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I'm currently powering a raspberry pi from a 12v battery using a 5v regulator purchased off the internet. It works fine, and I can connect to the Pi over wifi etc no problems. When I connect an audio amplifier, however, the output is SO noisy - bleeping when led's come on, a kind of crackling, and at worst when streaming audio over wifi it sounds almost like a lawnmower in the background. Can hardly even hear music over the noise.

Is it a ground loop problem that I have? If I just touch the end of the 3.5mm jack connected to the 12v amp onto any metal part of the pi (e.g. usb housing) the same noise comes across the speakers. I've tested this Pi with a normal home amplifier connected to the mains when the pi is also connected to the mains and no such problem occurs...

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    Using a 5v regulator with a 12v battery is kind of wasteful. You are converting the other 7v into heat. Meaning almost 60% loss. Better option is a Buck Converter. This is what most car phone-chargers use. These will also have the filter caps you need, like dfowler7437 explained. – Gerben Feb 28 '14 at 17:14
  • @Gerben Cool - I've now purchased a simple buck converter which seems to reduce the noise by quite a substantial amount! There is still a small amount which seems to be coming from the Pi, but it's definitely negligible compared with what I had - cheers! – Josh Feb 28 '14 at 23:54
  • You can still try adding some additional caps. You could connect them the the 5v and GND pins on the gpio header – Gerben Mar 1 '14 at 12:12
  • @Gerben I'll give it a go - would a 1uf capacitor be good enough do you think? – Josh Mar 2 '14 at 14:44
  • I don't know. I'm pretty new to this stuff. Just try it, and find out. – Gerben Mar 2 '14 at 18:15
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Sound like you have supply noise from your regulated supply. This regulator you mention is probably a 7805 or equalivent. You need to place some decoupling caps on it's input and output.

Take a look at this article where the caps are discussed. You could try a quick test by placing a 0.1uF or even a 1uF cap across the 5V output line. If the sound improves, you will know that supply filtering is required

Related Article on StackExchange

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