What could I expect to hear from a Class A amp?

Once system becomes linear (by negative feedback or otherwise) it doesn't produce IMD - just look at IMD specifications of class AB amplifiers. Because amplifier has limited bandwidth it introduces delay to signal and negative feedback cannot compensate in proper phase (is too late) to fast changing (high slew rate) input signals. Because gain of amplifier before feedback is in thousands momentary lack of feedback response causes spikes in output signal causing unpleasant odd harmonics up to a point of saturation. Momentary saturation of output transistors causes charge to be trapped at their junctions for a moment. For this moment there is no sound. We don't hear it since our brain fills the gaps but it makes us tired.

It is possible to design class AB amp without (or with minimum TIM). Sane designer would set up gain before feedback to get with feedback only about 0.5% THD (or even 1%). Than he would measure bandwidth before negative feedback and would limit it (with feedback) in input stage to the same value. That would guarantee no TIM. Also he would use many local negative feedbacks avoiding deep global one. I don't want to bore you with detail of amp design (and I don't design audio) but my point is this: If you see a class AB amp with THD=0.001% stay away from it (something has to give).

There are amps that allow to adjust depth of feedback and people claim that the best sound is at the lowest feedback and highest distortion. Designing class AB for THD=0.001% is insane since speakers have few percent of THD. (Look at Stereophile article "Life without feedback")

Buy an amp for the sound and don't even look at specifications.

Class A is the best but at the price of electric bills.

Bearotti, class AB amps usually operate in class A up to some power level. The exact amount will vary from a few milliwatts to several watts, depending on how generous the designer is with biasing of the output stage.

You mentioned a concern with low level listening. The Classé Model Fifteen, when biased to factory spec should deliver about 5.3 watts in class A into an 8 ohm load. That should be enough to keep you in class A for most listening at low volumes with reasonably efficient speakers.

Fabulous descriptions. I have visited this site regularly for a few years now. Had some basic input of my own.

But I'd like to add this.

The people on this site continually help build my audio knowledge with their unreserved pouring out of knowledge. It makes my keen interest in music and my secondary hobby in audio more interesting by the day.

An ongoing thank you to all the folks keeping Audiogon so alive and vibrant. There really is nothing else like Audiogon. Bravisimo!

I do appreciate the technical explanation. On one hand it's about education. On the other hand it builds credibility to one's belief. From what's expressed thus far, can I take it that Class AB has more issues to overcome? The combination of designer skill and his stand on debatable subjects makes it difficult to come up with a comparable sound delivery system. Whereas Class A design is more simple, but with the problem of heat and power consumption.

My second question if I may would be what enables Class A solid state design to incorporate the strengths of tube amplifier concept with less of the problems. Is it because of shared design? Somebody mentioned about 2 tubes and a resistor.

For further and deeper understanding of Class A design and operation visit http://passlabs.com/articles.htm There you can find several articles dealing with Class A and other amplification devices. Well worth the time to visit and read the articles from the man that for all practical purposes responsible for and defined high end in the mid 70s to today.

Nelson Pass when he was at Threshold clearly defined and manufactured some of the worlds best Class A amps and preamps. In 1991 he left Threshold and started Pass Labs and the in the years since these products have further pushed the envelope of Class A design. In my opinion no one does it better than Nelson Pass.