Eliminating ground loop in Bluetooth speaker circuit

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Joined Dec 23, 2014
I have built a Bluetooth speaker (based on this Instructable), which works except there is a faint clicking noise in the background. This is a basic diagram of the circuit for the speaker:

I am almost certain that the problem is caused by a ground loop, because I have tried using a separate power supply for the Bluetooth adapter and this fixes the problem. However, I need to be able to power the speakers and the Bluetooth receiver from the same battery.

I read online that someone else fixed a similar problem by adding an audio transformer to the left and right channels. I tried using an NTE1 1:1 audio transformer, and this did not help. With the transformer connected the speaker was actually worse, because it only made static noise and did not play audio.

If the problem is indeed a ground loop, I would not really expect an audio transformer to fix it because the problem is with the power wires rather than the audio wires. I think a ground loop isolator would solve my problem, but when I researched them online, the only products I saw were adapters made to be used with audio systems like this.

This is probably a really noob question, but I am not sure how to fix the ground loop problem with just small circuit components. How would I go about this?
I'm going to guess the Bluetooth dongle you're using as a switch to ground on Out- is injecting noise into the amplifier ground. Replace that with a manual switch and see if that changes things.

You're trying to identify a noise source - remove or filter each item until you see the problem go away.

If you have an oscilloscope, you should be able to see and quantify it. You could put a sine wave out then take an FFT and check the frequency response. You'll see a peak at the frequency of your input wave, anything else is noise.

Sounds like a fun problem, good luck!


Joined Jan 9, 2019
Simply disconnect the audio ground connection between the bluetooth output and power amp input. It will work well. The audio ground of both circuits are already connected to the main power ground. You can prove it by checking by a multimeter in continuity mode. No need for power or audio isolator. I'm using an xy-bt mini and pam 8403, powered by a single 18650 battery using the method I've mentioned above. Audio grounds are not connected to each other but it works without any noise at all.