fredrik
November 18, 2020, 5:22pm
424
Pin 15 is a summing node that’s held at 0 V by the input buffer. You should measure the voltages on the other side of the 100k mixing resistors (R19, R22, R23, R24, R25).
See here for approx voltage to frequency:
One more thing to note is that with the typical resistor/capacitor values, the 3340 is calibrated to behave nicely from ~1 Hz all the way to 20 kHz and beyond, and you have to feed in quite a bit of voltage to get an audible signal.
Assuming nominal resistor/capacitor values, the 10k tracking pot set to the middle position, and that I didn’t completely screw up my algebra, the CV for a given frequency is:
cv = 1.463 * ln(freq) + 0.239
so for e.g. 440 Hz you need to feed in just over 9 V in to…
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