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class A class a/b whats the difference
Old 13th September 2007
  #1
Gear Addict
 

class A class a/b whats the difference

Someone asked me this today and I couldnt give them an answer. I was told if something was class A that said something about the components in the preamp. But then I was told NEVE isnt class A at all so I kinda wrote off the difference. What is the difference?
Old 13th September 2007
  #2
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it's primarily a power amp issue... in a class A amp the transistors/tubes are on full tilt boogie all the time which tends to make them inefficient as hell but sonicly they tend to shine... as opposed to an A/B where one side of the amp is off and the other is biased barely on the 2 sides then alternate for positive/negative going signals also known as a push/pull amp...
Old 13th September 2007
  #3
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Gregg Sartiano's Avatar
 

The "Search" function won't let you search for class A (words need to be 3 characters min.), but if you do it in quotes, you'll find some threads & posts.

"Class A"

or

"Class AB"
Old 14th September 2007
  #4
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PhilE's Avatar
Quote:
Originally Posted by dementedchord View Post
it's primarily a power amp issue... in a class A amp the transistors/tubes are on full tilt boogie all the time which tends to make them inefficient as hell but sonicly they tend to shine... as opposed to an A/B where one side of the amp is off and the other is biased barely on the 2 sides then alternate for positive/negative going signals also known as a push/pull amp...
The Class A thing is a matter of taste, I personally like a lot of the Neve Class AB more than the Class A for the punch and transient speed they deliver. The richness of a class A amp is nice for other things but give me AB for drums any day.
As for Neve not being Class A that depends on which unit you are using.
Old 14th September 2007
  #5
Gear Guru
 
kafka's Avatar
I'd rather not discuss the technical differences between the two here, as there is plenty of excellent material on the web already. If I had to characterize the sound, I'd say that a class A/B amp has a tighter bottom end, and a class A has a more detailed upper mid and clearer highs. I suspect that my experience is less a characteristic of the class and more a characteristic of the amps that I've actually used.

The OP mentioned Neve in their initial posting. I don't really know their schematics well, so I can't say that Neve didn't make a class A/B preamp. However, the main reason for going to A/B is power efficiency, which isn't nearly as much of an issue with a preamp. Even in a guitar amp, it's only the very last stage that would be A/B. Every time a stage is based on a single triode or transistor, that stage will be class A.
Old 14th September 2007
  #6
Moderator
 
Tim Farrant's Avatar
 

Here are a few threads which discuss the subject

Is a Trident Fleximix pre a class A circuit?

Class-A??
Old 14th September 2007
  #7
Gear Addict
 
Capstan Cappy's Avatar
 

1.Class A amplifies in the most linear part of the curve and AB does not
2. CLass A always has its transistors open explaining the power consumption and its effeciency wich is low, AB is half open and therefore is more efficient..BUT Class A does not have any cross distortion while AB has some, and B has a lot more
3. CLAss A has less harmonic distortion (not by definition but a good design does)

colour and performance of both depends on the components and design, enouf CLAss A have tight bottems etc , but this we already knew
all depends a bit of expereince people had with both classes to describe characteristics i guess
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