#1
What are the differences between the classes of amps? I did some research but didnt understand much. Is class a full tube amps and class ab hybrid or something like that? please explain it to me.
#2
only ALL TUBE amps are put into classes, and they are put into classes dependant on how they work.

single-ended amps are usually configured in class A, and push-pull amps are class AB, B or C.

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#3
Basically, Class A is the 'best' you can get, but obviously there is still a wide selection with the A class, AB is below that, and B below still... But I never pay attention, alot about chosing an amp is down to oppinion anyway, just like anything to do with music.

Edit : Maybe I'm wrong, who knows.
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#4
Quote by FuzzLove
Basically, Class A is the 'best' you can get, but obviously there is still a wide selection with the A class, AB is below that, and B below still... But I never pay attention, alot about chosing an amp is down to oppinion anyway, just like anything to do with music.

No it isn't. It's all how the amp works. Different classes suit different people.

EDIT:

http://www.ultimate-guitar.com/columns/the_guide_to/understanding_amplifier_classes.html

Read that
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Last edited by Lil Macker at Sep 4, 2009,
#5
class AB amps IMHO are better for cranking, because as a typical characteristic, class A amps seem to have a fair amount of hum when you crank them.

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#6
If an amp has a class it should have tubes in both preamp and poweramp then? am i right? no hybrid or ss?
#7
if an amp is officially put into a class, its all tube.

some hybrid amps (here i refere to the vox valvetronix) have circuitry that can reconfigure the preamp to run in class A or AB.

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#8
Thanks guys that was really helping. btw cant a solid state device be class a or b?
Last edited by blind.quardian at Sep 4, 2009,
#9
Read it till you brain hurts

And if it's too early to deal with that:
(taken from http://www.ballewsmusic.com/Class-A-vs-Class-AB-Tube-Amplifier-Design-s/193.htm since the page is displaying wacky)

_____________________________________
POWER AMPLIFIER DESIGN

Class A (Vox) vs. Class AB (Marshall & Fender)

In order to understand the difference between these two types of amplifier designs (there are others) you must first understand a little about tubes.

Simple tube theory part 1 - The most basic tube used as an amplifier consists of three elements: Cathode, Plate and Grid.

The Cathode is heated (by the heater, another element in all tubes except in very old designs where the cathode is the heater) and forms a cloud of negatively charged electrons. The Plate has a positive charge that attracts the electrons. The Grid is the audio input to the tube and usually controls the flow of electrons. There is another part of the tube called a heater which heats the Cathode

Amplification happens when a signal is applied to the grid and flows through the plate. Because the signal voltage is relatively low and the plate current is relatively high, the small changes produced by the audio signal at the Grid becomes much larger at the Plate, hence amplification.

In a class A circuit, a positive voltage is applied to the Grid which controls the flow of electrons. In this circuit design current is flowing at all times through the tube.

In a class AB design a negative voltage is applied to the grid which controls the flow of electrons.

Class A is a term given to an amp that runs its tubes at full current all the time, unlike most tube amps that alternate between running one set of tubes and the other set, each for one half of the wave.

Each type of design has its advantages and disadvantages.

Class "A"

Advantages -The tube is ready to amplify the signal at all times. The signal is instantaneously amplified because the tube does not have to "wake up: from a less than full operational state. A 30 watt Class "A" amp will sound louder than a 30 watt Class "AB" amp. Because current is maximum at all times, the amp will have a smooth compression. There is not a lot of headroom because of the lower plate voltages used in Class "A" amps. Instantaneous amplification and smooth compression make for an amp that is responsive to the touch: the amp feels good and playing it is a satisfying experience. Class A amps sound great at low volumes, and even better as you turn them up.

Disadvantages -Maximum current at all times means that the tubes are being strained even without playing. Shorter tube life, lower power rating than a Class "AB" amp with the same tube configuration. Power transformer needs to be upgraded in order to handle the high current demands.

Class "AB"

Advantages- Longer tube life because the tubes are "idling" with lower Plate Current. Higher power ratings with the same tube configuration. More headroom, tighter bass response and less continuous demand on the power transformer.

Disadvantages- Not as "responsive" as a Class "A" amp.

_____________________________________
#10
solid state technology is not put into classes, as they use transistors and (depending on the company) usually have about the same efficiency and behaviour.

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Vox Valvetronix VT20+
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Danelectro Cool Cat Drive
Boss EQ


#11
I disagree (see the above wiki) - in our guitar world we don't use classes for SS amps, but in the electrical engineering world SS amplifiers are too. It comes down to the circuit design, not tubes vs. transistor ICs.
#13
IMHO, I don't really like Class A because you don't get any crossover distortion out of them. It adds a certain thickness that other distortions don't replicate. Also, Class A gives you zero powersupply sag because the current is the same all the time, so it doesn't jump up current demands, which creates sag.

If the amp sounds and feels good, play it. Most of the "class modeling" and "hybrid class" and "pure class A" is pure marketing bull**** anyways. Example: a Vox AC30 is NOT class A. So bite me.
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#14
Quote by Poster_Nutbag
I disagree (see the above wiki) - in our guitar world we don't use classes for SS amps, but in the electrical engineering world SS amplifiers are too. It comes down to the circuit design, not tubes vs. transistor ICs.


The way I understand it, I agree.

But, digital appliances are also rated [my Sony Walkman mp3 player is a Class B Digital apparatus]
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#15
Quote by Silver-spear94
solid state technology is not put into classes, as they use transistors and (depending on the company) usually have about the same efficiency and behaviour.



Wrong wrong wrong wrong. Amplifier circuit design is what determines it's class not whether it's a solid state or tube design.


EDIT: I am a novice when it comes to electronics design so you guys who actually know what you're talking about, I welcome corrections.

Amplifier classes of operation are Class A, class B, class A/B, class Cand class D.

Class A uses a single output device to handle both positive and negative parts of a sine wave. This is the purest amplifier design but it is inefficient.

Class B uses 2 output devices. One handles the positive half of the signal the other negative. This is efficient but when they switch distortion can be introduced.

Class A/B is a combination of class A quality and class B power efficiency where both ouput devices operate at the switching point to provide less distortion.

Class C only uses half the signal.

Class D is essentially digital amplification.
Last edited by BobDetroit at Sep 4, 2009,
#16
Quote by Silver-spear94
only ALL TUBE amps are put into classes, and they are put into classes dependant on how they work.


nah, that's not true, all power amplifiers have a class, just they tend to mention the class in the marketing blubs when talking about tube amps.

Quote by FuzzLove
Basically, Class A is the 'best' you can get, but obviously there is still a wide selection with the A class, AB is below that, and B below still... But I never pay attention, alot about chosing an amp is down to oppinion anyway, just like anything to do with music.

Edit : Maybe I'm wrong, who knows.


you are. that's what the marketing people want you to think, unfortunately. neither is better.

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#17
Quote by Silver-spear94
only ALL TUBE amps are put into classes, and they are put into classes dependant on how they work.

single-ended amps are usually configured in class A, and push-pull amps are class AB, B or C.


Not true, any signal amplifier can be fit into one of the standard categories. A lot of SS/MOSFET amps are class AB, B, D, G or H, or hybrids.

Quote by BobDetroit
Class D is essentially digital amplification.


Not true. Class D

Quote by Wiki
The letter D used to designate this amplifier class is simply the next letter after C, and does not stand for digital. Class D and Class E amplifiers are sometimes mistakenly described as "digital" because the output waveform superficially resembles a pulse-train of digital symbols, but a Class D amplifier merely converts an input waveform into a continuously pulse-width modulated (square wave) analog signal. (A digital waveform would be pulse-code modulated.)


I'm too lazy to type, but that's a good summary.
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#18
Quote by Dave_Mc

+1, i always link to the aitken articles, they're great.

Yep, good site, pretty easy to understand as well even if you don't know too much. I figure if people care, they'll read things. If they don't feel like reading it, it's not worth the time to write out
#19
^ exactly.
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#20
Quote by STABxYOU
Not true, any signal amplifier can be fit into one of the standard categories. A lot of SS/MOSFET amps are class AB, B, D, G or H, or hybrids.


Not true. Class D


I'm too lazy to type, but that's a good summary.


As well, Solid State amplification is not digital amplification. Transistors have high efficiency, so Class D amps are usually SS, but this does not make them digital.
#21
I'll bet you wish you hadn't asked.

To really understand this you need to know a fair bit of electronics. I'll try a simple explanation.

Your sound signal is a complex wave which goes constantly up and down. By the time it gets to the speaker it has to go positive pushing the speaker forward and negative pushing it back.

In a class A amp a single output stage handles all of this voltage swinging it all the way from top to bottom. (though there are ways of using two or more tubes or semiconductors to do the job together). The advantage of this is a smoother sound and a simpler design. The disadvantage is that the devices are on all the time and are inefficient wasting a lot of power as heat.

The next class of amp developed was class B. Here the transistors or tubes are paired with one taking the positive side of the swing and the other the negative side. This is more efficient and the amp runs cooler and can give much more power with the same tubes (or trannies). The problem comes at the point where the two devices crossover handing the signal to the other device as they never in practice do this smoothly. This creates distortion which you really hear in the quiet bits of the music.

To solve this problem designers leak a little current into both sides of the amp at crossover so both sides work at this point and you have a little bit of "class A" at crossover with the loud sounds being dealt with in class B. This is class AB for obvious reasons. Nearly all commercial amps transistor FET or valve are AB amps or have been until recently. The exceptions are a few "boutique" amps and a handful of hi fi amps which use class A and the newer digital amps.

It is nice to know this stuff and if you become a designer or even a keen builder of amps you will need to know this but when choosing an amp use your ears and choose the one that sounds good.
#22
Quote by ticklemeemo
As well, Solid State amplification is not digital amplification. Transistors have high efficiency, so Class D amps are usually SS, but this does not make them digital.


I realize this, in fact I even specifically mentioned it.
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#23
In the end, it doesn't matter at all. Tube amps (you won't see the class mentioned with any other amps) are either A or A/B, and while there is a difference between the classes, it's so much smaller than what other differences in the circuits cause it doesn't matter at all.

Just get a good amp (with good I mean something YOU like) and ignore the class thing.
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