Electronics > Projects, Designs, and Technical Stuff
Need help with ground loop
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laejf:
I've made an audio amplifier-board to be used as a portable speaker with a class D amplifier and a USB port for connecting a bluetooth module that sends audio signals via a 3.5mm jack. When connecting the BT-module I seem to get a ground-loop and the amplifier gets noisy. The noise goes away completely when connecting the BT-module to an isolated voltage source. The problem is that i don't want to add another source to the build so I'm wondering if I could somehow make the USB port floating with a single supply or if there is another alternative. I've tried:


* Filtering out the noise with a common-mode choke connected between the USB port and BT-module. No difference.
* Bypassing with different size capacitors. No difference.
* Disconnecting ground on the USB port such that the module is only grounded through the 3.5mm jack. This made the noise much worse.
* Disconnecting ground on the 3.5mm jack. No difference
I've attached images of the schematic and board as well as videos that shows the noise when my phone is connected and disconnected to the BT-module.

Any help and feedback is appreciated. Thank you.


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Connected

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Disconnected
laejf:
The images was apparently not inserted in the post.

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Rerouter:
Cant easily read your schematic, but at a guess, add a series 1uF capacitor on your signal and signal ground wires to prevent any DC currents inducing a voltage.
laejf:

--- Quote from: Rerouter on August 09, 2019, 12:58:41 pm ---Cant easily read your schematic, but at a guess, add a series 1uF capacitor on your signal and signal ground wires to prevent any DC currents inducing a voltage.

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The 1uF capacitors on the far left in the schematic are doing this on the input-pins of the TPA3123. I'm not sure about adding one in series with the ground connection as this would create an open circuit for the DC voltage and let through only the noise(?)
001:
the main problem is not a groud loop
check EMI at D class amp chockes
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