Electronic – Ground Loop? Noise from 12v to 5v converter manifest in bluetooth audio source

audiogroundloopsnoisepower supply

I've created a custom, bluetooth audio harness for my Jeep WJ using off the shelf parts.

  1. Amp – Clarion XC1410
  2. Converter – 12v to 5v buck converter
  3. Bluetooth Audio – Logitech Wireless Speaker Adapter

12v is supplied by the vehicle stereo harness in the dash. The amp and converter both connect to the 12v here. The converter supplies power to the BT adapter and the audio output from the adapter is connected to the amp. I have a constant alternator whine (vehicle on) in varying degrees when configured this way. Today I isolated some components to identify the source of the noise. While the converter is connected to an isolated power source the noise disappears. I would prefer to have the converter connected to a switched 12v power supply in the vehicle. Can anyone help me figure out why this is happening and how to address it?

Best Answer

From your description it's probably a ground loop.

You're presumably supplying ground to your DC-DC and BT at both power in and signal out (to the amp).

I'd break the loop, probably by having the connection to the amp grounded at only one end of the cable. I wouldn't break the loop at the power side because if you were to do that then DC-DC would have to use the amp's ground as a return path, which would be less than ideal.

An audio isolation transformer, like this one from ebay, should do what you need with minimal fuss.