Thrax Audio Teres Mk2 Monoblock Amps by Moreno Mitchell


For the past eighteen months, I have been blessed with Thrax Audio Spartacus Pure 300B Power Amplifiers in my home audio system. Thrax Audio has been a mainstay in the audio community for years. Thrax Audio owns the reputation and mastery of craftsmanship coupled with creativity in design and, most importantly, advanced technologies, resulting in an audio sound beyond reproach.

The Thrax Philosophy.

“Human vision, hearing, and other senses are not absolute measurement devices. They compare the difference between a reference and the tracked signals, and it changes over time. ​The hearing system registers sounds and requires some time to assess them. It then starts to track the changes, giving less importance (losing interest) to long and sustained signals with no change. ​It adapts to the surrounding (residual) background and concentrates on the constant changes in signal properties.

Motion or flashing lights attract your vision in this exact same way. This phenomenon allows you to follow a conversation between two people in a noisy environment or listen to the voice of a singer undisturbed by a busy musical piece. It is so natural to us that in your office you realize how noisy it is only when the noise stops.​ If the background is quiet the following sound appears louder and clearer. Anything different from the pitch-black background attracts your attention. Or if your hearing has adapted to a residual noise you start losing information (your brain does not pay attention to it). To make an analogy it is like increasing the contrast in a picture by darkening the background instead of increasing the brightness. The bright light will blind you and you will not see better, but removing the strenuous light makes your reference (black) stable and the picture becomes more vivid and sharp. It’s like watching a movie in the cinema with the ambient lights on or off.

Let us put this in the context we are interested in. Music is written with notes and pauses that represent sounds and SILENCE. The quality and quantity of silence in between notes is just as important as the pitch and timbre in the notes themselves. ​It is rather complex why we have all those artifacts in our precious music through the reproduction chain but it is immediately apparent when they are reduced, and simply amazing when they are almost gone. Serenity and expressiveness come to mind when you experience it. It just sounds right.”




The beginning of my Thrax Journey

As previously stated, my Thrax Journey began a few months ago. I first experienced the Thrax sound at an audio show and was completely mesmerized. From that point on, I made up my mind Thrax would be the perfect system for me. I began my Thrax Audio journey by purchasing a pair of Spartacus 300B Power Amplifiers and a Thrax Dionysus Preamp. A short while later, I added the Thrax Maximinus Mk2S DSP controlled 32 bit/384kHz Audio DAC; the combination was perfect; however, as most of us audiophiles do, I could not rest on my accomplishments without wondering how a complement of all 300B tubes sound in my system would sound. I upgraded to the Thrax Statement Libra Differential Balanced 300B Tube Preamp; the Libra offered four 300B output tubes and a separate output stage. At this point, I was set for life, or was I?

With the addition of the Thrax Libra and Maximinus DAC, my system was cooked with oil for the better part of three months. My chest stuck out like the Michelin Man. However, I still was not done finding new ways to reach the next level. After researching and inquiring about bi-amping, I wondered how my system would perform with another set of amps connected to my Y.G. Acoustic Sonja 2.2i bi-amp speakers. I had read many conversations regarding this subject. However, I had yet to take an interest in actually accomplishing it. There are pros and cons from forums and articles addressing the subject of bi-amping speakers. One of the main cons I noticed was problems getting the amps to correlate. However, on the flip side, the main pro was that natural sonic beauty is like no other sound once done right. Do I have the resources to accomplish this, and what would be the overall cost? And lastly, do I have the budget?

One of the benefits of being a Thrax owner is that there are multitudes of options when it comes to technical feedback and resources. I contacted Rumen Atarski (Thrax’s Founder and Chief Designer) for advice. Mr. Atarski made himself available and was extremely friendly and very upfront. I was very impressed with his willingness and enthusiasm in assisting me with making the best intelligent decision. I was happy to know I already had all the necessary components except for investing in another set of interconnects. Mr. Atarski also explained in detail how fortunate I was to own the Thrax Libra Preamp since it is capable of separate dual outputs and is perfect for accomplishing my Bi-amping objectives.    

Putting it All Together

The next step was to map out how to put together the required components for goal accomplishment. I had no previous experience with Bi-amping, so I had to rely on expert feedback and intuition. After communicating with Rumen, he provided explicit tips and suggestions; however, the ultimate choice would be up to me. After researching many power amplifiers, I realized my choices were many. With all said and done, I chose to stay with the Thrax family. This was a relatively easy choice due to my experience living with the Thrax Spartacus; I wanted to stay in a signature sound that always encapsulated me. My ultimate choice was settled by adding a pair of Thrax Teres Mk2 Monoblock Power Amps.


Thrax Teres Mk2 Hybrid Monoblock Power Amps


·        Long-life input vacuum tube 

·        Custom phase splitting transformer 

·        Silicon carbide rectifiers 

·        Shunt-regulated power supply for the tube stage

·        Solar cell bias of output stage

·        Microprocessor-controlled operation

·        NO feedback 

·        Special grade screened power transformer 

·        JFET/MOSFET cascade output devices 

·        Modular construction

·        Available in stereo and mono version 

·        Transformer input on the XLR for true balanced operation

·        Solid machined aluminum chassis

Teres was first introduced in 2015 in the Monoblock version. It featured the legendary C3g input tube biased by a lithium battery. Those are recognizable by the metal C3g tube in the back and the plastic lid of the battery compartment. In 2018, the Stereo version was developed, featuring a more sophisticated shunt regulator and improved circuitry using the now-established 6N6P dual triode. 2020 saw the launch of the Mk2 version, which added all advancements from the Stereo version to the Mono, as well as a new super-screened power transformer design and the use of the 6N6P tube—now the established standard for all Thrax hybrids and the Dionysos preamp.

A single-ended tube input stage loaded with a phase-splitting transformer controls two separate out-of-phase single-ended amplifiers for output. The tube handles all the needed voltage gain. It uses a new generation of our choke-rectified shunt-regulated power supply, providing a noise-free operating point, clear tone, and unbelievable dynamics. The output stage’s power JFET cascodes form a bridge that, when unbalanced by the input signal via the two transformer windings, restores balance by adjusting their current conduction through the load. The two output stages enclose the load in their control loops and try to correct each other’s errors, reducing the distortion to insignificant amounts and leaving the “character” of the input stage untouched. Those provide no signal gain; they merely satisfy the load’s hunger for the current.

The amplifier is biased to reduce the heat generated, so only the first few watts are in true class A. Music has a crest factor of 10 on average. This means that we usually listen at 1/10th of the peak levels. For most users, this translates to under 5W. Peaks can reach over 100 watts during playback, but only for milliseconds. For those peaks, the amplifier switches to class B using only one leg of the output stage capable of delivering up to 250W/8Ohm and 350W/4Ohm. Not sharing a common reference point apart from the load makes the second output stage correct for any error produced by the first one. 

The result is an amplifier capable of extreme power while delivering exquisite smoothness and low-level resolution.

The interstage transformer isolates the driver stage and is not influenced by the output stage, maintaining tone, color, and resolution at all power levels and loads. Having the output stages floating around the load prompted the use of a unique biasing technique powered by solar cells. This was the quietest galvanic isolated power we could come up with. Using optoelectrical conversion, we control the bias by adjusting the light intensity in the control circuit. Teres is an example of modern technology that solves age-old problems, allowing us to go beyond what was possible. The physical appearance of Teres has the kind of understated elegance typical for Thrax. The exquisite aluminum finish adds to the presentation of a solid block of metal.

Getting Started

The Thrax Teres amps were ordered and shipped directly from the Thrax factory in Sofia, Bulgaria. The amps took one month to complete and arrive. They were shipped safely and securely via sound and sturdy flight cases. Professional packing, with no detail overlooked, these quality aspects speak volumes when it comes to a company that puts quality first. At first glance, both amp’s build quality was impeccable. They just looked solid and exquisite. The design of the Teres is on the same lines as the Spartacus 300 B’s, “pure quality.” Once I muscled each Teres amp from its flight case, I positioned them in the temporary place for the break-in process. The idea was to burn them in full range while connected to the Y.G. Acoustic Sonja 2.2i Speakers. With both Thrax Spartacus 300B power amps disconnected, I ran music through the Teres amps for the next three weeks. With a recommended 150 hours, the Teres sounded mightily impressive right out of the box. The Teres exhibited a very relaxed, non-tubey sound; the energy in the room revealed a quiet, transparent footprint that is a Thrax signature. The sound was warm, energetic, vibrant, and very dynamic.  Although I was extremely pleased with the sound of the Teres, I still missed the musical dominance experienced with the Thrax Spartacus 300B amps. There is no better musical enjoyment than when experienced through sixteen 300B tubes synchronizing in unison.  

Putting it all together

Once the Thrax Teres amps burned in, I reintroduced both Thrax Spartacus Power Amps to the system. This was accomplished using two sets of Albedo monocrystal interconnects connected from the Thrax Libra preamp to each amplifier, and an extra pair of Hemingway Sigma Speaker cables connected independently to all four amplifiers. I was nervous about syncing the sound, such as ensuring the output levels for both amplifiers were perfect. The Teres amps were connected directly to the bass unit of the Y.G. Acoustics, while the Spartacus was connected directly to the mid/highs on the Speaker’s bi-wired section. It was time to make sound adjustments once I was confident I had everything connected properly. According to Rumen, this experience sets Thrax Libra apart from all others, and he was correct. After making a few adjustments while listening to a few of my favorite songs, I was locked in within a few adjustments. I have not touched the outputs since. The syncing of the outputs made me very nervous; however, it was relatively simple and rewarding.

The Sound

The rewards of bi-amping were immediate. The cost of the components, cables, and time spent were well worth the benefits. I don’t know why more pure audiophiles don’t bi-amp, although I did notice some bi-amp exhibits at Axpona 2024. Living only with the Thrax Spartacus for the past 18 months was more than sufficient; however, if the opportunity presents itself to polish my game, then why not? What are some differences/improvements experienced since adding the Thrax Teres amps?

·       Increased low-level resolution

·       Tighter, deeper bass authority

·       Increased headroom on the Spartacus amps

·       Pitch-black background, imaging depth (3D)

·       More air in the mid and upper frequency/increased clarity

·       Sound stage depth and width were the best I have experienced

·       Tons of increased resolution

Since bi-amping by adding the Teres amps to my system, I have noticed that the Spartacus power amps are working less hard since they only power the upper portion of the Y.G. Acoustic mid/upper frequencies. One example: prior to the new addition, to reach a sound pressure level to fill my listening room with music, the amps would be required to deliver at least 8-10 watts of power; however, with the new addition and setup, the Spartacus is barely delivering 1 to1.5 watts per channel. (Very efficient).

The Listen

Listening to some of my favorite tracks made this Journey all the better and allowed me to validate the benefits of b-amplification. One album of note is my reference copy of Herbie Hancock’s River, “The Joni Letters”. This Grammy Award Winning Album has a plethora of ear-pleasing selections that I have been familiar with for years. I first noticed how very clear and concise Mr. Hancock’s keyboard notes sounded. The well-defined tonal cues were as I remembered, but I could also distinguish a separation of each key struck as if the tonal balance was quieter. Norah Jones and Tina Turner’s voices on consecutive cuts were ever so slightly focused, like fine-tuning a well-focused television to the Nth degree. However, the cymbals on the cut “Solitude” were astonishing; the cymbal solo captured my audio senses like never before. I can’t explain why, but adding the Thrax Teres has allowed the Spartacus to maximize its overall capabilities in the mid/high frequencies. I had to play these selections repeatedly for me to come to grips with what I was hearing.

I primarily listen to traditional and contemporary jazz. When I desire to listen to modern jazz vocals, I usually listen to Diana Krall. One of her top recordings is the “Live at the  Paris Olympia” CD. Playing this CD through my Esoteric K-01Xd Hi Resolution Player captivated my aural senses. There are exquisite instrumental solos demonstrated throughout this excellent recorded CD that, along with the instrumental solos, Diana’s voice synchronizes perfectly with the band, thus making music blend on a different plane. All these accolades were easily captured through the Thrax ensemble. With the lights turned out in my listening room, I physically/mentally placed myself in the middle front-row seat, enjoying the live concert from start to finish.  

On the contemporary side of the house, Soprano saxist Marion Meadows has been a mainstay in my jazz collection for years and is still going strong. His “Dressed to Chill” CD, released in 2000, is also one of my favorites. The I Can Fly selection is one I can listen to repeatedly. It is seductively recorded and plays with a smooth water flow effect when played through the Thrax ensemble. In other words, the notes throughout flowed like a college marching band stepping in perfect unison. This hobby has to be the best imaginable, and I am blessed to be a part of it.

Although I can continue writing about my musical experiences and testimonials since the Thrax bi-amplification experience, I will leave it with this last one. “The Bill Evan Trio 1980 recording titled “I Will Say Goodbye” is a recording masterpiece. The title track has mesmerized me with various musical notes from a trio of musicians. This CD is worth listening to in its entirety. Mr. Bill Evans is a legendary musician who should be in every jazz audiophile’s audio collection. With the Thrax components in the chain, I could hear and feel the music in my soul.

The Wrap Up

To put things in perspective, my Journey has been rewarded with a pot of gold. After researching the bi-amping topic for many months, I am elated to have taken the plunge. There is a plethora of information on this topic, some of which frown on bi-amplification. I wonder why; maybe whoever wrote the negatives needed the correct ingredients, in my humble opinion, and based on what I have experienced as captured in this review. Suppose one has the budget and correct components and wants to take one’s audio experience to the highest level. I highly recommend accomplishing an audio bi-amp setup. If you can do it with Thrax Audio components, I guarantee you will contact me and the Thrax Audio Team to thank us all.



Price: $34,000.00 USA

Weight  –  25kg 

Dimensions  –  340x450x230mm  

Power   –  450Wmax 115/230V 50/60Hz 

Max. input level –  7V Rms 

Output Power –  250W/8Ohm 350W/4Ohm 

Gain +16db 

Input impedance –  47k Ohm  

Output impedance  –  0.35 Ohm 

Signal to Noise –  112db 

Frequency response –  20-20,000Hz +/- 1db 

Copenhagen Blvd Bl 289
Druzhba 2, 1582 Sofia

U.S. Distributor


Moreno’s Associate Equipment
Thrax Spartacus 300B Tube Amplifiers
Thrax Teres Hybrid Power Amplifiers
Thrax Libra 300B Tube Preamp
Zesto Audio Andros Deluxe II Phono Amp
Pro-Ject RPM 10 Carbon Turntable/ Van den Hul Stradivarius Cartridge
Otari MX5050BIII-2 Reel-Reel Tape Machine
Thrax Maximinus DAC
Esoteric K-01Xd CD/SACD Player
Auralic Aires G2.1 Network Transport
Waversa EXT Reference Plus
Roon Neutrilik Plus
Sean Jacobs Power Supply
EtherRegen Network Switch
Y.G. Acoustics Sonja 2.2i
REL G1 MKII Subwoofers (2)
Hemingway Sigma Speaker Cables
Hemingway Sigma, Beta, Alpha Power Cords
Albedo Metamorphosis Signature and MKII Monocrystal Interconnects (3 sets)
Albedo Gravity III Power Cords
Ansuz Digital DTC Supreme
Ansuz Audio Interconnect DTC
A.C. Conditioners
Puritan PSM156
Sound Application TT-7
Inakustic AC4500 Power Station
Townshend Audio Seismic Platforms
StillPoints Stands S.S. Ultra 6’s
StillPoints Equipment Rack
Synergistic Research Black Box (2)
Room Tube Bass Traps
Ansuz DTC Power Box




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