification device.


The DAC-1, with the modifications outlined in the Introduction, is the most revealing, transparent, and musical digital source I have personally experienced or owned. Focusing on any area revealed new and undiscovered musical cues, not just glaring, in your face differences, but shades of timbrel nuances, and macro and micro details seemingly obscure or at best opaque.


This was the first DAC that provided me with a truly adequate (in the strictest sense of the word), reproduction of the musical event or recording. There was never a sense that something in the recording was vague, missing, or leaving me wondering what I was hearing. My listening experience with the DAC-1 was/is experientially full and satisfying.


Resolution for many listeners sometimes means a lean, clinical, razor sharp presentation lacking body and depth, or lacking the emotive musical qualities that connect one to the music. In sometimes stark contrast, the resolution presented by the W4S DAC was always musical, fluid, naturally revealing, visceral. It was never clinical or cold, unless the recording itself was analytical, clinical or cold. Instrumental images were naturally three-dimensional, as was the reproduction of the recorded venue whether it was a multitrack studio recording or the live concert hall.

Vocal definition was nuanced, communicating the ebb and flow of the performer’s intonation, dynamic contrasts (loud to soft, and soft to loud) were more apparent, as was diction and enunciation, revealing the actual formation of the vocal delivery. Choral and solo performances were wonderfully intimate and personal.


Musically, the DAC-1 renders vocal resolution naturally, evenly. Vocal textures are clearly discernible, sometimes smooth, silk-like, pure tonality (e.g., Kathleen Battle) or coarse like burlap or canvas (e.g., Johnny Cash, Marc Cohn), and everything in between, including breathy, wispy, bright or dark.


Some of my favorite classical music is performed on the pipe organ. I believe it is one of humanity’s crowning achievements in musical instrument creation. Yet, I stopped listening to classical organ music when I went digital, so many years ago. Compared with some of the better analogue (vinyl) rigs I had at the time, digitally rendered organ recordings sounded flat and lacking substance and body. To attain an acceptable sonic "entry point," equivalent to my wonderful Thorens TD-125 MKII, SME tone arm and cartridge (now why did I get rid of that lil' treasure!), was five to ten times the cost!


Thankfully, a lot has changed since then, including the entry cost for near reference level sound quality components like the W4S DAC. Listening to classical organ music is a thrill on the modified DAC-1, unleashing the power and majesty of the pipe organ, its dynamics, detail and luster! Here’s an older recording that sounds wonderful on the DAC-1.

• Johanne Pachelbel, Music For Organ - Werner Jacob



texture |ˈteks ch ər |


the feel, appearance, or consistency of a surface or a substance : skin texture and tone | the cheese is firm in texture | the different colors and textures of bark.

• the character or appearance of a textile fabric as determined by the arrangement and thickness of its threads: a dark shirt of rough texture.

• Art the tactile quality of the surface of a work of art.

• the quality created by the combination of the different elements in a work of music or literature : a closely knit symphonic texture.


verb [ trans.] [usu. as adj.] (textured) give (a surface, esp. of a fabric or wall covering) a rough or raised texture: wall coverings which create a textured finish.


The sonic character rendered by the DAC-1 is distinguished from some early DACs and CDP’s I’ve owned and auditioned by its ability to unravel fine musical textures. Vocals, musical instruments, massed strings, orchestra’s and choral performances revealed all the timbrel character, nuances and shadings missing in lesser designs, making it easier to discern differences between similar instruments. While it has always been part of the recording, the newly discovered information was a revelation that made listening to music fun, enjoyable and fulfilling. With the modified DAC-1, it was just easier to relax and listen to music hour after hour. My longest session with the DAC-1 was nearly five and a half hours, well into the wee morning hours!


By the way, I enjoy binaural recordings way more with the DAC-1. I’m convinced more than ever that binaural recordings require a high resolution source with very low jitter in order to reproduce key timing queues, the result of capturing music the way we hear. Binaural recordings are more naturally rendered due to capturing the imaging present during the recording. Soundfield recordings attempt to reproduce imaging through manual studio manipulation of microphone placement, panning, and/or added spacial effects. Below are two recordings that show off the effects of the binaural recording technique:


• Rachmaninov Plays Rachmaninov: Zenph Re-performance

• Explorations in Space and Time: Chesky



Vocal reproduction, male or female, solo or choral are reproduced sans sizzle. Sibilance, on the other hand, occurs naturally during singing or conversation, but reproducing/recreating it naturally is apparently not so easy. There are lots of examples of bad recordings, where sibilance is unbearable. Assuming a decent recording, with the DAC-1 when sibilance is reproduced, you can clearly hear the texture and inner working of its creation, development, formation and resolve. This is, for me, where the proper recreation of texture of the musical event translates into musical enjoyment. It’s the natural recreation of what we hear at a live performance, but take for granted due to existentially “being in the moment.” The ability to clearly reproduce the inner texture of the voice, dynamics, phrasing and intonation, the rising and falling of the singing voice in performance makes clear the emotional intentions of the composer, conductor. It just sounds real.



Bass resolution is not something we spend a lot of time trying to describe. As the foundation of music, it elicits more of an emotional response; it’s what "moves us.” With the modified DAC-1, listening to the whack of the bass drum (or kick drum) actually reveals in your mind's eye the movement of the membranophone (the skin stretched across the cylinder) as it is struck by the beater, hearing (sensing?) the back wave of the drum as the membrane moves back and forth. You can feel the attack, hear the timber and tone of its tuning. This level of bass resolution and texture is equally inspiring with Jazz, Rock, or Classical.



The splash of a cymbal reveals the same inner texture and color evident in vocals. It’s not all flash and sizzle, but rather the unraveling of the inner workings of what characterizes the sound of the cymbal, whether it is struck or brushed. The timbre of the different types of cymbals (Hi Hat, crash, splash, Ride, etc.) are clearly distinguished.


Violins were rendered with body and weight as well as the full harmonic expansion into the “air.” I’m always cautious when I hear thin, wispy sounding violins, as my experience during a live performance is anything but. Massed strings were reproduced with all the rosiny textures of multiple bows on stringed instruments playing together, in concert.


Hopefully, I have conveyed my impressions and observations of the resolution and texture possible with the modified DAC-1 or the stock DAC-2. If you wanted to, you could deconstruct the instrumental characteristics necessary for a CSI episode on audio criminology. What is so unique, seemingly, about my experience with the DAC-1 is that this level of resolution/texture results in increased musical involvement! Rather than focusing on the technical merits of the DAC, you are drawn into the emotional flexing that the musicians were trying to elicit, and thus the message.


balance |ˈbaləns|


2 a condition in which different elements are equal or in the correct proportions : overseas investments can add balance to an investment portfolio | [in sing. ] try to keep a balance between work and relaxation.

• Art harmony of design and proportion.

• [in sing. ] the relative volume of various sources of sound : the balance of the voices is good.


The DAC-1 has excellent distribution of energy throughout its frequency response. Everything feels properly distributed, only the performance itself providing emphasis as dictated by the composition, conductor or musicians. The output from the DAC-1 provided solid performance in its bass reproduction. It’s not overemphasized, bloated, too lean or loose. Rather its solid and taught with the proper sense of support; no loss of steam with the DAC-1! The DAC-2 version can substitute as a preamp too!


musicality |ˌmyoōziˈkalətē|


tastefulness and accomplishment in music : she sings with unfailing musicality.

• the quality of being melodious and tuneful : his speaking voice hinted at musicality.

• awareness of music and rhythm, esp. in dance : the audition panel was looking for coordination, musicality, and flexibility.


How can we ascribe a human attribute to an inanimate object composed of sheet metal, various earth elements, and flowing electrons?


In the context that the modified DAC-1 is simply a transport, I find myself more easily immersed in the music. When I listen to music through the modified DAC-1, I feel like I “get the message” more clearly.

When I listen to a piece of music through a transducer whether it be an amp, preamp, loudspeaker, or in this case, a DAC, I try to imagine being in the moment with the performers. How well I am “transported” to the recording venue is what makes something like a DAC part of the musical chain, at least for me. In the case of the DAC-1, it's a very clear window into the musical event.



At no time did I find myself focusing on any particular spectrum of the music with the Wyred4Sound DAC. If I was drawn to the cymbals it was because of the added information about its formation and resolve; or the sibilance on hearing the development of a consonant, the sound of the breath partly obstructed when combined with a vowel to form a syllable; or of a bass note particularly resonant as defined by the construction of the musical instrument, its characteristic sound.


When we get a new audio component, there's a tendency to try out all our sizzle and dazzle music tracks, our "reference material." The DAC-1 provided me a very different experience from my earlier days with my Enlightened Audio DSP-1000, later the 7000, the wonderful sounding Ah! Njoe Tjoeb CDP, or more recently the Meridian CDP considered by many to be excellent, if not near state of the art. With the DAC-1 I found myself engrossed in entire albums.



2, p3

3 See the section on "Enter the Audiophilleo 2"

4 Bob Katz, Mastering Engineer, Digital Domain, Orlando, FL; Formerly Recording Engineer and Technical Director of audiophile label Chesky Records




Amine Slimani's review of the Audiophilleo 2 (AP2) piqued my interest. I wondered, "What would the lil' grey box do for my modified Wyred 4 Sound DAC-1?" From a jitter perspective alone, the AP2 boasts the lowest published jitter specs of any S/PDIF transport that I could find.


Everything I heard related to the W4S DAC remains true. I believe the W4S DAC is comparable to DACs multiple times the asking price of either model (DAC-1 or DAC2). However, adding the AP2 clearly reveals limitations in its USB implementation. Adding the AP2 transforms the W4S DAC allowing it to play in a different league!


NOTE: Nothing is perfect in audio reproduction, but I believe Amine's review is very conservative in its optimism and praise. Listening to the AP2 and W4S DAC combo is stunning! Please read on!


I believe that the implementation of the USB interface, at least in the Wyred 4 Sound DAC-1 or DAC-2 should be substituted for the Audiophilleo 1 or 2 S/PDIF transport. The difference is so startling that going back to the USB interface is like swapping out the Leica M9 for an iPhone for photography. If you require corrective lenses, the difference is like first waking in the morning, seeing out of focus, and then putting on your spectacles (especially if you're near-sighted)--everything snaps into focus. Sadly, all the reviews on the W4S DAC that I have read were auditioned only using the USB interface. The W4S DAC is capable of far greater resolution than is being currently experienced. (EJ! Take notice!)


As anxious as I was to try it out, my buddy beat me to the punch. My first experience with the Audiophilleo 2 was in a near six-figure reference level audio system, including the Wyred 4 Sound DAC-2 (yes, we believe it's that good). And before I could tear myself away from work long enough to audition it, I e-mailed him to ask what he felt the value proposition was. He quickly shot back:


Question: what quantum leap does an Audiophilleo 2 make to your system?


Answer: more than a $10K improvement to your system. Probably more than $20K. Collect pop bottles if necessary to purchase one.


That got my attention! Exaggeration? My buddy is not easily impressed.


After just an hour in his custom Rives Audio designed media room, I headed home, and without asking permission from my dearly beloved, I sent Phillip my Paypal order. I couldn't wait and had it shipped 2nd day. Upon its discovery in my audio kit my wife (still smiling) said, "Merry Christmas!"


I don't believe Amine mentioned it in his review, but let this one cook for the specified 200 plus hours. Even out of the box it's a revelation, but letting it simmer bears more fruit. Like pruning a tree to produce more fruit.


The Audiophilleo 2 is about truth of timbre, detail, delineation, nuance, resolution and refinement. Imaging is solid, holographic. The AP2 illuminates the recesses of the recorded venue be it a studio or concert hall. Be prepared to hear the most subtle (intimate) vocals, and purity of tone. As Amine mentioned in his review, instruments (including cymbals, yes, cymbals) and vocals have a warmth of timbre (saturation?) that surprises and excite the auditory senses.


If you've listened to a musical score before, listen to it again with the AP2. There's so much more! Yes, it's the exact same recording. Yes, you've heard it a hundred times, but you may never have heard it like this before! What's even more remarkable is that listening to it again, and again doesn't bore! It's as fresh as when you heard it the first time with the AP2!


I continue to be amazed, awe struck, mesmerized by how the AP2 compliments the Wyred 4 Sound DAC. I concur with the title for Amine's review, "…The Missing Link." I recall first hearing the (second) Sheffield Labs direct to disc recording of Lincoln Mayorga and Distinguished Guests, "The Missing Linc." In the day, it was the standard bearer for what was to come. The Audiophilleo makes a similar impression!


NOTE: I still own many of the Sheffield Labs Direct to Disc LPs. However, I no longer own a turntable or phono preamp. The tape transfers are similar, and offer a window into the history making sessions, but nowhere near the discs.


The last impression I want to leave is probably more psychological, but it appears to be specifically related to what happens when something is just "right." With the AP2, music through the W4S DAC sounds real, and therefore is easier to listen to. It's not clear why, but the W4S DAC 2 coupled with the AD2 is a killer combination. Even though I was wondering about the AP2 benefits on the W4S DAC--after all, the ESS9018 is supposed to be immune to jitter--the difference was more than I expected. Music has never sounded so natural.


NEWS FLASH! There was a rumor that Phillip was designing a battery power supply. In an e-mail he confirmed it was true, and he hopes to make it available early next year, January 2012. I tried to get an early version, but it's still in the testing phase. He's confident about it enough that he's reworking his Web site.

Told you it was good...