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The PAM8403 amplifier is very noisy

me_Cris

Hi!

I was thinking of participating in a challenge but I ran into another challenge. Sweat smile
I'm using a small circuit with PAM8403 as a replacement for some speakers with dead audio circuit. In addition, I also have addressable LEDs in the case (this how they came) and I was thinking of using an MCU to control them. But I just noticed a very sharp and annoying noise produced when I power the LEDs, and it doesn't go away even when playing music.
I made a msall PCB, the schematic is below. The power supply is at 5V [USB]. I placed some capacitors in the idea to support the supply voltage.
What ideas do you have? What could I improve? 

Thanks!

The schematic:

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The layout:

image

PAM8403 module:


image
The initial amplifier + controller board:

image
image

The speakers:
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My assembly:

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  • Most likely this is just digital noise coming through - you need to make sure you've got good routing to avoid it being picked up, good ceramic bypass capacitors nearby, ideally a separate analog ground plane that joins the main ground away from the digital and perhaps even consider some kind of filtering on the power (e.g. inductor choke) if it's really bad.

    Ensuring the bypass on the LEDs is good is also important, especially if you have a bad ground, the noise could come around due to ground bounce. The addressable LEDs are PWM so they switch on and off "hard" and that modulates your supply and power distribution network.

    Personally, I'd say using a differential input audio amplifier, rather than a single-ended type like you have, would be a better choice and routing pairs of audio lines to that amp, that way if the noise is induced, it is induced into both legs of the audio signal and thus cancels out.

  • in reply to Gough Lui

    I have some PC speakers powered by 5V [USB], the original board had a digitally controlled amplifier [via push buttons] and an unlabeled IC [for LEDs], all on the same board. The PAM8403 is a module soldered onto a PCB, and for the connections I had to use JST connectors.
    I don't know much, but I'm still experimenting.

  • in reply to me_Cris

    can you measure the current the complete led circuitry is drawing?

    and try an inline choke to power the leds 

    maybe a photo of the old board and complete unit ? 

  • in reply to acdc90

    Hi, I'm a little late with the reply, I don't have much time during the week. Sweat smile
    I added pictures to the post.
    I'll experiment with the USB power supply part.
    I think LEDs (there are 7 per speaker) of this type consume enough mA (tens), and since I want to create some visual effects, I'm basically witnessing a "symphony" of noise.

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  • in reply to acdc90

    Hi, I'm a little late with the reply, I don't have much time during the week. Sweat smile
    I added pictures to the post.
    I'll experiment with the USB power supply part.
    I think LEDs (there are 7 per speaker) of this type consume enough mA (tens), and since I want to create some visual effects, I'm basically witnessing a "symphony" of noise.

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