I found this scheme called "FET DISTORTION".
I enclose the youtube demo with the reference site and the schematic.
SchematicDEMOI thought of converting it on stripboard inserting 3 trimpots instead of 3 resistors to drain.
He says he was inspired by a pedal of some manufacturers, but will not reveal the real name, remaining in anonymity.
Hoping to be helpful, I greet you.
I have not had time to test it, but there should be no errors.