I built a case that houses:
- A battery pack as UPS with 5v and 12v outputs https://www.amazon.com/gp/product/B07H8F5HYJ
- 2 audio stereo amps (12v power) https://www.amazon.com/gp/product/B07V42HVYW
- A Raspberry Pi (5v power) with 2 stereo usb soundcards https://www.amazon.com/dp/B01N905VOY
Everything is wonderful except for one problem:
There is an enormous amount of interference in the speakers. These noises correlate perfectly with the activity of the Raspberry Pi, and when I power the Pi with a separate 5v power supply all noise is gone.
So I built an RC filter for the 12v that goes to the 2 amps. I put a huge 4 Ohm resistor (https://www.amazon.com/gp/product/B008ML0LE4) with 6 capacitors of all sorts of values (3 chemical, 3 ceramic) and it is better but still unacceptably loud.
Is there a better way to clean up a DC power?
And if I feel lazy, is there a little device I can buy that does that extremely well so I don't need to build one more thing from scratch?