I had a related issue with my set-up - using the Pi to turn my amp on and off (intentionally) via a GPIO pin + relay. During testing I powered the Pi with its own DC supply (isolated) and connected the GPIO to a relay inside the amp (also isolated). This worked.
However, when connecting the audio things went downhill. The amp ground (earthed) and the floating Pi ground were connected. Lots of noise brown-outs etc etc.
My situation was complicated as I wanted the amp to power the Pi and have a single umbilical carrying audio and power from amp to Pi. Attached is the topology.
The only way to fix this, that I could see, was to isolate the audio signal using a pair of transformers. I made my own PCB for this, but the function is the same as: https://alexnld.com/product/car-rca-ampl...uppressor/
So either your ground loop is causing issues, or when the amp is on the power supply can't supply the necessary voltage and current to the Pi.
What I learnt was that not all USB cables are equal and not all power supplies actually deliver. I had to make my own umbilical with thicker gauge wire to avoid additional voltage drop and made it as short as possible.
Tristan
However, when connecting the audio things went downhill. The amp ground (earthed) and the floating Pi ground were connected. Lots of noise brown-outs etc etc.
My situation was complicated as I wanted the amp to power the Pi and have a single umbilical carrying audio and power from amp to Pi. Attached is the topology.
The only way to fix this, that I could see, was to isolate the audio signal using a pair of transformers. I made my own PCB for this, but the function is the same as: https://alexnld.com/product/car-rca-ampl...uppressor/
So either your ground loop is causing issues, or when the amp is on the power supply can't supply the necessary voltage and current to the Pi.
What I learnt was that not all USB cables are equal and not all power supplies actually deliver. I had to make my own umbilical with thicker gauge wire to avoid additional voltage drop and made it as short as possible.
Tristan
