NEW THÖRESS EHT HYBRID TRIODE MONO AMPLIFIER

THÖRESS is very pleased to announce the introduction of the (12.950 EUR) Hybrid Triode Mono Power Amplifier, the latest achievement. The new mono block offers 30, 40 or 50 watts of output power per channel into a 8, 6 or 4 ohm speaker load respectively combined with very low output resistance. Such providing excellent drive capability for speakers with medium to low efficiency and/or with critically low impedance which may present a challenge for our all-tube, single-ended triode amplifiers. While offering the same level of ultimate sonic excellence obtainable from the later devices!

“Our Mono Block relies on a unique minimalist single-ended, zero-feedback vacuum tube MOSFET hybrid topology. Decidedly ignoring the fact that many music lovers seem to persistently believe in the myth that balanced (push-and -pull) technology (and the associated XLR connectors and cable configuration) is generally superior over the non-balanced (single-ended) one. 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) available on the respective button of our website. The topology consists of a single-ended triode gain stage (6J5GT vacuum tube) followed by a single-ended, unity gain MOSFET buffer operated at high idle current. The EHT topology, as we call it after E.INTAKT-H.YBRID-T.RIODE (single-ended hybrid triode), allows to fully exploit and mate the most desirable characteristics of both the vacuum tube and solid state devices determined by their very nature.

 

In order to attain the relatively high power output with lowest possible distortion it proved advantageous to place an additional unity-gain vacuum tube buffer (12HG7 operated in triode mode) inbetween the gain stage and the MOSFET output stage (giving a two-stage vacuum tube driving arrangement preceeding the output buffer compared to the single-stage arrangement utilized in our EHT Integrated Amplifer). The vacuum tubes within the EHT Mono Block are complemented by a set of solid state devices such as light emission diodes, MOSFETs and bipolar transistors, in this way providing the tubes with optimal operation conditions and let them perform at their very best. An approach which could be suitably classified as contemporary solid state interleaved tube technology and should by no means get mixed-up with common tube-transistor hybrid technology.

The EHT Mono Amplifier is built with meticulous hand construction using our proven point-to-point wiring techniques, whereas much care has been taken in arranging each aspect of the internal construction to ensure the highest reliability, low noise performance and ease of service. Particularly when combined with our underhung voice-coil 1D66 or horn based 2CD12 loudspeakers the sonic presentation of the EHT Mono Blocks will be of the utmost refinement and will certainly meet the needs of the most critical and experienced music enthusiasts. These amplifiers are ultimate components in every sense and the perfect complementary power amplifiers to partner with our Dual Function Amplifier or Full Function Preamplifier.

The EHT Mono Block allows for on-the-fly adjustment of the gain (input sensitivity) in 8dB-steps in view of optimal sensitivity matching with respect to the loudspeaker (efficiency) and the preamplifier (line gain), by means of a 4- position rotary switch located on the rear panel near the input jack. Gain: 2dB, 10dB, 18dB, and 26dB (full gain). Optimal sensitivity matching is highly desirable as it ensures that the idle noise of the line preamplifier can be kept within inaudible limits and that the preamplifiers-s volume control can be operated at a higher angle of rotation so as to allow for conveniently fine volume adjustment.

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 with lower distortion can be more easily obtained with the EHT than with the all-tube single-ended triode amplification principle. Simply because in the former case the critical power tube driven step-down output transformer stage (the typical all-tube impedance matching output arrangement) can be fully omited. As a result, the voltage swing required from the driver stage is up to 10 times lower (!!!) for an EHT configuration compared to an all-tube output topology for a given power output, resulting in a proportional reduction in over-all distortion. This crucial

  

insight was the basis for our pursuit of the described hybrid concept and finally resulted in the launch of our EHT Mono Power Amplifiers and the EHT Integrated Amplifier.

In spite of its obvious advantages, elegance and extremely high sonic capability, the EHT concept has never been utilized in a serial audio product before, as far as we know. Probably due to it-s low power efficiency and rather tricky implementation.

Our EHT mono blocks operate with impeccable thermal stability in spite of the total absence of negative feed-back and are fully short-proof at the outputs without the aid of any sound degrading protection circuitry. Moreover, a switch-on delay device (often found in commonly constructed solid state or hybrid amplifiers) is also omitted simply because no disturbing noise or dangerous signal is being developed at the output when the amplifier is powered on or off. Attributes further underlining our minimalist design approach.

As it is the case with all THÖRESS amplifier components, the EHT Integrated Mono Amplifier is equipped with a mains transformer produced in-house to ensure the highest possible quality and reliability. This component features a dual-coil arrangement on a large tape-wound cut core (C-core) and is deadly quiet, of course. In order to eliminate even the slightest interference of residual transformer vibrations with the circuit this part is mounted to the chassis via isolation elements. The fact that all power transformers are produced in-house enables us to readily make dedicated power transformers for all kinds of mains voltages such as 100Vac (Japan), 220Vac (South Korea, China ML, Thailand, Russia, Indonesia) and 245Vac (Australia).”

• Vacuum Tube MOSFET Hybrid Mono Power Amplifier offering 30, 40 or 50 watts of output power into a 8, 6 or 4 ohm speaker load respectively.
• Single-ended, zero-feedback, class-A operation.
• Based on our unique EHT schematic. Single-ended triode gain stage
• (followed by a unity gain vacuum tube buffer) driving a unity-gain, single- ended MOSFET output stage operated at high idle current.
• Offering the same level of ultimate sonic excellence as known from no- compromise all-tube single-ended triode amplifiers, while leaving exotic, costly power tubes out of the play.
• Excellent driving capabilities for critical speaker loads due to very low output resistance (high damping factor).
• Total avoidance of any sound degrading protection circuitry.
• RCA jack for signal input.
• On-the-fly selectable gain (input sensitivity) in 8dB-steps via 4-position
• rotary switch located on the rear panel; gain 2dB/10dB/18dB/26dB.
• Full hand construction; point-to-point wiring throughout.
• Ultra low noise, dual-coil C-core mains transformer made in-house.
• Mains voltages: 230Vac, 115Vac via jumper setting; customizable for
• 100Vac (Japan), 220Vac (South-Korea, Thailand, China Mainland, Russia) or
• 245Vac (Australia).
• Electrolytic capacitors made in Germany in the power supply.
• Nonmagnetic aluminum casework; front and rear panel with anodized
• printing; powder coated lids.
• Dimensions: 434x434xH184mm,
• 184=20/casing feet+134+30/tubes over case.
• Dimensions of the shipping crate: 550 x 550 x 250 mm; weight 14 Kg.