This project was developed from the following sources: Analogguru's EH_BigMuffPi_OP-77 schematic, Analogguru's EH_BigMuffPi_OP-78 schematic.
The opamp version of the Big Muff is said to be 'not as scooped' so I decided to build it. The PCB does fit in a Eddystone B enclosure but I haven't mounted the tone stack switch on/off.
Build pictures:
Layout:
Tone stack simulation (from the Duncans Amp Tools Tone Stack Calculator):