Built this a while back for a friend, who finally got around to putting it through its' paces with his Les Paul. He loved it, but said that the Gain pot had little effect overall on the sound. I swapped out the gain pot (it was maxing out at 60k instead of 100) and it sounds better, but it's through my little practice amp (with a Squier strat, soo...:shrug
I read on the comments from John K that the original schem had a 250k pot for gain (among others) - would that have a pronounced difference over a 100k (leaving the others as-is, based on the layout)?
Re: Prescription Electronics Yardbox - Gain Pot has little effect - higher value?
All it looks like is a 2nd volume knob for the most part. The less resistance there is, the more output there should be. Higher resistance will probably change the sound a little more to your ear. It's hard to say, for me at least, what it will sound like though. I would expect it to sound thinner/less full as you increase the resistance. The 250K might give you a little extra that's noticeable.