Christiaan Punter 1 March 2018
Ayon Stealth DAC and Ayon CD-T II Signature CD Transport
All-tube DAC/Preamp and Transport combo with a superb level of musical involvement
The Stealth is a fully-fledged DAC compatible with PCM and DSD signals, converting both of these natively via a wide range of connection methods. It also has an analog preamp built in with analog volume control and complete with two analog inputs. Importantly, the signals from these inputs remain analog throughout the DAC: they are not digitized and converted to analog again. The Stealth has a dual differential class A output stage with two 6H30 tubes per channel. There is no negative feedback of any kind and there are no solid state devices in the signal path: even the rectification stage is tube-based.
I’ve had the Ayon Sigma DAC in the system on several occasions. The Sigma is positioned as Ayon’s entry-level DAC and considering the industry trend to position serious DAC prices at the 10k mark, at 3995 euro it is priced incredibly sensibly, and even more so if you consider how great it is. Nevertheless, it took only a few audio tracks for me to strongly suspect that the Stealth has a more sonorous, more voluptuous sound than the Sigma. A cross-comparison confirmed my suspicion and also revealed an interesting detail about the filter- and upsampling options. The Sigma can sound a little dry with no upsampling but becomes smoother and more appealing with 24/192 upsampling switched on. Its bass then becomes thinner and treble more apparent but switching to Filter 2 nicely compensates for this. This way, both its owner and myself find the Sigma to sound best. Note that the manual describes filter 1 as having a slow roll off, sounding smoother and filter 2 having a fast roll-off, sounding more analytical but in practice, I experience this in reverse. When I asked Gerhard about this, he confirmed that this is indeed stated incorrectly in the manual and has been flagged for updating in a next revision.
The Stealth sounds smooth, rich and seductive right from the start, even with Filter 1 and no upsampling. Filter 2 further increases the naturalness and rolls off the treble while upsampling adds a more ethereal quality to the sound which I feel is not needed for this DAC. Because I prefer its slightly tighter sound, I conducted the comparisons with Filter 1 and no upsampling. This also made for equal comparisons with the Bricasti M1 DAC and the Aqua Formula xHD DAC. The former also uses no upsampling and is generally preferred using its linear filters and the Aqua is a bespoke discrete Ladder DAC, NOS, filterless design. Different systems and taste will dictate different results, so please always just experiment with the filter- and upsampling settings to find your own preference.
Unlike the Sigma, the Stealth has an analog preamp built in with analog volume control and complete with two analog inputs. Importantly, the signals from these inputs remain analog throughout the DAC: they are not digitized and converted to analog again.
Before employing the Stealth as a preamp, first I wanted to assess its qualities as a standalone DAC, via the Jeff Rowland Corus + PSU preamp. The rest of the system consisted of an AudioAanZee Reference Flow music server with Euphony Drive, a PrimaLuna DiaLogue Premium power amp with KT150 tubes and recently refurbished Apogee Duetta Signature speakers as well as Wilson Watt/Puppy 8 speakers. Connection to the Stealth and all other DACs, for the purpose of this review, is always via USB, using the same AudioQuest Diamond USB cable.
While not as even-handed as the 10.000 euro Bricasti or as transparent and refined as the 13.6700 euro Aqua, the Stealth DAC has a sound that appeals immediately. It sounds big and generous, with a richly colorful and free-flowing midrange and smooth, fluid, well-extended treble. There is a mild thickening in the upper bass and lower midrange that is not there with the other two DACs, which indicates that the Stealth is not entirely as transparent or as neutral as these DACs. The strange thing, however, is that technical precision is not very relevant for musical enjoyment, sometimes rather the opposite. This is definitely the case here, the Stealth drawing me into the music and not letting go until the clock tells me that it is time for bed.
The Stealth also has two analog inputs and what better way to test them than by using the Aqua Formula xHD DAC for this. Reassuringly, several relay clicks are heard when switching to the Stealth’s analog inputs. The Aqua, connected with AudioQuest Water interlinks, indeed sounds more accurate. Compared with the Stealth’s built-in DAC, the delivery is more even-handed and detailed, with a more articulate bass. I don’t blame the Stealth though. I would say it is only fair as the Aqua Formula xHD is twice as expensive. And who knows what a 14.ooo euro Ayon DAC would be capable of?
Interestingly, using its analog inputs, the aforementioned thickening in the upper bass and lower mid is still partially there and this seems to indicate that it is mostly the built-in preamp that is responsible for the unit’s character. Would the more expensive Stratos improve on this particular aspect? Perhaps it does, but ultimately this is no issue at all. Switching back to the Stealth’s built-in DAC the sound becomes less articulate and precise but also considerably smoother and richer, which definitely has its own charm, especially when used with the very revealing Wilson Watt/Puppy 8’s. As always it is the system-match which defines the relative success of any audio component and the Wilsons sure love what the Stealth does.
In conclusion, while I know that tubes can actually have less coloration and distortion than solid state equipment it is probably a conscious decision taken by Ayon to voice the Stealth the way that it is. Also, I don’t think that many tube lovers are craving for absolute accuracy. Rather, these people want the music to speak to them on an emotional level. And this is exactly what the Stealth does incredibly well. Its particular character, while noticeable when switching from the aforementioned DACs, actually has a tendency to enhance the emotional acceptance of the sound once you are used to it, which is basically after a couple of tracks.
So far though, I am still using the Rowland Corus preamp. What will the Stealth do when driving the power amp directly?
Stealth as DAC and Preamp
I will not beat around the bush: it truly amazed me how well the Stealth performed as a standalone DAC and Preamp. Up until now I had been listening to it through the Jeff Rowland Corus preamp + PSU, but when connecting it to the PrimaLuna DiaLogue Premium power amp directly, you could definitely hear how the last layer of solid-state influence dissolved, the system now sounding utterly free-flowing but every bit as powerful and energetic, arguably now even moredynamic! Up until now when removing the preamp and listening to a DAC directly usually made for better bass but always came with less appealing aspects such as a flatter soundstage or dry treble. But the Stealth is not just a DAC, of course, it is also an analog preamp!
My audio buddies JW and JC were also present during this session and they, too, were quite flabbergasted by the increase in naturalness and life-like believability. Without the Corus, a level of control, or perhaps superimposed pacing, fell away, which sometimes made me feel that the rhythm was now less evident. But how could this be? The Stealth’s preamp section was always in the signal path and adding what is basically a second preamp downstream should not make matters any better.
But the longer I listened to this setup, the more the sheer emotional content of the music simply took over from my calculating brain. Pretty soon I was completely immersed in beautiful music. In addition to the living and breathing sound, the soundstage was now also a lot deeper. It was much more like being at a live venue looking at and listening to real humans playing in different positions on a stage that extended way backwards. What’s more: when focusing on PRAT and bass articulation again I noticed that there was actually nothing wrong at all, and I couldn’t understand why I felt these aspects took a step back. Apparently, I just had to get accustomed to the new, freer delivery. In any event, I was now fully enjoying all the tracks that I cared to play. As one would suspect, the fully tube based system was fabulous with Jazz, but it was just as capable of fully conveying all the aspects of heavy R&B, Dub-Techno, and complex electronic music.
After hearing various tube power amps in my system I had already fallen out of love with the model 6 transistor power amps and I could no longer truly appreciate most of the transistor power amps that I tried after that. Surprisingly, while it can certainly be beaten by more precious designs, the very affordable PrimaLuna DiaLogue Premium power amp never fails to deliver the musical message. Substituting its EL34’s for KT150’s further strengthened the aspects that are most important to me and so it happens that the very expensive Corus preamp was partnered with the very affordable DiaLogue Premium power amp. The secret, I fear, is not in an amp’s absolute quality but in the application of tubes. For power amps, I had already made up my mind and even if I had not yet decided on a final brand, it was going to be a tube amp! But I never doubted the Corus + PSU, which is a transistor preamp, and a darn incredible one at it!
No matter which speakers are used: the Ayons always perform with verve
There is no way around it. Now having heard the level of musical involvement that is possible with the Ayon Stealth as a DAC + Preamp, I’m afraid that I am now completely spoilt for transistor designs.
After more than 5 years’ production time of the CD-T it was decided to rework it and equip it with some special features. Like the original, the CD-T Mk II only plays Redbook CD’s but according to the maker it is designed to play these with new levels of resolution, dynamics, and musical naturalness. Ayon has kept the legendary Philips CD-Pro 2 drive, the dual digital tube buffer with 6H14 and the chassis. Special attention was paid to the new clocking system, the modified power supply and the new dual ground system.
With the Signature version, there is now also the possibility to upsample CD’s to DSD 128 by means of the optionally available DSD-converter module, which is included in this review sample. The CD-clamp-system has changed from being attached to the lid to being a separate clamp that is put on manually, separate from the top lid.
I asked Gerhard why they decided to change this and he explained:
“The separate clamp is now bigger and much heavier and this stabilizes the CD much better, it is a real sound improvement. Besides this, the CD rotation noise is also less.”
Digital outputs are now galvanically insulated from each other as well as available twice. Contrasting with the tube-only SPDIF outputs of the original CD-T (although the AES/EBU output was not tube-buffered), the CD-T II now offers separate solid state and tube-buffered outputs, that can be switched between on the rear-panel. The I2S output has remained and there are now also DSD L, DSD R and word clock outputs on BNC.
Sound – 16/44 SPDIF
Using the SPDIF connections, the transport outputs the native 44/16 signal. When using the I2S output, the signal is internally upsampled to 88.2kHz and this cannot be defeated on the player.
When asked, Gerhard explains:
“Over the last 12 years customers want upsampling and therefore we made it non-switchable and this makes it even better sounding instead of adding switching devices”.
When using the CD-T II transport via its I2S connection, the Stealth’s display indicates to have switched to 24/192 upsampling, and this cannot be defeated on the DAC either. This does not indicate that the DAC is (also) upsampling but the indicator is simply lit to indicate that the source signal is upsampled, in this case in the transport.
I had already compared the original CD-T with two of my Levinson players (no.390S and no.37), and it has to be mentioned: the Ayon sounded better. Not smoother as one would expect, but more dynamic and actually more involving. That was quite a surprise at the time, especially given the fact that all these players use the same Philips CD Pro2 transport, and one of the Levinsons had actually been serviced very recently during which not only the transport was replaced but also all the important capacitors.
Although I had already established that the Stealth is not only a very fine DAC but actually makes an even better DAC+Preamp, I wanted to assess the CD-T II in known circumstances so it was first listened to using my usual solid state reference system, so the Stealth DAC was left out of the picture for now. Connected from its transistor-buffered output via Belden RG59 interlink to the Aqua Formula xHD DAC which was connected to the Corus + PSU preamp, I set out to assess how the CD-T II’s SPDIF outputs compared to server replay, all in Redbook 16/44.
Music Server aficionados should probably look away now because I am going to write that the transport actually sounded better to me! The AudioAanZee Reference Flow music server sounds very smooth and musical and the Euphony Drive has further improved its existing qualities, but it takes literally no time at all to realize that the CD-T II simply sounds better. One might expect the transport to sound smoother or more fluid, but these are aspects where this server actually really excels. Rather, the CD-T II sounds more vivid, more dynamic and lively, and temporally also more involving. With the latter, I mean that subtle temporal changes are more apparent rather than being smoothed over. The server by comparison still sounds pleasant: just as airy, just as relaxed and just as finely detailed, but somehow the entire experience is flattened.
When switching from the CD-T II’s transistor output to its tube-buffered output, the sound becomes even freer, perhaps less articulate, but somehow more involving still. Furthermore, the soundstage grew even deeper. Put very simply, the transistor output could be said to be more accurate but the tube output sounds more free-flowing. Personally, I lean toward the more articulate transistor output but the beauty is that there is no urgency to choose between them because the player simply offers both options, and the transport sounds superb with both outputs.
Sound – I2S and DSD upsampling
The CD-T II does more than just read CD’s: it can output them in I2S and even upsample to DSD and then output to separate DSD L, DSD R and word clock BNC connectors. When using the I2S output, the transport always upsamples to 88.2kHz. This is a good choice because it is precisely double the CD’s native 44.1kHz sample rate. If Ayon would have opted for 96 or even 192kHz then this would have meant that the upsampled values cannot be divided and always have to be averaged, which usually results in softer transients. This is why I normally prefer to leave signals in their native resolution but, alas, this setting cannot be changed. Then again: soon after I started listening to it I realised that the CD-T II sounds perfect just the way it is. Evidently, the upsampling is implemented in a very careful manner.
The Aqua DAC also decodes DSD and also offers an I2S input but because there is no real standard for this format, manufacturers tend to implement them differently and, alas, the CD-T II’s implementation is not compatible with the Aqua’s. One could make a special ethernet cable with bespoke pinout that should work but for the purpose of this review, I did not want to investigate this. So, here the Stealth DAC comes back into the picture. And because the Stealth had already convinced me of its preamp qualities, the Corus was left out, making the review system now 100% tube-based.
Comparing SPDIF to I2S is easily done because the transport allows connecting all its cable combinations simultaneously. I’ve often heard I2S provide a deeper soundstage than the SPDIF connections and in this case, this is also true. SPDIF offers a slightly forward sound than I2S. The bigger difference between the two formats, however, is in terms of bass. SPDIF sounds more ballsy than I2S (which I like) but I2S sounds quite a bit more precise and articulate (which I also like). I lean toward I2S but which of the two is preferred will ultimately be personal and dependent on system synergy. Fortunately, just as with the option between tube- and solid state outputs, the choice is yours.
DSD upsampling seems like a good idea because Delta/Sigma DACs by nature work in a direct stream kind of way. This is one of the reasons why many modern DACs (for example the PS Audio DirectStream and the Matrix X-Sabre Pro) sound better with DSD (native or upsampled) than they do with PCM. In the case of the CD-T II and Stealth DAC however, it works out differently. When comparing I2S or SPDIF to the 3-BNC DSD inputs directly by switching between them repeatedly on the Stealth DAC, the DSD signal certainly sounds smooth and fluid, but also softer, with rounded transients, and less overall power to the delivery. Bass notes, in particular, are less weighty and less punchy. Much as I wanted to like this special DSD implementation I personally prefer the more powerful and dynamic PCM over the I2S connection.
There’s one more input option on the Stealth DAC, which is a separate “DoP” I2S input. The manual states that this input will allow DSD over PCM but that at this time it is not yet enabled. I tried it anyway and as it turns out it currently carries the same signal as over SPDIF: upsampled 88.2kHz PCM. This connection sounds like something of a mix between the regular I2S input and the DSD inputs: more relaxed, but also less powerful than the standard I2S input.
The DSD upsampling function is a 995 euro option for the CD-T II transport. Personally, I would leave it out when purchasing it, but this is very much a relative matter. I know that there are many DSD fans out there and depending on personal taste and system matching, one might have a view different from mine. As with virtually all aspects of these two high tech products, the choice is yours, all the options are there, for the user to freely choose between.
CD-T II + Stealth
I can be very brief about this… these two components combined quite simply make for the most musically involving front end that I have used in this system so far. The Stealth truly sounds great with the Music Server, better actually than any other DAC+Preamp combination used so far, but when combined with the CD-T II the two components form something of an otherworldly music machine.
These two components are clearly designed very cleverly and always with the best music replay in mind. They also offer very good ergonomics and the beautiful and rock-solid metal supplied remote controls put the plastic units of many more expensive competing products to shame. But because the Stealth DAC has so many inputs, I would have loved to see the option of choosing inputs directly, rather than only toggling through all of them in one direction. Or to have the option to disable unused inputs. The display, while excellent, is a little small, and difficult to read from my listening position, 5,5 meters from the front of the components and this makes it more challenging to find the desired input. Perhaps this functionality could be retrofitted with a new remote control? Other than this, I have nothing but praise for these spectacularly musical products.
There is no way around it. The Ayon Stealth DAC/Preamp and CD-T II transport play with a level of musical involvement not matched by any solid state combination that I tried so far. They make music in a way that defies the chasing of audiophile aspects. If one focuses solely on resolution, transparency or accuracy then it is possible to find components that perform better on those aspects, but the Ayons make a very strong case for proving that this is not the point. They present music not as individual pieces of a puzzle but as a musically relevant whole. Furthermore, you’ll have to bring one heck of a Music Server to the table if you are to equal the musical flow provided by the CD-T II. This powerful, dynamic and extremely musically involving pair has completely won me over. Highly recommended.