555 class D amplifier

The revered 555 timer has so many clever uses besides timing and oscillators. Here's an interesting experimental circuit that makes use of the 555 as a switching "class D" audio amplifier.

There's a single-transistor preamp. You would apply your audio signal decoupled at the preamp's input ("SIGNAL" node).

There's a push-pull transistor pair stage at the output to source and sink current to the speaker -- this can drive more power than the 555 itself.

Anyway, here's the schematic. Very hi-res, so click it to enlarge and then right click it to download so that you can zoom in as necessary.