CLASS A AMPLIFIERS

Much of the newer A/B designs will run up to nearly 25% of the output in pure class A and switch to AB for cooler operation and lower power draw.. and many of the newer A/B designs today rival and beat many of the older Straight Class A in my opinion, newer technology capacitors, transformers, transistors can make this possible. Older Thresholds, CODA, and Levinson's I owned are good, but my newer odysseys and many mcintosh amps sound better sometimes and do not run hot at all... so your taste after audition is going to determine if they are better for you or not, I hated the rediculous Heat and draw of electrical with low efficiency in comparison, so even if not sonically better I find some reliablity, ease of use, and cost benifits to the newer Class A-A/B designs.

Class A amplifiers nearly always exhibit more authority, but this has nothing to do with power.

I should point out that a Class A amplifier can be either push-pull, single-ended, tube or transistor. What is important is that the amplifying device or devices never goes into what is known as 'cutoff'. IOW the device or devices each amplify the entire waveform all the way up to full output regardless if single-ended or push pull.

Distortion is generated when an output device goes into cutoff. In a push-pull circuit, when the device is cutting off while at the same time passing off the signal to its complement that is just barely turning on, the resulting distortion obscures low-level detail (as in the case of Class AB2 and Class B push-pull amplifiers). This can be complicated by the presence of an output transformer in the circuit as magnetics tend to react badly to this sort of thing!

So ultimately, Class A is the lowest distortion form of amplification, regardless of the circuit topology or amplifying device.

The price paid is Class A amplifiers are less efficient as they are 'on' all the time and therefore they make a lot more heat. They also require fairly beefier power supplies for the same reason. Such is the price of increased performance!

Thank you very much to all of you for those very clear and competent explanations. I feel much more smarter now!

Those are all excellent answers but if you want to know how they sound different, visit a Plinius dealer as some of them are switchable between class A and A/B.

I am still at a loss for comprehending the general sentiment expressed in this thread that class A amps are only beneficial due to lower distortion. Heat dissipation and the efficiency of their use of power are well known, but they are also given credit for having a typically fuller sound and are known for their ability to control bass well.
I own very high biased (reportedly) class A amps but can't run them as pure class A. If and when they would switch to A/B is mysterious to me. I don't hear any noticible change in the sound. It is entirely possible they never reach that point, in fact they shouldn't because they supposedly run up to 125 watts class A which would blow my head off except for perhaps dynamic bursts.
Does anyone know if the claim that Aragon Palladiums are really class A in the first place. They don't distort much if at all, but they don't run really hot, temperature wise, either. Any one who knows something about these amps and can tell me something other than the canned corporate stuff would be appreciated. Sorry if that is a thread jack.
Also why all the advertising about class A capabilities if it doesn't matter?