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Line preamplifier

Price: 15 000 euro

Manufacturer: Thrax Audio Ltd.

251 Okolovrasten pat, Delta Center
1766 Sofia, Bułgaria
tel.: +359 2 988 95 55


WWW: Thrax

Country of origin: Bulgaria

Text: Wojciech Pacuła
Photographs: Wojciech Pacuła
Translation: Krzysztof Kalinkowski

Preparations for the test took me and the company Thrax Audio more than half a year. When I saw their products for the first time during the High End 2010 in Munich, I knew I need to listen to them. Those were big tube monoblocks, with triodes in the output stage, resembling Ayon tubes, packed inside a splendid crafted enclosure. After returning home I wrote an email asking to borrow the units for testing.

Quickly I received an answer:

Currently we have three products, just as you can see on our web page. And in production and sales there is only the Dionysos preamplifier. The monoblocks Spartakus should be ready in the third quarter of this year, and the phonostage Orpheus probably in the fourth quarter. Because the development of those products takes lots of time, we decided to present pre-production samples to a few people, and we are now booked full with orders. Our production capabilities are fairly limited, and we would prefer to have our friends listen to the products first, because then we will have trustworthy feedback. Taking all this into account, we think, we can send you our preamplifier for testing at the end of July.

As usual in such cases, “end of July” moved by a few months, but one afternoon the courier brought (not on his own, first I had to file a complaint, because the courier did not want to carry the box) a nicely looking wooden box, with the preamplifier packed inside. This is the way all audio products should be packed – not cardboard boxes, which change into something not even looking like a box after just one shipment – but something sensible, what would really protect the load. On the top of the box there is a milled (or burned – I do not know) logo of the company. I really liked that.
The preamplifier itself turned out to be equally interesting. The pictures on the web page do not show even a shadow of what the Dionysos is in reality. A proud name, which could be a synonym for “beautiful”, does not lie. The unit is sleek and made completely from milled, thick aluminum plates, bound together in such a way, that no bolts are visible. This is a fully tubed preamplifier, with a tube rectifier 6C4P-EV (6Ц4П-В), a tube voltage stabilizer SG15P (СГ15П) and a tube amplification stage made from one tube – a double triode 6N6P (6Н6П), where each half works in a separate channel. And when I say, that volume is controlled by transformers with switchable windings, then it turns out, that it is a very similar solution to the one used in my preamplifier Ayon Polaris III.
Different to the Austrian device, Dionysos is very user friendly, because it has a display showing the volume for each channel, separately for the left and right channel, it has balanced inputs and outputs (de-symmetrized and symmetrized in transformers – the circuit is not balanced), a bypass input, a record out output (can be used for a headphone amplifier), absolute phase inverter, which can be set and stored separately for each input, etc. Everything is microprocessor controlled. And it is small – my Ayon consists of two large units.

But not everything was so trouble-free. After the first email I received another one, to discuss the issue of fitting the preamplifier to the power amplifier. As it turns out, Dionysos will not work well in all systems. Rumen Todorov Atarski, the boss of Thrax Audio writes as follows:

Please call me to discuss a few issues – this is important, because our products are not “universal” and require some knowledge and experience. To give you an example, I just say, that the amplification of the preamplifier is max 20dB (x10) and the available attenuation is 52dB (in 24 steps!!!). So in combination with a classic CD player, with 2V output and a classic power amplifier, with a rather high sensitivity of 0.5V the usable attenuation will be limited to 10-12 steps until the sound gets too loud. But when connected to a power amplifier with a sensitivity of 4.5V (like some Krells), then it will be ideal. The same thing is true for our other products. Our power amplifiers need 4V on the input to reach full power, and have rather low input impedance. This is the reason, that anemic preamplifiers, based on ICs for example, can have problems in driving them.

Yes – this is a problem. Unless you have a CD player with variable output, like my trusty Ancient Audio Lektor Air. I could lower the voltage on its output and adapt it perfectly to the preamplifiers sensitivity. Even if the sensitivity of the power amplifier I used in the test Tenor Audio 175S has the quite high 1.3V on XLR inputs and 1.5V on RCA inputs. But you have to remember, that this is still a device difficult to apply, and it will fare best in a system with a power amplifier with low sensitivity, because only then low noise of the system can be exploited.


I used the following discs for testing:

  • Brenda Lee, Let Me Sing, Decca/Universal Music Japan, UCCC-9111, CD.
  • David Sylvian, Secrets of the Beehive, Virgin/EMI Music Japan, VJCP-68879, CD.
  • Jun Fukumachi, Jun Fukumachi At Steinway (Take 2), Lasting Impression Music, LIM DXD 038, silver-CD;.
  • Tori Amos, Boys For Pele, EastWest/Warner Music, 80696-2, CD.
  • Joe Pass, For Django, Pacific Jazz/EMI Music Japan, TOCJ-90027, HQCD.
  • Tomasz Stańko Quartet, Lontano, ECM Records, ECM 1980, CD.
  • Yoko Ono, Open Your Box, Astralwerks, ASW 88710, CCD.
  • Brian Eno, Another Green World, Virgin/Toshiba-EMI Limited, VJCP-68658, CD.

Japanese versions of the discs available on CD Japan.

The Bulgarian preamplifier is one of the best devices of this kind I heard in my system (and not only in my system, but I have absolute certainty only when I am talking about my system and controlled listening conditions). This is the same league as CAT SL1 Legend or Ayon Audio Polaris III, what speaks for itself. The listening session of this device took longer than usual, because I needed to employ a different methodology than with cheaper components, or those, that give their personality easier away, and of which I can describe the sound easier. In my reference system I exchanged my Polaris III for this preamplifier for four weeks, and I made tests for “Audio” using the Thrax. I tested, among others, the DACs (Pro-Ject Box USB, Audinst USB DAC HUD-mx1, Musical Fidelity V-DAC, Arcam rDAC, Cambridge Audio DacMagic, Xindak DAC-5, Stello DA-100 Signature, Music Hall dac25.2, Wavelenght Proton, Mytek Digital Stereo96 DA, Cary Audio Xciter DA, Benchmark DAC-1 PR, Naim DAC, CEC DA-1N; test was published in the issue 11/2010), the power amplifiers (Balanced Audio Technology VK-255SE, Mark Levinson No.532H, Pass Laboratories XA60.5; test was published in the issue 12/2010), and finally the integrated amplifiers (Atoll IN400, Luxman L-507u, Mastersound Compact 845, Pathos Acoustics InpolRemix, QUAD II Classic Integrated; test to be published in the January issue). It was a lot of work, but it was successful. In all those tests the Dionysos was used as a reference device, or was part of the system I plugged the devices into. It never failed me. And then I listened only to it, exchanging it for the Polaris III.

The tonal balance was set splendidly in this device. The sound is very well balanced, better than in most solid state preamplifiers, which often imitate tubes (Accuphase C-2810 or Luxman C-1000f – those are not bad, they are splendid, but I wrote about this trend while those were reviewed), and also better than in the tube preamplifiers I listened to lately. Sadly including my Polaris III. The sound of Thrax is very open. It is not “electronic” in the way we perceive hi-end preamplifiers from 10-20 years ago today, this is a much more organic, closer to what I hear from systems WITHOUT a separate preamplifier, with the volume control integrated into the CD player, as for example in the Ancient Audio player. Like I said, this is an open sound. The upper treble, problematic in cheaper devices, because it is either glassy or annoying – those are cases, where the designers wanted to get an open sound at all cost – or damped and warmed – where those problems are tried to be remedied by withdrawing this part of the frequency spectrum, here is brilliant: precise, expressive, but without a trace of brightening, without perceptible distortion (at least I could not find and name them).
This allows the preamplifier sound in a very dynamic and expressive way. And again – expressiveness on this quality level does not mean coloration or irritability but showing the events in a more verbatim way – like it is reality. This is aided by splendid dynamics, which allows for what I described before. Because the biggest problem of our home equipment is not even that it has bad timbre or lacks resolution, but that it sounds like a cardboard box – lifeless, choked and muffled. Anyone who heard a live concert – amplified or acoustic – feels that: the live sound is completely different to the one coming from the loudspeakers. And we should get used to the idea, that we will not surpass that, that the size of our listening rooms, as well as electronics and loudspeakers we use, cannot reproduce that event.
But we cannot forget about that. We have to try and fight the problem. Dionysos shows, that much can be done in that aspect and that most other preamplifiers compress sound – to a bigger or lesser extent, but they do compress.

The tested preamplifier shows the sound in a very direct way. When on the disc For Django, in the title track, Joe Pas guitar enters, it electrifies us immediately. This is helped by a good edition (HiQualityCD) and good recording, but with other preamplifier the sound was not as exciting. The shape of the guitar was reproduced very well, as were the contours of the percussion. I had the same with the pieces opening the disc Boys For Pele Tori Amos, recorded “clean”, without using any overdubs, in one take, using Leslie and Marshall amplifiers for the harpsichord and piano. The instruments had a very large volume, one I would not expect from a guitar amplifier. It was warm – that was the timbre set on the amp – but it was not muddy sound, it was not even warmed. It had a very direct attack, it vibrated with emotion and transmitted the acoustics in which it was made to my listening room. A part of the puzzle is the higher than usual resolution and differentiation ability. Here the Dionysos – an I am speaking about my experience here – can compete only with a combination of variable output of a player with a power amplifier. Reading this, you should remember that I do not know all the preamplifiers in the world, and for example Soulution 720, or Kondo M-1000 MkII could show me something, I have no idea about. But I must base on something, and this something is my experience. And comparison with a CD – power amplifier direct coupling, without a preamplifier. And both elements tell me, that the Dionysos is a special case of a preamplifier, which is incredibly resolved, tonally open and at the same time keeps organic sound, not castrating it from harmonics and not brightening it.

The opposite part of the sound spectrum is also noteworthy. The bass is incredibly strong, full and dynamic. It has power, if needed it is fleshy, and if the recording requires it, it can almost not be heard. Usually it is somewhere in the background, and the midrange and treble are built atop of it (please look at the experiences in “Hi-Fi+”), but it like a crouching tiger and hidden dragon. I heard such good lower bass only once at home, when I tested the set Krell EVO222+402. But it had to be a set, because the preamplifier and power amplifier EVO alone were not as impressive. Anyway the Dionysos repeats this experience, building the mood splendidly, taking everything into a different dimension, seemingly apart from everything else what surrounds us. And it is not about pounding. Yes, the club mixes of Yoko Ono songs from the disc Open Your Box sounded great, had a splendid support, rhythm and dynamics. But for me more important was the way, how this springy and strong bass allowed to built everything above it, the vocals, trumpets, guitars, etc.

Let’s take for example the disc Jun Fukamachi At Steinway (Take 2) recorded in the Direct-To-Disc technology (I’ll just remind, that this is not about recording on a classic carrier, meaning tape, hard disk, etc, but directly on the master, that will serve to press vinyl discs – this is the most perfect way of going from microphone to vinyl), or rather its digital representation, a CD prepared by the company First Impression Music, issued on silver. The owner of the original Direct-To-Disc mastered vinyl is Mr. Winston Ma, the owner of FIM. He transferred the signal from the turntable to a digital recorder working in DXD technology, 24 bits and 352,8 kHz. The signal was then transferred to 16/44.1, but still splendid sound was achieved.

To make it even more interesting, Mr. Ma recorded the same tracks twice – once using the cartridge van den Hul Colibri, and the second time using the FIM Black Ebony. The result is overwhelming! You can clearly hear, that the FIM cartridge is better, the sound is more direct, nicer saturated, and the upper registers of the piano have more energy, are more natural, more similar to what you can hear standing a few meters away from a Steinway piano. I know it well, because I did arrange microphones for many pianos, and I know, that a strong hit on the keyboard can throw us out of our seat.

Everything depends of course on the playing technique, the piano player abilities, but if everything is there, then the sound of the midrange and treble is incredibly strong. That happened in the second case, with the FIM cartridge. But because I wanted to talk about bass, then I’ll just say, that in the beginning the diamond touches the disc (Mr. Winston Ma recorded everything, and did not edit anything), then it can be heard just as if I would be listening to a real, expensive turntable. Of course you listen to music and not to distortion and extra musical events, but because I know that sound by heart, I can evaluate it, transferring it later to the sound of a given musical piece. And this touching sound was deep, well damped, and it was “aside” the sound of the piano. This is a known phenomenon, but here it was repeated splendidly. It could not be done that well, without a perfect stitching of the treble and midrange and fleshy sound of the bass.

There is not much I can write about the midrange. It is just splendid. Smooth, full, precise, energetic. It is better than in any preamplifier I heard to date. It will be easiest to describe comparing the Dionysos to other, well known preamplifiers. This will be also a good time to point to elements, that are better in other top shelf gear. Not by much, but still better.
The most obvious comparison was with my Polaris III. The Austrian preamplifier sounds more with the midrange, it is a tad smoother. But it is not as open, only now I could hear, that the upper midrange is slightly warm there, and slightly withdrawn. It results in the vocals being seemingly nicer and slightly warmer. Because the midrange in the Ayon is a bit underlined (I’ll repeat – I hear it only now) it seems that the voices – Brenda Lee from the monophonic, issued by Decca disc Let me Sing, but also male voices – for example the vocal of David Sylvian from the disc Secrets of The Beehive – are nicer, free from the irritating recording artifacts. It is only that the Dionysos showed them better, maybe not smoothing them as much, but together with acoustics, with a better body and shape. It was similar with Stańko’s trumpet on the disc Lontano, which seemed bigger with the Ayon, and in reality was lacking some information from the upper part of the spectrum, and thus was less true. In “reality”, during normal listening, the differences I am telling about now, are not as pronounced as it might seem from reading the above, but you cannot pass by them indifferently.

The CAT SL1 Legend, the line/phono preamplifier, sounds with a sweeter sound. The Accuphase C-2810 was warmer, and warmest the C-1000f Luxman. Also the Nagra PL-P (HERE) it was rather “tubey”. If I would want to order them in terms of timbre, from the warmest to the most neutral one, then it would look like this:

Luxman C-1000f → Nagra PL-P → Accuphase C-2810 → CAT SL1 Legend → Ayon Polaris III → Thrax Dionysos → Music First Audio Mk II Copper

Going from the warmest to the most neutral device, or even the slightly bright (Music First) means here going from the most “closed” to the most “open” sound. As you can see, choosing between tube and solid state technology has nothing to do with that. If I would have to find something, then it would be the complication of the unit – I mean going from one device with the most components inside to the most simple one – what can be simpler, than a passive circuit with an autoformer in the Music First Audio Mk II Copper? I believe nothing – but even if there would be one, I would not know what it might be. The Ayon and Thrax are similarly simple, where we have transformers for volume control and singular amplification stages. It is also interesting, that this order shows also the increasing resolution.
But when we talk about saturation, about the way of handling bass – its tightness and fleshiness – the order will be different:

Music First Audio Mk II Copper → Nagra PL-P → Luxman C-1000f → CAT SL1 Legend → Accuphase C-2810 → Thrax Dionysos → Ayon Polaris III

But regardless of how I make the lists, it turns out, that the Dionysos is the most versatile device, because the vertical axis runs somewhere around it, a line which separates the warm from the cold, the light from the heavy, etc.

But it will not play as good as other preamplifiers in every case. Its open sound will not fit well in systems, where there is a lot of treble, and most of all, a lot of upper midrange. Here the CAT shows, how everything can be better integrated, how everything can be brought together, in a way, that there is no treble or bass, but there is only Music. On the other hand the Polaris can go very low and strong. From all the mentioned devices only the Thrax has this subrange more differentiated – while keeping (in general) a similar timbre and amount of the bass, it shows better elements of the sound of contrabass or bass, making us forget for a moment, that we deal with a recording.
The sound stage can also be shown a little better. I am not fully sure, that what I wrote here is 100% true, because I am talking about some impressions here. It seems, that the Polaris III and CAT show a more saturated, denser sound stage. It seems, that after switching to the Thrax everything runs to the virtual sources. It might be the result of better focusing in this preamplifier, but I am not sure. For me it sounded as a slight withdrawal.

But whatever we say, the Dionysos is a fantastically made, splendidly equipped preamplifier in one box, that sounds as good, and in some aspects even better, than other, many times bigger, two boxed products from other companies. Bravo, bravo, bravo!!!


The preamplifier Dionysos is the first product of the new, Bulgarian company Thrax Audio, based in Sofia, the country capital. This is a line preamplifier, based fully on tubes. The rectification is handled by the tube 6C4P-EV (6Ц4П-В), voltage is stabilized by constant current sources feeding a shunt regulator with a vacuum tune reference SG15P (СГ15П), and the amplification is handled by the double triode 6N6P (6Н6П). All tubes are Russian, NOS. Interestingly, the amplifier tube is the only active element in the sound path – one half works in the right, and the other in the left channel. So we have only one amplification stage, like in the more expensive Conrad-Johnson preamplifiers, or in my Ayon. This means, that the unit inverts absolute phase.

The enclosure is brilliantly made from thick, aluminum plates, bolted in such a way, that the connection lines are barely visible. The screws are also not visible. The front was milled from a very thick aluminum block, so that it is curved smoothly around the knobs. The most important one is the big volume control knob, and two green LED displays, hidden behind acryl windows, showing the volume separately for each channel. The balance between channels can be set from the remote controller as well as with small buttons on the fascia. The remote is very chic – metal, black with chrome plated ends, and it is easy to operate. We can control the volume, balance, change inputs, invert absolute phase for each of the inputs separately, activate mute and switch off the preamplifier.
All these functions are also available from the front panel. Unfortunately the knobs and indicators are not described, what seems a bit too much of an extravagance, even if it helps in keeping the fascia clean.

Looking from the left we have the power switch with an indicator LED, which changes color from red to green after the unit is being powered up. Next button activates the recording out output. To the right we have two buttons to select the active input, and between them a button for changing the absolute phase. Its activation is indicated by the LED of the chosen input changing color from green to orange (unfortunately the LEDs are not described, so you have to guess which input is active).
The back is looking as solid as the front, what is not so common in hi-end. We have there splendid RCA and XLR sockets – although the preamplifier is not balanced, on input and output there are desymmetrizing and symmetrizing transformers present, which allow us to use balanced devices with it – a player and a power amplifier.
There are four unbalanced inputs, and two balanced ones. One of the inputs can be changed into a bypass one, what can allow the preamplifier to work in a home cinema system – the signal from the selected input has a fixed gain selected by pressing a button. There are also recording outputs, switches to cut the signal ground from the cabinet ground, and four outputs – two RCA and two XLR. Interestingly, the recording output is buffered by a floating amplifier with a transformer input , and thus its usage does not influence the sound quality. In a separately milled “window” there is the IEC socket, a mechanical power switch and a “level set” button. This button can be used to set the level of any chosen input and place it in the bypass function. This input will then be indicated with its LED lighting up red. The voltage level is memorized in the internal memory, so it will not disappear even after we power down the Dionysos. The unity gain level is set, when the volume level indicators show “24”.

To get inside we have to remove the carbon doped plastic feet first (I see here a place for the CeraBall finie elemente). After unbolting the bottom plate, we gain access to screws holding the top cover.
We can immediately see a combination of splendid engineering – first of all thought through mechanics and topology – and NOS elements combined with new ones. You can clearly see, that each element was considered, that the elements were chosen for their sonic capabilities, and the price came always second. Once again, after the Absolutor, I see elements from the Soviet Union, which were so disdained even not so long ago, when those were popular, and now returning to being used. Of course not all of them, but when we talk about tubes (I cannot stop thinking, that my player, Lektor Air, has the 6H30 tubes made in USSR), resistors or – like it is here – mighty oil capacitors, here used in the power supply, then the army stock is being heavily used.

Like I said, first of all, the brilliant mechanical structure catches the eye. The PCB with the amplification section and the power supply is bolted to two aluminum bars (a nice touch – the bars are anodized blue) and those are not bolted to the bottom plate, but to the sides of the cabinet. The whole power supply is also mounted to the sides, with a nice big transformer, NOS oil capacitors from USSR and a nice, very big choke from Lundahl. To the second side panel two big output transformers were bolted, coming from the Japanese company Hashimoto Electric and even nicer, really catching, closed in solid, metal cups, transformers for volume control and input decoupling.
From below we can see a few integrated stabilizers, and many transistors working in the solid state voltage regulating circuits. All are bolted to a long, big heat sink, located on the other side of the PCB.
The inputs are soldered into small, oblong PCBs, with relays – each channel has its own PCB. From there the signal goes to the permalloy transformers from SLK Transformer, and then using splendid Oyaide cables – those are high quality PCOCC-A wires, rarely seen – to the main PCB. The mentioned heat sink divides the PCB in two parts – the power supply and the amplification circuit. In the amplification section we have only one tube, the triode 6N6P (6Н6П). Next to it, we can see a few, high quality passive and active (opa656 op amp) elements, among others capacitors from Wima and precise resistors. To the side, there is an additional PCB with two rows of relays, keying the individual sections of the autoformers. The relays are controlled by integrated switches.
On the other side of the heat sink there is the power supply, with the tube rectifier 6C4P-EV (6Ц4П-В) and a voltage stabilizer using the SG15P (СГ15П). And on the tubes we can see ferrite muffs, that should protect them from electromagnetic radiation. The heating is rectified in solid states rectifying bridges, separately for the power supply and the amplifier tubes.

A fantastic, brilliant setup.

g     a     l     l     e     r     y


  • CD player: Ancient Audio Lektor Air (previous it was Prime, tested HERE)
  • Phono preamplifier: RCM Audio Sensor Prelude IC (tested HERE)
  • Cartridges: Air Tight Supreme, tested HERE, Miyajima Laboratory Waza, tested HERE.
  • Preamplifier: Ayon Audio Polaris III with Re-generator Power Supply; version II tested HERE)
  • Power amplifier: Tenor Audio 175S, tested HERE and Soulution 710
  • Integrated amplifier/headphone amplifier: Leben CS300 XS Custom version (reviewed HERE)
  • Loudspeakers: Harpia Acoustics Dobermann (tested HERE)
  • Headphones: Sennheiser HD800, AKG K701, Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro, 600 Ω version (reviewed HERE, HERE, and HERE)
  • Interconnect: CD-preamp: Acrolink Mexcel 7N-DA6300, article HERE), preamp-power amp: Wireworld Platinum Eclipse
  • Speaker cable: Tara Labs Omega Onyx, tested HERE
  • Power cables AC (all equipment): Acrolink Mexcel 7N-PC9300
  • Power conditioning: Gigawatt PF-2 Filtering Power Strip (reviewed HERE)
  • Audio stand Base – under all components
  • Resonance control: Finite Elemente Ceraball under the CD (article HERE)
  • Pro Audio Bono platform under CD