#1
the different effects of Class A vs Class A/B. i get the idea, but i am curious about the differences in wattage, headroom, tonal qualitys etc. hell a total explaination would be awesome.

i have read up a little bit on it, and will more, but i am looking for somthing that states it more in a simple way, so i can further understand the more complex way.

thanks.
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#3
thanks for the link.

i have been reading that for the last 20 minutes or so, and some of the technical jargon is a bit over my head, but basically what i am getting is that

class a are more inefficient and distort less, and class a/b are more efficient and distort more?

what does the >180* and 180* mean, what is the degree measurement of.

could you explain more the tonal effects and differences.
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



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#4
nope. I have no idea. I've only owned 2 amps that claimed to be class A. Whether or not they are actually class A, I think Aiken would put under some scrutiny.

As far as I understand it you can bias any amp to be close to class A specs but it wouldn't be really class A unless it had a class A specific transformer. Most amps do class AB and can run in something like class A.

The bias is hotter and you get less output per tube and therefore less headroom. The amp will break up faster and push harder. Look up the orange AD5 or the THD Univalve. The univalve I know is true class A. The AD5 is said to be class A. Both are single ended. Class A amps don't need a phase inverter.

Ya that's all I know.
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#5
Quote by AcousticMirror
nope. I have no idea. I've only owned 2 amps that claimed to be class A. Whether or not they are actually class A, I think Aiken would put under some scrutiny.

As far as I understand it you can bias any amp to be close to class A specs but it wouldn't be really class A unless it had a class A specific transformer. Most amps do class AB and can run in something like class A.

The bias is hotter and you get less output per tube and therefore less headroom. The amp will break up faster and push harder. Look up the orange AD5 or the THD Univalve. The univalve I know is true class A. The AD5 is said to be class A. Both are single ended. Class A amps don't need a phase inverter.

Ya that's all I know.


thanks. i will try to read up further.

so you are saying bias on class A is always higher than on class A/B? and that class a amps are lower wattage thus less headroom, and less output than class A/B.

i always heard people saying this, and want to know if it is true. would a class A amp be warmer than a class A/B tonally due to this? or is that it just happens that amps that are class A are designed to be warmer due to demand? or is it just B.S.?
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alright "king of the guitar forum"


Quote by trashedlostfdup
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youre just being a jerk man.



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#6
Class A is yes less efficent, and generally have a nice top end, think of a vox ac30, its famous tone is largly due to it being class A. I think in class A the tubes push out all the signal, while class a/b is something like push/pull, one tube (or matching pair) does one half of the phase spectrum of the signal (everything from zero up on a sine wave graph) and the other tube or pair does the other half (everything from zero and below on a sine wave graph)

180* is a measurment of degrees... it has to do with phase if I remember correctly. So 180* phase change is the of the sound that topposite phase he tubes "create". Like a phase 90, it changes the phase of the sound by 90 degrees. its kinda equivalent to standing in front of your amps speaker then walking and standing the same distance but at a right angle to the speaker...

Class A's normally have a nicer top end, or more defined one, as stated an AC30, but you can only get so much wattage, While a class A/B can get you more power and headroom because its significatly more efficent, however if you don't bias the tubes well you can get crossover distortion, which is (if i remember correctly) the distortion as a result of the tubes not doing a clean jump at "Zero" phase. Its been a while since I've looked at stuff like this as I was trying to jump into amp schematics and building, and this is sorta my dumbed down and loose way of looking at it...
But google probably has a better answer than me...lol
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#7
Quote by trashedlostfdup
thanks. i will try to read up further.

so you are saying bias on class A is always higher than on class A/B? and that class a amps are lower wattage thus less headroom, and less output than class A/B.

i always heard people saying this, and want to know if it is true. would a class A amp be warmer than a class A/B tonally due to this? or is that it just happens that amps that are class A are designed to be warmer due to demand? or is it just B.S.?


you'll have to wait for gumbi to answer you on this one. I've heard full on power tube distortion maybe like 10 times and I've hated it every time. Great at a concert. Not so great in your ear.

edit: the vox is class ab.
Prs se Holcomb is the answer
Last edited by AcousticMirror at Sep 30, 2010,
#8
Quote by Ethanb08
Class A is yes less efficent, and generally have a nice top end, think of a vox ac30, its famous tone is largly due to it being class A. I think in class A the tubes push out all the signal, while class a/b is something like push/pull, one tube (or matching pair) does one half of the phase spectrum of the signal (everything from zero up on a sine wave graph) and the other tube or pair does the other half (everything from zero and below on a sine wave graph)

180* is a measurment of degrees... it has to do with phase if I remember correctly. So 180* phase change is the of the sound that topposite phase he tubes "create". Like a phase 90, it changes the phase of the sound by 90 degrees. its kinda equivalent to standing in front of your amps speaker then walking and standing the same distance but at a right angle to the speaker...

Class A's normally have a nicer top end, or more defined one, as stated an AC30, but you can only get so much wattage, While a class A/B can get you more power and headroom because its significatly more efficent, however if you don't bias the tubes well you can get crossover distortion, which is (if i remember correctly) the distortion as a result of the tubes not doing a clean jump at "Zero" phase. Its been a while since I've looked at stuff like this as I was trying to jump into amp schematics and building, and this is sorta my dumbed down and loose way of looking at it...
But google probably has a better answer than me...lol


thanks for the response. you helped me understand it a lot better.

that is what i am tryint to slowly bring myself into. i want to start a project from the AX84 schematic, but mod a bunch of things on it, and really alter it to make it my own.

just to clarify, the amount of degrees is of the sine wave. class A does the whole spectrum in one set of powertubes, and a class A/B, the spectrum is split in the tube or in a set of two tubes.

thanks. hopefully gumbi will jump on here...
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
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#9
Quote by trashedlostfdup
thanks. i will try to read up further.


i have read about this topic, i have tried different versions of classes of operation, i spent a ton of time playing and reading up on these amplification classes. i frankly find it hard to notice the differences. so good luck with the tone hunt.

Quote by trashedlostfdup
so you are saying bias on class A is always higher than on class A/B? and that class a amps are lower wattage thus less headroom, and less output than class A/B.


single ended class A is cathode biased, if that is what you're asking, so you don't actually set a bias on it like A/B.

Quote by wikipedia
To establish cathode bias, a resistor is placed between the emitting element, or Cathode and the negative return of the "B" or HT supply. Current drawn through this resistor by tube conduction places the cathode slightly more positive than the negative return. The grid input is returned directly to the negative supply, causing it to be negative with respect to the cathode. Thus, changes in tube conduction are automatically compensated by changes in bias.


so you aren't really running significantly higher or lower plate voltages between class A and A/B operation as far as i can tell.

else, i think what you may be referring to is that the class A amps are less efficient. they are less efficient cuz they are ALWAYS running, even with no input signal. in fact, from what i have heard, their current draw is at it HIGHEST when idling with no input signal.

furthermore, true class A operation has it's tubes working with the entire input signal. the angle thing has to do with conduction angle. wikipedia explains fairly painlessly about conduction angles and the basics of the classes of operation.

http://en.wikipedia.org/wiki/Amplifier_class#Power_amplifier_classes

Quote by trashedlostfdup
would a class A amp be warmer than a class A/B tonally due to this?


warmer? maybe... but like i said, just pigeonholing how an amp sounds based on just mode of operation is not really reliable. preamp design, tone stack, and tube selection have MUCH more influence on how 'warm' or 'sterile' and amp sounds imo.

i find class A tends to 'butter' up when pushed (based on my supro's and my THD bivalve). but my THD tends to become much more harsh with bigger power tubes (like KT88's) and tends to be more buttery with lower power tubes (like EL84's). i like EL34's and 6L6's in it cuz it is a good firm tone but just enough butter.

class A push/pull (i own an orange TT) is supposed to function just like class A, but tends to function more as A/B at higher volumes, requires use of phase inverter tube as well.

class A/B does have more headroom, seems to handle low end with more stability. has a great 'attack' that is awesome for percussive styles. but again i feel other parts of the amp have much more influence over tone.

Quote by trashedlostfdup
or is that it just happens that amps that are class A are designed to be warmer due to demand?


demand? can't grasp that? do you mean people want the tone of class A? i think people on this forum would prefer class A/B more to tell truth.

Quote by trashedlostfdup
or is it just B.S.?


the differences are there, i have even played a few power sections that allowed for both A/B and A operation and we compared them (VHT 50/50). there was some difference, but i have heard plenty of eq boost or cut knobs with much more noticeable difference.

to tell truth, i would design an amp to play toward the strengths of the operation i choose to run at. so i would choose class a operation i want to butter up and have more prevalent power section saturation. i choose a/b when wanting an amp with more headroom and attack with better low end handling.

i personally run a bunch of styles. i usually run my orange or50H (a/b) with my THD bivalve (class A) with a music man (hydrib a/b)

btw, almost all preamp sections are run in class A, so when what was talked about above is just the operation of the power section.
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Last edited by gumbilicious at Sep 30, 2010,
#10
wow. thanks gumbi.

just to clarify... what i meant when i said demand, was that people wanted warmer sounding class A amps as opposed to the more sterile ones, so that is what manufacturers built. it was just pure speculation in attemt to reach a conclusion.

just to clarify again... when i said it was B.S. i was saying that it was B.S. with what people are saying and it has no difference.

thanks a lot everybody, i will keep researching. i am thinking of a 5x 12AX7 and 2x KT88, high gain solid state rectified single channel amp with volume, gain, and a single tone knob that operates the same as the Orange knob that makes it bassier one way and brighter the other that has full impact when turned. and i am thinking of having a foot switchable boost for the last gain stage.
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
2017-07-07 2017-07-07 Update and a Chat On Noise Constraints *** NEW FRIDAY 7/7
2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
2017-02-21 How to Hot-Rod the Hell of your Stratocaster for $50! (Tuesday 2017-2-21)
Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/