Using the variac was cool. I stumbled on something similar by accident. The keyboard power cable would get unplugged sometimes when jamming in our tight quarter

Using the variac was cool. I stumbled on something similar by accident. The keyboard power cable would get unplugged sometimes when jamming in our tight quarters. When that happened it would revert to battery power and when the batteries were almost dead it would have a great distorted sound(it was plugged in to an amp) so we put a pot between the converter and the keyboard to dial in that crazy sound.