Why would anyone want class AB amp when class A always sounds better ?

Cost ? Heat? Reliability?
Why would anyone want class AB amp when class A always sounds better ?

Because Class A does not always sound better. Obviously.

class A always sounds better 
Who says?  Absolutes are rarely applicable in this hobby IMHO. 

Yes, they are sometimes applicable.
Miller, what's wrong ? Give us an example. I'll give it myself. Gryphon Diablo 300 class AB integrated sounds better than Sugden class A integrated. But it's not a fair comparison, not what I mean, of course.
As a direct example, some feel that the Luxman 509X class AB at $9.5k sounds better than the Luxman 590axii class A at $9k. Can’t get much more absolute-busting than that. Same company, both integrateds with same features, essentially same price, both current products.
Other than seeing the operational state of A or A/B on  a scope or test equipment, no one can "hear" such conditions.

A  "matter of fact" from the wisdom is needed  to clarify my unqualified babble based on taking 101 electronics decades ago. 

Clas A amps DO NOT always sound better.
They should in theory perhaps but this ain’t theory now is it?
Provactive silly question.
Of course not what you mean.
Who cares whatever that is?
Yes, mapman, done right they do. 
Gryphon, Accuphase, Pass, Luxman etc.
"Some feel" funny things, that's for sure.
D'Agostino amps might be an exception in that they are top level and can compete with almost any SS.
Class A amps require devices that can handle more current or more devices in parallel in order to produce the same power. Higher capacity devices or more devices in parallel (or both) add complexity and force the driver stage to work harder. This is not "free" from a performance (sound quality) perspective. So it's not at all clear that a class A amp will sound better than a class A amp, and certainly not for the same build cost. 
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Miller, what's wrong ? Give us an example. I'll give it myself. Gryphon Diablo 300 class AB integrated sounds better than Sugden class A integrated. But it's not a fair comparison, not what I mean, of course.

Well honestly now I don't know what you mean. In the OP you say "Class A always sounds better." But you just gave an example where you yourself say class AB sounds better. So you disproved your whole point. While proving mine: Class A does NOT always sound better. But then you ask me what's wrong? Nothing wrong. I am right again. As per usual. 


It's just too hard to keep the snark in, right?
Haven't we all had enough of such meanness?
Because Class A does not always sound better. Obviously.

They always do, but it has to be the same amp designed to take both settings low Class-A bias and high Class-A bias without being stressed.

Halo JC1’s always sound better in high class-a bias
Gryphon Antillion always sound better in the highest class-A bias
etc etc etc

The more and more class-A bias the less xover distortion there is and so on the louder you go, on and on till the amp reaches clipping when the amp is in full class-A never switching off either complimentary side of the push pull transistors. Then there's single ended class-A tube and SS but they have to be either capacitor or transformer coupled, not my cup of tea.

Cheers George
Audiophiles love some things.
If distortioin is kept low, no audible difference.
Today you can have really good sounding amps in A, AB or D designs.
So preference rules here.


Class A amps (almost) always measure better, not sound better.
Always "unless" the power supply/s can't handle the extra juice need for the higher class-A biasing, then they do sound worse.

Cheers George
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Class A runs very hot and very inefficient , big watts in pure class A is big bucks .
that's why excellent amps ,integrated like Coda give you that option how much bias into class A ,my CSib integrated is close to 20 watts into pure class A , before going to class AB seamlessly to 150-300 wpc If you speakers are fairly efficient 
the amp rarely would ever leave pure class A .
The build quality and engineering skill has everything to do with the end results.
pass labs, class A monos , Coda 16  amp just as a sample just in the U.S  alone.
In Europe Denmark makes several superb class A Amps , as well as classA-AB amps . For power hungry maggis you may need a Big power amp in Class AB 
there are even. Excellent ClassD amps and hybrids that sound good 
and many lower powervacuum  tube amps are in class A up to around 20 wpc and sound very good ,each amp has its own sonic signature.
your speakers have Everything to do with the requirements of your amplifier
and what sound you prefer.
ducati1098rr22 posts
Wow the viper is drawn to another thread.
For a 22 post member who stalks, your way too uncool/and technically inept to associate your self with Ducati, better suited to mo-ped.
Stick to what you believe in, in those little black dots https://ibb.co/LpDpf3f

Now, now George. You are starting to sound as narcissistic and ill tempered as MC. 
Oh puhleeeze, everyone knows that Qobuz streaming in HR through a  Hybrid-Digital Purifi Eigentakt amp sounds better than a record player through A or AB.  C'mon out of that dark ages cave you analoggers are in...
There have been only a handful of true class a amplifiers made it takes a lot to make one and very few have ever accomplished it. In solid state amps only a handful and in tube only a handful also they are incredibly difficult to make and unreliable due to heat generation because of the 10 percent efficiency. So most of the makers if not all stopped making them. Now most makers build an amp to play class a to a certain watt level then switch to ab mode because of this and this results in the amplifier still sounding like a class a amp because it is at low powers.
Miller didn't say a bad word. If he wants to sound right - fine.
Going too far into the subjectivity will get us nowhere.
I mentioned D'Agostino class AB amps as being more than competitive.
Maybe his class A amps would've sounded even better. I bet, he didn't want huge size and heat, so he opted not to do it.

I can chime in on this. I owned a Plinius SA-103 @ 220w into 4ohms which is class A biased driving a pair of Legacy Audio Focus speakers @ 95.4 db sensitivity. I always felt like it lacked power. Indeed, there were certain passages where I would drive it to clipping. One of which was Loreena McKennitt’s vocals on the Dante’s Prayer track from the Book of Secrets album. I decided that was unacceptable and that I needed more power. I sold the SA-103 and purchased a SB301-MKII class A/B which is 470 watts into 4ohms. The difference was amazing. I had all of the great Plinius sound and none of the "lack of power" issues. The bass was driven with much more authority, the highs were crystal clear and well defined. I wasn’t quite sure what to expect but now I wouldn’t trade my amp for anything. YMMV but in my experience the additional power of the class A/B amp trumped the class A hands down.
I am sure George and some others could offer an explanation of what happened beyond just formal power ratings.
I like Loreena and Dante's Prayer track is one of her very best. 
I am sure George and some others could offer an explanation of what happened beyond just formal power ratings.

Here we go, watch out for the flame throwers !!

Stereophile: Legacy Focus
Not only are there two minima in the bass of less than 2 ohms, and another of less than 3 ohms in the mid-treble, but there is an amplifier-crushing combination of 3.3 ohms magnitude and 60 degrees capacitive phase angle at 20Hz. Fortunately, it is rare in music to have high levels of energy this low in frequency.
They Legacy’s might have been 95db, but they were a "savage load" for any amp right through the bass up to 150hz, 1.8ohm load with 40 degrees of - phase angle 55 at 30hz!!! that could simulate lower to the amp in the bass

Especially bad for complimentary push pull Mosfet amp with a lot of A bias they don't do current very well into low impedance.
Bi-Polar amp (BJT’s like Ago, Gryphon, JC1 Krells would have far better with these sort of speakers)

And what looks to me like a "average amount" of storage reservoir capacitance for a Class-A especially, may have the watts, but looks like not much for reserve for current. Sure it got 2 trannies but where’s the massive stack of power supply caps

Cheers George
Very interesting topic.  My partner and I just finished building a pair of mono block El-34 pure Class A power amplifiers.  Took them to a customers home to compare to his Jeff Rowland Model 7 mono blocks driving Mirage M-1si speakers, probably like 85 db.  The Rowlands controlled the bass a little better (Update - just added a larger capacitor size and the bass was even better with the Class A amps but we would have to go back to compare).  The rest as they say is history. The Class A had tone, musicality, dimension, that made the music so beautiful, piano was just stunning.  We were stunned on how good an old Cat Stevens CD sounded and a few tracks of the old Jeff Beck CD Blow by Blow, Santana Abraxas, etc.  The guys wife's eyes actually teared up.

Oh sure like someone already stated above, it comes down to the design implementation.  There are some Class A amplifiers that probably are not as good sounding as class A/B amplifiers, I have not heard every single one of them so who knows but in designing amplifiers, we have not been able to make one that sounds better to our own ears.  Do Class A products run hot, sure do.  Does that mean they won't last as long, no it does not.  As for head room, that depends on the design - that can happen with any amplifier not matter how many watts they are rated.  But the pair we just finished are simply killer!  My Vandersteen Model 5As never sounded so good.

Happy Listening.  

Mirage M-1si speakers, probably like 85 db.

Nice speaker BTW.
M1’s are nowhere near as bad a load as the Legacy’s above
The Mirage M-1si’s impedance curve in fig.1 indicates a load which should be easy to drive.

Cheers George
Class A does NOT sound better (as the thread starter claimed). I owned pure class A Krell monoblocks which definitely didn’t sound better than my current Pass Labs class A/B mono blocks. This statement of the threadstarter is way too general ...just like a V8 is always faster than a V12 or boxer 6 .... 
I had a lot (or heard -) of class AB amps (high-end): Luxman, Esoteric, Hegel, Audio Analoque, Jeff Rowland, Accuphase, Mark Levinson, d’Agostino,...not of them all ,sounds better than Ear Yoshino 509 monoblocks or Wavac MD 805m. : the purity, detail, 3D. If you really enjoy your music, this is the best. You can’t put it very loud,  but you have to to really enjoy it. Tubes get warm and have to be replaced after a while,but a real music lover will take that in. In transistor, I had a few class A amps:some of them sounds to “dark”, detailfull,rather “flat”.
Class A does NOT sound better (as the thread starter claimed).

He doesn’t mean different manufacturer amps.
The same amp/s will sound better without any xover distortion, and the way to get it is with more Class-A bias if all else can take the extra juice that it needs to do take that extra class-A bias, and it will sound better for it.

Just have a listen to the Halo JC1 monoblocks they have a switch on the back that raises the Class-A bias quite considerably, you clearly hear which sound better, same with the Gryphon Antillion with it's switchable bias.  
Cheers George
It’s satisfying to see there is still some original member’s left here on audiogon with substantial exsperince, that said, I wanted to thank georgehifi, and bigkidz that know the truth about class A bias amplifier’s. Of all people, me and inna know about over blown publicly about an audio product, we both had a Luxman L-509X integrated amplifier at the same time, we both burned in the amplifier, turned out the amplifier had exaggerated treble that did not sound like the real event that is on stage, the bass was weak and not fulfilling, the mid-range was terrible, the sound stage was subpar at best, needless to say we both sold the amplifier’s at a big loss, 8 or 10 months old New!, I already own my main system through all this witch is pure class A system running class A digital direct to the amplifier that is class A, as bigkidz said in his post, very emotional real sounding system, this system made red neck’s cry, LOL!!!
class AB is MUCH more efficient.
class A produces an INCREDIBLE amount of heat, at idle.
Anyone has Mark Levinson ML-2 to spare ? I don't think so. Old Gryphon ? Nothing again. Very bad.