THÖRESS EHT Hybrid Triode Mono Amplifier - Pair

SRP: $17999

THÖRESS is pleased to launch the Hybrid Triode Mono Amplifier (EHT Mono Block), our latest achievement. The most powerful amplifier model of our product line delivers 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 critical impedance behavior which may present a challenge for our all-tube single-ended triode amplifier models. While offering the same level sonic excellence without involving exotic and costly power tubes. The sonic presentation of the EHT Monoblock is of the utmost refinement and easily measures up to the highest expectations of even the most critical and experienced music lover. And of course it is  a perfect complement to our DFAmp or FFPre.

BUILT

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.

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). Decidedly ignoring the fact that many music lovers still persistently believe in the myth that balanced technology (and the associated cable configuration with XLR connectors) is generally superior to 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 paper (THÖRESS - Behind the Curtain) downloadable on the ABOUT button of our website.

STABILITY

The 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 on 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.

EHT  PRINCIPLE

The EHT topology consists of a SINGLE-ENDED TRIODE GAIN STAGE followed by a current buffer in form of a unity gain MOSFET OUTPUT STAGE, also operated in single-ended (class-A) mode with high idle current. It allows to fully exploit and mate the most desirable characteristics of both vacuum tubes and solid state devices determined by their very nature. Despite its elegance and extremely high sonic capability, it has never been utilized in a serial audio product before, as far as we know. Probably on account of its low power efficiency and because its implementation is rather tricky.

The EHT topology 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 the all-tube amplification principle, without compromising sound quality. Due the fact that the typical all-tube impedance matching output arrangement consisting of a power tube loaded by an iron-cored output transformer with high step-down ratio can be omitted. As a matter of consequence, the voltage swing required from the driver for a specific power output is up to 10 times (!!!) lower for the EHT configuration compared to an all-tube circuit. Resulting in a proportional reduction of non-linear distortion as a quite substantial benefit.

GAIN  &  BASS  BOOST  SELECTOR

 The EHT Mono Amplifier allows for on-the-fly adjustment of the voltage gain of the amplifier by means of a 6-position rotary switch on the rear panel adjacent to the input jack. When the gain switch rest in positions 5 or 6 the mid-band gain is 10dB (3-times) whereas the bass response of the amplifier is mildly boosted. The mapping between selector positions, gain and sound effects is described by the chart below.

Position 1 2 3 4 5 6 Gain 4dB, (1.5x) 11dB, 3.5x 18dB, 8x 26dB, 20x 10dB, B+ 10dB, B++

Notably, the bass boost functions do not rely on clumsy and sound degrading conventional tone control circuitry. They are realized in a smart way by interposing solely one additional capacitor (per channel) to circuit.

The gain selector allows the user to match the gain of the power amplifier to the gain of the line device with respect to the efficiency of the loudspeaker. Optimal gain matching between these components is desirable in order to avoid idle noise issues and to allow for conveniently fine volume adjustment.

The bass boost functions are usefull for a variety of applications...Equalizing loudspeakers with slim bass response or limited bass extension. Adjusting the low frequency response of the system to the acoustical conditions of the listening environment (small loudspeakers in large rooms!). Restoring tonal imperfections of the listening program, often given by a lack of bass extension. Or simply for activating a more full-bodied presentation in case the user is in the mood for listening to music in an enriched and laid back way.

TUBES

In order to obtain the relatively high power output with our EHT Monoblock with lowest possible distortion it proved advantageous to extend the basic EHT schematic by adding a powerful unity-gain vacuum tube buffer (12HG7 power tube operated in triode mode) inbetween the triode gain stage (7A4 triode) and the MOSFET output stage. The 7A4 tube is an octal-base single-triode from the famous ?J5/?SN7/?A4 family of tubes with fairly low transconductance developed in the early times of tube electronics. Whereas the 12HG7 is a fairly late (all-glass) development with high gain and very high transconductance, making it an ideal choice for buffer applications. Both tubes are unarguably among the most linear amplification devices ever developed in the history of electronic technology and as such are a perfect choice in the context of minimalist zero-feedback circuit design.

MAINS  TRANSFORMER

The EHT Mono Amplifier is equipped with a mains transformer produced in-house featuring a dual-coil winding structure over a large tape wound cut core (C-core), which 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 readily customize the amplifier for all kinds of mains voltages.

F E A T U R E   O V E R V I E W

• Vacuum Tube MOSFET Hybrid Power Amplifier offering 30, 40 or 50 watts of output power into a 8, 6 or 4 ohm loudspeaker load respectively, utilizing two vacuum tubes (7A4 and 1x12HG7).
• Ultimate sonic excellence on par with no-compromise all-tube single-ended triode amplifiers, without involving exotic and costly power tubes
• Excellent driving capabilities for critical loudspeaker loads due to very low output impedance (high damping factor).
• Unique minimalist EHT schematic.
• Total avoidance of sound degrading protection circuitry.
• On-the-fly adjustable gain via 6-position rotary switch on the rear panel entangled with bass boost facilities implemented without clumsy and sound degrading conventional tone control circuitry.
• High grade electrolytic capacitors made in Germany in the power supply.
• Low noise dual-coil C-core mains transformer made in-house, for for 230Vac, 100Vac (Japan), 120Vac (USA, Canada), 220Vac (South Korea, China, Thailand, Indonesia),  240Vac (UK) or 245 Vac (Australia).
• Full hand construction, point-to-point wiring throughout.
• Nonmagnetic aluminum casework, front and rear panel with anodized printing, powder-coated lids.
• Dimensions  434x454x184 mm,  184=20 (feet)+134+30 (tubes over case), 454=434+20 (speaker binding posts), weight 15Kg.
• Dimensions of the shipping crate: 650 x 650 x 350 mm.