Thrax Audio Heros power amplifier review

I’m more then thrilled with what we could set down as a power amplifier mecca test of comparing the illuminating Thrax Audio Heros and Teres power amplifiers. As a top of the cherry the Spartacus mono blocks will join in at at a bit later date to conclude the complete the exploration of the current production of Thrax power amplifier line. 
As you can read more in depth below all new Thrax products are born as a complete different approaches to the ultra high  end reproduction of the sound. So these power amps do actually  not compete with each other, but offers a variety of choices suited to different system setups. And before you ask why Thrax is offering a such array of amplifiers the answer is very simple.  Because they can! Intriguingly inspiring…
Heroes mono blocks represent the company finer exploration of Class A Hybrid tube fet technology. They offer 100 watts of Class A via unique hybrid transformer loaded amplifier design that embrace the renowned concepts with the contemporary high tech. You won’t see output transformer in typical Class A amplifier and still you’ll find them in Heros. Its not a non working concept, but as following this route cost a money. I love the logics behind such concept and the difference is as factual as it gets. But more about this latter. 
Teres on the other hand is a transformer coupled hybrid power amplifier based on classic tube amplifier topology. Single ended tube input stage is loaded with a phase splitting transformer, which controls two separate single ended amplifiers out of phase for output. Teres implements audiophile super long life C3g input tube, silicon carbide rectifiers, shunt regulated power supply, solar cell bias of output stage, battery bias of input stage and microprocessor controlled operation. They have no feedback, uses special grade screened power transformer as well as JFET/MOSFET cascode output devices. Now if thats not enough to get you interested, then recheck of many priorities is mandatory. 
In my preview of the Thrax Audio Orpheus phono preamplifier here: link I already gave a great overview and insights of this Bulgarian High End audio manufacturer. Anyhow… To wrap it up shortly. These days you’re rarely encounter such a proficient, self sufficient and highly resolved manufacturing premises. And one needs to understand the Thrax Audio for what it really is to appreciate it on the level its deserves.

Driven by Rumen Artarski unlimited passion for highest possible musical reproduction Thrax Audio unique venture is more of the extreme, ultra high-end audio design laboratory then your typical high-end audio manufaktur. 
Few months ago at my company/factory visit I’ve had a chance to see and understand the inner workings of Thrax as company. It was an eye and mind opening experience that led me to respect it even more. 
Anyone knowing Rumen feels the similar about him. He’s one of the rare connoisseurs and high-end audio aficionados. Broadminded and culturally embossed person with and exquisite taste and knowledge that surpasses your typical expectations. 

Thrax Audio spirit for me reflect the traditional Japanese approach to the production process where the creational phase is as important as the end result. One must really see Rumen collection of rare tubes, exotic output transformers, chokes etc. to fully understand the dedication and unabridged enthusiasm. There is simply no other company doing the things the way Thrax Audio operate. This is also due the Mr. Artarski being a successful business carrier, that created an immense safe grounds for the in depth R & D of the Thrax Audio product. They can have a complete different time frame and research complexity then most of the gear out there. As a company they are not hard press from the very first moment that new product development starts. No typical taximeter ticking clock is needed. This leads to a complete different sets of the products that can operate on much very different and proficient level. 

We discussed many things with Rumen, past and present at my visit and over our corespondency. I wanted to understand his mindset and why he’s pursuing his venture the way he does. I’m no rookie when it comes to the history of high-end, basic designs, different topologies etc. But during our conversations I’ve found myself hitting the conversation stop button too often! Yes, he’s done his homework overtime and overloaded.
Seeing the literature, prototypes, schematics and amount of contemplating behind the products left a lasting impression with me. It still resonates and it’s a great reminder whenever I’m starting to contemplate about the actual meaning of high end audio. Being inspired, my reading was revived with much more complex material.


Heros is the second power amplifier coming out from the ultra high end brand Thrax. The need for it arose from the fact that many people are not wiling to live with tube amplifiers for many reasons. Having small kids, pets, or the servers to deal with the tubes…

Let us set the realistic expectations down. Contemporary speaker design requires quite some power. Most of the loudspeakers are simply not efficient enough to produce realistic levels with a 50W tube amplifier.

Common sense falls into the Rumen modus operandi, but always with a great twist. This is why from the ground up he wanted to created an amplifier without exposed tubes and having on board at least 100W output. This clearly opened up the compatibility with wider range of speakers along with realistic power match.

It was possible to “pump” up the Thrax Spartacus power amplifier, still Spartacus is already in the upper echelon league and scaling it up would put on the sky high price sticker, making it of little sense by wanting to open up the doors into the Thrax sound to more people.

As with other projects Thrax team spent quite some time and funds in trying to find the right solution in designing more affordable tube amplifier with indirectly heated tubes. In the reality check, they just ended up in the swamp of hundreds of similar designs, thus straying away from Thrax philosophy of meaningful and no copy cat designs.

As with the Spartacus project, they put their hands on many similar products and practically explore many of these tube based designs. Down the quest two things came up in the sum up. They’ve encountered common, known problems and found out some solutions that actually performed quite well. Rumen tends to think out of the box and repeating on something being already established is not his agenda to pursue. He wanted to create something different and viable.

Initial goal was to create a true differential design from end to end avoiding the problems arising from phase splitters.Too often sonic signature of an amplifier is defined by the input and phase splitter rather then by the output stage and this was a challenge.

Heroes were set to output of the 100 W in Class A. Now, for this you mandatory need multiple parallel output devices and in principle instantly pushes things into the AB class topology and regime. As Thrax team explored this kind of AB design along the quest, practical sound output was lacking desired qualities of effortlessness and see trough effect. In the tube design implementing multi-grid tubes (tetrodes/pentodes) sets for a higher efficiency and paralleling multiple output devices, thus as mandatory producing negative impact on the sound.

Thrax engineers did found some good examples by running triodes in class A, but at the expense of enormous heat dispatching and very low power output. Tubes age differently under this conditions, some even drift, thus paralleling was out of the question without special biasing logic.

Resulted solutions summed up with the class A operation and single pair of output devices. They needed to find a viable single tube being capable of delivering the desired power and keeping the longevity at reasonable time frame.

They experimented with an array of exotic tubes capable of delivering the desired result, but again at the expense of great massive proportions and enormous heat. Class A tube amplifiers can achieve efficiencies greater than normal solid state amplifiers due to the transformer loading and this ignited the idea that would combine both of the worlds. Embracing the great qualities and simplicity of the tube circuits with the power advantages of solid state.

Instead of attaching a tube front end to a solid state output stage as in most hybrid designs Thrax team have created something different. They replaced the output tubes in a tube design with solid-state compound devices. Well, is not exactly as simple as swapping a tube for a transistor, but the story unveils…

In order to create this unique circuit, the architecture of the amplifier had to be different. In mirroring the tube design logic the cathode follower tube can be replaced by a Jfet with a minimal change in the operational logic, if the Jfet can handle the voltage and power needed. They managed to implement a cascode that does it. From that point amplifier started to  morph into a working concept. Differential input stage with a solid-state follower loaded by a transformer. Still, not everything was smooth in the developing process. Tube needs a higher voltage than the output stage as it provides all the gain, so two power supplies were needed in order to keep the power dissipation at a reasonable level. Further on coupling between the stages had to add another transformer to isolate the voltage difference, in a word a “classic” one.

This gets even more technically interesting. The output transformer follows the voltage swing of the anode of the tube to 99% (the gain of the follower). Output was needed to be a transformer seen as a load to the tube and the cascode acting as impedance multiplier. In this way tube sees hundred times the transformer impedance and controls the Jfet, opening up the possibility of a single differential gain stage! By following that design the efficiency of the output stage is approaching the theoretical limit of 50%. This allowed Thrax engineers to create smaller and much more cooler amplifier.

The end result is impressive, smallest scale 100 W Class A amplifier with just a single gain stage. Interestingly, Nelson Pass has created a similar design, but without tubes.

This topology offers a see-through transparency and the sound voicing depends entirely on the quality of the input tube.

By this unique approach Thrax Heros encapsulate all the benefits of the class A designs without sounding warmish, slow or rounded. I’ve explored many Class A designs and yet Heros managed to reveal something unheard so far; non reserved power, harmonic rich sound and surprisingly unusual transparency.

Recreating the realistic sound illusion is too often a huge burden not many amplifiers being able to take. Many resolve in certain ability of sound recreation, yet sadly being more of an abstract processes rather then managing to encapsulate the real musical impact. Here Thrax Heros step in with their intrinsic ability to convey music close to what it really is.

How often do we ask ourself if the product under the scope can cope with reality, realism of real people presence/playing and actual live energy projection. Are we in the same space as the the performers. Is the interlocking and interactiveness being established?

This is where boys differs from the grown ups. And exact same feeling belongs to the Heros sonic experience. Level of realism and layering of the sound emerges with multitude of anchor points forged into the primal equivalent of the music. Music was plummeted with sudden prima attacks equivalent to the real live music experience. That should sum it all…


These days I’m not lightly inspired or awaked out of the equality of all the gear coming in and out. Thats why many times I don’t even explore further if a certain criteria is not met. Regardless of the price. 

There are so many mediocre high-end audio products eschewing the chewed circuits and designs, that its not even funny anymore. Call it a matter of globalization and greed in a simplified reasoning. A clear indication of non strange logical conclusion of why most of the sound results of amplifiers are bland and boring! Its also a matter of the goals wanted to be met. For most companies the main ruler is a quick turn over and cashing in. Whit this kind of modus operandi what can be expected as the end result? Saving on the everything and calculating to the last bit leads to employment of electronic engineers knowing little or nothing of the high-end and ultra high-end audio industry mechanics. Initial job of proper design and “voicing” in most cases actually never happens. 
There is a huge difference between designing a typical amplifier and high-end audio counterpart. Many tried to cross the bridge from the other side, but few of them succeeded. Thrax Audio employs the people with specific high-end audio skills and with decades of particular experiences. Sometime, if needed they would bring in the top most specialists, even if only for the  specific project being developed. 
And the difference between typical and ultra high-end audio potently designed power amplifier? Night and day! Not even a debate is needed when comparing the sound of such two side by side. 
This is why I’m pushing the agenda of intelligent research and making the proper homework for people are in the process of upgrading the system and changing or purchasing new high-end audio components. I do believe in common sense and intelligible nature of people willing to shelve out such a hefty amount of the money. 


Bauhaus, art deco, with unprecedented elegant simplicity, that cuts with the contemporary aura and fails to be ostentatious like most of the high-end audio gear at any point. Elegant and timeless. Love it!

Front panel is direct and minimalistic. There is a large circular knob for on/off stand by mode. Back panel reveals standard IEC connector with on/off switch. Heros offers a selectable gain to match with the dedicated preamplifier and selectable speaker impedance. You can choose between both RCA and XLR inputs with a dedicated switch. Everything is straight forward and hands on.


Thrax Audio Hero power amplifiers have shown their DNA and recognized sound orientation from the first few notes being played. They carry the familiar “voicing” I’m used to from the Dionysos and Orpheus. Continuity is not easily achievable. Especially with building different components one wants to open new, uncharted territories, yet without loosing the most important orientation. And for Thrax this is clearly the sound of the real music.

There are many critical points that embarks a level of needed attributes to let any product reside on the plane of the high-end audio. What to talk about the ultra high-end, even more niche market. Thrax Heros sits both firmly and boldly on their designated throne without even blinking…


Leonard Cohen last two albums represents some his finest music up to date. They are both very well recorded and can easily reveals whats is possible within any system. Call it simple pop or whatever you want it. To really sing these songs needs more then properly designed electronics. Same demand goes for Lokua Kanza latest album Nkolo. Pure impact of the african lyrical compositions. Simplistic yet complex at the same time. To get into the core of the songs like Elanga Yu Muinda is no easy task. Here even few of the best specced amps fall short of the vibrancy needed to encompass Lokua soulful composing. 

Grieg Unheard Reza e iRagazzi fantastic album is another album encompassing majestic execution that really needs a profound amplifier in order to come alive and Janos Starker protégée Maria Kliegel endearing playing falls even more so in line of the proficient demands and sound attributes.   
Thrax Hero mono blocks step a further into the rendition these albums and artists with an unfettered hologram like three dimensionality. They could render the music under the scope precisely and with the omnipotent dynamic barrage which can minutely shift from pianissimo to forte fortissimo without a sweat and without loosing a pace. Even most importantly the essence of music is touched and revived withe Heros. 


I’ve been asked too many times about the reasoning behind the ultra high-end and here is a simplified answer. For a real connoisseur and music lover the real quest is always connected to the exploration of the possibilities. There is no place for narrow mind orientation if you’re on the ultimate quest.

As with everything in high-end audio the proper matching is a must. There is no black and white reasoning in matching the components and creating a high-performing realistically sounding system. Point is, do not expect instant magic without matching candidate for Heros.

In the industry where we’re are seeing to many lots of reissued and re-chewed ideas I’m always enthralled by the ultimate machines and uber. People in general need to escape entrapping closed mentality and their view of the ultra segment of our industry. Most of the high-end car and watch enthusiasts and even aficionados cannot afford the bespoke creations, yet still they uber passionately admiring them. They simply want to see and known what’s possible and how far things can be pushed. This is the needed attitude.

Thrax team shows profound dexterity and they are stalwart to the Rumen Artarski strong determination regarding to how Thrax products should sound like.

Heroes possess an intricate translucent nature that reveals music for what it is. Its never easy to establish a potent medium of profound interaction between performer and listener. Heroes, rich in tonality, zesty and radiant are capable of harmonically contoured reproduction that is both elusive, lyrically and most important sound wise reiterated at each play.  

The unrestrained, enchanted music flow is most inspiring. Heroes hybrid concept brings most inspiring level of transparency, details and constitutional points of upper echelon league of the performance. For any Class A amplifier this is quite an achievement.

Thrax Audio Heros mono block amplifiers radiate unique inner sanctum reminiscent of renowned tube amplifier potency without actually crossing the “other” side.

Heros brings the open nature voicing, that is surprisingly transparent for the Class A and mighty harmonic potent. They will need a proper matching speaker to reveal their full nature. Once set in the fine-tuned system Heros act captivatingly convincing,

While many still day dream about Kondo, Shindo etc. I’m wholeheartedly pointing them to try, explore and compare it with Thrax creations among other few real gems. Bold step is more then worthy of consideration when one wants to step out of an old paradigms.. Many of past designs simplify the sound projection offering a remnants of the musical events. Music emerge and expands under the Heros baton with complex colors pallet yet without expected saturated tint. A massive change.

Thrax Heros are not even in the uber pricing level as some other utterly priced gear on the market, but without Rumen determination, world view and genuine music loving this amplifiers would certainly carry crazy price tag.

Heros are another exploration from the Thrax high-end audio brand. As I’ve written before, they can afford to explore the exotic side of ultra high-end audio and intimately I’m attached to such boldness. Thrax Heros certainly represent a healthy new breeze of the high-end products being more than worthy of highlighting and awarding.

I have no second thoughts to put myself out again and reward Thrax Heros with an award. Heros are most radiant Class A amplifiers I’ve had pleasure to encounter and and a project much more complex and refined then expected.

Text: Matej Isak

Price: 26.000 EUR with VAT


Tube amplifier architecture with simplest signal path
Transformer coupled input and output
JFET/MOSFET cascode output devices
Silicon Carbide diodes in power supply
Microprocessor control
Selectable gain
Selectable speaker impedance
Audiophile 5687wa tube used
Fully balanced differential operation
Both RCA and XLR inputs
Compact chassis built like a tank
100W Class A power output


INPUTS: 1 unbalanced RCA connector, 1 balanced XLR connector
OUTPUTS: 100W in 4Ω/8Ω
POWER SUPPLY: 115 or 230 V
DIMENSIONS: 210W x 400D x 230H mm
TUBE COMPLIMENT: 1x 5687 amplification


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