Here's a simple buffer from JHS. It really only uses one side of the opamp (why not just use a TL071?) and … | Diy guitar pedal, Guitar pedals, Semi acoustic guitar
Effect pedal circuits: the Buffer | Effect Pedal Kits
Best DIY buffer pedal | diyAudio
Preamplifier Subsystem | Details | Hackaday.io
Switching: A Buffered Bypass – the historic original – TH custom effects