??? WHY WHY WHY ??? Class A vs Everything Else

@joeycastillo 

+1

Class is one of the design choices… there is many others, material component choices that voice any amp. 

Ralph, I hate to disagree, but a pure Class B amp (like the Quad 405), switches from the upper set of transistors to the lower set with no region where both are operating.

@lynn_olson I hope you understand that I am familiar with classes of operation. 

As you point out, class C 'has holes in it' which is precisely what is happening when you have a crossover distortion artifact. Neither output device is on so the distortion is created. If you think about it, that's class C not B. 

The Quad 405 had no A region, and relied on the feedforward system to supply current and voltage for +/- 0.7V region where all output transistors were turned off. As a result, it ran quite cold, but if you had a good enough distortion analyzer, you could see the switching region along with a spray of harmonics.

Exactly. In order to actually be B, the output device, as I said earlier, would have to be on precisely 50% of the time (as seen on the Wiki page you linked)- that is to say, it only amplifies the upper half or lower half of the waveform; the ability to precisely set up the output section so it can do that is the problem I'm talking about : Any more than that its class AB and if it cuts off before zero its class C. Put another way, if it were really class B there would be no crossover artifact. But there is that spray of distortion, which tells you the output device cut off before it should. Class C. 

Like I said, a lot of people really haven't thought this thru. 

Keep in mind that nearly all audio amplification is done in Class A: Class AB or Class D stages are only used in the final stage of amplification to drive inefficient loudspeakers.

I use my class D on horns. Its well suited as it has a very good first Watt and is also very low noise. The days where class D was just for brute power are gone.  

Many manufacturers claim sliding-bias Class AB is Class A. It isn’t. That’s marketing talking. True Class A is inherently inefficient and gets hot, whether tube or transistor.

Actually the claim I've seen is sliding class A,not AB. The idea is the output devices never go into cutoff and both are conducting all the way through the entire iteration of the waveform; by definition class A. The tricky bit is a circuit that dynamically changes the bias with the amplitude of the waveform. That unavoidably causes distortion.