there's a helicopter in my ts808

[boog]

Any suggestions for this?  i had a ts808 board from general guitar gadgets and built it pretty much according to the schem, but i added the 'fat bass' mod from amz;  they already had the holes in board so i figured, why not.  whenever i activate the switch (bypassing the cap to ground in the clipping loop) i get this crazy helicopter sound when i'm not playing.  if i'm playing, you can't hear it.  stop playing and it's like the opening scene in 'apocolypse now'

[R.G.]

It used to be called "motorboating". Your circuit is oscillating at a very low frequency. This is usually a problem with power supply decoupling.

However, you might want to read "Debugging Thread: What to do when it doesn't work".