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Using a 555 timer as a sawtooth generator for the comparator, and a single ended output MOSFET stage with a BJT driver stage. I should note that the sampling frequency is somewhat low at 220kHz, and should be as high as you can get it. A NE555N timer can go as high as 3MHz, but since that's the upper threshold i recommend using a sampling frequency of 2 maybe 2.5MHz. The output is 28Wrms, and my best estimate for the draw is 30W although it's hard to average it and measure it. Anyway, the efficiency is surely above 90% as expected. I haven't measured the THD, because it'll be high at this sampling frequency. The filter will be more efficient at separating the high frequency ingredient from the low frequency signal, when the sampling frequency is higher. I read that some company pushed their class D amps at 50MHz sampling frequency, and got a near class A performance, although I'm not really sure about the credibility of such statements. But the higher the sampling frequency the higher the sound quality, and the efficiency too. I should note that at higher frequencies the MOSFET gate capacitance may prove to be a problem, and a better driving stage should be considered.
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