[mwbajor]

I did not read the article in-depth but class D audio amplifiers use variable pulse widths and then filter it before the speaker. Aside from very good efficiency you also remove the need for a transformer using this method hence why its used.

[hdhfjkrkrme]

As a down side they are extremely difficult to design for good quality output. Basically impossible for an amateur.

[dekhn]

ladyada made a board design that incorporates a class-D amplifier chip, it's open source: https://www.adafruit.com/product/1752 https://github.com/adafruit/Adafruit-MAX9744-Amplifier-PCB

I'm not sure which is the hard part you're referring to- implementing the amplifier itself, or the board around it. I don't think an amateur would want to build their own class-D from raw components except for pedagogical purposes.

(i've been pretty happy with the results, I used the board to drive a couple speakers and the amplifier is not the first thing I'd fix to improve the audio quality.