WP-20 VCO does not oscillate

Juno60 · Joined: Feb 09, 2006 Posts: 27 Location: Germany

Hello everybody!

I've made stripboard layout for the WP-20 VCO (attached) and built it up. I plugged the output (tri) to my mixer and powerd the vco up (9v battery). But there's no sound. I checked the layout and the soldered board. No shorts, everything is correct soldered. I also checked the voltage at different point on the board and found no fault. Has anybody an idea where the problem is?

As I understand the circuit it must be able to power it up, change the frequency by turning the 220k pot (frequency, or "modulation" in original design switched to manual) and listen to the sound it produces. Or is it necessary to hook up a control voltage?

Cheers
Chris

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By-Tor · Joined: Apr 24, 2007 Posts: 11 Location: UK

Hi!

I looked at your stripboard layout and it looks OK. The only thing I could see was that you appear to be using a 10n non-polarised capacitor across pins 8 and 9 whereas the original schematic shows this as an electrolytic i.e polarised capacitor with the positive end connected to pin 8. I'm not sure if will make a difference, but it may be worth a try.