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Class D vs Class A or A/B

#44
seamonkey said:
You know it's not, but the other metrics are also below human hearing.

Those moving to class-d can comfortable move knowing there is not compromise in sound.
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except the onset of clipping is absolutely dreadful. I would rather have an amp that has a little bit of THD all the time and gradually gets more HD asit approaches clipping than one which stays clean until it goes over the cliff.
There is also that no class of amp is inherently better.
Class A has better clipping characteristics.
Class D has better power to weight ratio.
Class AB is kind of the goldilocks of the two, though of course that can depend on how it's implemented. I have heard some horrid clipping from AB amps of course. But then there are AB amps that go into and out of clipping without batting an eye. None are as good as Class A, but 500 watts of class A would be insane.
 
#45
Calaverasgrande said:
except the onset of clipping is absolutely dreadful. I would rather have an amp that has a little bit of THD all the time and gradually gets more HD asit approaches clipping than one which stays clean until it goes over the cliff.
There is also that no class of amp is inherently better.
Class A has better clipping characteristics.
Class D has better power to weight ratio.
Class AB is kind of the goldilocks of the two, though of course that can depend on how it's implemented. I have heard some horrid clipping from AB amps of course. But then there are AB amps that go into and out of clipping without batting an eye. None are as good as Class A, but 500 watts of class A would be insane.
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I think this is a pretty simplistic generalization IME.

There are class A topologies that are just as dreadful as some class D topologies with regards to clipping.

Every topology and class of amp, IF well designed to address this, can enter and exit clipping just as gracefully. This is one (of many) attributes that separate better amps from the rest of the pack.
 
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#46
agedhorse said:
I think this is a pretty simplistic generalization IME.

There are class A topologies that are just as dreadful as some class D topologies with regards to clipping.

Every topology and class of amp, IF well designed to address this, can enter and exit clipping just as gracefully. This is one (of many) attributes that separate better amps from the rest of the pack.
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I'll take your word for it since you do that stuff for a living.

In my experience with both class a tube amps, class a tube and solidstate preamps, and the class AB tube/solidstate amps and preamps, the main thing I hear is a different distortion characteristic.
I am guessing that AB stuff tends to have more negative feedback?
I know I am reaching there but I am kind of muddled on my understanding. Most of the stuff I have read is either over my head or obvious marketing BS meant to promote one brands product over another.
 
#47
(Global) Feedback is independant of class. Class AB can be low or high feedback designs, as can class A. Class D can even be no feedback.

It all comes down to WHAT happens during clipping. There are a lot of different things happening and how thay are addressed determines the behavour. Savvy designers address this in the design phase and consider very carefully the ramifications of their design choices.

I will say that in general (though there are exceptions) very high feedback amplifiers tend to be less graceful clipping... in part because there is usually less stability margin available and this is important in non-linear operation.
 
#48
A lot of technical talk here going right over my head but I do have a question regarding all this. What, if any, point is there to non class d amps going forward? Take the GK 1001rb for instance vs. the mb800. What advantage would the bigger heavier rb have over the mb?

I realize they are two different styles of amp but beyond any tonal difference, which I assume could be replicated in a class D rb, and maybe the biamp thing, why would someone buy an rb series over an mb?
 
#50
Warmuth said:
A lot of technical talk here going right over my head but I do have a question regarding all this. What, if any, point is there to non class d amps going forward? Take the GK 1001rb for instance vs. the mb800. What advantage would the bigger heavier rb have over the mb?

I realize they are two different styles of amp but beyond any tonal difference, which I assume could be replicated in a class D rb, and maybe the biamp thing, why would someone buy an rb series over an mb?
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That's a very good question, and IMO the differences in well executed power amps is very small... WAY to the right of the decimal point. The pro audio world has shifted almost completely to SMPS and class D already (with the exception to Lab Gruupen which is a class d rail tracker and an AB output stage, and QSC which remains mostly SMPS with class H except for the 380 (class D) and the various powered speaker amps (class D)
 
#51
B-string said:
The way the class H RB series goes into and out of the power supply rails gives the signature G-K growl. Class D operates differently and can simulate only to some extent. If you are not interested in the growl then.....
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IMO, I don't think there is anybody here on this forum (me included) who could tell the difference between a class H amp and any other equiv. powered amp (assuming well designed products.) By far and away, the preamp is responsable for the characteristic or signature tones of their various amp lines IMO. I have done enough double-blind listening tests between power amps to be quite confident of this. Bob (Lee) has no doubt done more than his fair share of listening tests, with their otherwise identical class AB and H models as well, it would be interesting to hear his opinion on this.
 
#52
agedhorse said:
IMO, I don't think there is anybody here on this forum (me included) who could tell the difference between a class H amp and any other equiv. powered amp (assuming well designed products.) By far and away, the preamp is responsable for the characteristic or signature tones of their various amp lines IMO. I have done enough double-blind listening tests between power amps to be quite confident of this. Bob (Lee) has no doubt done more than his fair share of listening tests, with their otherwise identical class AB and H models as well, it would be interesting to hear his opinion on this.
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Sorry I was quoting Robert A Gallien on where the signature growl comes from on his designs. You could have the discussion with him if you like, I'm sure he would enjoy intelligent conversation. :)

Myself, I am never able to play loud enough to enjoy that transition.
No reason the RB series could not use class D for the woofer and horn amps as the H.M.S. happens in the preamp section. The RB series uses linear power supplies, the MB series uses SMPS (where the real weight savings happens).
 
#53
The 400RB is not class H, it's a class AB amp. Where would the growl come from on this model then?

Just trying to provoke some thought here.
 
#54
According to Mr. Gallien, the classic growl comes from the output stage "hitting the rails". This can happen when you overdrive the output stage both in class AB and class H if I read that right. I believe most class D implementations out there aren't even allowed to hit the rails which may explain why my GK MB200 doesn't have the classic GK growl.
 
#55
Warmuth said:
A lot of technical talk here going right over my head but I do have a question regarding all this. What, if any, point is there to non class d amps going forward? Take the GK 1001rb for instance vs. the mb800. What advantage would the bigger heavier rb have over the mb?

I realize they are two different styles of amp but beyond any tonal difference, which I assume could be replicated in a class D rb, and maybe the biamp thing, why would someone buy an rb series over an mb?
Click to expand...

Indeed. It was just a thread I was reading into thinking it will just stagnate, but some really interesting technical info here, even though like you I do not understand most of it! :)
 
#56
WingKL said:
I believe most class D implementations out there aren't even allowed to hit the rails which may explain why my GK MB200 doesn't have the classic GK growl.
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Class D output is not limited by the rail voltages but by the modulation limits. That can be avoided through the use of a limiter - as can clipping in class A/B.

You could say that class D hits the rails by design every half cycle of the clock signal.
 
#58
There is no real difference between class AB and class H, they are both exactly the same amp. The class H just has an additional power supply rail that's enabled to increase efficiency. Other than that, they both clip exactly the same, function exactly the same and without knowing if an amp is AB or H, there's no way to tell from the outside. Even the measurements (on properly designed amps) will be virtually identical.

In fact, any amps that have smaller versions that are AB will be built up on the same PCB that includes unstuffed componenets for the class H rail switches that are used on the larger models. They are that close to "identical".
 
#60
B-string said:
Thought provoking indeed. Is it the way the preamp handles over-saturation or the way the out section deals with it. Might be interesting to fire up the old 800RB and send it's pre to a class D (IPR1600).
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Let us know what you discover. You might just start a whole new thought provoking series of threads ;)

While you are at it, try it with a standard class AB amp of the same power driven at a comparable volume and see what the differences are...
 

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