Class A versus A/B

opusarlo

Active Member
OK, I have scoured the web tonight while working in the hopes of learning why people pay massive dollars for those huge class A amplifiers. The irony is, the more i read about them, the worse they are for everything. power hungry, inefficient, hot...so then, why would I want to spend the long dollar on a class A or class A - A/B? Why not just get the more efficient class A/B?

Not a troll post..I am on the cusp of purchasing an amp and want to learn why the Adcom 5802 commands around 1000-1500 while a Yamaha MX-630 "Class A" can't even crack $1k.

Please be gentle. I am still learning here. My goal is to have a system capable of handling a pair of Maggies...i hear I need between 300 and 500 WPC
 
I have worked on many class A / AB amps and usually I can't hear the difference between the 2 modes. The one time I heard a difference I thought it sounded more harsh in class A, and the amp was working properly. A class AB amp, when properly biased, has negligible crossover distortion. You can't see it on a scope. I am not going to say it isn't there, but you can't see it, and I contend it is inaudible.
 
Most Magnepan speakers need quality high current amplification over quantity amplification.

I think Levinson really was the first to step up with a class A amp back in the late 70s and their impact in the marketplace seemed to be the seminal movement into the huge marketing hype leading to many Class A marketing schemes.

As the doc stated, a class AB amp properly functioning has so little notch distortion it is not audible.

Almost all amps have some parts of their circuits run class A, but there are many other, much more important factors, to consider in finding the right amp to run any particular set of speakers not the least of which is getting the speakers to work with your room not have them work against each other.
 
I can’t really tell the difference between Class A and Class A/B modes on my Yamaha M-45. It does run significantly hotter in Class A mode since it is biased higher by a factor of ten, but I usually just run A/B.
 
The reason why Class A is so fancied by 'high-end' aficionados is the brute force approach to solving a problem of amplification. Something like huge and heavy loudspeakers as an attempt to counter resonances or 1000lb turntables made of steel.

A medium power class A amplifier needs to be heavy (due to the large transformer and heatsinks) and big (to house these big things) and even heavier (to provide a sturdy frame and enclosure for all that heavy stuff. In theend you get your weight in equipment (or twice that if you are slender) and you have to pay an arm and a leg (or two) to get them.

Another reason class A amplifiers may have such a following is that they produce mainly even order harmonic distortion while class B and AB produce odd order harmonics. And tube amplifiers produce (lots) of even order harmonics. And it has been observed that we - humans - tend to enjoy even order harmonics more. So class A solid state amplifiers may exhibit a "tube sound".
 
I think the reality is that most amps promoted as "class A" are pseudo class A, they do not really meet the accepted engineering standards for that type operation.

Except for the handful of models made by Levinson, Krell, Threshold and and I believe spectral most all ultimately switched into class AB at higher output levels.

As in the Maggie question about compatibility with a Mac amp in the McIntosh forum, getting the right speaker location in the room will mean more to the best sound than the amp, especially the amp class.

The OP is making quite the jump to the other side of the speaker spectrum......going from horn based speakers to sheets.
 
Do you understand the classes of amplification?
A Class A amplifier is biased so that the output devices are "on" all of the time -- it is dissipating essentially full power whether it is amplifying signal or not.
Thus the heat and inefficiency.

A Class A (single-ended) amplifier has two properties that may have audible consequences relative to a Class AB or Class B (push-pull) amplifier.

1. Class A has no crossover distortion.
2.
The harmonic content of the harmonic distortion produced by a Class A amplifier is profoundly different than that produced by a Class AB or B amplifier. Class AB amp topology cancels out even order harmonics; Class A does not. The spectrum of distortion products of a Class A amp shows predominantly lower order, even harmonics; Class AB or B amplifiers show mainly high-ish order, odd harmonics. Even harmonics are euphonic (they sound good); odd order harmonics are dissonant and generally are thought to sound bad.

Note that these two comments hold regardless of whether the output devices in the amplifier are vacuum tubes or transistors.

If you need 300 to 500 watts per channel, I'd recommend a Class AB amplifier. I don't think Class A amplifiers of such power output are practical (although there have been some).
Actually, that was a very clear comparison. So, class A will sound much better than AB. With that said, if my amplifier uses class A up to 50 watts I will enjoy the sound up to 50 watts more than the sound after that. If I need juice for 110 dB pipe organ sequences playing through a pair of maggies, I will be happier with something more along the lines of an Adcom 5802 or maybe even a big old Rotel. Did I get that correct? The difference is in the sound quality and not volume, right?
 
Look at class D amps like Crown XLS and many others.

MX-630 is an A/B amp.
I have an iNuke already for the 2 subs, but I don't want class D for my mids and highs. want a versatile core setup that I can use for any number of circumstances including big maggies
 
I have worked on many class A / AB amps and usually I can't hear the difference between the 2 modes. The one time I heard a difference I thought it sounded more harsh in class A, and the amp was working properly. A class AB amp, when properly biased, has negligible crossover distortion. You can't see it on a scope. I am not going to say it isn't there, but you can't see it, and I contend it is inaudible.
This was very reassuring to read. One less thing to worry about. This makes my buying choice so much easier. Thank you
 
The reason why Class A is so fancied by 'high-end' aficionados is the brute force approach to solving a problem of amplification. Something like huge and heavy loudspeakers as an attempt to counter resonances or 1000lb turntables made of steel.

A medium power class A amplifier needs to be heavy (due to the large transformer and heatsinks) and big (to house these big things) and even heavier (to provide a sturdy frame and enclosure for all that heavy stuff. In theend you get your weight in equipment (or twice that if you are slender) and you have to pay an arm and a leg (or two) to get them.

Another reason class A amplifiers may have such a following is that they produce mainly even order harmonic distortion while class B and AB produce odd order harmonics. And tube amplifiers produce (lots) of even order harmonics. And it has been observed that we - humans - tend to enjoy even order harmonics more. So class A solid state amplifiers may exhibit a "tube sound".
This helps a lot - I only listen to pipe organ, and even then only angry pipe organ and I listen at very high volumes...Class A does not seem to fit into that equation very well. THank goodness...I could never stomach paying 12k for one monoblok...hell no.
 
What Magnepans? What size room? Seriously doubt you need that much power.[/QUOTE
in the world of hifi, who would ever focus on what they need? lol. I just hear Maggies like power so Imma givem them all the power they may need. I have my iNuke set to pour 2k wpc to subs that are each rated at 1k rms. I did not do this because I suck at number. I did this because of the 40-50% rule...make your audio gear work at 40-50% of its capacity for the most efficiency.
 
Actually, that was a very clear comparison. So, class A will sound much better than AB. With that said, if my amplifier uses class A up to 50 watts I will enjoy the sound up to 50 watts more than the sound after that. If I need juice for 110 dB pipe organ sequences playing through a pair of maggies, I will be happier with something more along the lines of an Adcom 5802 or maybe even a big old Rotel. Did I get that correct? The difference is in the sound quality and not volume, right?

Class A does not necessarily sound better than A/B, there are a lot of different bias setups.
 
Which is your local reference.....St Marks, laGrave, Fountain St. or Park?

Most of the local organists in GR back in the day used various dual woofer Mac speakers and when we got their new offerings on display they all would show up to audition the new products. I did voice many of them with the Mac MQ equalizers to solve some of their room boundary issues.
 
I think the reality is that most amps promoted as "class A" are pseudo class A, they do not really meet the accepted engineering standards for that type operation.

Except for the handful of models made by Levinson, Krell, Threshold and and I believe spectral most all ultimately switched into class AB at higher output levels.

As in the Maggie question about compatibility with a Mac amp in the McIntosh forum, getting the right speaker location in the room will mean more to the best sound than the amp, especially the amp class.

The OP is making quite the jump to the other side of the speaker spectrum......going from horn based speakers to sheets.
It would be much easier to understand my motives after you listen to Widor's concerto 6 in G minor for pipe organ. I recommend you listen to Jan Kraybill's performance. Listen to it between 100 and 110/115 dB. I have extra horns (Altec 508 B) on top of my Cornwalls just because the pipe organ destroys the highs in my Cornwalls when I crank it. I also have a modest stack of subwoofer repair receipts from my Cornwall subs because pipe organ also eviscerates Cornwall subs. Pipe organ music is quite literally a music of mass destruction if you do not tweak your system just for it. This is why I am going with Maggies and 2 infinite baffle subs along with a DAC and DSP.
 
Which is your local reference.....St Marks, laGrave, Fountain St. or Park?

Most of the local organists in GR back in the day used various dual woofer Mac speakers and when we got their new offerings on display they all would show up to audition the new products. I did voice many of them with the Mac MQ equalizers to solve some of their room boundary issues.
I sincerely prefer the hidden gems. For instance, Coopersville Christian Reformed church has an amazing pipe organ of 1700 pipes. There is also St. Paul's Episcopal organ (muskegon) with 3000 pipes...what a beast...I tend to stay away from mainstream organs. Thank you for asking. Do you play? Also, have you been to the house on 3rd street that has an entire organ installed in it?
 
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