I have been trying to get clean audio from raspberry pi 0w. Tried PWM audio + audio amplifier but the audio is noisy. So bought a cheap usb sound card and added an 3W+3W PAM8403 Amplifier. Now the sound quality is much better.

Now i have a different problem. At volume (alsa) 2% I could not here any sound and at volume 3% its too loud and if I still increase to 5% the volume its distorted. Added 10k resistor between sound card and amplifier as below
enter image description here Now volume got reduced but still high.

How do i get smooth volume control?
Increase the 10k ohm resistor
Add a resistor potential divider between left channel & ground and right channel & ground (resistor values?)

1 Answer 1


The USB sound adapter that you refer to seems for headphones, not for input on amplifiers. Depending a bit on the output circuitry of that sound stick, you could provide a typical headphone load, or a voltage divider, or preferably, both. If the stick provides a current-driven output, then adding additional resistors in series would seem counterproductive.

I would suggest a circuit like this:

enter image description here

(also for the other channel)

You can vary the R1 and R2 a quite bit, but I would start with both at 470 ohm. This gives the USB stick a reasonable load and would divide your output by 2.

  • Different USB card for amplifers! Do they specify it or are they available under different name? Anyways i will try the suggested circuit.
    – kk345
    Apr 23, 2021 at 8:10
  • Sometimes, but not always. Your specified "Boost the signals for Headsets". Some have a "line out" connector for amplifiers. In general, I would always try to get some form of manual. Apr 23, 2021 at 9:29

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