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 9720 VCO OSCB drift 
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Joined: Thu Jan 27, 2011 4:01 am
Posts: 13
Post 9720 VCO OSCB drift
Hey again, Scott.

After messing around with my newly completed set, I've noticed that OSC B drifts about a step/half-step per octave. I was reading over the manual and it says that IC 5, Q8 and Q9 should be examined, as well as surrounding components. I'm not sure if it was doing this beforehand, but any ideas on why this might be?

Mon Sep 05, 2011 2:35 am
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 723
Post Re: 9720 VCO OSCB drift
Hello James.

Just to be sure, drift would be when the pitch slowly changes over time. I think you might be telling me the pitches produced don't match the note being played and this is likely just the setting of the Scale trim. I would have set these when yours was here, but it is might have gone off somehow???

VCO A and VC0 B each have a scale trim labeled as such and they should be at about the same settings (I'm remembering about 1:00 as usual, with 7:00 being the ccw and 5:00 being cw). When pressing octave spaced notes on the controller, the trim and panel control should work to dial in octave spaced frequencies.

Power-up the MIDI2CV8 with the low-key on the controller held down to assert the low-key transpose, send the pitch cv to both VC0s via the P1 connector, set the panel controls so they're sounding in unison for a note pressed up in the second or third octave or so, and if needed, adjust the B Scale so notes played down in the lower octaves are still in unison. Repeat until no further adjustment is needed.

Scott Lee

Tue Sep 06, 2011 4:03 pm
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