How can I eliminate hum when connecting a Bluetooth receiver to an FM transmitter?

Brendan November 6, 2014
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Hi-
I have a .5W FM transmitter that I use to broadcast audio throughout my apartment (there is at least one radio in each room). I also have a small Belkin Bluetooth audio receiver that I use to connect to various Bluetooth-enabled devices (phones, tablets, PCs). I had hoped I could use the two in combination to easily broadcast audio throughout my home from any of my various sources. The problem I am encountering is that connecting the Bluetooth receiver to the FM transmitter creates an awful hum- I problem I have never experienced when using the receiver straight into an aux input, and which does not manifest itself with any other type of audio source connected to the transmitter. I suspect it may be a power issue, but am unsure how to proceed. Any suggestions on the best approach to take to troubleshoot?

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  1. Col. Panek
    November 15, 2014 at 1:07 am

    You have a "ground loop", a 60 Hz signal flowing through the ground side of the cable between the devices. If you unplug the receiver from the AC line and it immediately stops, you need a new power supply that doesn't leak so much power into the ground side. Try flipping the AC plug around on either the transmitter or receiver. Make sure they are plugged into the same outlet. Find another power supply if it runs on a wall wart. If all else fails, replace it with a battery.

  2. Bruce E
    November 6, 2014 at 11:16 pm

    If the hum is from power, putting a 60Hz band-stop filter between the the transmitter and receiver should cure the issue and have little impact on the overall audio quality after a bit of tweaking of the levels.