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Old 12-06-2016, 10:13 PM   #1
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Join Date: Jun 2013
Location: Marin, CA
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My Ride: 2003 330cic
Ground loop noise from USB power - SOLVED!

So I hacked together a Bluetooth device that connects to the Aux input so that I could play my iPhone over my stock nav unit. I ran a 5v USB line from the fuse box, and it worked great.

As long as I was actively playing music or a podcast.

If I stopped the playback I got horrible interference, which I suppressed using a standard ground loop suppressor, with moderate and unsatisfying results.

On a tip, I tried a DCDC isolating step down converter, and it has been life changing. Turns out the noise was from the actual usb power being noisy (I had been using a $6 simply step down converter).

The product:

I made a quicky enclosure for it on my 3d printer and plugged in the bluetooth device. No noise. None. Zero. The DC power was clean.

Might be something to try if you are using a pi-based approach or a USB powered DAC. I searched for a long time for this solution. Hopefully it helps!

Last edited by Archbid; 12-06-2016 at 10:14 PM.
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Old 12-06-2016, 10:52 PM   #2
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Join Date: Nov 2016
Location: Chicago
Posts: 8
My Ride: BMW i3
It makes a lot more sense to cut the ground loop at the Bluetooth power inlet than trying to isolate the audio signal outputs galvanically or through transformers that have a non linear frequency response. Great work!
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bluetooth, ground loop, interference

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