Quoted from Quench:I just measured R10 in circuit on three other boards and they read 130k ohms.. Something in that circuit might be suss.
Anyway change U8 and see how it goes. Note the original U8 chip is a 4049U (U for unbuffered). I can't remember whether its critical for it to be the unbuffered version of the chip or not. i.e. you can buy a 4049B (buffered) or 4049UB (unbuffered). Get the unbuffered to be sure. Don't worry about any extra letters in the part number - they're usually manufacturer specific.
4049B works ok as the lower 4049 chip but it changes how the tones sound slightly. The component list I think actually calls for 4049B, but all the boards seem to have been built with MC14049UBE
