I built two a while back for my cabs, based off of Segasonicfan's schematic. They work great. While there is no potentiometer in the circuit, the rate of fire works good for the older PCBs I own - Darius Gaiden, Raiden 1 and 2, 1943, Metal Slugs, Aero Fighters MVS, etc. I getting old now, I can't jam on the fire buttons anymore like I did in the 80s