[sdiy] simple noise gate circuit?

[gregory zifcak]

hi,
i'm trying to get rid of bleedthrough on a few devices (realistic reverb, 
ring mod, nintendo). any ideas for a simple noise gate circuit? i don't mind 
if it's a somewhat harsh clamping down on the signal below the threshold. it 
would be fun to have a variable threshold, but if this complicates the 
circuit i can forget about it. i'm guessing a noise gate is basically an 
envelope follower controlling a vca; how can i do this with the least amount 
of parts?
thanks for any suggestions,
greg