Step 1: Power Supplies
The heart of a audio amplifier or preamplifier is its power supply. By using custom designed and manufactured transformers, Doshi Audio had made the investment in the foundation of the V3 . We surrounded this power transformer with Schurter KFA series IEC inlets, huge filter capacitors, “soft start” high voltage circuitry, 5 stages of regulation for the different plate, screen and bias voltages. W e were already at a level few, if any, of our competition can deliver.
Then, we took it further. The Evolution series adds passive power factor correction to the power supply, it replaces the high voltage rectifiers with schottky type rectifiers, adds regulated filament voltages to the input section and a huge high voltage film capacitor to the plate voltage supply to lower its impedance.
Passive power factor correction – Electrical regulations are getting ever more stringent across the globe. Countries require equipment to become more efficient, less noisy to the environment and electrical grid and all the while, power is getting noisier. Every Doshi Audio product now employs passive power factor correction in its power supplies. This is not a cheap or easily implemented decision but the outcome is an enhanced linear power supply that is able to draw current over a greater part of the waveform than a standard linear power supply. This results in a quieter, more efficient supply that runs cooler, creates less noise on the grid and internally in the equipment. This combined with the schottky rectifiers and filament regulation gives the Evolution series a power supply that is twice as quiet as the V3 series. Never has a tube amplifier (or preamplifier) been able to achieve noise levels this low.