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Thrax Audio - TERES + LYRA Power amplifier + loudspeakers

04-19-2015 | By Wojciech Pacuła | Issue 78

Thrax Audio

To be honest I can't remember how it started. In my own review of Dionysos preamplifier for January 2011 I wrote that I'd firstly learned about existence of Thrax Audio one year earlier during High End 2010 Show in Munich. But now I really can't remember any details. It seems though that I somehow knew already then that it was a brand worth interest. I was the first, or at least one of the first people who reviewed Rumen Todorov Atarski's product (outside his homeland, Bulgaria). For a few years it was also the only review in Poland, as it took few years to find a proper distributor in our country.

Since the foundation of this company its core product has always been a linestage—as if Rumen thought that it was a key element of the system (I always thought exactly the same thing) – that is quite a unique approach in audio world. For the first few years all other products were presented always as prototypes. As you can read below, in fact he started his audio adventure by designing loudspeakers. It took him many years before the first model, Lyra, was finally released in 2014. Just like his preamplifier and power amplifiers also speakers are quite a unique design.

Last month you could read in HighFidelity what a CEO of YG Acoustics, Mr Yoav Geva, had to say about his loudspeakers (see HERE). Not only do they use many interesting solutions for the drivers and crossovers, but also cabinets of their speakers are quite particular, being a key factor in achieving a final sound. These cabinets are made of aluminum slabs using vibration-free pressurized assembly, creating sort of monolith design, that reminds me of products of another American company – Magico.

Not more then 5-6 years ago using any other material for speakers' cabinets than wood (in one of its forms or the other) was thought to be eccentric (at best), possibly harmless but having nothing to do with "true" audio. These eccentricities included materials like: glass, concrete and aluminum. Today, after the audio world recognized the amazing Crystal Cable speakers (glass) and both above mentioned manufacturers of aluminum speakers, the general view on what is and what is not the "right" material for speaker's cabinet has changed significantly.

Thrax Audio

Thrax Audio Ltd., a manufacturer of Thrax products, decided to use most rigid, vibration-free enclosures for their products. Based on the experience of other manufacturers, they knew how to do it—it "only" required them to buy crazy expensive CNC machines. So they did. It didn't take long before they had such an advanced machinery and such an experience with using them that some renown European high-end  manufacturers started to commission enclosure production to the Bulgarian company.

Thrax Audio

A casing of the new power amplifier, Teres, looks like it was carved of solid aluminum block—the fit and finish is that good. Actually it was made of aluminum plates put precisely together, with outer surfaces of side panels  milled in such a way that they look like radiators.

This amp is getting really hot under stress as the current mode uses a pair of single transistors per phase. It is a unique design as there are only two gain stages in a cascode: a single penthode C3g in the input stage and JFET followers in the output. C3g is an octal tube with metal body. Input and output stages are coupled with a single transformer. There is no negative feedback loop.

When it comes to electronics aluminum casings are very common, even such advanced ones as Thrax's. But aluminum cabinets for speakers are still quite rare. Lyra speakers are the newest addition to Thrax portfolio despite the fact, that  Rumen Atarski's first audio project ever was speakers.

It is a two-way, three-driver design, with drivers in D’Appolito array. The concept is quite unique because of extraordinary rigidness of the cabinet, very special, aluminum bass-reflex port design, and very special crossover. The latter sports a huge capacitor for tweeter and that's it! Speakers and amplifiers use a high quality, user-friendly Furutech speaker binding posts.

Thrax Audio

A few simple words…


Thrax Audio | CEO

The story of Teres.  As you know Spartacus is our statement amplifier, 2 gain stages with Class A push pull output stage. Many people were scared by the exposed tubes and all were requesting a bit more power. So I started working on a circuit that will have a tube controlling a power MOSFET that can replace the output tubes in the Spartacus. Solid state and inductive loads don’t go well tighter and many devices let their gray smoke out. Fortunately for us new devices were introduced to the market that could withstand the high voltages and power required. This gave birth to a unique cascode system for the output. It is still operated at high voltage but not nearly as high as on the tubes. The output transformer used to load this cascode made it sound and behave as a tube amplifier and simplifying the input, as to be essentially a single stage device. So Heros was born.

A year later all our dealers started asking for more power and bigger amplifier with the same character. There was no commercially available output transformer of sufficient quality for power above 200W, so the only option was transformer less output stage. This automatically prevented the use of Heros driving system, so I went back to the drawing board. We resorted to the topology of Spartacus again and implemented it in Teres. we use an input tube for voltage gain and a transformer for phase splitting (same as in Spartacus), but here we replace the standard push pull output with 2 totally independent single ended followers based on a scaled version of our cascode. Running them out of phase to each other and sharing the load, forming a bridge that is unbalanced by the phase splitting transformer signal in order to be re-balanced trough the load with a mirror image of the same signal. The output stage has no character of it’s own, so the sonic color of the the tube stage is the overall character of the amplifier.

Regarding Lyra. The development started around a driver developed by BMS. It uses a ring diaphragm. It was patented more than 15 years ago. During the research for wide bandwidth horns at Spherovox new profiles with different directivity properties where developed. We just adapted one of the designs for high end audio.

It uses a custom "short" version of the driver and the special horn to cover the 1.5k-20k range with an outrageous sensitivity of 112db/W. We use a combination of the horn loading and the High Pass filter to tailor the response of the tweeter while severely attenuating it to mach the mid/bass unites. There is no stress for this driver at ANY level. It practically has lower intermodulation distortion than the amps.!

The 6.5" drivers are used only bellow the 1.5kHz crossover. This prevents them from exiting the breakup modes of the magnesium diaphragms. In order to get the perfect time/phase alignment the front panel of the speaker is carved from solid accommodating for the relative positions of the drivers. Geometry is optimized for listening distance of 3.5m. The solid aluminum prevents any vibrations in the enclosure and specially the front.

THRAX AUDIO in High Fidelity

• TEST: Thrax Audio MAXIMINUS + DIONYSOS + SPARTACUS – D/A Converter + preamplifier + power amplifier, see HERE

• INTERVIEW: Rumen Atarski | Thrax Audio – CEO, see HERE

• TEST: Thrax Audio DIONYSOS - linestage, see HERE

Recording used for the test (a selection):

• Abraxas, 99, Metal Mind Records MMP CD 0102, CD (1999).

• Abraxas, 99, Metal Mind Records/Art Muza JK2011CD07, gold-CD (1999/2011).

• Aquavoice, Nocturne, Zoharum Release ZOHAR 077-2, CD (2014).

• Bob Dylan, Oh Mercy, Columbia/Sony Music Labels Inc. SICP-30579, Blu-Spec CD2 (1989/2014).

• Helen Merrill, Helen Merrill with Clifford Brown. Singles box, EmArcy/Universal Music LLC (Japan) UCCM-9336/8, "Limited Edition" 3 x SHM-CD (1955/2014).

• J.S. Bach, English Suites 1, 3 & 5, perf. Piotr Anderszewski, Warner Classics/Warner Music Japan WPCS -12882, CD (2014).

• Leonard Cohen, Popular Problems, Sony Music Labels SICP-4329, CD (2014); review HERE.

• Leszek Kułakowski Ensemble, Looking Ahead, ForTune 0043, "No 031", CD (2014).

• Ludwig van Beethoven, Sonatas op. 109, 110 and 111, piano: Evgeni Korolov, Tacet 208, "The Koroliov Series Vol. XVI", CD (2014).

• Pet Shop Boys, PopArt: Pet Shop Boys – The Hits , Parlophone/Toshiba-EMI TOCP-66252-54, 3 x CCD (2003).

• Porcupine Tree, The Incident, Roadrunner Records/WHD Entertainment IECP-10198, 2 x HiQualityCD (2009).

• Queen, Queen Forever, Virgin/Universal Music LLC (Japan) UICY-15347/8, 2 x SHM-CD (2014).

• Sting, All This Time, A&M Records 212354-2, SP CD (1991).

• Voice Factory, Voice Factory Sings Chopin a Capella, Voice Factory, CD (2014).

• Zapach psiej sierści, soundtrack, music Włodzimierz Nahorny, GAD Records GAD CD 019, "Limited Edition 500 Copies", CD (2014); review HERE.

Whatever will I write later, whatever assessment will I pass I would like to send a strong signal already now to all electronic music fans, to those who like close, palpable presentation, and to those who expect not a huge space far behind speakers, but a close sphere built around listener sitting in its center: all of you can can search no further. If you can afford this system just buy it and keep it for ever.

It is a system of a very strong sonic character. What it offered might not have been exactly my cup of tea, but it did not matter at all. This time I didn't mind at all to fall for something offering quite different qualities from those I usually search for. The quality of the above mentioned sound features is so high that this Thrax system could be exhibited in the Museum of Sound as a perfect example of a high class, sophisticated piece of art.

Thrax Audio

Lyra speakers together with Teres amplifiers build a warm, rich sound that is also amazingly vibrant. This is obvious no matter what recording one plays, no matter what music genre. The precision this system forms the sound with, makes you wonder about choices of other  audio designers, in particular those who create loudspeakers. If you use Thrax amps with most of speakers using paper drivers you will realize that they tend  to mask problems generated by other elements of the system. Lyra show us that paper, which under certain circumstances sounds warm and soft, is used to mask a roughness, harshness of the sound.

I think that these solid, metal cabinets of Lyra speakers work in similar way. If one uses a low distortion, precise drivers in such z high class cabinets they will start to act as sort of magnifying glass providing listener with information about any problems originating from any element of the system. To use that to one's advantage one needs a very well designed crossover and a high class system driving these speakers.

Not all manufacturers utilizing paper or plastic cone drivers for their loudspeakers with wooden cabinets do that because they can't do any better. Anybody who knows JBL, Spendor or Harbeth speakers can vouch for that – these "antique" technologies and materials, properly used, deliver outstanding results. But more often then not using them will result in less favorable sonic results.

Thrax chose a different, I think most difficult way. There are only very few companies that took the same path and succeeded—YG Acoustics and Magico are best examples. Thrax system produces similar results. Anybody who claims that transistors produce a "cold" sound, and metal cabinets and drivers deliver a "dry" sound, has really no knowledge of the audio industry and audio products. If he based his opinion on particular products, these particular products must have been faulty and not the technology or solutions. The latter offer particular benefits, have some flaws of their own, but are surely not a bad choice—only a particular application might be wrong.

Was it because of elimination of cabinets resonances, or usage of amazingly linear C3g tube, (whose cousin,  C3m, I knew from some other top products), or most likely due to many elements working together, these speakers create a dense sphere made of air, sounds, details that surrounds listener. If only recording we play allows that. Because when we play a recording that was made in such a way, that we perceive sound as coming from far behind speakers, than Thrax allows the sound out of this sphere. That's how the latest Piotr  Anderszewski CD recorded in Warsaw with J.S. Bach's English suites 1, 3&5 from Warner Classics, sounds like. I have a version of this recording released in Japan. This type of production focuses on a soloist presented quite close to the listener, but it does not create a "wow" effect as there are not so many other sounds coming from sides or from behind us. It is not a very lively sound. Thrax system did not try to "light the presentation up", didn't try to deliver the very essence of the music, it simply conveyed the recording in a way it had been made proving why other recordings, like Anderszewski from Carnegie Hall sounded better.

Quite a different result we shall achieve with recordings where some spatial spatial effect were used, were out of phase sounds were used to create an impression of sound coming even from behind listener. These recordings create an impression of surround—multi-channel sound. There are quite a lot of such recordings. The best ones were prepared using the Q-Sound system, like, for example: Roger Waters' Amused to Deathor Sting's Soul Cages.

There are also some Polish interesting recordings of that kind. I really like the group Abraxas so I often listen to their album 99. They are representatives of so called art-rock (progressive rock), and this particular album was recorded in 1999 by Jacek Gawłowski, who received a Grammy Award in 2014 for Włodek Pawlik's Night in Calisia. For that album he was involved as a producer and a mastering engineer. He was also involved in a project of re-issue of first four Czesław Niemen's albums.

Anyway, on 99 between tunes there are additional pieces of music that include very special spatial effects. The reviewed system recreated those spatial effects in an amazing way. I have not heard any multi-channel system (regardless its price level) that came even close to Thrax's performance. Bulgarian system delivered extremely rich sound, surrounding me continuously, without and division for front and back sounds.

This system will present in a very interesting way also some recordings that are usually not "liked" by most audio systems. I mean those recorded with microphones placed very closely to instruments, mixed from multiple tracks, usually as multi-mono—this actually means 99% of music material that's been produced for many years now. For example—the latest Leonard Cohen's album, Popular Problems. System delivers the foreground very close to the listener. It is a large scale, rich sound so it creates an impression that we sit in the first row, just in front of the stage. This manner of presentation was even clearer when I listened to Voice Factory album with  Chopin's music, sang (a Capella) by NOVI Singers (album comes from GAD Records). Microphones were placed so closely to singers that it created an impression of a very small distance between listener and singers standing in my room. The reviewed system provided also information about quite aw realization, not so perfect voiced were taken by microphones placed very closely.

Tonal balance is set quite low. Speakers deliver very clear, rich sound, with bass going really, really deep. The lowest octave is "indicated" mostly with higher harmonics, but these are delivered in almost perfect way which creates an impression that we listen to much larger speakers and the we can really hear even lowest notes.

Treble seems warm but also very vibrant. Cymbals sound seems bit darker than in reality, even slightly darker than delivered by my Harbeth speakers. But there is no "rounding" or "softening" of leading edge. It's a rare combination—sound are not "lightened up", and yet the decay phase is rich and long enough.

The key element of this presentation is midrange though. Many good things can be said about deep bass and rich treble, but they both seem to only complement midrange that is amazingly rich and complete. Images are not precisely depicted as they are presented very close to the listener. Their energy is extraordinary though. Sound is quite energetic despite the fact it is also quite warm.

This particular set of features should satisfy all fans of music I mentioned before, plus fans of electronic music. I believe that if Tadeusz Łuczejko, whom I met a few days earlier (a musician, member of  Aquavoice, an organizer of Gorlice Ambient festival could have listened to his albumNocturne on Thrax system, who would have loved it. The sound was very essential, rich, mature but also very pure.


I have defined a potential owner of this system at the very beginning of this text. Thrax does not like compressed  signal, as it decreases scale of the sound, and creates an impression of the whole sound coming from area in axis in front of the listener. It does happen even with well produced recordings like Porcupine Tree's  The Incident. The whole structure of the music seems to fall apart, there is chaos instead. Thrax doesn't forgive that. Classic recordings with a lot of air BEHIND performers (and above them) tend to be re-interpreted as the foreground will be shown closer to us and there will be less of the air in a distance. Also phantom images won't have a real depth.

But if one listens to the music I mentioned before sound will be amazingly palpable. It will fulfill expectations of those who search for a rich, clear and close sound rather than presented in a distance. Depth of the sound in outstanding and I am sure that one could credit low-distortion drivers and resonance-resistant (coloration free) cabinets for that. Make and finish is top class. Also elements used for both products are of top quality. Rumen Atarski developed a system he can be proud of.



Teres is a monaural power amplifier. It is a hybrid design, with C3g pentode (in triode mode) in the input stage and transistors in the output stage. According to Rumen Atarski there are only two (!) gain stages. What's more, input stage (tubes) are loaded with transformer—it is the large cube in the middle of the casing. Behind it there is only a second cascode gain stage based on JFETs and MOSFETs.

Thrax Audio


Developing a device based on such a simple concept requires a lot of time and effort. At least if sound quality and good measurable parameters is what we want to achieve. Teres is uniquely simply design. Input section is placed on a PCB bolted to the back panel of the device. It includes almost complete power supply section for C3g. Power transistors are placed inside two small aluminum boxes. These have a shape of a section of cylinder. They are bolted to the sides of the device and they produce most of the heat one can easily feel after turning Teres on.

Thrax Audio


In the middle there is a large toroidal transformer and two large smoothing capacitors. On top of them designer put a small board with SiC Shottky diodes. This material called carborundum is used in many top designs, one of them being SPEC Corporation Designer Audio REQ-S1 EX phonostage.

Amplifier sports RCA and XLR inputs, but the device works in an unbalanced mode. Signal is balanced in coupling transformer. The whole circuit is controlled by a microprocessor that sits on separate board and sports a separate power supply. Teres works without negative feedback.


Lyra is a two-way, three-driver monitor. It sports a vented enclosure that is made of aluminum plates screwed together. Also bass-reflex port is made of aluminum. A mineral wool was used for internal damping.

Drivers are screwed to the front baffle from inside, so the screws are not visible. A solid aluminum carved front panel incorporates a horn with specific directivity and frequency response. Its shape was developed by a company Spherovox. A ring diaphragm compression driver was custom built by German company BMS.

Two mid-lowrange magnesium diaphragm 6.5'' woofers work together. These look like top line SEAS drivers. They sport a magnesium membrane and copper phase plugs. They work below 1,5 kHz.

Loudspeaker sport a puristic crossover of  the 1st order, built of the most expensive elements including Mundorf silver capacitors and a huge coil. Even speaker posts were chosen to achieve the best sound quality—these are the same posts that are used in amplifier—Furutech FT-816.

The only thing these speakers miss are matching stands. For now any solid 70cm stands should be fine, but since these are high-end speakers they will show any problem with accompanying system including low quality stands.

Specifications (according to manufacturer)



• 1 x RCA

• 1 x XLR


• 250 W/8 Ω

• 350 W/4 Ω


Frequency response: 34-20 000 Hz

Nominal impedance: 4 Ω

Maximum power: 250 W

Dimensions: 210W x 385D x 520H mm

Weight: 35 kg/PC

Finish: black or silver, anodized aluminum

Sensitivity: 90 dB

Price (when reviewed): 24 000 EUR + 16 000 EUR/pair

Thrax Audio Ltd.
251 Okolovrasten pat
Delta Center 1766 Sofia | Bulgaria 
[email protected]


Text by Wojciech Pacuła

Images by Wojciech Pacuła | Thrax Audio

Translation by Marek Dyba

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