Too myopic to trouble shoot, need help!

DIY STUFF
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Hello, I have built a 6 oscillator module for my synth and I am having some issues that hopefully a bigger brain can figure out. I have built 8 modules so far that all work perfectly, but this one is stumping me.

It is essentially 6 reverse avalanche oscillators going into the “super simple mixer” with cv control on each oscillator. Everything functions, the oscillators are humming along, but I am experiencing a few problems…

1-output is lower than I expected coming from the tl072, not loud enough to match other modules

2- when I touch the volume pots I get a crackle or pop, and when turning the pots up from silence they sound scratchy, When holding the output jacks with my hand the crackle goes away. Putting it through the MS20 filter it makes the MS20 input knobs noisy as well.

3-when I turn all oscillators all the way up the volume completely cuts out.

Something def isn’t right, and as this is my first attempt at putting different ideas together on my own, I need some guidance… How can I make the output louder and get rid of this odd grounding behavior??

Here is some useful info…
-have tried different chips
-tried different pots
-tried different grounding methods (grounding from the oscillator to pot, or daisy chaining everything together
-am getting proper voltage to chip

Thanks in advance.

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  1. The mixer stage gain is (minus) the ratio of the feedback resistor to the input resistors, so swapping in a higher value resistor for the feedback should give you more volume. You could do it on either of the two op amp stages but I’d go for the first one. R9 in the schematic, connecting to TL072 pins 1 and 2.

  2. I’m guessing a grounding problem. You don’t have a conducting panel and I don’t see any wires connecting to the pot bodies, that might be an issue.

  3. That’s pretty normal, there’s a current range where the avalanche oscillator works and it abruptly stops working both below and above that range.

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You are the man! You are almost always first to help with great wisdom. And yes, until I find a suitable means of making panels I am stuck with carboard canvas modules lol.

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so I checked ground continuity and everything checks out. Every place where ground should be it is there. Does it matter where I take ground from to go to the volume pots?
right now I have single ground going to every pot on pin 1, output from oscillator going to pin 3, and the wires going to the output jack on pin 2.

It’s wired so each group of 2 oscillators has a single output wire. Is that bad?

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Are the metal bodies of the pots grounded?

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hmmmm, I don’t really know what you mean by pot bodies… I haven’t had to ground the pot body on any other build thus far.

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I’m just guessing really. I’m referring to the metal shell the pot is contained in. Yours appear to have a plastic dust cover surrounding that. The shell is in electrical contact with the bushing and shaft, but not with any of the terminals. So if the pot is not mounted to a grounded metal panel the shell, bushing, and shaft will be floating. That’s OK sometimes and may be OK here, but since you mention noise when you touch the shafts (which would not be connected to anything else that might cause it) I’m guessing that might not be OK here. You can try soldering a wire from the pot body to ground. Or maybe add a layer of foil to your panel which the pots would make contact with, and ground that.

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and you were right… I just haven;t had to do that yet, but adding a wire attaching all pot bodies solved the snap problem. Now I need to figure out why the pots sound scratchy when turning volume up and down… These oscillators are weird and kinda wonky to work with.

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