Cheap bluetooth speaker - find signal on PCB

Thread Starter

Motanache

Joined Mar 2, 2015
540
I have a bluetooth speaker which PCB looks like in this picture:


It had one speaker, so on the PCB is a mono output.
I intend to use it with an audio amplifier and I'm looking for a stereo output on PCB.

The 8 pin IC is 8002 and is an audio amplifier.
The big IC I do not know what it is and I have not found references about it
 

Thread Starter

Motanache

Joined Mar 2, 2015
540

In the picture is IC 8002 audio amplifier.
At this Bluetooth speacker I added TDA1557.

The problem is that it has a noise and I have not managed to deal with it.
A low frequency noise. It sounds like a rectangular signal. It seems to be a self-oscillation.

I tried, but I could not eliminate this noise:
- To move the components apart - without success
- Place LC filter on input 12V or on 5V output (I use a 12v-5v car adapter )

Regarding the search for the stereo signal I tried with a resistor connected to the input of the amplifier -- without success.

This PCB is from a bluetooth speaker like this one:

I removed the battery and noticed it works without battery just powered on the mini usb.
Now I pulled out the speaker And on pin 5 of the IC in the first picture I connected the input of TDA1557.
It works but has that noise.
 

Thread Starter

Motanache

Joined Mar 2, 2015
540
I then put on pin 8 to IC but no difference. The difference should have been 180 degree phase which you cannot feel when hearing.
 

Thread Starter

Motanache

Joined Mar 2, 2015
540
yes
Input for TDA1557 is one of the two pins(pin5 or pin 8) and GND.

I replaced the battery of this small bluetooth speaker with a capacitor. Without success, no difference.
 
Last edited:

Thread Starter

Motanache

Joined Mar 2, 2015
540
If you remove the 4Ω speaker and replace Rf with 10kΩ resistor you should get a gain of 1.

I have 10Ω instead of the original speaker.

But with this resistor Instead of the speaker and without it there is no difference.
If I look in the figure that AO has internal resistors with the same thing(40k and 40k give unit amplification)

That schema is found on the internet, I do not know what value is Rf in my case.
I can not change it because they are small SMDs and close to one another.

.
 

Thread Starter

Motanache

Joined Mar 2, 2015
540
I powered with 5V in the battery connector and the noise has considerably reduced.
But there is still a little noise.
 

Thread Starter

Motanache

Joined Mar 2, 2015
540
I do not have the schematic.

I bought that bluetooth speaker with radio, at a lower price than an audio bluetooth module.
 
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