I just know this is going to show my age...

Craig Anderton is a guy that used to publish DIY projects in
Contemporary Keyboard magazine (now called just Keyboard these
days). He also published a number of books on recording, and DIY
projects for musicians (with his latest book on Digital Mastering
being published in Jan 2002).

A number of his projects were marketed (as DIY stuff) by, and still
available from Paia... including a low end (but still kind of
useable) DIY vocoder, spring reverb, and something called the
QuadraFuzz.

http://www.paia.com/vocoder.htm
http://www.paia.com/hotsprgs.htm
http://www.paia.com/quadrafz.htm

Anderton's whole approach was to de-mystify electronics used in the
audio/recording process, with one aim being to make electronics
affordable for musicians. He's been writing on the subject for over
30 years.

I can remember reading his articles back in the late 70's... ahh, the
good old days. Did I say the 70's Damn... I'm getting old.

Regards,
Kevin