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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:

image

The layout:

image

PAM8403 module:


image
The initial amplifier + controller board:

image
image

The speakers:
image

My assembly:

image

image


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  • Decided to quickly try that amp board, my results won't necessarily help at all since my setup is completely different and I don't have LEDs/microcontroller attached. I'm not near 'scope so I couldn't grab any traces.

    I'm using a very high quality audio cable (double shield), but there is about 3 cm bare at the board end. Speaker is 8 ohm (I only wired to the right channel).

    For the power supply, I plugged into an Anker mains-to-USB adapter.

    It's quite a noisy amp, there's reasonably noticeable hiss. With the 3.5 mm plug unplugged, I hear mains buzz; it needs to be shorted for that to go away, leaving just the hiss.

    Then I plugged the audio cable into a battery-powered MP3 player. It sounded fine.

    However, then I attached the audio cable to my laptop instead, which was powered from another port on the same Anker adapter. It was intolerable, lots of electronic noise sounds. If I unplugged the laptop and let it run on batteries, then the sound became acceptable again.  

    image

    I tried a few things; additional decoupling (220uF electrolytic cap on the power rails, no difference. Then added a choke preceding that (a 1 mH common-mode choke with the windings wired together to be a normal single choke), still no difference. Then removed the electrolytic and re-soldered the choke as common-mode, then tried two of them : ) and also tried adding it to the audio connections too. Still no difference.

    image

    Then I remembered I was not using the official laptop charger - I attached the laptop to the correct charger, and the amplifier remained on the Anker one. Noises gone. The official laptop one has 1k resistance from the USB shield to the earth pin. The Anker one doesn't have an earth connection (i.e. SELV).

    I'm guessing perhaps the laptop puts enough noise into the charger, that it egresses on all the other ports (common-mode or differential or both - don't know, guessing both!), and the filtering I was doing wasn't sufficient - I should have tried both differential and common-mode simultaneously but I didn't get a chance.

  • in reply to shabaz

    I'm waiting for the PAM8406 version which should not be so noisy.
    I didn't achieve much using the ferrite bead + capacitors filter.

  • in reply to me_Cris

    Can you make photos of your assembled amp., that show us details about your built? 

  • in reply to geralds

    Of course, you can see in the post.

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