I believe the advantage of class A is that the tubes don't go into cut-off so there is no crossover distortion.
Single ended class A will not cancel 2nd order harmonics created in the output stage so there is less harmonic distortion. Maybe that is why people say class A is more "muddy" or "warm".
I thought instrument pushpull tubeamps were classAB
and only the very small single ended guitar tubeamps would be classA
I thought instrument pushpull tubeamps were classAB
and only the very small single ended guitar tubeamps would be classA
Not true, there are some boutique guys that use class A push pull like Allesandro. He gets 10 watts from two EL84's.
Class A p-p amps do not have the dynamics that a AB amp would have. You do not get power supply sag with Class A. You can also get more dynamics due to the voltage on the screens changing. Class AB can also get pushed to the point where you get crossover distortion which also brightens up the sound. Also Class AB amps tend to run higher voltages than a Class A amp. This also can brighten up the sound. Mind you how all the parts of the amp has to be thought of as working as a whole. An AB amp can also end up sounding harsh rather than open if things are overdone. I see no reason a Class A amp needs to sound muddy, just choices the designer took if it does.
I meant single ended will have more harmonic distortion, jeez must have been a long day for me
As you can see from the responses, as an absolute statement "Class AB Push-Pull sounds less muddy than Class A" is not necessarily true. Of course "muddy" isn't exactly a technical term, but I'll assume it means the amp has booming bass that throws off the tonal balance as both sorts do pretty well in the highs. (Normally, I'd say the cause of "muddy" sound is a lack of highs that results in poor definition of the bass and mids, but neck pickups are also called "muddy", and it's because there's much greater bass response in the neck position regardless of the pickup you use.)
In short, Class A amps are mostly practice amps, where "small", "cheap" and "quiet" are the design goals. Thus, they tend to use small tubes, such as the 6V6 and the EL84, which don't have the tightly defined bass their bigger brethren have. The also have small OTs and smaller power supplies. So yeh, in general, real world Class A amps are muddier.
As a generalisation, though, there is some truth to it. That's because in general, if you're talking a Class A guitar amp you're likely talking about a Fender Champ. Single ended, 6V6. Try a "typical" Class AB amp, and we're talking about a Super Reverb (et alia) with push-pull 6L6s and yes, you'll get much tighter bass response. Thing is, 6V6s are flabby in the bass. A push-pull 6V6 amp like a Deluxe will fall in the middle, and a 6L6 SE amp (if you made one) might even have tighter bass than the Deluxe.
In short, Class A amps are mostly practice amps, where "small", "cheap" and "quiet" are the design goals. Thus, they tend to use small tubes, such as the 6V6 and the EL84, which don't have the tightly defined bass their bigger brethren have. The also have small OTs and smaller power supplies. So yeh, in general, real world Class A amps are muddier.
Another thing to consider is that class AB1 amps are running class A at low power levels. Do they sound muddy under such conditions?
There are some amps are heavily biased into class A so that they don't transition to class B until driven hard. The VOX AC-30 is one such amp that has a reputation as actually being a class A amp.
Is the Vox AC-30 really class A?
There are some amps are heavily biased into class A so that they don't transition to class B until driven hard. The VOX AC-30 is one such amp that has a reputation as actually being a class A amp.
Is the Vox AC-30 really class A?
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