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I've got this cheap pam8403 modules and tried it with the raspberry pi 3 and there is a huge noise on the output. The power source is the same for both as you can see in the picture. Why there is this noise and what can I do to reduce it ? I don't want to separate the powers.

Here is the video

EDIT: I managed to reduce the noise by adding a transformer (which I got from and old dial up modem) on the input line between analog gnd and right channel. I also added some caps on power line. I thinks its the ground loop problem and this way the ground loop is isolated somehow. The only thing that is left is a small hiss sound which I think it's possible to reduce by adding some low pass filters on input line or on the speaker output maybe.

Raspberry pi Pam8403

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Unfortunately, the Pi's analogue audio output is hot garbage. It's incredibly noisy and subject to interference from both power supplies and components on the Pi itself. My advice would be not to use it for anything that you actually want to listen to.

You should be able to get a half decent output from any of:

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While it is true that RPis Soundquality is lacking, the problem is actually worsend by the pam8403. As you can see in this post: http://www.mikrocontroller.net/topic/372037 (last picture at the end), due to the fact that it can output up to 3watts per channel, they claim that 220pF capacitors to ground, ferrit cores on the speaker cables and higher end capacitors at the voltage input would improve sound quality.

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You need to add a low pass and high pass filter prior to the inputs of the amplifier, crank up the volume to the max on the Pi, and add 2 series 100 to 200 ohm resistors in series - 1 each to the right and left channel outputs. This will decrease the overall volume slightly, but the noise significantly https://othermod.com/raspberry-pi-zero-audio-circuit/

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