Class D wireless speaker problem with common ground

[nijunge]

I hope Im putting this question in the right forum so here goes.

Im building a wireless Bluetooth speaker so my elements are

Class D amp
speakers
18,5 Volt Li ion elements (5 elements and charge controler)
Bluetooth receiver (12V )
Step down power converter 18,5 Volt to 12 Volt
Step down to USB charger circuit
external charger (18,5 Volt)

My problem is a mid range noise and as I investigated this I found:
That if I took the ground of the 18,5 - 12 Volt step down it stil gave power to the bluetooth circuit, It turned out that the step down gets ground from the amp through the audio cable
It is the Bluetooth circuit that gives the noise as if I disconnect the audio to the amp its gone.

Do you guys have any suggestion on what to do to
1. dont get the ground over via audio
2. shield form the noise

Bonus info : If I power the BT circuit with a separate battery the noise is gone.

with hope ;-)
Niels

 

[Jerms]

Ground loop isolator in the audio line....
https://www.amazon.co.uk/201-087UK-Jack-Ground-Loop-Isolator/dp/B0161F22WQ

I got that one, mainly because it had the right connectors. Plenty on Amazon/eBay with RCA plugs, and a few open frame, circuit board jobbies if you don't mind a wait from China/HK.

 

[DUG]

...

Bonus info : If I power the BT circuit with a separate battery the noise is gone.

with hope ;-)
Niels

Probably a ground loop.

One way is to use an isolated DC-DC converter to power your BT circuit.

 

[nijunge]

Thanks for the advice, I will look for either a loop isolator

Im not sure I understand the other solution, but I will investigate that as well

Thanks Guys

 

[Jerms]

Isolating DC-DC converter doesn't have a common power or ground with the power input.

This is an example on a board.... The only one I've seen actually....
https://www.amazon.co.uk/Yeeco-DC10-24V-Isolated-Regulator-Smartphone/dp/B015E4835U

If you need smaller wattage or amperage, there are components available from e.g. Murata that you can build into your own circuits.

J.

 

[Buehgemeiste]

It is very likely that the bluetooth module has differential outputs and that the amp can be configured with differential inputs.
You should investigate that.

 

[nijunge]

Thanks