Schematics

Preamp

The current preamp is Duncan Monro's design for an amp he calls the Blues 112. The schematic is on his site. It has several neat features that allow the amp voicing to be controlled with a rotary switch. He calls the settings "Clean, crunch, dirty and hi gain."

There are 3 tube stages, the tone stack and another tube stage for a 3+1 configuration. In addition, there's a op amp with diode clipping that sits at the input, like a built in distortion pedal. The 3P4T rotary switch affects this circuit, and tube stages 2 and 3 in the following way:

This is the part of his circuit I copied with his permission. He adds reverb and an effects loop, and then designed his own power amp and power supply.