can someone please give me the definition of Class A?

[versuviusx]

hi i was wondering if anyone could give me a definition of class A circuitry?
what are the prerequisites of it being class A?

[ulriggribbons]

A class A amplifier stage basically means that the device (be it tube or transistor) is conducting current throughout the complete cycle of signal swing. think of it as always on.

It is the most linear(has the lowest distortion) of the different class operations, but also the most inefficient. I'm sure this is all over the net. google for Amplifier Classes or Amplifier Design.

Edit: Check this pdf from Crown Audio:

http://www.crownaudio.com/itech/pdf/137234.pdf

Regards

ju.

[Stephen B.]

The way I understand it is to think of our trusty sine wave. In a class A amplifier, the amplifier will amplify the whole wave. In an alternative called Class AB (or push-pull in the hi-fi world) the signal is first split into two parts, the positive voltage and the negative voltage and amplified separately, then recombined. Does anybody know if there are other ways other than class A or class AB?

[soundguy]

A google search wil churn out more info than you thought possible, perhaps challenging the notion that the internet is for porn.

Im all for knowledge, but understanding theory of operation probably doesnt translate to a whole lot for someone just starting with this stuff.

The most important thing to realize is that if your amp isnt class A, it isnt a big deal, like, AT ALL. Marketing people have turned a tech spec into jargon which makes you wonder how long it will be before we see people advertising that they have .03 percent total harmonic distortion. Considering that we already see idiiots advertising that their shit has great third harmonic distirtion, something tells me we wont see THD specs in the ad...

At any rate, fender never made a class A amp [edit: reading this over Im wrong about this, but probably %97 of their designs were push pull a/b). Didnt really hurt fender too much, did it? I think the only marshall that ran class a was the 18 watt blluesbreaker combo. A vox ac30 is a class a guitar amp. The "black" 1176 that people fiend over came in several versions, some with a class A output stage, some with a class AB output stage. Yes they sound different, yes daily people are fooled that all "black" 1176's are the same. Neve 1073's are class A. 1081's run class A throughout the EQ but the output stage is run class A/B. There are many many many many neve consoles that use class A 1073's on the input but then use class A/B amplifiers for the mix buss makeup gain, meaning that the entire sound of the console, before it hits the world, runs through a class AB summing stage. Also worth noting, with a passive mix buss, the buss amplifier design is especially critical, yet neve went with a class a/b design. Not all neve consoles that use class A EQ's are run entirely class A. Why might you ask? Because the consoles were designed to SOUND COOL not look cool in an advertisement, so the appropriate cool sounding summing stage was applied for the righteous sound.

If I was given the task of putting together a studio with an entirely class a/b signal path, it would so not be a limiting factor on any level whatsoever. You could still have all the best shit ever made and make recordings that would totally slay if you knew what you were doing.

By all means learn about this stuff but dont think for a second that there is some paradigm of audio that class A brings that is just so beyond the pale of everything else causing you to spin out into thinking that you need to buy even MORE shit that cant afford.

dave

[ulriggribbons]

game... set... match.... soundguy

[vatoben]

here's another good explanation:

http://www.mesaboogie.com/US/Smith/ClassA.htm

[joel hamilton]

Like Dave said. AND: It depends on WHOSE class "A" or "AB" you are talking about.None of which makes something the holy grail of audio. The fender amp is the PERFECT example. "didnt hurt them too much." Awesome...

The output stage in certain 33609 (neve compressors) is A/B, and that didnt seem to bum anyone out either... There are a zillion exam,ples of a "push pull" amp design that rocks...

[Zeppelin4Life]

Basically class A has a continous signal ALWAYS flowing. the result is more pristine audio quality. the downside is it tends to be less efficient. Leave a bunch of class A pres on all day, your power bill will be significantly higher than a few B or AB. thats true. but if your buying a class-A anything you can probably afford that, right?

As for guitar amps, the AC-30 seems to the be the standard when it comes to class-A output

[soundguy]

Basically class A has a continous signal ALWAYS flowing. the result is more pristine audio quality.

this is absolutely dependant upon the design and by no means proxy of all class A designs. I'll let you listen to some class A designs I have done and you can hear how terrible class A can sound. You comment is also completely subjective.

dave

[Zeppelin4Life]

.What the signal flow? wrong. class-A always has a continuous signal, its part of its guts. Soundwise? well, of course that it varies, plus people have very strong opinions (no shit, welcome to audio!) but this is a Class-A vs. Class-X (B, A/B, D)...as if we had the same pre build..so theoretically, you cant argue that Class-A is not supposed to sound better. Countless bassists hate tubed amps. i know many drummers who use piccolos as main snares. O-P-I-N-I-O-N! But you can't argue with the science of it..never

For the poster, Incase your wondering

Class-B is a little more efficient, it uses two 'push-pull' elements. Prone to cross over distortion (due to the two amps switching)

Class-A/B-Similar to B, but like A in the fact that no driver is ever completely 'off'. some distortion, but very smooth compared to B in terms of cross-over. Still a little more efficient that A

Class-C. youll probably never see this in Audio.I've heard of them in RF radio stuff. biased below cutoff, I believe

Class-D. digital in a sense. but thats all I know..this is also rare.

[soundguy]

.What the signal flow? wrong. class-A always has a continuous signal, its part of its guys. Soundwise? well, of course that it various (no shit, welcome to audio!) but this is a Class-A vs. Class-X (B, A/B, D)...as if we had the same pre build..so theoretically, you cant argue that Class-A is not supposed to sound better. Countless bassists hate tubed amps. i know many drummers who use piccolos as main snares. O-P-I-N-I-O-N! But you can't argue with the science of it..never

Considering that you did a fine job of laying out that opinion is the bottom line of evaluating what comes out of a speaker, its moronic to sugges that simply because a amplifier is continuously conducting that it sounds better as you sugggested with your statement "basically class A has continuous signal ALWAYS flowing. the result is more pristine audio quality". If you want to discuss facts that you can look at on an oscilloscope and hope to have people take you seriously, do not back them up with a completely subjective opinion on the subject. This is my big problem with the current trend in advertising rigth now, saying something is operating class A as if to suggest that its some kind of plus feature. Who gives a fuck how your circuit is working if it doesnt sound good. Desinging a circuit in class A does not mean you are going to get more pristine audio quality. All it means, pretty much to me is that you are gonna get, in most examples, maybe more heat disapation and thats about it. Desinging a circuit that is running in class A any given percentage of the time just means that as a designer you've chosen a mode of operation that has advantages and disadvantages both of which need to be taken into consideration to get the most "pristine audio quality" out of the circuit which of course is completely subjective so far as the designers taste and operating goals of the citcuit concerned.

dave

[Zeppelin4Life]

Desinging a circuit that is running in class A any given percentage of the time just means that as a designer you've chosen a mode of operation that has advantages and disadvantages both of which need to be taken into consideration to get the most "pristine audio quality" out of the circuit which of course is completely subjective so far as the designers taste and operating goals of the citcuit concerned.

I tihnk you frogot smoe periods in their, man.


but to make this post worthwhile, everything you say is true. but I was trying to point out that the general idea of class A is that it is of higher fedelity. it might not be for everything, and sometimes it doesnt sound better. thats the answer. but theoretically it is.

Class A:
-Continuous flow of the cycle
-'pure' with no cross-over distortion/error
-generally expensive
-excess energy (lots of xtra heat), inefficient

[wardshorsehead]

im only 16, what the hell do I know?

sorry, but while dave's passion for shit to sound good can sometimes cause him to forget common courtesy, this isn't one of those times.

a little manners goes a long way, hype is hype, and dave is right.

that'll be $35 dave.

frank

[joel hamilton]

The compressor I used for the vocals of Frank Black, Ludacris, and Nina Persson is not class A. The mic pre I used to record the guitar of Marc Ribot, Mark Linkous, and Frank Black is not class A..... All of that was fine for those people, seemed to work out okay.... I never even for one second thought about that. I just went with my gut as to what would flatter the performance.I only reference the names because they have a budget, so if we needed everything to be "the best" we had it. Not once was anyone, (even the A&R guys!) like "are you sure you want to go with a class A/B output stage on that???"

If you ae a tech, this will matter a lot I guess. I am not, I record music, and other annoyances

[MD]

As for guitar amps, the AC-30 seems to the be the standard when it comes to class-A output

Great stuff everyone. Very educational for me.

In case you every want to know more than you want to know:

http://www.aikenamps.com/VoxAC30classA_2.html

-MD