Thrax Audio

It was at the largest and most exciting audio show in the world: Munich’s High-End audio show where I first laid eyes on Thrax Audo of Bulgaria. I felt it right away, after a few seconds of listening, that the Thrax had that special something. You know what they say about first impressions? And in my case, this first impression was very long lasting. Since Munich High End, I’ve heard Thrax Audio more than a few times and each time I was quite impressed with their exceptional sound quality. It’s the type that draws the listener deeply into the music’s core with its captivating sense of space, detail and harmonic cues. Although the venue and the speakers were different each time, I was absolutely convinced the electronics were hugely responsible for the magic I encountered. I said to myself, “ one of these days I’m gonna review these electronics.”

I had a nice long conversation with Rumen Artarski of Thrax Audio at last year’s Munich High-End show. I mentioned how much I enjoyed his products over the years, but – of course – I requested a chance to review the Spartacus mono power amplifier and Artarski said “yes.” Even better, he told me I should review the combo that features the Spartacus with their matching Dionysos line level preamplifier.

Need I mention that I was only a tad ecstatic!

Rumen Artaski, founder and chief designer of Thrax Audio, discovered his passion for audio when he was just 12 years old. He enjoys listening to European jazz, world music and, of course, Classical. His brother had an impressive rock record collection but at that time none of the records were available in Bulgaria, they were only available copied on tape. Artaski started running a very lucrative small business for his brother, transferring records (LPs and 45s) to tapes while his brother was out having fun. Artaski spent countless hours recording on all kinds of equipment and started buying and selling equipment, becoming very involved in how to make things sound better (Don’t we all). In 1990 he moved to Denmark, and enrolled in the Danish Technical University in Copenhagen to study electronics and acoustics. While in Denmark, he was buying equipment there and selling it in Bulgaria and vice versa. During this time he developed an interest in pro audio. As a true audiophile, he wanted better recordings, so he moved to London to study record engineering/producing. After graduating, he worked in a recording studio. He got hands on experience and was always tweaking the monitoring system, replacing cables and amps. He got to design and build a recording studio and, in 1998, he moved back to Bulgaria and started a number of businesses. One of them was a high-end audio shop in the center of Sofia (Bulgaria’s capital). Most of his clients were very wealthy with a genuine interest in music. He was selling Wavac and Kondo Audio Note amplifiers but the preamplifiers had no remote control. He wanted a product that sounded as good as these but would also be user friendly with a remote control. As far as he knew, none were available on the market at that time. Rumen Artaski went to the drawing board and designed his own remote controlled tube preamplifier that was good enough to pair with the very best. This led to two years of R&D in attenuators and amp topologies, power supplies and so on. And follow by another year of research and tests, involving thousands of man-hours of listening and comparisons. After showcasing the first prototype in an audio trade show, he received five orders and Thrax Audio was born.

Rumen Artaski states: “The works of Japanese tube gurus are a source of inspiration for us. Shishido San’s designs with transmission triodes manifested trough Wavac Audio and Kondo San’s creations at Audio Note Japan are the best examples of the Japanese vacuum tube art currently in production and the different approaches taken to achieve the same goal. Their attention to detail and manufacturing quality inspired us to try and do better. The works and concepts of another Japanese designer came closest to the direction in which we were heading. Never implemented commercially, however, the designs of Sakuma San are a tough example to follow. Directly heated triodes with inductive loads seemed to deliver the effortlessness and tonal richness we are after.”


The Spartacus is a two stage shunt regulated Directly Heated-Triodes (DHT) push-pull mono power amplifier in pure class-A design. It features one of the simplest possible signal paths with absolute zero feedback (wire-vacuum-wire-vacuum-wire). To achieve exemplary performance with such a simple design, Thrax Audio uses the very best components from around the world. The Spartacus uses Directly Heated-Triodes (DHT) which delivers an extra order of magnitude and better distortion performance compared to indirectly heated ones. However, not all DHT’s are the same. Emission Labs manufactures some of the finest tubes ever made and the Spartacus utilizes a pair of Emission Labs 520B-V3 output tubes that produce a powerful 70 Watts per channel. Only the best will do, and for this design Artarski chose the highest quality Permalloy core output transformer custom made by Tamura. Rumen Artaski is a perfectionist and to cancel some of the already negligible distortion even further, a linear driver stage was implemented which supplies the two output tubes with exactly the same signal in phase for one and out of phase for the other. Using DHT was the obvious choice and a KR Audio PX25 also was used. The PX25 tube produces enough power and voltage swing to accommodate a two-fold overdrive and positive grid drive if needed. A step-up transformer was implemented to give the cleanest possible voltage gain.

The Spartacus has one of the most sophisticated and innovative power supply designs in the industry. To reduce power supply noise-noise is as we all know public enemy #1- choke input full wave 6022C rectifier tubes are utilized to practically eliminate switching noise and anything that comes before the choke, instead of the normal arrangement of diode bridge rectifier and electrolytic capacitor bank. The choke keeps the voltage on the capacitor bank quite constant and a small bank of the highest quality film capacitors is used. A power supply operates best when the load is constant. A constant current source is a device that passes the exact same amount of current no matter what happens on either end. A shunt regulator will keep a constant voltage across itself by changing its conductivity no matter what. Cleverly, it has a built in timer that counts the tubes’ working time. When tube replacement is due, after switching the unit on, the green LED will keep flashing after warm up time elapses. The Spartacus has a unique circuit design which keeps the current in both output tubes the same even as the tubes age and cannot be perfectly matched. The microprocessor constantly checks the system function to make sure the system is operating properly; if not, it shuts down to protect the tubes.

The Spartacus is milled from impressive solid plates of varying thickness 6061T651 aircraft grade certified aluminum. The chassis is meticulously thought out; the power supply section is mounted on a mid-level plate with a circuit board on top and the transformer and choke below, making the center of gravity low enough to have a signal transformer mounted on the top plate to avoid magnetic interference. There are no screws visible anywhere on the chassis and it is made in house with a CNC machine. The layout of the front panel is elegantly simple with an ON/Off switch in the middle. On the top panel there are the arsenals; a total of seven tubes two transformers, two output impedance switches for 4 and 8 Ohms to match loudspeaker impedance. There are three switch positions for input matching as with most preamplifiers; H-high gain, to be used with a preamplifier with very low output impedance capable of driving 600 Om loads and providing 2V, M-medium gain; moderate input impedance for a 4V preamplifier; and L-low gain, to be used with some 8V tube preamplifier with a higher than usual output impedance. I set the switch to M-medium gain when paired with the Dionysos. In the rear there is input for RCA and XLR and beautifully made.


The Dionysos is a single ended, single triode stage transformer coupled with a remote controlled line stage preamplifier. The line level amplifier is the foundation of any high-end audio system. It is in charge of source selecting, signal conditioning, and volume control. The line stage preamplifier has to match the output of a source to the input of the power amplifier. The output has to provide an absolute optimum driving signal to the power amplifier’s input stage; it must be low impedance, DC free, truly balanced, and isolated from noise sources and other components in the system. To create a better volume control, painstaking research and evaluation of various approaches was carried out. Rumen Artaski chose a fundamentally different and simple solution; he opted for transformers with various winding ratios instead of the usual potentiometer and resistor ladders. However, transformers have two drawbacks: they are very expensive and difficult to design. Thrax Audio states “Potentiometer and resistor ladders as sophisticated as they might be, have a fundamental flaw. They operate by dumping the unnecessary signal across a resistor. It is like driving a car with fixed engine power (signal) and adjusting the speed with the brakes (resistor).” Dionysos is a fully tubed circuit design with tube rectification using a 6C4P-EV (6u4n-B); voltage stabilization is via a SG15P (Cr15n); constant current sources feeding a shunt regulator and voltage amplification is via a single twin triode 6N6P (6H6n). All tubes are NOS Russian issue. The power supply is impeccably designed. It uses a special custom made C core transformer with a gap in the core with a symmetrical field canceling winding to prevent any saturation of the core from distorted mains or a DC component in the main. Two identical sets of windings (essentially two power transformers) are on the same core. This way all the nasty magnetic and electrostatic leaks cancel each other out, and do not influence any of the other components in the chassis.    

The Dionysos is a single box finished exquisitely utilizing ultra-high quality custom made parts throughout and featuring a meticulously crafted chassis. Like the Spartacus, it’s made of a 6061T651 aircraft grade certified aluminum machined from plates of various thickness. Ergonomics are simply beautifully thought-out. What good is advanced technology, if it’s not user friendly? Artaski anticipated all the needs of audiophiles. The Dionysos comes with a brilliantly designed full function remote control to die for. As much as I loved the sound of the Kondo Audio Note G-70 preamplifier I recently reviewed, I missed having a remote control. As a reviewer and an audiophile I believe that a remote control is an absolute must. While I’m reviewing, I constantly have to change equipment for comparison and adjust volume levels, and the LED readout makes this very convenient. Don’t get me wrong I do need the exercise but I like to get that in the gym – not while listening. Another must have feature is an phase switch; I could control phase on the Dionysos with a touch of a button on the remote control. I believe a phase switch should be mandatory on all preamplifiers. As a matter of fact at least half of all classical recordings are recorded out of phase. So, having a remote control with a phase switch makes listening much more pleasurable. You can listen both ways while sitting in your sweet spot and, at the touch of a button, you’ll hear which way sounds better. The Dionysos’s front panel is thoughtfully laid out. The large volume control knob is in the middle. The tape and mute button are to the left and input select previous, phase switch, and input select- next are on the right. There are six inputs-four pair RCA unbalanced and two pair XLR balanced and four pair outputs-two RCA unbalanced and two XLR balanced. All inputs are balanced differential unless the grounding option is engaged on the RCA inputs. There are two sets of outputs for bi-amping capability.

All of Thrax’s parts are meticulously selected after many hours of listening tests and constructed by experienced craftsmen with Swiss built quality. They really took their time to research and develop these products; it took them two years of painstaking evaluation of amplification topologies and circuit design in their lab. Rumen Artaski and his team are perfectionists who are passionate and strive for nothing but the best. Uniquely, Thrax produces only one level of performance for each model; there is no entry level or premium model, no compromises. Thrax is one of the very few companies that goes to this extreme, using only the very best custom-made quality parts available for specific design sourced from Japan, Germany, the US, Sweden, Canada and the UK. Every Thrax gear has been run for 72 hours at the factory initial break-in for reliability and sound quality testing. Cleverly, both the Spartacus and the Dinoysos have a standby mode. When in standby mode all the amplifier circuitry be turned off for minimum power consumption, leaving only a small standby circuit running.     

One sunny afternoon my doorman called to let me know that I had a shipment from DHL. I was expecting a Thrax shipment and boy was I right; there were four boxes in the lobby! The Thrax gear was shipped in heavy-duty wooden crates with sensible wooden handles and as I expected, some of the tubes were shipped separately and had to be installed.  Removing the top wooden plate revealed secure foam-lined innards and the gear was nicely protected by a plastic cover. It didn’t take long to set up, all tubes for the Spartacus marked accordingly. Setting up the Thrax was straightforward; I used my reference Jorma Design Unity cables throughout the system. I did my listening to the Spartacus and the Dionysos as a set and I used ASI topline feet to assure an even more exceptional sound. 

The Sound: The Magic!

Even though the Spartacus and the Dionysos arrived with only 72 hours of initial play time, they sounded superb right out of the box. I could see immediately that its sound quality, rather purity woud become instantly addictive. And, as they settled in for a couple of weeks, they continued to improve. Incredibly, the system’s reproduction of timbre is stunning in its realism – about as good as that of the Ongaku, the amplifier which in my view, is the world reference in proper replication of instrumental texture and tone. Timbres are richly rendered, with density of color and warmth that makes even the best solid-state sound a touch mechanical or artificial. Normally, I don’t do any serious listening until the gear is more or less fully burned-in, but the Thrax was different. I knew that the Thrax gear was something special and that it belonged with the very best. I recently reviewed the legendary Ongaku and in many ways the Thrax combo is like the Ongaku in character; better yet, it produces more power to drive more demanding loudspeakers. The Spartacus drove my Consensus Engineering Conspiracy loudspeakers effortlessly with power and finesse. Voices and instruments sounded vividly alive with a remarkable high level of purity. I was in trouble; I was losing sleep staying up through the wee hours of the night listening to my favorite recordings.

Listening to the Conspiracy loudspeakers driven by the Spartacus and Dionysos for past few months convinced me that these Thrax products are some of the most musical and involving electronics I’ve heard to date. They render instruments and voices with a natural and organic quality. It’s the kind of sound that as soon as the music starts playing, everything just seems right. One doesn’t need to think about anything, except for musical enjoyment. The Spartacus sounded like an SET with the power of a push-pull design. Its power output of 70W had no dynamic limitations; the system plays cleanly at respectable volumes, and it handled crescendos with delicate ease. This is an amplifier with seemingly unfettered dynamic contrast along with a powerful and full bottom-end. The Thrax didn’t sound big and bold or polite and restrained; it didn’t sound any way at all, but simply did what the music asked, no more, no less. I was in audio heaven! The Thrax electronics midrange is glorious in timbre, tone color, liquidity, and freedom from grain. The Cassandra Wilson’s vinyl recording of the New Moon Daughter (PPAN BST32861) arrived during my review. The Thrax reproduced Wilson’s husky and hypnotic voice with a touch more three-dimensionality than I remembered from this reference recording. I was startled-first by the immediacy and solidity of her image, then by the complexity of Wilson’s husky voice and coming through with a harmonic truth that surprised me. It was as if I was hearing it live for the first time. As good as my Karans are in the midrange (which is one of their great attributes) the Thrax portrayed the midrange with a greater sense of musical realism and emotional involvement.

One evening I put on the Beaux Arts Trio recording of Beethoven’s Piano Trio N0.1 in E flat Op.1 N0.1 (Philips 6725 035), dimmed the lights and sat back in my sweet spot. The Piano Trio was rendered exquisitely authentic in both weight and tonal acuity. The strings and piano were stunning, emerging from a background both blacker and more alive than I recall. The strings were a touch denser and more complex than with my reference Karans and proved enough, in fact, it took my breath away. I couldn’t stop listening to the Piano trio over and over through the Thrax electronics. One thing’s certain, Thrax has an uncanny ability at digging into and thus revealing layers upon layers of subtle details.

As I have said, the Spartacus monos and the Dionysos preamplifier reproduce large-scale orchestral music with great ease. When the music demands drive and scale, Thrax simply responds on a dime. In fact, the Spartacus monos 70 watt sounded like a powerhouse driving the Conspiracy and the Kharma DB9-S’s. Orchestral climaxes are reproduced with great authority and the timpani in the orchestra has a stunning impact. Listening to Dvorak’s Symphony N0.9 in E Minor, Op.95 with maestro Fritz Reiner conducting the Chicago Symphony, was an awe-inspiring experience. The Thrax had full control of my Conspiracy loudspeakers and were easily able to scale the dramatic heights of full orchestral crescendos. Play the first or the third movement and you’ll hear the ability of the Spartacus to deliver sudden dynamic shifts with convincing power. I was equally impressed with the Thrax combo’s effect on my system’s spatial performance. It was good as the Kondo’s. The Thrax electronics has an uncanny ability to portray a large sense of space and the instruments within the space, and the distance between them. The overall impression is like hearing a lifelike three-dimensional staging.

The Thrax Spartacus mono power amplifiers and Dionysos preamplifier are world-class electronics in every way this audiophile deems important. The Thrax Audio products embody an achievement in design, engineering, construction, and most of all, sonic performance. The Thrax electronics set a high benchmark for all others to be measured against. Sonically speaking, and in my system, the Thrax is good as it gets. The overall character of these electronics is pure, intimate, and emotional, leading to heightened musical expressiveness. The Thrax gear could never be qualified as inexpensive BUT, considering its performance versus some pretty stiff competition, I would qualify it as reasonably priced. I enjoyed the performance of both the Spartacus and the Dionysos but, unfortunately, I was able to only afford Dionysos at this time, so I ordered one to mark as my new reference preamplifier. Need I say more?

My hat’s off to Rumen Artaski for creating these masterpieces and I’m sure Kondo san of Kondo-Audio Note and Shishido san of Wavac would be very proud of Rumen Artaski’s achievements. The Spartacus mono amplifiers and the Dionysos preamplifier are my Stereo Times 2013 “Most Wanted Components” award! Highly recommended!

key kim

KK:  Please begin by telling us about how you first got interested in audio?    

RA:  My involvement with audio started when I was 12. We just moved back from Mexico to Bulgaria and my brother who is older than me had managed to accumulate a very nice rock record collection. At the time of the Iron Curtain none of those records were available in Bulgaria, so for people to get the records the only way was to copy them on tape. Taking advantage of that I was running a very nice small business for my brother while he was out partying. I spent countless hours recording on all kinds of equipment. Buying and selling equipment became part of the job. In the late 80’s I started looking at UK Hi-Fi magazines ( “looking” as I could not understand English). This got me started. 


KK:  Did you have formal training in audio electronics, or are you self- taught?

RA:  I’ve studied electronics and acoustics at the Danish technical university in Copenhagen and studied record engineering and producing in London.


KK:  What type of music do you listen to?

RA:  I listen to a variety of music. It’s all depends on my mood and the equipment I am listening on. I enjoy listening to European jazz, classical music, and world music but somehow rock has fallen of the list.


KK:  How would you define the high-end?

RA:  High end for me is defined by products that stand out above the rest. No compromise designs that transcend the time they were created in and our industry as a whole. Only bold designs making a statement. It is a pity that this has become so “commercial” and every product now is high end. The term has no value. But for me there is a category of products that I refer to as “State of the Art”. These are the pieces combining physical beauty, function and performance, inspiring awe and interest in non audiophiles.  Achieving this is quite a task. But some manage to do it!


KK:  What is your design philosophy?

RA:  Fix the cause of the problem not the artifacts.


KK:  Tell us about the company; do you do all the designing or is there a design team?

RA:  Thrax has a design team of 5 engineers and myself. Each specializing in a particular field we have one engineer specialized in tube circuits and has 40years experience! ( we refer him as “vacuum head”), others specialize in microprocessors, CAD/CAM and so on. The vast experience I have in multiple fields of installations and gear lets me define the tasks very concretely. I would come up with the concept and topology and they make it work.


KK:  Analog or digital – do you have preference?

RA:  On the Analog vs Digital I could say that people are very biased one way or the other but the truth is elsewhere. The value of Vinyl is in the countless priceless records out there that will never be available on any other medium or if available will be a mediocre copy. As a format vinyl has many flaws and it is a miracle the quality of reproduction we can get out of it. Properly done digital is also very good these days. I would say even better than anything else but most of the recordings done in the 80’s and 90’s suffer from deficiencies in the convertors used to record them. Let’s be honest, even today most studios use cheap A to D converters and preamplifiers. Few can afford a proper monitoring system let alone the full signal path (I know I have installed quite a few). Possibly the best sounding replay is that of master tapes on a “modernized” tape deck if the tape is of a recording done by organizations with limitless budgets at the time, like the BBC or some German state organizations.


KK:  What do you see for the future of high-end audio in general?

RA:  I see high-end audio being split into two tiers, luxury ego booster products selling exclusivity more than anything else and high performance but usable audio products for those that spend their money on music. Plenty of companies trying to do both will fail in misery.


KK:  My last question is: What does the future hold for Thrax Audio?

RA:  Thrax continues its R&D and we have improvements on the current line and at some stage we will introduce replacements for the current products, but we have no plan at the moment for other products in the line. We cover both sources digital and analog, we have a preamplifier and two power amps Spartacus and for “tubephobics,” The Heros hybrids.


KK: Thank You for your time.


Spartacus Mono Power Amplifier Specifications


– 1 unbalanced RCA connector

– 1 balanced XLR connector

• Output: up to 70W in 4 Ω or 8 Ω

• Power supply: 115 or 230 V

• Power consumption: 380W

• Dimensions: 210W x 440D x 420H mm

• Weight: 35Kg

• Finish: Black or Silver anodized aluminum

• Tube compliment :

– 1x PX 25 amplification

– 2x EML520B-V3 amplification

– Г- 811 shunt regulator

– СГ-13П voltage reference

· 2 х 6Д22С rectifier

Price:      $48,500.00

Dionysos Preamplifer Specifications

• Inputs

– 4 pair unbalanced RCA connectors

– 2 pair balanced XLR connectors

• Output

– 2 pair unbalanced RCA connectors

– 2 pair balanced XLR connectors

– 1 pair unbalanced RCA connectors – tape out

• Attenuation steps: 32

• Volume Control Range

– Minimum gain: -46dB

– Maximum gain: +18db

• Power supply: 115 or 230 V

• Power consumption: 45W

• Dimensions: 432W x 400D x 120H mm

• Weight: 15Kg

• Finish: Black or Silver anodized aluminum

• Tube compliment :

– 1 x 6H6П amplification

– 1 х 6Ц4П rectifier

Price:      $21,500.00

Company Info:

Thrax Audio Ltd.

251 Okolovrasten pat, Delta Center

1766 Sofia, Bulgaria

Telephone: +359 2 988 95 55

FAX: +359 2 988 95 56

Mobile +359 888 561 269


USA Importer: HIFI imports


Contact 719-640-6999




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