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Bluetooth module high frequency and buzzing noise
Bluetooth module high frequency and buzzing noise
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Old 25th August 2019, 11:03 AM   #1
davidhozic is offline davidhozic
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Join Date: Feb 2019
Default Bluetooth module high frequency and buzzing noise

Hello,

I've recently got a 5V bluetooth receiver audio board to play music remotly to my speakers, before I soldered the power I tested it via a 5V phone charger and it worked fine..
When plugged into the DC-DC step down board the BT receiver board is making first high frequency noises and then it's just buzzing.
Any ideas how I could fix that problem?

Bluetooth board:VHM 314 Bluetooth Audio Receiver board Bluetooth 5.0 mp3 lossless decoder board Wireless Stereo Music Module-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

Wiring diagram:
Click the image to open in full size.

Last edited by davidhozic; 25th August 2019 at 12:45 PM.
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Old 25th August 2019, 08:19 PM   #2
ubergeeknz is online now ubergeeknz  New Zealand
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Join Date: Aug 2018
It's due to a ground loop - the Bluetooth chip draws current in short bursts and this also affects the signal ground (as they are connected together), causing the noise you're hearing.

There's four possible solutions, one of them you already tried...

1. A very oversized ground connection. I'm not convinced this will work but it may be worth a try.

2. A 5v - 5v isolated supply. This will break the ground connection on the power feed side so the signal ground "floats" on the noise along with the signal hot. I've tried this with good success, the chips are cheap enough, eg
AliExpress

3. 1:1 audio transformer on the signal side. Results may vary but this should also address the problem.

4. Seperate power supply altogether for Bluetooth module and amplifier.

I've tried bypassing the noise with all manner of capacitors and chokes, with very limited success. In the end I found option 2. a straightforward and effective solution.

Last edited by ubergeeknz; 25th August 2019 at 08:21 PM.
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Old 25th August 2019, 08:26 PM   #3
davidhozic is offline davidhozic
diyAudio Member
 
Join Date: Feb 2019
Quote:
Originally Posted by ubergeeknz View Post
It's due to a ground loop - the Bluetooth chip draws current in short bursts and this also affects the signal ground (as they are connected together), causing the noise you're hearing.

There's four possible solutions, one of them you already tried...

1. A very oversized ground connection. I'm not convinced this will work but it may be worth a try.

2. A 5v - 5v isolated supply. This will break the ground connection on the power feed side so the signal ground "floats" on the noise along with the signal hot. I've tried this with good success, the chips are cheap enough, eg
AliExpress

3. 1:1 audio transformer on the signal side. Results may vary but this should also address the problem.

4. Seperate power supply altogether for Bluetooth module and amplifier.

I've tried bypassing the noise with all manner of capacitors and chokes, with very limited success. In the end I found option 2. a straightforward and effective solution.
Ok thanks, I'll try option 2
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Old 19th September 2019, 12:23 PM   #4
surfdabbler is offline surfdabbler  Australia
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Join Date: Aug 2019
I've read this thread with interest, as I have recently bought an all-in-one board with amp and blue-tooth system together...

This one

It has a similar issue where there is some Bluetooth noise getting through into the amp. I have not resolved the issue on my board, but I've read that that the bluetooth signal is being fed through from the bluetooth RF circuit being too close to the headphone jack location, and the headphone jack is fed directly to the amp. I also read that someone else fixed the issue by running the full double-ended audio signals from the bluetooth chip to the amp, as my original board has an op-amp to convert the double-ended audio signals to single-ended.

Currently, your signal is coming off the bluetooth board as three lines - a ground line, a left signal and a right signal. If you can find a left+/left-, and right+/right- signal, and take these four lines through to the amplifier, this might help. It's a lot of work to figure this out and test it, and it will change your whole volume control setup, working with a differential signal.

I'm still working through possibilities to resolve my board, but I'll be interested to watch how you go with yours. It's interesting to know that your first board didn't have the issue, but your subsequent boards do have the problem.
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Old 20th September 2019, 02:59 AM   #5
phase is offline phase  United States
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Join Date: Oct 2004
Sometimes conducted noise can be thwarted by the use of common mode chokes.
These would go on the power leads to each device.

As mentioned, an isolated supply would be best.
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