Explain Class D amps to "non audiophile friends"

Realremo, Imagine just one mechanical switch that switches between +10V and -10V. Output of this switch after averaging (filtering) will be zero volts if switch was the same amount of time (for instance 1s) at +10V and -10V positions (total cycle time of 2s). Manipulating ratio of times changes output voltage.

For instance:
1.5s at +10V and 0.5s at -10V will result in output of +5V because (1.5*10+0.5*-10)/2=+5
or
0.5s at +10V and 1.5s at -10V will result in output of -5V because (0.5*10+1.5*-10)/2=-5.

Real frequency of switching is very high (in order of 500kHz) where mechanical switches would not work - hence Mosfet transistors (fast switches). Mosfet transistors are even manufactured in two different technologies for use as switches or linear transistors.

Fascinating technology!

The main thing I wonder about is how much better even will it get over time for hifi audio purposes.

There would still seem to be some practical upside in maturation of this particular technology though I would say it has clearly evolved to the point of being highly competitive with others already in hifi audio. I expect it could widen a lead practically over time moving fore ward if it has not to some extent perhaps already. The bigger question will be how much will it matter? Similar to the discussions about value of high res digital audio sources I would think.

Mapman, I suspect that it will get much better because of semiconductor speed. Things based on timing scheme like Sigma Delta DACs are limited in resolution by timing accuracy while traditional DACs are limited by tolerance of components. Semiconductors are getting much faster every year including high current Mosfets.

"Semiconductors are getting much faster every year including high current Mosfets."

Exactly!

Much technological progress over the last half century has evolved around the speed of semiconductors as evident in the myriad of increasingly functional electronic devices that never stop coming and likely will not in the foreseeable future either I would bet.

A quick look around today versus 5, 1, 20, 50 years ago quickly confirms that!

I look forward to the day when I might consider replacing my current Class D amps with something that is even better perhaps even for a fraction of the current cost.

Might high end audio be the one frontier so advanced that advances in semiconductor technology might fail to conquer it along with the rest?

I think not.

Time will tell even if it has not already started to do so for some.

is that a class-D amplifier is a very minor tweak of a switched-mode power supply (SMPS)

05-22-12: Kijanki
Bombaywalla - it is the other way around. Class D was invented tweaking SMPS.

Kijanki, I think that we are saying the same thing.... :-)