I have a couple of battery- powered speakers which have USB power outlets.
I have the Zynth and another RPi-based synth.
When I try and run either synth from the USB supply and feed the audio output back into the speaker, I get a lot of background noise. I assume it is coming from the ground link, since if I take power from one speaker, and feed the audio to the other speaker all is good (i.e. it’s not a noisy USB power supply problem).
The speakers have 3.5mm stereo inputs (not balanced).
I want to be able to power a synth from the speaker and hear clean audio from the same speaker.
What’s the solution?