There's a update for this. Improved stability?
"NOTE: I made a small change, instead of connecting the input level pot to (-) I connected it to the vgnd (output U1a)."
I think that means hooking Level 2 (wiper) via the series 47k resistor to pin 1 of the LM324 instead of pin 9. Don't quote me on that though. I haven't built it, yet.
Project pages here:
http://electro-music.com/forum/topic-55465-0.htmlDescription from a different thread:
http://electro-music.com/forum/topic-67873.html"The first stage (U1c) is a voltage summing amplifier or adder which adds the CV with the offset voltage. Without a CV signal I can control the frequency with the offset control and with a CV signal I can add (you probably guessed it) an offset voltage. However it does invert so the second stage (U1b) inverts it again so that a positive CV signal gives a higher frequency. The schematic I posted is the VCO I used in my modular lunetta which is powered by a single supply, so the - is just the GND connection. However a summing amplifier does need a reference voltage to work properly which is provided by U1a.
note: I later changed the circuit by connecting the level pot to this reference voltage as well instead of - which gives a much better control. The way it is drawn in the schematic it would actually have an effect on the frequency when nothing was connected to it. "
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