the first thing is to work out where it is occurring.
Take the voltage from pin 7 of the TL072 that is connected to the 56k feeding the LM394. Monitor it on a scope, or feed it into the CV input of the other VCO. If it warbles, you problem is likely to be in the mixer stage. If the voltage on pin 7 is steady, it's the core having issues.Clean off any flux that may be left on the rear of the board.
Check the supply voltage AT THE CHIPS.
On Sun, Aug 16, 2015 at 2:14 PM, Stephen Richards okayjustalittle@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:Hi Ken and all,One of my CGS48 VCO's has suddenly started completely loosing control of pitch.Every output is displaying the same behaviour. The pitch is wavering like a mosquito and occasionally jumps or drops dramatically in pitch.Supply voltage is fine , chips seem fine. I swapped the LM394s from my working VCO , no change.FM, PWM and SINE TO SAW shaper all working.Any ideas where i could start testing ?
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