The Electro-Harmonix Big Muff has had many versions during its lifetime. The unit we have here is the V4 one which is associated with Billy Corgan of the Smashing Pumpkins. The unit uses the EH-1322 board and is all stock. As to sound, try it out for yourself using the TonePedia player, compare it to other models too. The EHX Big Muff Pi V4 was in production for approx two years, so it is relatively hard to find.