Hi all!
I have a 4x channel, 40 watt (per channel) amplifier that I designed and built based on the E-TDA7386. It works amazingly, but for one problem. I added a bluetooth audio receiver module found here:
and when I play music via this module, there is a constant low humming. But when I pause the music, the humming stops in about 1 second.
Any thoughts?
Thanks in advance!
How are you powering the device? I would guess the power needs a lot more capacitors on the output. You are likely hearing the BlueTooth device drawing extra power when it received a message from what ever is sending it. Then much less power between transmissions.
I am powering it from an L7805. There is nothing else powered from the regulator, only the Bluetooth Module.
I did place a 10µF cap on the 5v line.
Try a 1000uF cap.
Hi,
Put some lower values as well.
Can you please post image(s) of you project, so we can see your component layout?
Tom... 
I just tried adding a 1000uF and 100nF cap on the 5v, and nothing changed. Still the same buzzing sound when I play music, but nothing when not playing.
it’s a ground loop problem, put B0505S between 5v and your bluetooth board
Ok, thanks for narrowing it down. I've heard of ground loop problems before.
The B0505S is a DC - DC converter? Electronic Components Distributor - LCSC Electronics
Is there anything else I can use to fix the problem?
This circuit has a ground loop protection:
you said yourself amp by itself is fine, the problem is when you connect BT module. B0505S is isolated converter, it breaks ground, if not completely it should significantly reduce the interference
The Bluetooth Module is connected the whole time. It only buzzes though when music is playing, and then stops buzzing ~1 second after I pause the music. The bluetooth is attached the whole time.
It probably has mute function that puts output low when no music, it’s a cheat. Ground loop problem is huge, requires science, why bother if you can just mute the noise?
Isn't a ground loop problem from using two ac outlets? I am only using one.
no, if you are interested, read about it more, but in short, you have some currents travelling in the ground connection, so the ground has to be designed in such a way that it eliminates those currents. fine when you are sole designer but when you start connecting 3rd party devices you start getting in trouble. this is why isolated converter could help in this case
Oh. That explains why my amp works fine, but with the Bluetooth Module it hums.
Should the Bluetooth Module be soldered directly to my board like in post #6? Or should I separate it and attach it to my board with wires? Maybe even power the module with a separate, not on-board, 5v source?
Also could I make my own isolated converter? I have copper wire and several ferrite ring cores.
you coud try different ac/dc suppy from mains but you can also try b0505s, they are cheap and redily available
Is the circuit in reply #9 your circuit or a generic one similar to yours, but not yours?
I don't understand the PCB layout in reply #6, you have what I think are 2 rows of 4 ground connections but they are not, so far as I can see, connected to each other. What is on the other side of the PCB?
No, the circuit from reply #9 is not mine. It is from here:
https://www.circuitbasics.com/design-hi-fi-audio-amplifier-lm3886/
Here are the schematic and PCB photos:
There is a ground plane on top and bottom of the PCB.
The schematic is changed since then. U4 and U6 are added along with pretty much all the components on the bottom part of the schematic.
