I am building a rhythmic led headphone prototype, but unfortunately I am missing something or am doing something wrong because my project is not working properly. The project is as follows: I bought - A pair of one dollar headphones. - Two tip31c transistors. - One pam8403 module, to improve the signal of the two channels. - Two 5v led plates for both right and left channels - A usb cable.

I am using this diagram: enter image description here

But something went wrong, because the pam8403 only works disconnecting the tip, i've test the output right and left channel of pam8403 and works fine with speakers of test, but when i connect the tip31c in one or both channels it makes a (bip a sound hit in bot out channels) that it repeats infinitely, and the leds are blinking in a static secuense repeatly infinitely, and not with all power, not following the music or music signal provided by the audio input plug...

I dont know if is a problem of pam8403 or tip31c, important i need pam8403 because not all devices have the full power....

Can someone guide me?, i'm really noob in this...


PAM8403 is a Class D bridging amplifier so you are shorting out one of the drivers by grounding it, among other things.

Try using just the + on each side and use an RC low-pass filter like this:


simulate this circuit – Schematic created using CircuitLab

You may have to try other values of R and C to get what you want.

  • \$\begingroup\$ Ok, then i have to use the positive signal of both channels instead the gnd, in the out of PAM8403, and use the filter that you post, right? \$\endgroup\$ Jun 8 '20 at 3:05
  • \$\begingroup\$ That's my suggestion. You still need the ground connected to the PAM, of course. \$\endgroup\$ Jun 8 '20 at 3:05
  • \$\begingroup\$ thank you, a high voltage line 12v can affect if i use the positive channels? \$\endgroup\$ Jun 8 '20 at 3:06
  • \$\begingroup\$ The 5V ground and the 12V ground must be connected together. The PAM8403 can only handle 5.5V maximum supply voltage or it will be destroyed. \$\endgroup\$ Jun 8 '20 at 3:08
  • 1
    \$\begingroup\$ but i'm now are more closer, because now work inverted, and is much better than not work... \$\endgroup\$ Jun 8 '20 at 5:21

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