High Pitched Tone on Custom Mixer

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Hello folks. I’m sorry for my first post to be a plea for help, but there’s nothing to be done about that. On to the problem at hand.

I’ve recently been on a bit of a custom electronics fix as I’ve found that I love routing PCBs. I’ve mainly done digital logic based designs, but for my most recent project I decided to do something a little more analog. I decided to make a sort of audio mixer with 3 inputs and 3 outputs that could be mixed in any combination. I recently got all the parts and put my first prototype together only to find that it produces a horrendous high pitched tone on any output. I don’t know much about analog circuitry so I would like to know if any of you folks can spot what could be the problem.

https://dl.dropboxusercontent.com/u/472 … ematic.pdf

This is a PDF containing the schematic. The plugs are on the first page, the power circuitry, and one of the three identical output channels is on the third page. The OP amps are TI NE5532DRs and the charge pump is a Microchip TC7660CPA.

https://dl.dropboxusercontent.com/u/472 … %20PCB.pdf

This file is a PDF with the PCB layout. The bottom layer can be seen as light grey.

Thank you for any help you can provide.

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The noise is coming from your power supply inverter. The 7660 can be quite noisy and prone to latchup if you aren’t careful. First problem is that it looks like you have C38 backwards. Connect it properly and make sure it’s rated for at least the incoming power supply voltage. That should take care of most of the problem. I would also add decoupling caps at the V+ and V- terminals of all the opamps.

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Thank you for pointing out the backwards capacitor, now that you mention the power supply it seems obvious that that would be the problem. On the same note, now that you mention decoupling capacitors on the supply rails they too make a whole lot of sense. Thank you for the feedback.