plusuncold
Posts: 9
Joined: Mon Jan 28, 2013 1:24 am

RPi Radio with squeal

Wed Apr 03, 2013 9:20 pm

I've been working on a Raspberry Pi internet radio. The audio is spliced from the audio jack into the radio where it then goes into the radio's amplifier and speaker. Additionally I have the RPi powered off the radio's AC supply through a DC-DC step down transformer into the GPIO pins.

After I connected the transformer and RPi to the radio there's been a high pitched squeal coming from the radio. To troubleshoot the problem I cut the positive wire going to the transformer and the squeal stopped.

Does anyone know a solution to this? Is their a component I could put in to filter out the squeal?

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azeam
Posts: 194
Joined: Fri Oct 26, 2012 11:13 pm
Contact: Website

Re: RPi Radio with squeal

Wed Apr 03, 2013 9:32 pm

plusuncold wrote:I've been working on a Raspberry Pi internet radio. The audio is spliced from the audio jack into the radio where it then goes into the radio's amplifier and speaker. Additionally I have the RPi powered off the radio's AC supply through a DC-DC step down transformer into the GPIO pins.

After I connected the transformer and RPi to the radio there's been a high pitched squeal coming from the radio. To troubleshoot the problem I cut the positive wire going to the transformer and the squeal stopped.

Does anyone know a solution to this? Is their a component I could put in to filter out the squeal?

Image
Sounds like you have what is known as a "ground loop", google it and you'll find plenty of information. Either you get the RPi it's own power supply or get an isolated DC/DC converter (the first option is probably cheaper and easier).

plusuncold
Posts: 9
Joined: Mon Jan 28, 2013 1:24 am

Re: RPi Radio with squeal

Thu Apr 04, 2013 12:56 am

Thanks for the reply! I'll look into that - I figured some signal was interfering with the radio's proper 9V/GND but reached the end of my electrical knowledge!

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