This should come as standard on any amp with a serial effects loop. Works stupidly well and makes the amp's master volume so much easier to dial in for getting your favorite cranked amp tones without waking a soul. So much money wasted on power soaks through the years when a simple line level audio pot was all I needed. I got this via an Ebay link that Andy Fuchs posted in a thread I dug up for an entirely different reason. Wish I'd saved the link.