The PAM8403 is a cheap 3W Class-D audio amplifier chip typically found in USB speakers. Powered by 5V, it offers low distortion, and being more efficient than Class-AB design, is well-suited for portable applications. A breakout board is available for $1 on ebay. For more details on the chip, see the PAM8403 datasheet.

The board is a tiny 2cm x 2cm.

A comparison with a fatter 10W amplifier board from the 90's.



Schematic of my circuit. Note the inclusion of a pot to vary the brightness of the power led. The pot was initially used to cover the hole after the volume pot was drilled in the wrong spot by mistake. But upon reflection, why waste a perfectly good pot doing nothing? So the world's first amp with a variable power led was born. Brilliant!

Schematic

Top view of the amp in a Jiffy case from Jaycar.



Closeup of the PAM8304 module soldered on a PCB. The module does not use normal 2.54mm pin spacing which is a bit annoying. But I found 22AWG solid-core wire fits perfectly into the plastic spacer from a 0.1 inch header, thus effectively a diy header with bendable legs.



Bottom view of the PCB. I had to glue the 3.5mm line-in socket to the wall of the case, no easy way of mounting it. Selleys All Plastic Fix is the best glue for this.



Front view of the amplifier.



Back view of the amplifier. By then, I realised the box was upside down and after some teeth-gnashing, flipped it by rotating the power switch and knobs. Had to live with an inverted power led.



The finished amplifier driving a pair of 25W Sony bookshelf speakers.



Have a listen to the music and watch the power led being adjusted. How cool is that!