Class A Power in A/B amplifiers?

Well, @atmasphere read my previous post and responded appropriately while @georgehifi seemed to have ignored the point I was making, which is about audible benefits and sticks to cherry picking statistics which he feels must prove his point.

As I’ve mentioned like, forever: a measurement is not audible nor a preference. It’s just a number.

To be "better" to me it has to sound better. Otherwise it’s either equivalent or worse. We can argue that 0.01% THD is better than 0.03% THD, given equal harmonic distribution of the distortion, but you can’t prove one is audibly better since I assure you I cannot hear it.

And so, I have yet to hear evidence that any amplifier class is inherently superior all by itself. Even @atmasphere starts to get into feedback vs. non-feedback which occludes the entire discussion over amplifier classes. I might induce he’s saying feedback is more important than amplifier class. :)

I am going to state, categorically and forever that brand names are more important than amplifier class and that everyone who argues otherwise is a muggle.

Hi @atmasphere

Your technical explanations are, as usual, spot on, but since I failed to explain what I meant by by "proof" I am afraid you made a counter argument to a point I did not mean to make.

What I meant to say that my own ears have yet to discern a preference of Class A over Class A/B or even D which is even moderately consistent. The behavior of class A circuits vs. A/B in technical terms is more or less well understood, as you show in your rebuttal to my post, but not in the realm of personal experience.

To me, there is no proof class A is consistently or even broadly better than any other class of amplifier when each class is well executed.

Yes, some stellar Class A amplifiers exist. Do they make me go "wow this is what Class A means?" No too many other middle of the road or poor sounding Class A amps out there.   At best, I could be convinced that class A amps are an acquired taste which some develop and then never grow tired of.  Fair enough! It's a happy man who finds what makes them happy early in life!

Best,

Erik

Might be helfpul to understand how A and B differ, and that transistors are not perfectly linear. It takes a little current before they wake up and can act in a linear fashion. This is what causes the notch distortion during the crossing of 0V.

In Class A, both legs start at full on. Since they are balanced this ressults in 0V at the output, and maximum power draw through what are essentially to closed switches.

In Class B both are off, again, achieving 0V at the output and minimum power draw through essentially open switches.

The bias, or quiescent current, in an AB amplifier keeps both legs on enough to avoid the dreaded notch distortion without consuming 100% of the power in a true class A amplifier. The difference is that eventually as the output voltage shifts far enough away from 0Vthat one leg will shut mostly off, switching to B. When the voltage goes back towards 0V that leg now turns on, with some inherent distortion as they attempt to reach equilibrium.

Personally I find the arguments for/against Class A on technical terms alone lack overwhelming evidence. I've heard Class A I liked and Class A I really did not.  Same for A/B amplifiers.  So while it's fun to look at how engineers have take on the same challenge via a variety of methods I always find my ears better at determining what I am going to want to listen to than amplifier classes.