Oscillation in MXR envelope filter clone

[zeerust2000]

Hello all, I've just built an MXR envelope filter clone using the excellent board from tonepad.  It works fine, but I've noticed some oscillation (or 'squealing') at some settings.  My input and output wires are seperated (but not shielded).  I'm wondering if anyone esle has encountered this with this circuit, or has any advice in general on such oscillation.
Thanks in advance!

[Mark Hammer]

a) Apart from the squealing, does the unit actually work as intended?

b) A HF clock, whose duty cycle is manipulated by the envelope of the incoming signal, is the core "engine" of the circuit.  That clock is what you are hearing.  This is likely a job for revising your wire/control layout.

[zeerust2000]

Thanks Mark (sorry I've taken a while to reply, but my computer crashed severely).  Yes, the unit works fine and the oscillation is fairly faint.  I'll try to rationalise my wiring.  Would shielding certain wires help?

[mdh]

Another option might be to try to increase the frequency of the clock out of the audio range.  Mine runs closer to 35kHz, IIRC.  Based on some past discussion in this thread, you may be able to increase that frequency by decreasing the value of C8 on the Tonepad layout (the 100pF cap).  Of course, if you're going to go down that road, it might be best if you have some way of measuring frequencies.  My DMM does it, yours might, too.  I believe you can measure the frequency of that clock on pin 5 or 6 of IC 2 (again, assuming the Tonepad layout).