PAM8403 Amplifier

I have some old audio-visual speakers, that were once used on a stand at exhibitions. They are quite battered, but the little 3" drive units seem ok. I thought I might make a pair of book-shelf speakers using them - sort of "PC speakers" that are a bit better quality than my old Sony ones.
I needed a little amp to drive them and spotted various amplifier modules on Ebay and Amazon. The speakers are rated at 3W so this PAM8403 module, at 3W per channel, seemed very suitable. PAM8403 Module from Ebay.

The module is tiny. It runs off 5V and has a stereo volume control with an on/off switch. There are input, output and power connections and that's it.
I hooked it up to a bench power supply, and a pair of the A-V speakers. I connected the headphone jack of my tablet to the input and was straight away listening to music at good volume level.
With everything turned up max, the music was very loud, but not distorting, so I am not sure that I had enough drive level to get the the full 3W. There was about 200mV going in when I looked on the scope.

Of course when I moved the scope to the output all I saw was a big blur! This is a "Class D" amplifier, that works using Pulse Width Modulation.

This is what I see on the speaker output with no signal going in. Here the timebase is set to 1uS per division, and the vertical scale is 2V/division. So this waveform is at 240kHz and is 8V peak to peak.

I guess this is going to radiate like crazy, and if I use this amplifier it may be best to use one module in each speaker and keep the speaker leads really short. Lots of filtering on the power-supply too.

The quiescent current was about 20mA and even when the volume was at maximum it was only drawing about 60mA. So it is incredibly efficient - 90% efficiency if the data is to be believed.

I found the datasheet for the chip here: https://www.diodes.com/assets/Datasheets/PAM8403.pdf

Anyway the amp module looks great for testing out the speakers. I can decide whether to carry on using it later.
73
Hugh M0WYE