Very dirty bass boost. It does not do clean at all, and sounds akin to a solid-state Sunn with the gain cranked up. Excels with other pedals, by fattening them up and adding grit. Previous owner, Ttasselm, had a master volume knob added by T1M Effects. $75 shipped ConUS. Also interested in an Ernie Ball VP Jr. 25k or a Way Huge Swollen Pickle in exchange.