Noise on analog audio output

Noise is heard when connecting the amplifier board to the analog audio output of Apalis T30 + Ixora and playing the sound.

The noise sounds like quiet static, not a popping sound.

When you do not play any sound, you will not hear the noise you care about.

If you play back the system sound by clicking on the screen, you will hear it accompanied by noise together with the sound effect.
Even if the same amplifier board was connected to the analog audio output of Colibri iMX 6 + Iris, no noticeable noise was added.
This noise will not change even if the peripheral device connection is configured to the minimum.

I want to investigate what is the cause.

Can you check whether R11 and R12 are assembled on your board? You find these two resistors on the bottom left of the topside of the module (see picture below). If the resistors are present, please remove them and test it again. The resistors need to be removed in order to increase the quality of the sound.

Thank you for the quick response.
I confirmed it immediately.
old.png is in its original state, new.png has removed the resistors of R11 and R12.
I tried it for a while until now, but I think that noises no longer occur.

What is this resistor implemented for?
When removing the resistance, is not something bad happening?


Dear @kyas

It is absolutely safe to remove the resistors. They are part of an RC filter network, which turned out to make the audio amplifier oscillate under certain conditions.
In our latest production batches, R11, R12, C28 and C29 are not assembled anymore.


Regards, Andy

Thank you for your response.
Since it is said that it is removed in the latest production, we remove the resistor of the module purchased this time by yourself.