Does anybody know what this means? Is this a real issue, or something that’s resulting from KiCad not being aware of the internals of the IC that I need to turn off in the ERC rules chcker?
It’s an exact copy of the circuit I’m cloning, so I don’t know why this error is occuring, if it’s my problem or an issue with the original: schema-cave/VCA_Xim.pdf at main · noisereap/schema-cave · GitHub
Just like it says… you connected two outputs directly together.
It may be as simple as putting a resistor in series with each output, but it may be much complicated depending on what you want to do…
Why’s that bad though? This is a mixing circuit, so connecting outputs is the point of it.
Maybe it’ll work for the LM13700 as they are current output devices. But in general, for things like op-amps that drive voltages out, you need to think about what happens when one op-amp is trying to drive a positive voltage and the other is doing the opposite. They’re just both going to fight to get the voltage they want, sourcing or sinking current at their respective outputs and you end up cooking things.
In any case - I’d suggest bread boarding it to make sure it does what you want. If you want KiCAD to stop complaining you could put a 0Ω resistor on each output. You could even keep its footprint if you’re doing a PCB, and if it works with both outputs directly connected then just put in a jumper. If it doesn’t, you can put in a real resistor so all your bases are covered.
Cheers
Thanks, these are good ideas!
Right, connecting voltage outputs = bad, connecting current outputs = okay. But KiCad doesn’t know there are both kinds of outputs.
You could also get KiCad to shut up by editing the symbol to make them bidirectional pins or something. You can do that for just this instance of the symbol in KiCad 6, in 5 you’d have to create a private library and copy the symbol to there and edit that. Or you can just ignore the error.
Okay, just going for it… never made one this dense before, I think it’s kind of pushing it. But should juuuuust squeak into a 2.5cm module!
Good luck! Did you leave a couple mm clearance on the sides? Best if a 25 mm module has a PCB a few mm narrower than that. Kosmo Specification says 4 mm narrower.
I’m doing the panel now, but the board is 2mm narrower than 2.5cm. I didn’t know about the 4mm rule in the spec, but I’ve been doing 2mm and it’s worked for me on the others so far. I’m going to have to pull out the ruler for this one, it’s going to be very snug with 4 jacks…
Rule, shmule, just be careful what you put it next to in the case! 2mm is as good as a mile if everything’s lined up right.
It looks from the image that pin 8 of the LM13700 is not connected to the resistor. If you have already sent these off, it is still an easy fix.
I see you borrowed my trick of putting the caps under the IC socket! 
Is that an unconnected pin I see?
I did! I was a bit skeptical when I started putting the VCDO together and found it like that, but now I like it. Sneaky! As long as the components are a lower profile than the pot base…
I can see 3 missing connections,
The rule checker in kicad also gives connected, you have to select the tab. I have been caught out with this before. It is easy on a dense board for the ground plane, to not be connected to the ground.
Hope this goes well.
Good eye! I ran the DRC, but didn’t check that tab. Not sure why overlapping footprints is more important than missing connections!
Up at the top you have some very long there-and-back-again traces that could be shortened a lot by moving to the other copper layer. (Might need to flip some other track to make it work, or a via or two.)
The ground pins on the power header don’t need traces connecting them, they can just connect to the ground planes.
All the rules checkers are happy now, I’m not going to fudge with it any more 
This one is kind of an experiment, not actually sure it’s going to work. If it does, I might reapproach the idea in a different way, as a 20cm panel with a horizontal fader, mix level knobs, 2x3EQ, 1xHPF, 1xLPF and a “preview” output. Essentially, a minimal version of this:
Then, have two different lead/bass lines that can be mixed together the same way I would when mixing two tracks as a DJ.
