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Stereo valve pre-amplifier with a warm vintage sound, very low THD and sufficient current to drive up to two power amps per channel. Requires separate power supplies for low and high voltages

This circuit is designed to sit between your volume control and your power amp. It's main features are:
- Gain of 2, 3 or 4 - selectable with jumper switches
- Two EQ setting - flat and dynamic. Dynamic is similar to loudness i.e. enhanced bass and upper mids, but it is subtle
- Current follower - perfect for powering multiple power-amps from a single source

Note: you can place your volume control at either end of this pre-amp, though we recommend placing it after the pre-amp, before your power amp. This reduces the risk of a clipped signal reaching and damaging your power amp.

Assembled PCB: terminal-connectors and valves to be purchased separately. See datasheet for detail

Blank PCB: full parts list and assmembly instruction incl setup and biasing steps are in the datasheet

Specifications:

PCB Dimensions

139mm x 56mm x 1.6mm

Channels

Two (stereo)

Gain

Selectable - low(6dB), medium(9dB), high(12dB)

Input Impedance

Determined by volume pot - recommend 150-200kΩ

Devices

2 x 12AX7 valves

1 x 12AU7 valve

Frequency Response

Overall Range: 10Hz - 30kHz

Flat EQ Setting: gentle roll-off between 20 and 30kHz

Dynamic EQ Setting: Slight boost to bass and upper-mids

Output Impedance

< 500Ω

Supply Voltage

285v and 265v DC (regulated power supply module available)

Idle Supply Current

6mA

Transformer

220v +/- AC 12-20VA

Earth Nets

Power and Audio (separated by loop breaker)

THD

Typically < 0.004% - mostly lower 2nd order