I have read about digital amplifiers recently, and understand the concept. It seems like quite a neat idea. I designed this circuit off the top of my head just to experiment with the idea. It uses a frequency modulated 555 running at above 20khz, which drives a speaker via a driver then power transistor. I was amazed when this worked as intended straight off. The output is quite low; when you turn it up by raising the signal level at the input, distortion becomes evident very quickly, especially on low frequency signals. But with a 14v supply coming from batteries the output of higher frequency signals can be quite a respectable level.
As it is, i'm sure the circuit is quite pointless. Although the signal quality is ok, the passive filter i'm using is at 1khz, 12db, the woofer output from a 3 way crossover. Can anyone explain why the 3055 transistor gets fairly warm though (tiny heatsink, TO3 package)? I'm sure for the output level it gets as warm as any other amp. It must be only on or off? I even added inverters after the 555 to help square it, but it remains warm. Increasing the 100ohm base resistor lowers the temperature, but lowers ther output a bit too.