Class A amps

All this discussion about operating class is really moot if it involves ASSUPTIONS. Since I have been designing amps for over 40 years I am somewhat of an expert on the subject. The most important thing is the OVERALL RANGE OF LINEARITY. This property is obviously much easier to achieve with a class A design albeit at great expense. In the last 25 years or so, this whole situation has become rather moot as the better designs by most competent engineers have long overcome the biasing problem. The sad truth of the matter is that the average audiophile layman has absolutely no way of verifying that any given unit has been correctly designed. One must un-fortunately trust the reputation of the designer and today even that is no guaratee as there are a lot of what I call dilletantes touting themselves as great engineers. The real truth is that everyone can't be "King of the mountain". James Bongiorno formerly of Dynaco, SAE, GAS, & Sumo.

listening to all of the above, all i can say is with all the amps i had a/b amps never came close. But theres one company that mad my jaw drop was sim audio, great product, i dont own any of sim,but i gotta say,it sounds good for a class a/b amp, and there intergraded amps too.like i say I may not be someone building electronics but I can say I have the ears of years hearing all kinds of components. so is class a amps better,to me yes,if you dont think so i guess your still in maze.there are a lot of a/b amps out there,very few sound good and are some that do a good job, class a is better.im just dieing to hear a digital amp make its way. well bye everyone enjoy listening.

I am thinking about upgrading my ARCAM AVR 550 to a new ARCAM AVR 30.  The ARCAM AVR 30 has G Class amplification.  I believe the first 50 watts are pure Class A.  This will cost me an extra $3,000 ($6,000) total.  Will I hear the difference in sound quality and is it worth the cost difference.  The reason why I use an AVR receiver it to watch TV through two front towers, a center channel and two REL S2’s.  I use this to listen to 2 channel.  I need the flexibility.  
I would be curious what some of the experts in this group would say?

Kurumuka gave a great explanation.  Class A and AB can be both balanced and single ended.  Both are push pull and can be tube or ss.  There are some Class A SETs - single ended triode or single ended transistors where the +/- is handled by one tube or transistor.  These are always single ended (RCA) and are almost always very low power.  

Class A amps, because of the constant current, tend to be very fast and responsive.  They also waste 75% of the power going through them and run very hot.  Many at 130 degrees and in a small space, this is a huge issue. 

It also matters little how hard your drive these with the exception of low wattage, Class A tube SETs.  Because current running through the amp is constant, it doesn't make a difference if the amp is at 10 or 100, the amp is being "driven" the same. 

One issue is that they tend not to sound right until the get scorching hot and this can take some time.  Tube amps often have direct heated triodes which get them to temperature faster.  SETs are an exception and unless you are in the market for a low wattage SET, I will not share further.  

Class ABs are much more efficient, run in Class A mode to a point and then switch to class B.  This can vary wildly from amp to amp.  When driven hard, these can get very hot and you do not want to be pushing these to high volumes.  They can also seem a little slower than a Class A because of the non-constant current.  In practice, this is not a huge issue unless the amp is poorly made.   

Class B tends to be highly distorted and there are very, very few pure Class B amps on the market.  AB amps switch from Class A to Class B so that it can deal with increases in power needs with changes in volume. 

If you have an amp that has a switch from pure class A to AB (borg dune and warp), your speakers and power needs drive what mode you should use.