Based on the design by [Grumble] from synthforum.nl, with the following modifications:
- Redrawn in Kicad as a main and io-board
- Made potentiometers more center-sensitive through extra resistors
- Added PCBs for main and io-board
- Added a PCB front panel
- No mounting hole between mainboard and I/O board. There's a little space above the middle connector, if mainboard traces are moved.
- To increase gain from -1..1x to -2..2x: Change R4, R19, R20, R21 from 82k to 40k (39k should do fine).
- Gain pot pins should be inverted (they're on an inverting amplifier)
- LEDs are way too bright, series resistors (R31, R32, R33, R34) should be 22k instead of 1k
- All values are missing on mainboard and I/O board
A simulation is available on circuitjs.