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

Class A amplification is like Porsche. Not for everybody but always the standard of comparison. 

Love my Pass Labs XA25. First time with pure class A. Would really take something special to go back to A/B. Class D not for me. Only drawback is power consumption. Like the analogy with the Porsche. Luckily not the same price point for my Pass ;-)

An A/B class amp drives initially in class A, then at higher outputs switches to class B, if I remember correctly.

 My 100 wpc stereo AB power amp operates in class A up to 10 watts then the peaks cross into class B, peaking at roughly 100 watts. So the top 10dB uses class B.

 So truthfully, your AB amp will operate (admittedly, on listening volume and speaker efficiency) 99% of the time in class A. I am using 10watts where as a full class A uses 100 watts. Is the higher power bill worth that 10% for a 100% class A amp?

@bishop148 While I realize this is what all the engineering tells us regarding Class A/B, & NO ONE wants that to be true more than myself,BUT I have spent the last 3 days,almost 50 hours so far,swapping back & forth between the Class A/B SimAudio,which is not some fly by night amp but a highly regarded & favorably reviewed all over the world  amp,the Class D Creek & the Sugden gear..
 1 hour each amp,same exact music over & over & over,level matched with a Soundmeter app,full circle every 3 hours & it’s just NOT the same..From whisper quiet levels at 55db.to rocking 90 db.levels not even the SimAudio has,whatever it is,that the Sugden has..
 I’m not trying to convert anyone here,I’m not trying to convince anyone I’m right & their wrong..I’m just telling everyone what I hear & all I can say is,either keep what you have,NEVER compare it to anything pure Class A & enjoy the music..OR spend some time comparing 100% Class A against your favorite flavor amp & prepare accept the fact that there simply isn’t anything that sounds like Single Ended 100% Class A....
 As the saying goes,ignorance is bliss & like I said in my OP,I wish I hadn’t hooked up the Sugden gear because I was ignorant & blissful!
PS:I would add 1 other thing..The last 3 days has REALLY enamoured me to the Class D Creek 4040a..It is worlds away from the Ice powered amps I heard a few years ago that where bass heavy,glassy & a little hard at times..Mike Creek must be an absolute genius because this amp is a GIANT killer in every sense...
 

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. (Speakers with a 1% conversion efficiency are actually "efficient" as most loudspeakers go. 0.3% to 0.5% are more typical figures.)

Let’s break down a typical amplification chain:

* DAC conversion element, whether R2R, FPGA, or single-chip conversion -> lowpass filter (class A) -> buffer stage (class A)

* Linestage: single gain or buffer stage (class A)

* Power amplifier, which are typically 3-stage, whether transistor or tube: input stage (class A) -> driver (class A) -> output stage (class AB) -> loudspeaker

Note the only element of this signal chain that is Class AB is the final stage that directly drives the loudspeaker. Everything else, whether tube or transistor, is Class A. In a studio environment, with far more complex electronics, the same applies: Class AB is only used for final drive for loudspeakers, and not anywhere else, no matter how complex.

The reason is simple: everything except for speaker drive is very low power, and operating at low currents (microamps to milliamps). So it doesn’t get very hot unless you have a big studio console, or a rack full of effects boxes. So efficiency doesn’t matter. When efficiency is unimportant, Class A is the invariable choice in professional and consumer equipment.

But ... if you need a 100 to 200 watts to wake up a loudspeaker, efficiency does matter. A lot. My home theater system has a 2010 vintage Marantz MM8003 power amplifier, with a THX Ultra certification for 140 watts/channel. That doesn’t mean it sounds good or anything, merely that it cranks out 140 watts from 20Hz to 20kHz at specified distortion ... that it works as claimed. So far so good.

Suppose this was a Class A stereo amplifier, instead of Class AB. As mentioned in the Wikipedia link posted above, 25% is the best efficiency we can hope for in a Class A transistor amps. So our 280 watt stereo amp must dissipate 280 * 4 = 1,120 watts, all the time, from the heat sink. Uh oh. I can tell you that is a gigantic heat sink, about the size of a medium-size HDTV. Also a pretty good room heater, that’s plenty warm any time the amp is on. Hope you have good air conditioning, because you’ll need it. Or ... the amp can be normal consumer size, or rack-mountable, but those fans are going to be moving a lot of air. Think gamer PCs, with top-of-the-line video cards, noise levels.

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. If genuine Class A is desired, versus inflated marketing claims, get used to 20 to 30 watts/channel with an amp that still gets plenty warm.

The bad actor is the speaker, not the power amplifier. A miserable 1% conversion efficiency comes out as 92 dB/meter/watt, or in other words, 100 watts of electrical energy is converted into one watt of acoustical energy (which is very loud). It gets worse: the other 99 watts do nothing but heat the voice coil.

Which isn’t good, because the voice coil is very small, with an area of only a few square inches, and is deep inside the magnet structure. For heat to escape, the voice coil must then heat the magnet, and the magnet, in turn, heats the air in the enclosure. Of all those expensive watts that come from our treasured amplifier, 99% are wasted heating the voice coil. And most speakers on the market are even less efficient, typically 0.3% to 0.5%.

In loudspeakers, there is a direct tradeoff between size and efficiency. Bookshelf speakers will always be inefficient. Sometimes called Hoffman’s Iron Law, it is also expressed as an equation in the Theile/Small formulas that define bass performance. No way around it.

So you have a big amp, or big speakers, or Class AB or Class D. You choose.