A simple low-cost tube head vacuum tube preamplifier circuit

This is a simple and low cost tube head vacuum tube preamplifier circuit designed by PAiA Electronics:

Vcc – Pin 1IC1

+12v – Pin 8 IC2, IC3, IC4

-12v – Pin 4 IC2, IC3, IC4

Ground – Pin 8IC1

IC1–4049CMOS Hex Inverting Buffer

IC2, 3, 4–5532 Dual Low Noise Op Amp

D1,2–1N4001

D3, 4, 5, 6, 7–1N4148

All 1uf capacitors are 50v all others are 25v unless

Otherwise stated.

All resistors 1/4W, 5%

Channel 2 is the same as channel 1, IC4b is for the clipping table and IC3 is for the input/output driver. The input impedance of the TubeHead is approximately 20kohms, which is consistent with most equipment such as synthesizers, effects processors, mixers, equalizers, etc. 20k is too low for proper matching with high impedance sources like guitar pickups, but some small modifications can fix this. To use the TubeHead as an instrument pickup preamp, remove the 47k* resistor and 20pf capacitor from the feedback loop driving the op amp. Then change the 47k" resistor in the feedback loop of the driver op amp to 680k and the 22k resistor to 100k. The TubeHead can now be used to warm up a cold sounding guitar amp, or just provide a great preamp tone.