Cold joint? Try running the iron on the connections that misfire when you wiggle em.
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demons 
though hopefully Caustic has the right answer , I have heard demons are hard to get rid of …
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It’s a tedious exorcise
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At the very least, that wire has a sketchy connection somewhere. I’d start there.
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Mine did this, crimps all looked good, but had to solder directly to make problem go away.
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mine was a bit dodgy too, especialy with the switch moving on its mount… since we have a accurate reference voltage, it may be prudent to use a fully soldered joint ( over the connector ) to remove possible extra resistance.
Wired it in without the molex and got 4 octaves to work perfect but the high 5th dives when I switch to it. I think I’m going to keep it, sounds pretty cool especially running it through the delay!
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Sounds like a happy accident.
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@JUXTAPOZ74 my first VCO did this until I removed the molex and rewired the rotary. And I thought it sounded cool too! Almost like when you unplug the whole synth while the speakers are on. Sometimes I get some wild sweeps. I wonder if the 5th octave was going to ground instead of the max voltage
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Have you done all the tuning? Could just be that…
Rob
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Yeah I think I have it 1 octave higher than the other oscillator, but the 4 are in tune and stable. With 3 oscillators going really what does it matter right? It’s kinda cool to flip to it and have it dive down. It sounds like Defender or Joust, and I love the sounds on those games.
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So my 3rd oscillator is only getting 2.75 reference volts and won’t go any higher, any ideas?
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As shown here there aren’t many parts involved in that section of the circuit.
Double check that R42 is a 220 ohm resistor (and not 220k for example) and that its solder joints and the solder joints on the LM4040 are good.
Check that RV3 is a 100k pot.
Check that you have a 4.1V LM4040 (they are available in other voltages).
If they all seem to be the right values and R16, R17, R18 and R21 are all precision 10k resistors, chances are either the LM4040 or the U1 TL074 is defective.
With power off, remove U1 (you did use a socket didn’t you?), power back up and see if the ref voltage goes to the desired value.
- If the voltage at U4 pin 2 is 4.1V, power down and replace U1 with a new TL074.
- If the voltage at U4 pin 2 is still not 4.1 V replace the LM4040.
Edit: typo.
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I never did get my VCO tuners working with an arduino nano every, but since I’m cheap I went ahead and bought these:
Cheap nano clones. They are fiddley to get running and mine didn’t ship with a bootloader (Even though they are supposed to), but you can burn the bootloader with an Arduino Nano and some jumper wires. After that, things worked as they were supposed to and it seems to be running fine so far.
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Another cheap Nano clone source, these have the old bootloader (so you have to select that in the IDE, no problem):
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Hot dang, wish I had known about that when I was sourcing my parts! I spent like 30 or 40 bucks on all those Nano Everys. Time to think of some other project for them.
When in doubt check Tayda!
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?? never had a nano with no boot loader on it ??
they are ~£2 from china…
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Adding the bootloader used to be hit and miss. Got some chips without bootloader for a pal and it only took 5min per chip on a breadboard to sort it out. The cheap nanos from china are getting so much better, better than the legit ones possibly.
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It’s open source hardware. The Chinese ones are perfectly legit.
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