Усилители мощности моно — Doshi Audio Evolution Monoblock Amplifier

The Evolution Monoblock is a class A tube power amplifier from Doshi Audio, handcrafted in the USA, with one chassis needed for each channel. It builds on the V3 Monoblock, and most of the changes concern the power supply, which gains a larger transformer, passive power factor correction, Schottky rectifiers and larger reservoir capacitors. The input and driver circuitry was also redesigned for lower feedback and wider bandwidth.

Key specs that matter

Each chassis carries one 12SJ7GT, two 12SN7GT and four KT150 output tubes, supplied as NOS Hytron, NOS GE and Tung-Sol types respectively. Output reaches 160 W into 4 ohms, with the first 120 W in class A, and the maker rates at least 160 W RMS into its standard 5 ohm tap. Frequency response spans 10 Hz to 80 kHz at -3 dB, and noise sits at least 80 dB below 1 V. Input impedance is 20k ohms balanced and 47k ohms single-ended, output impedance is 0.5 ohms. The amplifier draws 200 W at idle and up to 500 VA. Each unit measures 432 x 305 x 533 mm.

Engineering and use context

Custom ClarityCap CMR capacitors are used at key points, and an aluminium constrained layer top plate improves vibration isolation. A microprocessor handles control and protection, including a front panel mute button, and bias is set from the front panel, where a display shows a three digit reading for each KT150 selected in turn with the function button. The manual recommends a value of 190, with a permitted window of 170 to 220, and each tube is trimmed by its own potentiometer to within 5 units of the others. Higher bias shortens tube life. Finish is natural or black anodised aluminium, and output impedances other than 5 ohms are available on special order. Doshi Audio covers parts for 180 days from purchase and labour for 24 months under its US limited warranty and requires a return authorisation before a unit is shipped back for service.

Pairing

The circuit is single-ended at the input, so the RCA socket is a direct input giving the shortest signal path, while the XLR socket feeds a unity gain differential instrumentation stage for balanced preamplifiers. A rear ground lift switch helps break hum loops with the preamplifier and other components, and a rear speaker mute override silences the output while speaker cables are changed.

Alternatives

For a single chassis solution, Doshi Audio also builds the Evolution Stereo power amplifier.