HEEELP: Music module noise cancellation second attempt

Ok, I am again desperately trying to solve my sound-output challenge. :wall:


Summary for the new members: When playing sounds with the GHI Music module, you are perfectly fine with a headset, but as soon as you connect an external amp, there is a lot of noise and the output is DC-offset. After a long discussion, I proposed to follow the VLSI guideline (http://www.adafruit.com/datasheets/vs10XXan_output.pdf) for connecting LINE-OUT in the right way - here is my plan of attack https://www.ghielectronics.com/community/forum/topic?id=13497&page=5#msg144218

No-one was really able to confirm that the route was right, and those involved took other paths in trying to figure out what to do.

I still have a marginal hope, that a few electrolytic capacitors placed in the right locations might solve the problem. But I am software guy…

Looking at the Adafruit MP3 board, they have placed some specific power supply decoupling, and they seem to have followed the guidance.

Any ideas on the next step here?

Simply add an audio isolation transformer between the output of the sound module and your external amplifier. An extra boost could be the use of an analog transformer for power your controller board instead of a switching power supply.

I am software guy myself, but it seems that your plan should work as expected. The only thing I would be slightly worried about are those short-circuit resistors, in your configuration they should act as voltage dividers.

If that would be me, I would have tried your circuit long time ago. Are you afraid of a magic smoke? :smiley:

It seems they have not implemented sigma-delta filter.
I wouldn’t worry about power decoupling at this stage.

Thanks for input…

@ iamin - Thanks for pushing me toward the smoke

@ RobvanSchelven - Do you mean one of these: http://www.mouser.com/ds/2/281/kmp_da100-185018.pdf

And how exactly do you want it placed…?

@ njbuch - more like this one… http://www.pac-audio.com/productDetails.aspx?ProductId=193&CategoryID=31

I assume it speak for itself how to place it

Thanks Rob, just ordered one of these:

Lets see if I can avoid the smoke…


I don’t see where you are seeing this as there is no resistance path to ground.