Class A vs class AB output tube distortion

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2/23/2000 8:32 PM
Max	Class A vs class AB output tube distortion Hi!     It's me again; I'm rather full of questions today.   I wonder, which is the best output tube distortion,class A or class AB one?     Thanks and best regards.     Maxx.

 

2/23/2000 9:08 PM

R.G.

Re: Class A vs class AB output tube distortion. This is a serious reply, in spite of how it sounds. There are so many different kinds of distortion that you have to decide what kind of distortion is "best" before you can decide whether Class AB or A sounds better.     Class A will have in general only grid-conduction distortion, while AB will have that as well as crossover distortion. Crossover is usually considered to be an ugly sounding distortion.

 

2/24/2000 3:44 AM

Todd

In addition, most of the distortion you'll probably be   comparing is Class AB distortion, unless it came from a   single-ended amp like a Champ, because there are so few   push-pull Class A amps out there. Maybe you've heard an   Alessandro English Coonhound or a similar pure Class A   amp (Vox AC-30 and Matchless are Class AB and cathode-   biased), but most of the amps on the market are Class AB.   Like R.G. said, you gotta pick out what "best" means as   far as distortion goes for you and go from there. Bon   chance!   TJK

 

2/24/2000 5:45 PM
Max	Thanks a lot guys!     Todd,don't say this to ken or few others;well i mean that the ac30 and matchless are class ab.Hush!Or you'll start an another class A/AB war!(g)     Thanks again.   Max.

 

2/25/2000 5:10 AM
Charlie	I was under the impression that a Vox Ac-30 was Class A push pull.     Charlie

 

2/25/2000 2:54 PM

Jim S.

It all depends upon where you draw the line. Most amps that are referred to as "class A" amps (such as Vox AC30 and Matchless models) don't really stay within true class A operation when they are cranked up all they way and the power section is clipping. At high volume levels, the power tubes will approach and then reach cutoff during one half of the signal cycle.     Also, keep in mind that, at low-volumes, a properly bias class AB amp will actually be running in class A operation. In other words, the signal to the power tubes is low enough that they don't reach cutoff at any point in the cycle.     Sometimes people will refer to the Fender Tweed Deluxe as a class A amp. Actually, it's a cathode-biased class AB amp that is biased on the "hot" side of class AB. So it has more of a class A "mix" to its class AB operation than larger, more powerful fixed bias amps.     Personally, I don't have any problem with calling cathode-biased EL84 amps such as AC30 "class A". As they say, it's close enough for rock 'n roll.

 

2/25/2000 5:47 PM
Max	Todd,i've told you,here it goes again. :o) Hi everybody!     Todd,i've told you,here it goes again.(g)     Best regards.   Max.

 

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