MP3 player interference when charging from same 5v supply


I have a circuit that samples the audio from an MP3 player, this audio is also split to an amp/headphones. There's is also a USB port to provide power to the MP3 player from the 5v circuit supply.

The issue occurs when the MP3 player is plugged into charge - I can hear intrerference in the audio. It's fine when not powered.

For comparison an iPhone doesn't have this problem, so I suspect it's the cheap MP3 player.

Is there anyway I can stop this interference? Using an additional dedicated 5v supply for the MP3 player works but I would like to avoid that.


It's the combination of the cheap MP3 player and the noisy 5V supply. You need to add extra filtering on the 5V supply to the MP3 player. Perhaps a 100 uF electrolytic plus a 100 nF ceramic capacitor from the supply to ground.

More information would help!


Thanks, tried that but didn't make any difference as far as I could tell. The noise is also synchronized to the mp3 display updating (scrolling text etc), as well as a regular pulse.

What information would be helpful?

My schematic/layout is here:

Sounds like a ground loop - the charging ground currents are travelling along same cable as audio?
How are the supplies to everything connected?

Everything is shared...

I had connected the Audio GND to AGND on the Teensy, thinking this would be ok, but I now realise the Teensy LC doesn't have AGND just GND.

Would a Ground Loop Isolator solve it?
Such as this: