Ayon Audio Sigma DAC Review – Enjoy the Music

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August 2014
World Premiere!
Ayon Audio Sigma 32/192 PCM And 2.3/5.6 MHz DSD DAC With Preamplifier
A warm and engaging DAC.

Review By Wotjek Pacuła

  Life’s easier for the big guys. Starting from kindergarten, through primary school and into the business world. And here we have the Ayon Audio Sigma DAC with preamplifier in for review, which is a culmination of years in design and engineering. And like with any other business, the principle also applies to the audio industry, including its passion-driven “audiophile” segment. Using the “mass scale” effect, big companies can offer products at a much lower price than small, specialized manufacturers. There are obviously downsides to this mass production approach. One of them being impersonal nature of the product such as found within the Ayon Audio Sigma DAC as reviewed here. On the other hand, the benefit of being the big guy is to have big money available. And big money translates, among other things, into more funds for investment and research. Hence, large consumer electronics companies are playing a vital role in bringing new and innovative solutions to the market. Let’s not be naïve, they are the real driving force for this industry and it is their solutions that keep pushing it forward.

Perfectionist audio has a different role. Its objective is to refine and perfect what has been developed by those with the necessary financial resources, and to translate it to the “language” of audiophiles who insist on truth at any cost. And we are speaking here in the language of the absolute. Hi-fi and high-end audio has its comfortable and quiet niche, like tube amplifiers and turntables, long since abandoned by the mainstream consumer electronics industry. There are also areas where it needs to constantly keep up with the market leaders, especially in computer audio. Here competition is life-and-death and everyone is fighting to be first in line. Big audio companies, like Marantz, are more successful in that regard. But if you are a specialist in a given area, or can afford to hire such specialist, you can take on and outdo even the biggest guys. When Michal Jurewicz, the owner of Mytek Audio, told me that he was developing a DAC that accepts the DSD signal with quad sampling frequency – the upper limit currently used in the recording studios – it seemed to be an exaggeration. Any reasonable person would say that double rate, i.e. DSD128, is absolutely sufficient and that Mytek is still ahead of the game with its Stereo 192-DSD DAC. He turned out to be right. Just before I received the Ayon DAC, I finished a review of several systems with planar magnetic headphones, including the HA-1 headphone amplifier with USB DAC and the PM-1 headphones from Oppo. The HA-1 is currently the most advanced DAC on the market, accepting quad rate DSD (DSD256) and PCM DXD (32-bit/384kHz).

Ayon Audio from Austria is a company with a well-established tradition, which has built its reputation on high-end tube amplifiers and preamplifiers. When the time came, it started offering CD players. They were characteristically shaped top-loaders with a tube output stage. Nothing has since changed in this regard, except for one thing: all Ayon digital sources today come equipped with digital inputs, including USB. The company’s lineup has also been extended to include D/A converters. At this moment, the company from the Austrian city of Gratkorn has three DAC models in its product lineup – the flagship Stratos, the less expensive Stealth and the newest and most affordable Sigma. The two former are the second generation products while the latter is an absolute novelty with no previous counterpart.

From the outside, all three units differ in certain details, such as Sigma’s lack of an input selector and volume knob. They have slightly different dimensions of 48 x 42 x 11 cm, through 48 x 40 x 11 cm, to 48 x 36 x 11 cm in the case of the DAC under review today. They also differ in weight, tipping the scale at 17 kg, 16 kg and 12 kg, respectively. Nevertheless, looking at any of them there can be no shadow of doubt as to their origin. This, of course, has to do with their characteristic chassis made of thick black anodized aluminum plates and profiles, with rounded corners. Gerhard Hirt, Ayon Audio owner and chief designer, adds chrome knobs to his more expensive products. The enclosures are machined in company’s own factory in Hong Kong, purchased by Gerhard a few years ago. Another common feature is a large red-illuminated front panel display screen. It shows information in two ways: on a dot-matrix display and via illuminated icons. The former shows the currently selected source and volume level. The icons inform the user about such details as the sampling frequency of the input signal (but not its word length) and its type – PCM or DSD. Flashing display indicates that the DAC is not synchronized with the source.

The Sigma is a D/A converter with built-in preamplifier. Since there is no information in the company literature whether it is an analog preamplifier, I assume that it uses digital volume control integrated in the DAC chip. It accepts PCM signal up to 32-bit and 192 kHz, and DSD64 and DSD128. I would normally add here that DSD is only supported via USB. However, Gerhard clearly seems to have a weak spot for this format, inherited – I presume – from his meetings and conversations with people involved in the recording studio and analog technology. My guess would be that the person who is in some way responsible for that is Dirk Sommer, the editor-in-chief of the German magazine HiFiStatement.net. The DSD signal can be, of course, fed in via USB, which is now standard. The Sigma adds to that a whole array of DSD-enabled inputs, including a RJ45 port, typically used for Ethernet and here used for DoP streaming, and BNC connector, which can both be used to stream the DSD signal from the Ayon NW-T network transport. But there is also a DSD interface on three BNC connectors, taken straight from the recording studio. The PCM signal can be sent through RCA and BNC coaxial inputs, XLR AES/EBU and optical TosLink inputs, as well as an I2S input on another RJ45 port. The latter is supported by both the NW-T and the CD-T transport.

The Sigma can be hooked up directly to a power amplifier as it has a preamplifier on board. The output signal on the XLR and RCA outputs can be set to “High” (+6 dB) or “Low” (0 dB), selectable by a toggle switch. Another toggle switch selects between “Normal” and “Direct Amp” analog output mode. The latter automatically brings the output level down to -40 dB on each power-on, which is useful to protect the power amp and speakers. If you do not use the pre-amplifier section, pressing an appropriate button on the remote control unit bypasses the attenuator circuit. There are two more switches, one per each channel, that are hidden at the bottom of the DAC case. They can be used for another 6 dB of gain reduction with high sensitivity power amplifiers, to eliminate hum and noise generated by the Sigma output tubes. The remote control unit itself is fairly typical for this manufacturer, with a metal top and plastic bottom. It is not particularly user friendly or best-looking, but one can get used to it. You better not lose it, though, as it is the only way to activate the upsampler (24-bit/192kHz) and choose between the two digital output filters. “Filter 1” is a slow roll-off filter with no phase shifting and pre-ringing; “Filter 2” is a classic brickwall-type filter with symmetrical oscillations or ringing before and after the transient.

Ayon sigma

The electronic circuit is mounted on three PCBs, separate for each section. The largest board houses the actual D/A converter with its power supply and a regulated DC filament supply for the output tubes. The tube output circuits, including analog filters and a gain stage, are mounted on two smaller boards. One of them also contains the plate voltage supply circuit using a rectifier tube. The USB interface is built on a small PCB, mounted to the main board. It sports an XMOS chip with two very nice quartz oscillators, thermally and mechanically compensated. They clock the output signal, separately for the 44.1 and 48 kHz sampling frequency families. The XMOS chip has its own clock oscillator. The DAC chip is ESS ES9018S Sabre32, recently very popular in inexpensive and very expensive converters. It is used here in an 8 mono to 2 stereo configuration, with four D/A converters per channel. The flagship Stratos sports two such chips for a 16 mono to 2 stereo configuration. The chip is clocked by another great looking clock oscillator, with fantastic Sanyo capacitors in its power supply.

The I/V conversion is performed by Burr Brown OPA2134 op-amps mounted in IC sockets. The circuit includes Wima polypropylene and Nichicon Fine Gold electrolytic capacitors. Right next to them are four very large Mundorf M-Cap Supreme polypropylene capacitors. The same capacitors are used in the tube output circuits. The latter employ the 6H30 ‘super tubes’, first used by BAT and for some time imported exclusively by this American manufacturer. The rectifier tube sits in a classic ceramic socket but the output tubes are mounted in sockets from CMC, the same company whose beautiful RCA connectors can be seen on Sigma’s rear panel. According to Ayon, the I/V conversion circuit and the gain stage are fully balanced, while the output is single ended. More expensive DAC designs use a fully balanced topology throughout. However, the XLR output is not just a gimmick. Gerhard has come up with a special tube circuit arrangement which allows the use of a single ended topology with balanced output.

The power supply uses a low-noise R-Core power transformer with several secondary windings. Tube rectification is on the 6Z3 diode manufactured in China. Separate power supplies and voltage regulators are used for plate and filament supplies, logic and DAC circuits as well as the input and output stages.

A Few Words From Ayon Audio
In 2005 many customers and distributors asked for an Ayon CD player with tube output stage. Well, we had a lot of experience with tube circuit design and power-driver stages and so on, but not so much with designing digital circuits. In 2006 we launched our first CD player. We basically took a Sony mechanism with its own Sony servo board, added a common D/A converter and thus the CD-1 was born. We didn’t have any high expectations of this player.

We also had no idea that this was the beginning of a long digital journey for Ayon. The CD-1 became a big success around the world, with many great reviews and awards. This was the signal for Ayon to digital engineering and start in-house development for which we founded a kind of joint venture cooperation with Stream Unlimited in Vienna.

We started developing our second generation of CD players, including the CD-07, CD-1s, and CD-2.  We designed a new chassis, a new D/A converter, a new mechanism and output stage, the CD-1s had nothing to do anymore with the first generation CD-1. Then came the CD-5 and the Skylla, followed by the CD-07s, CD-1sc, CD-2s and CD-5s. In 2010 we introduced the S-3 network player, the first network player worldwide to feature a tube output stage, followed almost 2 years later by the S-5 reference network player and then the NW-T.

After 6.5 years of production of our Skylla D/A converter it was time to renew and expand the lineup with the new Stealth and Stratos, the first tube based D/A converters with DSD playback. At the end of 2013 we launched the third and latest generation of our CD-Players: the CD-1sx and CD-3sx, the first tube based CD players worldwide with a DSD-enabled D/A converter on board. In mid-2014 we are pleased to introduce the smaller brother of the Stealth and Stratos, the Sigma DAC. The Sigma is a breakthrough for Ayon and unique in its price range as it is also equipped with a DSD DAC and SE 6H30 output stage.

Our main goal has been to build a superb sounding tube DAC for around half the price of our famous Stealth DAC. It has been a very difficult project for Ayon because, on the one hand, we wanted to keep many advanced technologies from the Stealth DAC and, on the other hand, we were trying to lower the price as much as possible. 

Gerhard Hirt
Ayon Audio Owner


In Karl Jaspers’ philosophy, boundary situations (Ger. Grenzsituationen) are existential experiences that confound our certainties, stripping the world of its appearances. They enable us to read the ciphers of transcendence, which means to understand the meaning of everything, including the meaning of life. According to Jaspers, the boundary situations include abandonment, suffering and death. In order to make sense, that is to help us look behind the “veil of the world,” they cannot be escaped by managing them with rationality and objective knowledge alone but have to be experienced. In other words, they require an active participation on our behalf.


Since Jaspers, the concept has been evolving and it is no longer so clearly defined or “sharp.” A boundary situation now also includes experiences that change our point of view or our understanding of something, turning inside out the construct of the world as we understand it. And they do not necessarily need to be the basic existential experiences, like death. It may be any other memorable experience, I think.

It is not difficult to find such moments in our lives, filled with auditions and listening to music. The first and foremost is what can be called the “initiation” experience. It happens when, for the very first time, we listen to the music played back in a way that unlocks something new in us, opening up our eyes – metaphorically speaking – to the world of real music, not just some noise with melody and beat. A wonderful aspect of the initiatory experience is that it can be repeated, at an increasingly higher level, over our whole lifetime.

The reviewer is immune to such things. Daily listening to music on constantly changing audio products in various configurations, participating in music concerts and audio shows and meetings with friends kind of immunizes us, like a vaccine. Given all that, when we eventually do have this type of experience, it is always something.

I may have mentioned it somewhere, but let me repeat it here: I have recently heard twice the kind of sound that recalled my first-ever experience of this type, which happened when I walked into a music store, located in a seventeenth-century building at the Main Square in my home city of Krakow, Poland. The audio system was absolutely classic for that time: a CD player whose name I forget, a NAD 3020 amplifier and a pair of small monitors. But its sound moved me so much that I set out to eagerly look for something that would give at least half that “punch”. Many years have since passed and my expectations have obviously changed. The upside is a change of my audio consciousness and sensibilities. The downside – the price I now need to pay for those dreams. My two recent boundary experiences have been the auditions of the dCS Vivaldi digital system and the TechDAS Air Force One turntable. After them, nothing has been the same.

The Vivaldi costs insane money and sounds insanely good. Its sound is my current reference. But it doesn’t mean that nothing else “sounds” good to me anymore. One of the advantages of the “vaccination” I’ve mentioned earlier is the ability to evaluate audio products regardless of the price range involved. That’s why my recent auditions of several excellent DACs bring nothing but fond memories and smile to my face. Each one of them had that special something that touched my heart and made me think that I could happily keep it. They were (in no particular order): the Accuphase DC901, the Meitner MA-1, the Thrax Dionysos and the Ayon Audio Stratos. The latter also comes with a great preamplifier on board, and has become a part of the audio system that has been built over the years by Tomek, one of the founders of the Krakow Sonic Society.

When I bumped into Gerhard Hirt during the High End 2014 show in Munich and after we gave each other a big hug, he showed me his two new products: the long-anticipated production version of the Spheris III preamplifier and a much more modest-looking box with a display screen on the front panel. “The Sigma may be my least expensive D/A converter, but you don’t even realize how much it inherits from the Stratos that you have auditioned.” Gerhard is not the kind of person who gets easily excited over anything. He works hard, does not sit still for a moment and wants to implement every new upgrade as soon as it is ready, without looking at the cost. Other companies often prefer not to change anything and keep selling a given model until they replace it with something completely new. I have a feeling that while Gerhard is an excellent businessman he does not calculate when it comes to the sound, but simply follows his heart.

Hence, I wasn’t too much surprised that after hooking up the Sigma to my system, the sound was not very different from what I’d heard with the flagship Ayon DAC. I’m referring here to the sound on the coaxial input, with the signal fed from my Ancient Audio Lektor Air V-edition (with Philips CD-Pro2LF) used as a transport and the volume level set to “Max” in the Sigma. This is an important provision to which I will return later.

I have known digital components from Ayon Audio from the point “zero,” in other words from the company’s very first CD player and first USB input. They have been evolving incredibly fast and, in my personal opinion, heading in a good direction. The Sigma sound is saturated, slightly warm and dense. It is very resolving, but it’s the kind of resolution that weaves the individual sounds together, instead of dissecting them. The latter used to be characteristic of high-end digital components for many years, which made many a music lover turn away from digital audio formats. I’m sure that if they had heard the Ayon DAC, they would have thought twice back then.

The thing that attracted me the most was the combination of fleshiness and resolution. These sonic aspects used to be attributed to analog recordings, with a special nod towards vinyl and now also towards DSD files (reel to reel tape is a whole different story). Here, it benefited literally each CD I auditioned. However, it was particularly striking when I listened to the album “Billie Holiday” from 1952, remastered and released on SHM-CD in Japan as part of the series “David Stone Martin 10 inch Collector’s Selection”. The sound was amazing and maintained a kind of “internal concord”, characteristic of recordings before multi-track and multi-session era. Holiday’s vocals were big and strong. Her accompanying band with Oscar Peterson and Ray Brown was perfectly audible. The same trick was repeated on Nina Simone’s album “Silk & Soul” from 1967. The vocalist was shown close to me; her voice had a large volume and was very authentic. Both discs also feature tracks that are much brighter, with more distant and brightened vocals. The Ayon showed them nicely, although they were not so intimate. The more expensive DAC from the same company was capable of something more: by going deeper into the individual sounds it brought more music out of them. The Sigma was not as resolving and selective. It did things its own way, making the lesser quality recordings sound similar to each other and smoothing them out to the point where they are listenable.

It may also happen that we become fascinated with something else, right from the very beginning. When I was playing Kraftwerk’s bootleg “Live on Radio Bremen” recorded in 1971, followed by Kenny Burrell’s “Soul Call,” I sunk into my sofa, on which I sit during the auditions, feeling fully relaxed. The Austrian DAC played both albums absolutely stress-free, bringing out the same transcendent quality of such different music. Transcendence in this case translated into calmness and suspension of disbelief. I could hear perfectly well that they were just recordings, but only when I wanted to hear it and when I paid attention to it. And it was not so easy to transition from holistic to analytic perception as the Sigma tends to provoke the listener to turn off the critical part of one’s consciousness.

When you get used to it and are willing to hear it, you will notice that the sound is somewhat “made up.” You will realize that it elicits a certain desired response. The Sigma does it mostly by means of slightly boosted upper bass and lower midrange. This always results in a closer foreground and larger volume. These are good changes. They have usually been associated with tube-based audio components, although the DAC under review is not a typical tube design. Today it is no longer a clear-cut distinction, and in a blind test many listeners would actually point to some solid state components as sounding tube-like. It can also be easily noticed in Sigma’s sonic signature. So why am I talking about its great sound and what prevents me from pointing out this coloration?

To answer this question, I had to audition more albums and audio systems. I am not sure if my answer will be satisfactory to everyone. It is the only one I have, though, and I do not even look for another. In my opinion, the coloration is deliberate and has been well thought out. It is not to deceive anyone. On the contrary, it is an attempt to bring us even closer to music. The “hidden hero” of this sound is resolution. I know, I’ve already mentioned it. Except that now its role takes on a completely different meaning and becomes crucial.

I believe that over the years the high-end audio industry has been developing in the wrong direction. The quest for neutrality at all costs has been a curse. And equating low distortion with purity – in a “clinical” sense – has been really stupid. In my experience, the lower the distortion, the warmer the sound, the more “naturally velvety” and softer. Many speakers with ceramic and diamond as well as some metal drivers are a perfect example.

The most notorious distortion we face in digital audio systems is jitter. There are many types of jitter and we fight with them in various ways. Often, minimizing one type results in increasing another one – such is life. The reduction of jitter and of the total harmonic distortion have one thing in common: the lower they are, the more natural and denser the sound. And the more it takes on the characteristics of “diversity in unity.” It means that there is more and more information that is increasingly better ordered. In the end, the sound can no longer be called “detailed,” even though it has everything. And so it is with the sound of the Sigma. It is presented in one “package”, without being artificially segmented into separate categories. It is up to us to decide if we want to focus on its individual aspects.

The tonal balance of the Sigma is shifted downwards and can be called “warm”, bearing in mind everything I have said above. The upper treble is incredibly resonant and rich in nuances. The cymbals decay slightly faster, which results in a sense of intimacy and closeness to the sound. The recording venue’s acoustics is denser and less differentiated, and the reverb added by the sound engineer is shorter than on the Accuphase DC-901 paired with my Ancient Audio Lektor. This is the price we pay for “presence.” It is also worth paying attention to the low bass control in your system and in your listening room. The Sigma has a very deep low frequency extension, and the bass is energetic and well differentiated. But it is not as punctual and tight as on the Stratos or the Accuphase DC-901. It sounds more like the Meitner DAC or the Audio Research Reference CD9.

As the new entry-level model in the Ayon Audio DAC lineup, the Sigma is not far from the flagship Stratos. The subtle differences I referred to earlier can be identified, but they are not obtrusive. This is a fantastic DAC that will not be out of place in the best audio systems I know. In most aspects, apart from the soundstage depth and bass differentiation, it sounds better and more convincing than my long-term reference Ancient Audio CD player.

The above remarks are based on digital inputs using high-end external CD transport. The file player bit resolution is reduced, regardless of what kind of use of files. The USB input is very engaging and will give much joy to all users who play music from their computers, or use digital music players with a USB output, such as the Aurender. Tomek, who owns the Stratos, uses the Aurender X100L and the pairing is perfect. Still, I think that a good CD release played back on a quality CD player sounds more coherent and resolving. I know that this opinion does not make me very popular, but I cannot help saying what I really think. The only exception are DSD files. Too bad it’s such a niche format, because native DSD files sound insanely good – calm, smooth and soft.

The biggest difference between the two Ayon DACs we are talking about is the sound from their USB input and the quality of their built-in preamplifier. The Stratos’ preamp is so good that adding to the system the Polaris III, a two-piece flagship Ayonpreamplifier, brought only the kind of benefits that I could easily do without. In the case of the Sigma, an external preamplifier will improve the selectivity, resolution, liquidity and depth of sound. This is quite a lot. Having said that, taken on its own merits the built-in Sigma preamplifier is actually pretty good. It will not, however, replace a dedicated specialized preamplifier.


Ayon has this to say about the Sigma: “Full-featured D/A converter with a class-A triode vacuum-tube output stage.” There is no specific mention of a preamplifier in its name. I think that Gerhard knows very well what he is doing. The DAC sounds so good on its fixed (non-volume controlled) output that once you buy it there will be no much sense upgrading to the Stratos, for example. Just add to it the Ayon CD-T transport and NW-T network transport (with a new firmware that supports DSD) and you will have a digital source for life. What you will need, though, is a quality preamplifier. If you do not fancy another component in your system and want to keep the character of the sound offered by the Sigma, you will need to buy the Stealth or the Stratos instead. A dense, deep and resolving sound – the Ayon is insanely good at that. The Stratos and the best DACs from other manufacturers are better at differentiating the bottom and top ends, showing them with more energy and focus. Nevertheless, the Sigma is so engaging in what it does that we forget the above and simply enjoy the music. An exceptional product, indeed!

Type: High resolution vacuum tube DAC with preamplification stage
Accepted Formats: Up to 32-bit/192 kHz (PMC) + 2.3 MHz/5.6 MHz/1-bit (DSD)
Digital Inputs: S/PDIF via RCA, AES/EBU via XLR, optical TosLink, BNC, USB, I2S, DoP
and three BNC for DSD
Output Impedance: 300 Ohms for both XLR balanced and RCA
Tube complement: Two 6H30 for analog output and 6Z3 for power supply
Dynamic Range: > 128 dB
S/N Ratio: > 120 dB
Frequency Response: 20 Hz – 20 kHz (+/- 0.2 dB)
Total Harmonic Distortion (THD) @ 1 kHz: < 0.002%
Remote Control: Yes
Dimension: 48x36x11 (WxHxD in cm)
Weight: 28 lbs.
Price: $4499 USD