voltage controlled multiplier (NE5517 or LM13700) Bob Pease

[Paul Perry (Frostwave)]

http://www.elecdesign.com/Articles/Print.cfm?ArticleID=2482

not sure if this has been here before.. but, anyone wants a cheap tremolo, just crank it with any slow oscillator!

And while we are on the subject of hand drawn multiplier fx circuits, here's one from a master:
http://www.lynx.bc.ca/~jc/pedalsHarmonic.html

[Dirk_Hendrik]

Which took me quite a wile to decipher......

[Paul Perry (Frostwave)]

I should have said, anyone making a multiplier into a trem, need sto apply some voltage offset to the LFO signal, otherwise you have a (very slow) ring modulator!