Effects loop for SV20ish amp

[pdf64]

Was an input trimmer fitted?
If the supply voltage is too low and input signal too high, that or any circuit will clip.
Or the send signal may have been too high for some pedals to cope with.

[statorvane]

Attached is the layout I developed.

If I were to do it again, I'd add true bypass to the loop (switch). As designed the loop is persistently in the signal path.

[audiosalvage]

Thanks for the layout