Dac+ noise issue

HI all

Slightly odd one perhaps, but making me struggle.

I have currently two Pis with DAC+.

Each Pi feeds a separate left and right via phono leads to a 6 channel Rotel Amp.

One set of speakers is in the Bedroom the other in our Garden

When I power both the Pis from a single PSU (be it an Anker USB charger or a regulated 10A 5v supply) There's terrible static on all 4 speakers from the moment the Pis are turned on.

If I disconnect the phonos from one Pi, the static vanishes.

If I run the Pis from separate power supplies the static vanishes.

So far I've plugged the amp into a different mains circuit than the Pis and their power supply, with no difference.

Tried to earth the amp to the water system, with no difference.

Swapped all the cables, and power supplies with no difference.

Even tried a 3rd Pi with Dac+ again, the same symptoms.

What do I do next to allow me to run my Pis (eventually 3) off the same PSU?




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