Oscillation frequency is too high

[r00n]

Hello EEvBloggers,

I have built 6 x  VCO depicted in the schematic. 5 of them are working perfectly and I have these tuned to the correct pitches and Volt/octave tracking is working wonderfully, within 1% over 8 octaves. 

The last one, doesn't want to behave.  It is oscillating at a high pitch that is not even audible for most of its range, for my old ears.  I have checked all the components and matched them with the other 5 working circuits and everything is ok.  I have done some voltage measuring at various points around the switch when its open and closed, and the tuning pots comparing again to the working VCO's, but this had not led me to finding the fault.

Any ideas on what component to check would be helpful. My trouble shooting skills are obviously useless.

Thanks so much. Appreciated

[Whales]

If it's running, but at the wrong freq, then I'd suspect (in this order):
 - bad timing capacitor (C7 on pin 11)
 - unexpected shorts or miswiring
 - bad timing resistors

I bought a mixed pack of ceramic capacitors years ago and it turns out a lot of them were mislabelled or bad by a few magnitudes   I wouldn't recommend using bulk/standard ceramics for the timing in this circuit, but you might be.

Some photos of the units you have built would be very useful.  Are you building them deadbug, manhattan, copper tape, on a PCB, solderless breadboard, ...?

[r00n]

building on a PCB. I had to google dead bug and Manhattan
i shall desolder the cap in C7 and measured it. It is a styrene one.

May i just clarify please, the timing resistors are R14 AND R15?

[Whales]

Those, but also (at a minimum) the resistors on pin 15 too.  There might be others in there, I tried to look at the datasheet for the AS3340 but it doesn't seem to give any nice and simple explanations.