Class A Electronics

  • Thread starter Thread starter Whiskey Jack
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Whiskey Jack

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Hello all,

I am wondering if anyone has can tell me exactley what 'class A' means. This term is thrown around consantly by musicans and sound techs in an attempt to sound knowlegable, but I've yet to meet someone with a good understanding of the concept,

Can anyone help?
 
I'll try. :p


In a class A piece of gear, one device (tube or op-amp) is used to amplify a signal.

In a non-Class A device, separate devices are used to amplify the positive and negative halves of a signal. When the signal aproaches 0, one shuts off and the other turns on. There are various classes that do this, and they can all sort of be lumped under the heading "push-pull".

The benefit of Class A is that the signal never has to switch from one device to another. This switching causes a certain amount of distortion, called crossover distortion.

The drawback of Class A is that since one device handles the whole signal, it is always on. In a push-pull circuit, each device is off for half the signal swing. This lets each tube or op-amp run cooler, and the device will run cooler overall. Also, since only one device is handling the whole signal, the amount of amplifying it can do is limited. This is the reason high-powered tube amps use push-pull circuits in the power section.


In a tube guitar amp, for instance, the pre-amps are almost all class A. The power amp sections are mostly push-pull. When someone talks about a Class A tube amp, they mean the power section.
 
EC gave you the technically correct answer, and here's the wise crack answer. Which is every bit as correct:

Calling a device "Class A" is a marketing ploy to justify charging 4 times what the amplifier is worth.

I'll add that any competent circuit design engineer can make a non-Class A amplifier with distortion 1000 times lower than anyone could ever possibly hear.

--Ethan
 
Ethan Winer said:
I'll add that any competent circuit design engineer can make a non-Class A amplifier with distortion 1000 times lower than anyone could ever possibly hear.

--Ethan
Click to expand...
:)

Yes indeedy, thanks. And a shitty Class A piece is a shitty piece, period.
 
thanks, a bunch.

I was tending to think that was the case but wasnt sure if it was my cynical attitide towards flashy talkers that was clouding my judgement.

The technical description does help alot also.
 
Class A is where the transistors (fet, tube) are biased so that they alway conduct electricity. The transfer curve of a device has nonlinear areas where it starts conducting and where it saturates (low conduction and high conduction areas). In class A the signal is confined (by the design) to the linear area between. THis is the defination of class A.

-REgards,

PS Nice to see another Ethan onthe list!
 
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