Spin Semiconductor

Hi,
I've built a simple guitar reverb pedal using hall reverb program.
It's sounds good but I've noticed that when I pick hard on strings (with high values of reverb time) there is a cracking noise on the high frequency (llike a sssshhhh) on the reverb part only (not the dry signal).
The schematic is simple : input buffer, FV-1 , output mix (dry from the buffer + reverb from FV-1). I've put a simple low pass RC before the Fv-1 (around 7 khz) and after FV-1 (around 7 khz).
Is it possible to modify the program to eliminate the High frequency harshness?

Difficult to answer, could be you are clipping an internal register. Is the clip LED turning on?

The clip led turns on only if I hit hard the strings near the pickup with all my fingers.

Will need more info, a recording of the sound, what does it look like on a scope, any other measurements you can make.