here are some links to sites with lots of audio circuits that some of you may find usefull :)
http://www.epanorama.net/schematicsforfree/Audio/Circuits/index.php
http://www.mitedu.freeserve.co.uk/Circuits/Audio/audio.html
http://www.synthdiy.com/ > a very good site with tons of info and stuff about synths
http://www.electronics-tutorials.com/oscillators/oscillators.htm
http://www.armory.com/~rstevew/Public/SoundSynth/00_PenfoldSynth/pench2.html
http://www.electricdruid.net/index.php?page=projects
http://www.aaroncake.net/circuits/
http://www.uoguelph.ca/~antoon/tutorial/xtor/xtor7/xtor7.html
http://members.lycos.co.uk/rsquare/viewthread.php?tid=11 > info about 555 timers
http://www.uoguelph.ca/~antoon/gadgets/555/555.html > more about 555
http://www.musicsynthesizer.com/
http://www.uni-bonn.de/~uzs159/
http://www.kpsec.freeuk.com/index.htm
http://www.queencircuit.com/Audio/
there
have fun!
Great bunch of links.