Class A vs. Class A/B
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Pierre
Stratologist
Re: Class A vs. Class A/B
Remember that class A is benched on clean tone. If you distort a class A amp and talk about the class A sound, it's just like mentioning how well a plane handles on the ground. It's nice, sure, but flying is what it was made for
By the way I mention this since you talk about Mesa and those are rarely clean amps
Class A and A/B also involve different circuitry. Most (if not all) of nowadays amps with more than one tube are A/B. A Vox AC30 is A/B for instance. Most class A amps are single ended. I don't think you can compare the two as the circuitry could be quite different in two 'similiar' amps...
Remember that class A is benched on clean tone. If you distort a class A amp and talk about the class A sound, it's just like mentioning how well a plane handles on the ground. It's nice, sure, but flying is what it was made for
By the way I mention this since you talk about Mesa and those are rarely clean amps
Class A and A/B also involve different circuitry. Most (if not all) of nowadays amps with more than one tube are A/B. A Vox AC30 is A/B for instance. Most class A amps are single ended. I don't think you can compare the two as the circuitry could be quite different in two 'similiar' amps...
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BigDaddy
Guest
Re: Class A vs. Class A/B
Are you sure about that?........most people don't understand what class A or A/B is. It's not what you say it is by the way. It's one of the most misused and mis-understood terms. Not as bad as what I heard in the 70's.....I was told there were English watts and American watts, that's why Marshall's are louder. I would say that if you do not know what you are talking about don't misguide others. I would not begin to explain class A and A/B since I do not completely understand it myself and I build amps. It a classification for operation.
Are you sure about that?........most people don't understand what class A or A/B is. It's not what you say it is by the way. It's one of the most misused and mis-understood terms. Not as bad as what I heard in the 70's.....I was told there were English watts and American watts, that's why Marshall's are louder. I would say that if you do not know what you are talking about don't misguide others. I would not begin to explain class A and A/B since I do not completely understand it myself and I build amps. It a classification for operation.
Pierre
Stratologist
Re: Class A vs. Class A/B
It concerns the waveform and where it's biased I believe. With class A it's on 360 degrees, class A/B 180 (i.e ALL push pulls would be AB no?). That's about as technical as I can go But yes, I'm 99% certain the AC30 is class A/B and that most amps today advertized as A are in fact A/B.
It concerns the waveform and where it's biased I believe. With class A it's on 360 degrees, class A/B 180 (i.e ALL push pulls would be AB no?). That's about as technical as I can go
But yes, I'm 99% certain the AC30 is class A/B and that most amps today advertized as A are in fact A/B.
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BigDaddy
Guest
Re: Class A vs. Class A/B
Most amps that say they are class A are not, yes you are right. If you bias your amp to 100% max dissipation it becomes class A, I am not 100% sure that is the only thing involved. As I say I am not sure......A lot of people think that just because an amp is single ended it's class A and that is wrong. I wish I knew more but I don't and most of the people on this board don't either...
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The AC30 is AB. One thing though any amp like a Matchless eat tubes that's for sure so if you want an amp like that be prepared to buy a lot of power tubes. they are biased hot and have high voltages a no-no with cathode biased amps. But that's how they get there sound.
Most amps that say they are class A are not, yes you are right. If you bias your amp to 100% max dissipation it becomes class A, I am not 100% sure that is the only thing involved. As I say I am not sure......A lot of people think that just because an amp is single ended it's class A and that is wrong. I wish I knew more but I don't and most of the people on this board don't either...
.The AC30 is AB. One thing though any amp like a Matchless eat tubes that's for sure so if you want an amp like that be prepared to buy a lot of power tubes. they are biased hot and have high voltages a no-no with cathode biased amps. But that's how they get there sound.
guymanperson
New member
Re: Class A vs. Class A/B
class a is complicated shuzite
class a is complicated shuzite
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BigDaddy
Guest
Re: Class A vs. Class A/B
This is what I just read at the Amp Workshop from a very knowledgeable person.
How To" determine Class-A, -AB or -B operation
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"How To" quickly determine the class of operation of a push-pull amplifier? Simply measure the voltages(!):
Class-A: Vpq ~ 55-60% of B+
Class-AB: Vpq ~ 85-95% of B+
Class-B: Vpq = 98-100% of B+
where:
B+ = the high voltage applied to the center-tap of the audio output transformer (OT); often the "highest" voltage present; labeled "A" on Fender schematics.
Vpq = the high voltage applied to plates of the output tubes from the primary windings of the audio output transformer (OT); usually the "second highest" voltage present; typically taken from choke-filter output; labeled "B" on Fender schematics.
This is what I just read at the Amp Workshop from a very knowledgeable person.
How To" determine Class-A, -AB or -B operation
--------------------------------------------------------------------------------
"How To" quickly determine the class of operation of a push-pull amplifier? Simply measure the voltages(!):
Class-A: Vpq ~ 55-60% of B+
Class-AB: Vpq ~ 85-95% of B+
Class-B: Vpq = 98-100% of B+
where:
B+ = the high voltage applied to the center-tap of the audio output transformer (OT); often the "highest" voltage present; labeled "A" on Fender schematics.
Vpq = the high voltage applied to plates of the output tubes from the primary windings of the audio output transformer (OT); usually the "second highest" voltage present; typically taken from choke-filter output; labeled "B" on Fender schematics.
TattooedCarrot
New member
Re: Class A vs. Class A/B
In laymans terms it is the difference between running an engine at full throttle ALL the time (class A), exactly Half throttle (Class B).
Class A/Single Ended is a sweeter fuller tone, since it has both even & odd harmonics included in it's output signal. This is because the even order harmonics are not canceled in the single ended design. Class AB, AB1, B, etc. all cancel the even order harmonics.
Class A/B, still a great tone, but not as harmonically rich, and complex as Class A. If you overdrive a Class A amp far enough, it will drift towards Class A/B operation.
In laymans terms it is the difference between running an engine at full throttle ALL the time (class A), exactly Half throttle (Class B).
Class A/Single Ended is a sweeter fuller tone, since it has both even & odd harmonics included in it's output signal. This is because the even order harmonics are not canceled in the single ended design. Class AB, AB1, B, etc. all cancel the even order harmonics.
Class A/B, still a great tone, but not as harmonically rich, and complex as Class A. If you overdrive a Class A amp far enough, it will drift towards Class A/B operation.
Chaos
New member
Re: Class A vs. Class A/B
In the simplest terms, a ‘Class A’ amplifier maintains signal fidelity without corruption due to saturation or cutoff. 100% of the signal is reproduced below these thresholds. The downside to ‘Class A’ is its inefficiency.
Class AB amplifiers clip part of the signal waveform. Class AB is a compromise that gains some of the efficiency of ‘Class B’ operation without the downside of crossover distortion. Most guitar amps use ‘Class AB because some distortion / compression / cutoff is desirable.
Class A amplification is usually found in audiophile applications. Distorting a ‘Class A’ amplifier defeats its purpose.
In the simplest terms, a ‘Class A’ amplifier maintains signal fidelity without corruption due to saturation or cutoff. 100% of the signal is reproduced below these thresholds. The downside to ‘Class A’ is its inefficiency.
Class AB amplifiers clip part of the signal waveform. Class AB is a compromise that gains some of the efficiency of ‘Class B’ operation without the downside of crossover distortion. Most guitar amps use ‘Class AB because some distortion / compression / cutoff is desirable.
Class A amplification is usually found in audiophile applications. Distorting a ‘Class A’ amplifier defeats its purpose.
Pierre
Stratologist
Re: Class A vs. Class A/B
And people, if class A mattered so much, wouldn't people have advertised their amps as such when they came out decades ago?
Jeremy summed it up pretty well. If it sounds great but is class AB, what's the matter?
Sorry, I didn't mean to say that all single ended are class A, just that most true class A amps of nowadays are single ended.BigDaddy said:Most amps that say they are class A are not, yes you are right. If you bias your amp to 100% max dissipation it becomes class A, I am not 100% sure that is the only thing involved. As I say I am not sure......A lot of people think that just because an amp is single ended it's class A and that is wrong. I wish I knew more but I don't and most of the people on this board don't either...
The AC30 is AB. One thing though any amp like a Matchless eat tubes that's for sure so if you want an amp like that be prepared to buy a lot of power tubes. they are biased hot and have high voltages a no-no with cathode biased amps. But that's how they get there sound.
And people, if class A mattered so much, wouldn't people have advertised their amps as such when they came out decades ago?
Jeremy summed it up pretty well. If it sounds great but is class AB, what's the matter?
Nightburst
New member
Re: Class A vs. Class A/B
I disagree on the 'distortion class A defeats the purpose' remarks!
I run my Bogner Ecstasy on class A all the time (I can actually switch between A and A/B) and while the cleans are much fatter sounding than A/B mode, the distortion is also noticable fatter.
I disagree on the 'distortion class A defeats the purpose' remarks!
I run my Bogner Ecstasy on class A all the time (I can actually switch between A and A/B) and while the cleans are much fatter sounding than A/B mode, the distortion is also noticable fatter.
Re: Class A vs. Class A/B
The best explanation I have read on class A is Randall Smith's white paper on the mesa boogie website.
http://www.mesaboogie.com/US/Smith/ClassA.htm
Class A boils down to plate current flowing in the tube at all times.
I have gutted a Fender sidekick practice amp & built a Class A single ended tube amp from scratch in it's place.
The single EL34 in my amp runs at about 70% max dissipation, with 60mA of current running through the plate at idle.
Here are pics of my amp:
http://s71.photobucket.com/albums/i135/nat67pics/
The best explanation I have read on class A is Randall Smith's white paper on the mesa boogie website.
http://www.mesaboogie.com/US/Smith/ClassA.htm
Class A boils down to plate current flowing in the tube at all times.
I have gutted a Fender sidekick practice amp & built a Class A single ended tube amp from scratch in it's place.
The single EL34 in my amp runs at about 70% max dissipation, with 60mA of current running through the plate at idle.
Here are pics of my amp:
http://s71.photobucket.com/albums/i135/nat67pics/
Boogie Bill
New member
Re: Class A vs. Class A/B
+1000 on Mesa's Class A White Paper.
Here's the deal: Class A or AB? Who cares? It simply doesn't matter!!!!
The amp sounds good---or, it doesn't!
You like it, or you don't!!!
Bottom line: listen to the amp. Don't get all caught up in playing 'the specs on the tech sheet". The TONE is either in the amp,....
...or it isn't.
And that's all that matters!!
Bill
+1000 on Mesa's Class A White Paper.
Here's the deal: Class A or AB? Who cares? It simply doesn't matter!!!!
The amp sounds good---or, it doesn't!
You like it, or you don't!!!
Bottom line: listen to the amp. Don't get all caught up in playing 'the specs on the tech sheet". The TONE is either in the amp,....
...or it isn't.
And that's all that matters!!
Bill
James Rock
Active member
Re: Class A vs. Class A/B
LIke said above it comes down to the amp like an AC30 while class A/B sounds closer to alot of class A amps then typical class AB amps (FENDER,MARSHALL ETC).
LIke said above it comes down to the amp like an AC30 while class A/B sounds closer to alot of class A amps then typical class AB amps (FENDER,MARSHALL ETC).
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BigDaddy
Guest
Re: Class A vs. Class A/B
nat67.........nice work. Really clean. Looks great. My work is messy, I'm all thumbs......arthritis in the fingers and hands. I can't even open my pill bottles sometimes.
How does the amp sound? Do you have anything recorded.
It's just cool man no matter what it sounds like....great work.
nat67.........nice work. Really clean. Looks great. My work is messy, I'm all thumbs......arthritis in the fingers and hands. I can't even open my pill bottles sometimes.
How does the amp sound? Do you have anything recorded.
It's just cool man no matter what it sounds like....great work.
