Explain Class A amp to non audiophile friends

here's my attempt at a semi-laymen view of the issue.

with Class A, a single output device (eg, transistor) produces the full output wave. That is, both + and - side of the sound wave.

with Class AB, the + side of the wave, and - side are produced by 2 separate output devices.

The result is Class A generally produces more coherent sound because the 2 waves in Class AB don't always match up perfectly resulting in "crossover distortion". Further, Class A is less efficient, and generates more heat because of the way the output devices need to be biased to operate in Class A. Conversely, Class AB is more efficient to operate, and to manufacture (all other things being equal).

LOL! Reading over this thread I think that Buconero117 has the best explanation, that being no explanation.
I very, very rarely try to explain any of my "crazy" hobby to "normal" people. I find it frustrating, much like trying to teach a pig to sing.
It only wastes my time and annoys the pig.

A couple of non-electronic analogies perhaps:

A complete duty cycle of waveform is 360 degrees, remember 10th grade geometey?

1) Imagine hand cranking a wheel.

With one crank and one (or two) hand(s) cranking all the way around with one crank this is Class A (powering 360 of the duty cycle with one or more devices (hands) to make the complete waveform).

Now imagine a crank on either side of the wheel at 180 degrees apart, but in this case using two hands, you can only push each hand for one half of the rotation, pushing off from one to the other to make the wheel rotate with each hand stopping to push the very instant the other takes over. This is Class B (180 degrees of powered rotation per hand, and not more, transferring the other the very instant the other stops working, of the duty cycle X 2 to make the complete 360 degree waveform).

Now imagine that, using two hands, as the other begins to take over, the first still provides a little assistance until the other is able to "take over" and complete the one half cycle push. This is Class AB (180+ of the duty cycle, dependent on the bias, X2, to complete the duty cycle to complete the waveform, there is a bit of "hand off" from one hand to the other before ceasing to powere the half cycle. You cna see why this is the most efficient because each hand gets to assist the other during the power on phase and gets to "rest" for most of the one half cycle. Walking is also like Class AB.

Another analogy is bicycling without clips on the pedals where you're cycling by pushing only from one foot to the other (Class B)during the push phase only and the other where you are using clips or clipless pedals, so that each foot helps all the way around, but during the power portion of the stroke, one foot dominates over the other, and then trades off to the other and so forth (Class AB).

If each foot could power exactly the same amount all the way around this would be Class A and could be performed with one or two(or more!)feet, but each foot would power the complete 360 cycle evenly and all the time.

Well the whole goal of running class AB instead of Class B is to pretty much eliminate crossover distortion by judicious biasing of the output devices and usually also the use of negative feedback. I'm not sure if it can be eliminated to the point where it never appears on a 'scope under any circumstances, probably not would be my guess, though it is worse at lower power, better at higher power. Still, that's a great question for a circuit designer with real tech knowledge. Here's a link to a bit of an explanation of crossover distortion: http://www.electronics-tutorials.ws/amplifier/amp_7.html

I guess the crossover distortion in a Class B or Class AB amp is measured as part of the overall THD spec, so I'm sure, like any departure from linearity, it's audible in some form or another, but it may be so small as to be a tiny component of the sound. You know, no amp is perfectly linear. I'm sure there are single-ended Class A amps with higher THD levels than some well designed push-pull AB amps -- it's just different distortion. With circuit design there are always compromises, it's always a matter of picking your poison.

What is the difference in a single ended solid state class A amp and one that is not single ended?