It's all in the FAQ

[petemoore]

If not it's most likely in the debugging page.
 Specially prepared for Newbs, and guys like me who have to read through stuff like that at least a few times.
 There's a page about opamp biasing and implementation around here somewhere, I think there's a link or something...great info.
 Anyway, if you're effect isn't performing 'right', there's probly something wrong with it, and debugging it with a DMM and audio probe Will tell more than a description of symptoms / guesses based on information in description.
 If it's an opamp build, check the pin voltages.