If you can ignore all the slow loading ads, Musique.com has a lot of different effects pedal schematics and tutorials that can be downloaded for free.

AMZ is a resource with information about guitar effects pedals, stompboxes, audio circuits and tips on how to build them. There are fuzzbox schematics, signal booster projects, audio mixers and much more available free.

Take a look at their schematics list – Link

Related:

Build your own effects pedal – Link