The times they are a-changing. The days of class AB amps are pretty much over for a decade or so now. Its all about the class D amps. From consumer electronics to cell phones.

This is a simplification, but if you know how a switching power supply works, what if you took a particularly stable one (switchers are legendarily unstable, earning the EEs lots of dough) and varied its output voltage in time with the music waveform, so essentially the switching supply IS literally the final PA? And that is basically a class D amp.

It takes some pretty modern analog semiconductors (and some decent inductors, and some PITA simulation and testing) but its reached the point where there's no real point in deploying older tech unless you've got severe RFI / EMC type issues to work around or you only need a couple milliwatts.

At the low end you can get twenty or so watts out of a little itty bitty SMD chip with no heatsink at all (well, the PCB itself..) and a thumbnail sized inductor (depends how big your thumb is). This is all off the shelf and fairly conventional. Not if you want to run off line power its a little more complicated than 12 volts but hardly awful.

I've been working on a little project on the bench that uses the usual line powered switcher chicom "means well" (the company name, seriously!) and runs cool as a cucumber at about 300 watts DC out. Now a class D amp as opposed to a power supply is slightly more complicated, but not much. Its a bit larger, but lighter, than a 3.5 inch hard drive. Also 300 real electrical watts is probably well over 2000 watts marketing power, or 2000 watts music power or whatever scam, so a realistic set of amps for a home theater surround system is likely a bit smaller. More weight is put into display and controls now than into the amps.

Another way to think about it is your modern zillion watt PC power supply basically weight nothing compared to the supplies I was using in the 80s/90s/00s.

Analog electronics is not as boring as some digital types think... there's a lot going on. For many years there are ham radio guys using a close cousin of the class-D design to generate a couple hundred watts of HF for peanuts in something that weights nothing. The day is probably coming in my lifetime where legacy broadcast transmitters will be a 1U rackmount with a very fat power cable in, a fat RF connector out, and thats it, no more closets or rack sized machines just a little 1U box.

(edited to add a link to

http://www.classeradio.com/8_fet.htm

which shows a typical amp of this design.. now don't freak out about 90% of the image is a variety of RF tuning gear the actual 400 watt 4 MHz or so RF amplifier is that hockey puck sized PCB in the upper right on the coffee mug sized heat sink... obviously an audio design would be immensely smaller and simpler, and 400 watts of real power is like 4000 watts of marketing power, so you could scale this down a bit...)

(edited one last time to add the interesting anecdote that 30-40 years ago analog electronics had heatsinks and cooling fans, but CPUs had neither, and the transposition is basically complete in consumer electronics... analog stuff no longer uses or needs heatsinks/fans but seemingly all CPUs do, you could cook bratwursts on my xbox 360 cpu cooling fan, for example but the 500 watt subwoofer loafs along with no heatsink or fan, this would have really freaked out an electronics guy from 1975, for example)