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Sequential Circuits Pro One A Oscillator

Posted: Sat Jul 13, 2019 7:47 pm
by tdlunsfo
I have a pro one on the bench in pretty good condition but I am getting some odd things out of oscillator A. Pretty much I get no oscillation unless I disconnect the Mod Wheels, and place the modulation switch in "wheel". This gives me a really low oscillation that can be controlled by oscillator A controls. Osc. B works great. Swapping the 3340s doesn't seem to make a difference. Any ideas?

Re: Sequential Circuits Pro One A Oscillator

Posted: Sun Jul 14, 2019 8:59 pm
by tdlunsfo
I've been doing some troubleshooting and apparently the oscillator is working but it is really high pitched. The octave switch works but anything above the first octave is above human hearing. I've been checking the resistor values and haven't found anything out of spec. Thoughts?

Re: Sequential Circuits Pro One A Oscillator

Posted: Tue Jul 16, 2019 4:58 am
by tdlunsfo
If anyone stumbles on this, the problem was a bad LM348 at U104 octave summer for oscillator A. Replaced it, tuned it up, and now synth sounds great.