atelier 13 audio

THÖRESS EHT Monoblock

"Reinhard Thöress set out to exalt the treasures contained in the Triode tube, through a classic approach that has proven itself and a deliciously Retro look, a sound result unlike any other in its density, its presence, its energy and its realistic spatial presentation, serving all the emotion contained in each recording. Those who are connoisseurs of Valve-halla will be delighted by the Thöress amplifiers and their rare musicality"

A Tribute to Professional Audio Components from the Golden Age of the Vacuum Tube!

EHT
MONOBLOCK

"DUAL SYNTHESIS"

single-ended hybrid triode

THÖRESS EHT MONOBLOCK

Single-ended Hybrid Triode Power Amplifier

THÖRESS is pleased to announce the introduction of the Hybrid Triode Mono Amplifier (EHT Monoblock), our latest achievement. The most powerful amplifier model of our product line provides 30, 40 or 50 watts of output power into a 8, 6 or 4 ohm load respectively, combined with very low output resistance (high damping factor). Such providing excellent drive capability for loudspeakers with medium to low efficiency or with critically low impedance which may present a challenge for our all-tube single-ended triode amplifier models. While offering the same level of ultimate sonic excellence - yet without involving exotic and costly power tubes! The Amplifier is built with meticulous hand construction using our proven point-topoint wiring techniques, whereas much care has been taken in arranging each aspect of the internal construction to ensure low noise performance, ease of service and the highest reliability for many years to come. The EHT Mono Amplifier is an ultimate component in every sense and the perfect complement to our Dual Function Amplifier or Full Function Preamplifier

EHT TOPOLOGY

The amplifier is based on a unique minimalist single-ended zero-feedback vacuum tube MOSFET hybrid topology which we call EHT Topology [ E.intakt-H.ybrid-T.riode, Single-Ended Hybrid Triode ].

We deliberately ignore the fact that many music lovers persistently believe in the myth that balanced technology ... and the associated XLR connectors and cable configuration ... is generally superior over single-ended concepts.

Readers who want to learn more about our view on balanced techniques and our general design approach are encouraged to read the "THÖRESS - Behind the Curtain" white paper, available on request.

The EHT topology consists of a single-ended triode gain stage (6J5GT,12J5GT or 7A4 vacuum tube) followed by a unity gain MOSFET output stage also operated in singleended (class-A) mode with high idle current. Basic analysis easily shows that ... The EHT principle represents the PUREST form of all possible single-ended triode power amplifier configurations!

Specifically, it can be shown that a higher output power can be more easily obtained with the EHT than with an all-tube amplification principle, without compromising sound quality. Simply, because in the former case the typical vacuum tube impedance matching output arrangement (power tube driven output transformer with high step-down ratio) can be fully omitted.

Therefore the driver voltage swing required for a specific power output is up to 10 times (!!!) lower for the EHT configuration compared to an all-tube topology, resulting in a proportional reduction of non-linear distortion. In fact this very crucial insight led us to the design of the EHT Integrated (and the EHT Mono Amplifier).

The EHT topology allows to fully exploit and mate the most desirable characteristics of both vacuum tube and solid state devices determined by their very nature.

STABILITY

The EHT Integrated Amplifier operates with impeccable thermal stability and is fully short-proof at the output without the aid of any kind of (sound degrading) protection circuitry. Moreover, a switch-on delay module (another protective feature often found in commonly constructed solid state or hybrid amplifiers) is also omitted because no disturbing noise or harmful signal is developed at the output when the amplifier is powered on or off.

GAIN & BASS BOOST SELECTOR

The EHT Mono Amplifier allows for on-the-fly adjustment of the gain (input sensitivity) in 7dB-steps by means of a 6-position rotary switch on the rear panel near the input jack.

When the switch rests in position 1, 2, 3 and 4 respectively [neutral tonality / flat frequency response], the [voltage] gain is :

4dB (1.5-times)
11dB (3.5-times)
18dB (8-times) and ...
25dB (20-times) ... maximum gain

Position 5 and position 6 are assigned with bass boost presets, respectively :

P5 : bass boost style-1
P5 : bass boost style-2

The gain selector enables the user to : match the gain of the power amplifier with the gain of the line device with respect to the efficiency of the loudspeaker.

Optimal gain matching between these components is highly desirable for two reasons :

Firstly, and in a matched scenario, the idle noise of the preamplifier remains inaudible even in the context of highly efficient loudspeakers.
Secondly, the volume control knob can be operated at a higher angle of rotation and, as such, allows for conveniently fine volume adjustment.
Note : Optimal gain matching is attained when the volume control on the line device on average rests near the middle position for a convenient listening loudness.

The bass boost functions can be applied for a variety of applications :

For equalizing loudspeaker components with slim bass response or limited bass extension.
For adjusting the bass response of the system to the acoustic conditions of the listening environment, .. i.e. [ small loudspeakers in large rooms ! ]
For restoring tonal imperfections of the listening program ..i.e. often caused by a lack of bass extension.
Or simply for switching to a full-bodied presentation if one is in the mood for listening to music in a non-neutral, enriched and laid back way.
Notably : The two bass boost functions act in a much more subtle way than common bass boost facilities, and do not rely on clumsy and sound degrading conventional tone control circuitry. Both functions are realized by interposing solely one additional capacitor [ per channel ] to the neutral mode circuit !

MAINS TRANSFORMER

The EHT Mono Amplifier is equipped with a proprietary mains transformer produced in-house to ensure the highest possible quality and reliability. This part features a highly elaborated dual-coil winding structure on a large tape wound cut core (C-core) and has been optimized for low body noise emission and low leakage.

Nevertheless, it is mounted to the amplifier chassis via isolation elements in order to eliminate even the slightest interference of residual transformer vibrations with the circuit. Since the mains transformer is produced in-house we can easily build transformers for all kinds of mains voltages on demand, for example 100Vac (Japan), 120Vac (USA, Canada), 220Vac (South Korea, China, Thailand, Indonesia), 240Vac (UK) or 245 Vac (Australia).

F E A T U R E O V E R V I E W

Vacuum Tube MOSFET Hybrid Mono Amplifier with 30, 40 or 50 watts of output power into a 8, 6 or 4 ohm loudspeaker load respectively, utilizing two vacuum tubes [ 6J5GT or 7A4 and 1x12HG7 ]

Superior driving capability for critical loudspeaker loads due to very low output impedance (high damping factor)

Ultimate sonic excellence on par with no-compromise all-tube single-ended triode amplifiers, yet without involving exotic and costly power tubes

Unique minimalist zero-feedback EHT schematic: single-ended triode gain stage (6J5GT tube) driving a unity-gain MOSFET output buffer operated in single-ended (class-A) mode with high idle current

Total avoidance of protection circuitry

On-the-fly selectable gain via 6-position rotary switch on the rear panel, 2 of which positions are assigned with subtle bass boost presets

High grade electrolytic capacitors made in Germany in the power supply

Low noise low leakage dual-coil C-Core mains transformer made in-house for 230Vac (115Vac via jumper setting), 100Vac (Japan), 220Vac (South-Korea, China, Thailand, Indonesia) or 245Vac (Australia)

Full hand construction, point-to-point wiring throughout

Non-magnetic aluminum casework, anodized printing on front and rear panel, powder-coated lids

Dimensions - mm :
- 434 W x 450 D x 184 H
- H / 184mm = 20mm (feet) +134mm + 30mm (tubes over case)
- D / 450mm = 434mm +16mm (speaker binding posts)
- Dimensions of the shipping crate - mm: 650 W x 650 D x 350 H
- Shipping weight : 15Kg.

Individually Made in Germany

MSRP $ 15,700

Show & User-System Coverage

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What the say ...

POSITIVE FEEDBACK

Wojciech Pacuła | Dec 16, 2020

JASKUŁKE'S PIANO usually sounds quite dark and dense. I mean not only the Sea disc, recorded in a specific way, with a piano covered with a duvet (it was supposed to be just a warm-up before the actual session), but generally about the sound of the instruments he plays. I do not know if it is a derivative of his playing technique, whether it is influenced by the choice of instruments, or finally is it a conscious choice of producers, but it is just like that.

I know this type of sound, because I hear it with devices whose designers wanted to reproduce not so much the "letter" of the recording, but rather its "spirit." Based on the assumption that since it is not possible to render reality perfectly, it must be made credible—and 'perfection' and 'credibility' are two different things in audio. If these were absolutes and if we lived in an ideal world, than yes, we would be talking about synonyms. In the real world, however, we only deal with approximations. A credibility approximation for designers such as Reinhard Thöress seems the most appropriate way, because it is very "human."

The sound of the EHT Mono is therefore characterized by incredible saturation. Something like this is difficult to achieve in audio, regardless of whether transistors or tubes are in play. It's a state of mind rather than a technique. With the tested amplifiers, the Jaskułke piano had not only a warm, dense sound, it was also complemented and densified. I mentioned the aura that consists of the sounds from the environment on this album—with Thöress amplifiers it was cool, but less important than the foreground.

Apart from the outstanding saturation, one of the basic features of the EHT sound—as well as a large part of this type of amplifiers—is bringing the foreground closer to the listener and making it bigger. If I haven't said it directly yet, I'll do it now—it's not an amplifier that celebrates details, that focuses on every creak of a pianist's chair, over every breath of a double bass player. If these elements are present in the recording, EMT Mono will pass them on to us. It's just that they will do it "casually", next to the music.

Everything in the presentation of these devices is—just like the gulls soaring overhead during the Jaskułke concert, and the bells in the recording opening the album Chwile... by Bogdan Hołownia, and then the cymbals in the Somethin 'Else from the Cannonball Adderley album, played from the great Esoteric SACD re-edition, there in the sound. But fullness was more important, volume was more important, consistency was more important.

When in the track Autumn Leaves the leader plays his saxophone, going down, even though it is an alto saxophone, it had a very deep sound, it was heard as if he was standing two meters away from me. On the other hand, Miles Davis' trumpet, played here with a muffler, sounded sensational, because it was strong, bright, but not aggressive. And Hank Jones's piano - it sounded like something from the albums I mentioned earlier.

The thing that says a lot about the character of the EHT Monos was how interested and involved I was listening to the sound of the double bass and kick drum as the driving force behind the recordings. Both instruments are played really well by these amplifiers. Normally, I would say that they are emphasized, but the technique used in the tested devices results in something other than coloration—it provides richness, and gives the recording a strong, solid, dense foundation of the truth about the sound.

Jean Michel Jarre from the Magnetic Fields sounded incredible! The Scott Hull's remaster from the Masterdisk studio is warm and rather dark in itself, but with the German monoblocks the bass was also saturated. I cannot imagine that anyone would be missing anything in this part of the range with these amplifiers. For many music lovers it may be a surprise how much information about space, dynamics, volume, and also treble, is "encoded" in the lower range of the band. The EHT Mono show that, without this, it is difficult to talk about a credible presentation.

Summary

So there is a saturation, warmth, density, strong bass, warm, silky treble and the primacy of the foreground. This results in an incredibly natural sound. But the sound is focused on timbre, not detail. You have to remember that. Reinhard Thöress's hybrid monoblocks offer a holistic view of the musical material and its reinterpretation. Their sound is soft rather than focused, rather warm than open, and rather close to us than presented in a perspective.

This is the sound for long, very long listening sessions, not only for playing loud, but also when the volume knob is set to the minimum. Even with quiet listening we get fullness and density with them, which is hardly ever present with other amplifiers. Go up with volume and the dynamics will appear, and the sound will fill the space in front of you. The amplifiers handled the difficult Harbeth M40.1 loudspeakers very well. They create events in their own acoustic environment, which is completely transferred to our room. It's a beautiful, organic, that is—a comprehensive and internally properly arranged—sound for those who value tonality above all else.