Mini desktop build + audio interference question

[datguy.dev]

Greetings,
So I wanted to build a RPI desktop. It is still in progress, but this is basically what I ended up with: (32GB SD, Berry booting Jessie w/ Mate desktop and RetroPi atm.)



An issue I have been having is audio interference; constant crackling. Especially, while it is processing. Here is the basic "portable" electrical configuration:

http://imgur.com/aL3XqMU
Running the Pi 2 on the DC-DC converter at 5.1V (no load; 5V with load) - stepped down from 12V - produces the interference. This is also with using the pins to power it (or Vin,Gnd). However, running the Pi from micro-usb with its own power supply eliminates the noise. But I really want to use just the 12V 3 Amp power adapter I have.

Do you think the noise would be eliminated if I went from the DC-DC converter into the micro-usb? I would have to order another cable so I thought I'd ask first.

Thanks!

[datguy.dev]

Did some testing.

I thought it could be a grounding issue... Grounded the pi directly to the DC converters IN, OUT, and the 12v power adapters negative. The noise did get quieter, but it was still squealing and not much better than before.

I thought it could be a bad/cheap power supply. Tried a 250w desktop PSU's 12v line and I get the same noise results plus noticeable scrolling on the screen. Tried grounding with this power supply as well.

I don't know, the only fix atm is a separate power supply for the pi.

[FM81]

I assume you have another connection (not shown in your picture) for the audio-signal from raspberrys OUT to amplifiers IN? It contains also three lines: left, right and (again) ground. A little part of the raspberrys supply-current (and this is full of noise) may go over this audio-ground-line and this creates the interference.

Solutions:
Ground loop isolator for the audio-signal.
OR
Supply raspberry from an fully isolated power. (example TRACO)

Best Wishes, FM_81