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

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.

Tubes have their problems too! It's very hard to find good "tubes" that will last like they should "these days". New TUBES can go BAD "at any time"...at any price! That's a BIG Problem.....!

Bearotti: You may want to further your knowledge by looking at texts and articles from other than manufacturers of audio equipment. Those sources are generally biased to promote their product and do not provide a complete picture. Keep in mind that there is nothing particularly difficult in processing audio signals. Techniques that work in one area of signal processing work in other areas. For eg. in the mid 1990's I spent considerable time on a design project which applied signal processing ideas initially developed in radar target identification to extracting late potentials in ECG signals as an early predictor of cardiac problems.

Also keep in mind that in some 'perfect' sense there are tradeoffs in such things as class a vs class ab amps. However, those tradeoffs are meaningless because - as I indicate above - properly designed AB amps will not result in signal degradation that is in any way noticeable (unless of course one uses the magic 'audiophile ear').

A good beginning point for gaining more knowledge are the books by Douglas Self. These have very little mathematics in the explanation and are readily understood by anyone with a high school math background. The same goes for amateur radio publications. (Engineering texts and publications require a minimum of a formal course, or the equivalent, in differential equations and some background in Fourier analysis - which takes a considerable time investment - generally not a good investment unless one expects to make a living as an engineer)

I am familiar with Nelson Pass's very best current products. I have the pleasure of knowing a dealer who employs Pass components powering the towering Apogee Full Range speakers.

There are 600.5 amps handling the huge bass panels. The XA.5 100 finesses the mid and tweeter ribbons.

Through all types of music, and loudness, I never saw the power needles ever move on any of the amps. That would mean they are all running class A.

So, do both the 600.5 and the XA amps sound the same? The answer is no. I don't know why they sound different, but they do. The class A amps are clear, and easy listening amps. The 600.5 is forceful, and less open.

The question here is what is the difference between a wholly class A amp, and a powerful Class AB biased towards running in class A for around a fourth it's power rating?