Предусилители — Doshi Audio Evolution Line Preamplifier

The Evolution Line Preamplifier is a valve line stage from Doshi Audio, the maker from Charlottesville, Virginia, in the USA, and it replaces the earlier V3 preamplifier. It is built in two cases, the power supply having its own chassis, and it is the companion of the Evolution Stereo Amplifier. The UK price is GBP 26,000.

Key specs that matter

The circuit uses two ECC99 or 12BH7 double triodes. Maximum gain is 12 dB, and it can be lowered internally. The signal to noise figure is 100 dB or better below 1 V unweighted. There are four stereo inputs, which can be RCA or XLR in any combination, and two stereo outputs, also RCA or XLR. A home theatre bypass input in XLR or RCA is standard. Power consumption is 22 W. The preamplifier and its supply weigh 17.7 kg together and are finished in natural or black anodised aluminium. Doshi does not publish dimensions or impedances.

Engineering and use context

The separate supply houses an ultra-low-noise design with high-stability regulation of the B+ rail, the high voltage that feeds the valve anodes, and Doshi states that noise is an order of magnitude lower than in the older model. Moving the transformer to its own chassis keeps its magnetic field and mechanical hum away from the valve circuit. ClarityCap Copper Matrix capacitors and TKD resistors sit in the signal path. The top plate is aluminium with constrained-layer damping, which turns vibration into heat before it reaches the valves, as valves react to mechanical vibration. Lowering the gain internally helps with sensitive power amplifiers or high-output sources, where the volume control would otherwise work only in the lowest part of its range. The remote controls input selection, volume and mute with discrete commands, so each input can be chosen directly instead of stepping through the list. The home theatre bypass fixes the gain for one input, so a surround processor can control the volume of the front channels while the preamplifier stays in the chain. Because the inputs can be configured in any mix of RCA and XLR, the preamplifier can be ordered to match the outputs of the sources it will be used with.

Pairing

Doshi's Evolution Stereo Amplifier is its matching partner, while the XLR outputs suit balanced power amplifiers from other makers. A second output pair allows a powered subwoofer or another amplifier to be added for bi-amping, and a separate phono stage is needed for records.

Alternatives

Doshi Audio offers no other line preamplifier, its remaining preamplifiers being the Evolution Phono and Evolution Tape models.