Audio Noise

I’ve purchased a FEZ Domino board with the mp3 board extension. I’m trying to use them like a little mp3 player; to do this, I add to the project a little audio amplifier (connected to the headphone jack of the mp3 board) and a AC power supply to power all the system. When system start, I hear a lot of noise (it seems a noise originating from the clock generator or the main chip itself of the Domino board) and the only solution I find is use two separate power supplies, one for the Domino and one for the amplifier. If I connect a headphone to the mp3 board, no noise at all. What can I do (a specific power supply filter? have you a scheme for this?) to use the system in my configuration?
Thanks in advance,

You could try a “ground lift” hardware part.
When I did the technical part for festivals and bands, I rather often used them. Ground lifts are great to reduce noise and interference in audio hardware.

More information on the subject:

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Good luck.

A good mixed signal design will have analog and digital circuitry wired separately. Ideally, you would have a separate power regulators but you can also get the analog power through some ferrite beeds and add decoupling capacitors on each side.

Probably some 100nF capacitors will do the job… :wink:

Hi everyone,

after some investigation I have founded where noise arises; it isn’t originated by the Domino board but by the MP3 module itself (it seems noise related to the serial communication). To avoid this, I connect the ground of the battery housing(Yes, I know, no battery is required when using the MP3 module with the Domino!) to the general ground and, magically, noise goes away! Please note that I haven’t professional electronic equipments to investigate deeper, so get it only like a ‘try it… use it!’ ::slight_smile:

Hi. General ground? ground of the fez or some gnd on the mp3 player? tia

Ok, this is my configuration: with the FEZ domino and MP3player I mount two DC power regulators (one for the FEZ and one for a little mono amplifier using a TDA7056 chip, both with the same ground, because I use only a AC transformer); that ground goes to the FEZ by the DC power supply and to the amplifier; if I don’t share that ground with the - of the battery housing I hear a lot of noise from the amplifier, if I connect that pin, the noise is greatly reduced. Please note that I use a 100n capacitor to block eventually DC voltage at the signal in of the amplifier and a 5K trimmer to adapt the amount of signal to the amplifier.
Thanks for the reply.