Thoress 300B Monoblocks Amplifier pair

300B Single-Ended Triode Mono Power Amplifier

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The SE300B Mono Amplifier is an all-tube power amplifier employing the famous 300B filamentary triode in single-ended (Class-A) operation mode for an output of up to 10 watts into a 4, 8 or 16 ohm loudspeaker load. 

The amplifier is entirely based on SINGLE-ENDED ZERO-FEEDBACK schematics, decidedly ignoring the fact that many music lovers persistently believe in the myth that balanced technology (and the associated cable configuration with XLR connectors) 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 paper (THÖRESS - Behind the Curtain) available as download on the ABOUT button of our website. 

The 300B power tube is excited by an extraordinary single-stage driver employing two EL822/CV2382 power pentodes operated in triode mode with high idle current and works into a tape wound cut core (C-core) output transformer (OPT) which is built in-house to the highest possible standards to ensure ultimate performance. The driver stage is so powerful that it could (theoretically) drive a loudspeaker load with very low distortion on its own whereas the OPT allows for precise matching of a 4, 8 or 16 ohm loudspeaker load to the power tube by way of jumpers soldered to its secondary terminals. 

These design choices are to a large extent responsible for the richly textured, clear, warm and dynamic sonic presentation of the amplifier, particularly when combined with high sensitivity-type loudspeakers, or our horn based 2CD12 or underhung-motor based 1D66 loudspeaker. 

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 SE300B Mono Amplifier is an ultimate component and as such a worthy complement to our Dual Function Amplifier or Full Function Preamplifier. It easily outperforms competitive products regardless of price and will certainly measure up to the expectations of even the most critical and experienced music lover. 

LOW NOISE OPERATION 

Specific design choices guarantee low noise operation even when the SE300B mono block is combined with a highly efficient loudspeaker such as our 2CD12 model. 

• Firstly, the 300B power tube is DC heated whereby the cathode point of the amplifier circuit can be balanced with respect to the filament of the given power tube by means of a control knob [ a rotary potentiometer ] on the rear panel. Once the balance adjustment has been carried out, the signal current is distributed uniformly over both ends of the 300B filament, and residual hum due to ripple of the heater supply voltage vanishes [ reaches a minimum ]. 

• Secondly, the amplifier has been specifically designed to have a moderate gain [ low input sensitivity ]. This ensures that the idle noise of the line device remains inaudible in all possible scenarios. Notably, this design choice also ensures conveniently fine volume adjustment. 

MAINS TRANSFORMERS

The SE300B mono amplifier is equipped with a mains transformer produced in-house to ensure the highest possible quality and reliability. This part has been optimized for low body noise emission and low leakage. 

Nevertheless, it is mounted to the chassis via isolation elements in order to eliminate even the slightest interference of residual transformer vibrations with the circuit.