YuSynth VCO Problem

reklrekl · Joined: Mar 28, 2013 Posts: 1 Location: Germany

Hi guys, i am looking for a solution for a Problem with my VCO:
The OSC runs at a fixed frequency (no matter if I turn the Pots or apply CV) and the Waveform sounds like some spikes running at 0.5 Hz. I cant show u the Waveform, dont got an oscilloscope yet....

At the pin1 of the OPA2137 i get a voltage of around -2.5 to 2.5 V when i turn the pots....

Thanks for any help!

Edit: triple-checked every connection now...

Edit 2: Here I have a view of the Output of U6 (TL074) at pin 1
Posted Image, might have been reduced in size. Click Image to view fullscreen.

and an image of pin 3 of the J111 (J112 in my case)
Posted Image, might have been reduced in size. Click Image to view fullscreen.

please tell me how these Images should look, i can imagine U6 shall look like that...

littlem4tt · Joined: Jun 30, 2013 Posts: 44 Location: uk

I had similar readings. Turned out it was fake lm394's.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

An easy way to check if the LM394 is fake is simply to take it off the socket and plug in the socket two BC547. If the VCO works fine with the BC547 then it should with the LM394.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

littlem4tt · Joined: Jun 30, 2013 Posts: 44 Location: uk

Actually the guy from ebay replaced the ic's!! I had already given positive feedback before i tested them but he still replaced them afterwards so i dont think i will name and shame. The package looked exactly the same as the previous ones so it was not his fault.

I made the cv standard module to help in calibrating the vco. I highly recommend this as an early build as i have now gone back and re-calibrated all my other oscillators against this wonderful module. Thanks Yves!