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.

Step 2: Audio Circuitry

Doshi Audio is an engineer owned company. Decisions are made based on best engineering practice. Every part of a Doshi Audio product incorporates this philosophy. We are continuously evaluating every part of our production process, up to and including the solder used in the boards. Improvements in key areas of every product give rise to the Evolution Series.

Amplifier products:
Introduction of the Copper Matrix coupling capacitors in audio coupling, British manufacturer ICW makes the best audio coupling capacitors under the Clarity Cap range. Their top of the line CMR series and CSA series are batch manufactured for Doshi Audio and used in our products. The attention paid to winding tensions and resonance control results in a capacitor that is absolutely neutral and has the best dynamic linearity of any product of its type. Driver circuitry changes allowing for higher clipping levels into the output section with lower drive impedance. This gives the amplifier higher peak power capability and extended frequency response. Lower overall feedback gives the amplifier prodigious peak capability while running the tubes conservatively.

Preamplifier products:
Every preamplifier has seen evolutionary change in the audio circuitry. Along with the aforementioned CMR capacitors, the phono preamps have revised MC sections with new series/ shunt regulation resulting in lower noise. Circuit changes allow for tubes to run more conservatively than before with better (lower) distortion, gain linearity and projected tube life. The line stage output transformer has been redesigned with a lower output impedance and redesigned power supply now has a signal to noise ratio over 110db. This is phenomenal performance for a tube driver.

Step 3: Chassis developments

Each chassis of a Doshi Audio product is constructed from 14ga stainless steel. This is not cheap, or easy. Only manufacturers that supply armed forces are able to bend and weld 14ga stainless. This tradition will continue with additions. The amplifier chassis has been made wider by an inch to accommodate bigger internal components, also the rear panel now has handles to protect the speaker terminals and assist in lifting (this was introduced in the latter V3 models too). The top plates of the V3 amplifiers and preamplifiers were constructed out of Du-Pont Corian because of its damping properties and made for a well damped chassis that contributed nothing spurious to the signal. However, Corian is difficult to keep from getting scratched and machine with precision. The Evolution series has made the move to a machined aluminum constrained layer top plate. This moves the cosmetics of the units into the upper echelons of audio equipment but what we
were not prepared for was the improvement in sound quality and perceived noise floor. The V3 series boasted of superb dynamic capability where the decay of individual elements in the music were easily perceived. This aspect is now vastly improved. There is now an inky – dark noise floor from where sound emerges and decays, giving shape and texture to transient information, color to timbre and humanity to voices.

Overall, the Evolution series has proven to be gratifying to its designer because it makes the music happen in a way that is tangible, emotional and worth spending time over. The V3 series Monoblocks and Phono Stage were reviewed by Stereophile magazine and found worthy enough to be included in the Class-A category of recommended components. Every Doshi Audio product has the distinction of being singled out for its musicality and we are proud to count many high-end and recording professionals among the owners of our products. These are not easily impressed individuals and they choose our products for their livelihoods. The V3 series was not an accountants dream, it was expensive to build and ship. The Evolution has not resolved these issues for Doshi Audio, it has however, resulted in a series of products that we are immensely proud of and deserve an audition against the very best the world can offer.