Explain Class A amp to non audiophile friends

Thanks Atmasphere,
It would seem(at least in theory) that class A operation although much less efficient is a more pure and less 'altered' form of signal propagation.Implimentation probably has much to do with the final sound quality when comparing class A vs class AB.

The last responder got it right technically speaking. I see confusion regarding Class A and Class A/B all the time. Some believe that Class A means the bias is such that the output (could be any devices in the amp) are turned on all the time. This is techically true. But, others don't understand that there is class A and class A. One is the output devices (or pre-drivers), input devices, etc. can be biased such that they are always "on". This could be the equivalent of a 100 wpc amp biased "on" at 2watts. it is still class A because the drivers are "always on". However, there is the other class A, where it is biased "on" at rated output power. This means that without an input signal present the output drivers are biased "on" at sufficient current that the drivers total output produces the current for 100 watts. This means that you really need a huge, beefed up power supply with expensive large transformers, etc. and expensive heat sinking. So, there is class A and class A. Class A/B is as discussed previously. So, like any electronic device, especially amps, you really have to read between the lines on the specs, to get the real truth. I have seen amps touted as class A at 150wpc, which were totally untrue. Because without large transformers, and stupidly large and expensive heat sinks, there is no way on this planet that they would be biased at 150wpc class A. Maybe 2wpc class A, but not the other. The old saying is still true. you can really tell the quality by how much it weighs. Get on Nelson Pass' web site on the DIY site, he really gets into detail to explain Class A and heatsinking and power supply design to the lay person. This is Engineering 101. There is no magic here. it is what it is. lots of manufacturers outright lie or stretch the truth regarding specs. others, such as Nelson Pass tell it like it really is. Seriously, his explainations are really good for non-Engineers to really understand amp design.

enjoy

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.