Explain Class D amps to "non audiophile friends"

>>05-22-12:Stanwal
In general efficiency is inversly related to sound quality.<<

That is simply not true.

Ignore the inexperienced post(er).

You will find PWM modulation in other places where it has nothing to do with efficiency. For instance SACD is the same as class D before filtering (operating at 2.8MHz). Also Sigma Delta DAC operates on the same principle.

Kijanki, what you wrote is absolutely correct but what you'll find is that a class-D amplifier is a very minor tweak of a switched-mode power supply (SMPS) where the input (DC) voltage reference is replaced by a (modulating) music signal. Do this simple swap & you have a class-D power amplifier. Compare a class-D audio amp & a SMPS & see for yourself.....

Bombaywalla - it is the other way around. Class D was invented tweaking SMPS. Engineers demoing SMPS showed that load regulation is so fast that SMPS can even play music.
Any linear power supply is in fact primitive switcher operating at 120Hz. Primitive because it requires huge transformers, big capacitors (to filter out 120Hz) has no line or load regulation, switches at max voltage, is susceptible to DC on line etc. That's why Rowland uses SMPS in preamps where efficiency is not important or power amps (model 625) that are class AB. Bad rap that SMPS has come mostly from primitive computer supplies.

Wolf_garcia, They sounded great from the beginning (at least to my ear). Second "version" was designed to make it easier for some critics to remove foot from the mouth.

I've read all the posts and I still don't understand how a class D amp works. What are the devices that do this "switching?" I get the difference between class A and class A/B, that thread was great, but for this one I think I need some kind of dumbed down explanation...more layman terms please?