Amplifier Classes how to identify

[rogeryu_ph]

Guys,
Kindly explain not so technical on how to identify or differenciate class A, AB, D amplifiers is? I have read some article still I don't grasp the idea 

Thanks
Roger 

[George Giblet]

The amplifier classes section here can't really be stated any simpler:

http://en.wikipedia.org/wiki/Electronic_amplifier

The statement "a theoretical maximum of 50% is obtainable with inductive output coupling and only 25% with capacitive coupling" isn't quite accurate when you consider solid state push-pull amplifiers.

[Sir H C]

Easiest way is to imagine that the tubes or transistors are lumberjacks and they have a big saw to cut logs.

Class A = the one or two lumberjacks sawing the whole length of the sawing motion.
Class B = One lumberjack Sawing when the blade is dead center to his side while the other guy rests, and the other guy sawing from dead center to his side.
Class AB = something between A and B.
Class C is when there is some time in the middle where the saw isn't pushed or pulled by either lumberjack (requires a saw with momentum).

[gez]

And Class D shreds logs then reassembles them as chipboard...

[Pedal love]

When class e is is involved, its a woodchipper....nevermind. It really is a case where one side conducts and the other isn't. Class a is really meant for different things when you say single ended the output tube conducts all the time-(its the only active device in the output leading to the speaker.) In the case of the Vox ac 30 class a push pull output, current flows through the complete cycle, almost completely on each side then both sides alternate so there is almost no real cutoff. I say almost as I really think the vox ac 30, is a really high biased ab push pull circuit and not a class a push pull circuit.

[brett]

lumberjacks and they have a big saw to cut logs

What a great analogy.

I suppose Class D is when the lumberjacks can occasionally pull the saw back behind where their body is positioned.  But doing it too often nearly kills them.

[rogeryu_ph]

Thanks guys i'll try to relate everything 

Roger

[brett]

This might also help...
A = all transistors working 100% of the time. (above and below "average").  Not very efficient.
B = transistors working 50% of the time (either above or below average). Very efficient.
AB = transistors usually working 70% of the time, but technically could be 51 to 99% (mostly on "one side" of signal).  Popular compromise.
C = transistors working less than 50% of the time (either above average plus a bit, or below average minus a bit)
D = weird stuff (occasionally managing 120%, but not for too long)
H, etc = some of these aren't even real classes - they're marketing ploys.

[Sir H C]

Just looking at a circuit and not doing the math you can not necessarily tell class A from B from AB.  Only if the circuit is single-ended.

[rogeryu_ph]

So guys, if you gonna buy a guitar amp what class would be the best? A, B, A/B etc..  Can you give a model and a brand also....

Thanks
Roger 

[brett]

Hi
that's a complex issue.
Some people like the classic sound of single-ended class A amps.  But they are inefficient, so don't expect high power ratings.
A lot of tube amps are Class AB, so there's a wide range of them to choose between.

A good approach is to check out what your favourite guitarists are using, and get something with a similar "feel".  For example, it's not much use buying a nice clean Fender amp if you want to sound like someone playing a filthy Marshall.

If you've got a good shop nearby, talk to the salespeople about their amps, and ask them if you can try out a few.  If possible, don't rush into anything, but spend six months or so having a listen and a think.
cheers   

[JimRayden]

So guys, if you gonna buy a guitar amp what class would be the best? A, B, A/B etc..  Can you give a model and a brand also....

Thanks
Roger 

If you are about to buy an amp, forget about classes or any other technical mumbojumbo, class AB is just as much a tube amp as class A and sounds at least as good if you're not into champ/princeton-mojo. Just go to a music store and try a bunch. You might even find a solid state amp that pleases your ear, then you'll have cash left for a whole bunch of 3PDTs. 

---------
Jimbo

[Joe Kramer]

Hey Friends,

My understanding of amplifiers is that they're classified according to the bias point of the amplifying device.

Here's a mental image that I use.  Picture a lightbulb.  It can be fully on, fully off or anywhere in between.  Let's call the fully off state "zero."  Now imagine a simple sinewave.  It swings from zero, into the positive zone, back to zero, down into the negative zone, and completes the cycle by returning to zero again.  Now say we want to use our lightbulb to mimic the up and down swing of the sine wave.  Well, immediately we have a problem: starting at zero, we can make the lightbulb indicate the positive swing of the sinewave by lighting up, but when the wave swings into the negative region below zero, our light bulb won't show this.  It can't go any farther below zero, but simply goes black for the whole negative swing of the sine wave.

But there's a way to trick the light bulb into showing the whole swing of the sinewave:  we can inject some power into the lightbulb so that it sits halfway lit-up at rest--a bias voltage/current.  Now our bulb's "zero" point is actually fifty-percent on.   When we send our sinewave in, now the lightbulb goes from half-lit to full-lit on the upswing, and then from half-lit to almost off on the downswing, and this way it mimics the entire swing of the signal.  When you have an amplifier set up this way, with a bias point of about 50%, and with the amplifying device passing the whole swing of the signal, it's called "Class A." 

Following the same idea of the lightbulb, a class B amplifier would use two lightbulbs , one to show the positive swing of the signal, and the other to show the negative swing, with the concerted "output" mimicking the whole swing of the signal.  The reason class B is considered more efficient is because the two amplifying devices don't need the constant 50% bias point.  Each one turns off almost completely when the other one turns on, and when there is no signal, almost no power is being consumed because they are both almost off.

Hope that helps.

Sitting Halfway Lit-up At Rest,
Joe

[rogeryu_ph]

Hi Joe,
I immediately visualized you lightbulb analogy. Good analogy.
Class B seem to be efficient as per your analogy co'z its using two amplifying device which would share the load unlike Class A. What about A/B class how or what concept design is this? Using the same analogy.

Jim/Brett,
Unfornately last two months I already bought an amplifier a Fender FM65 DSP and it's on sales. I was then not aware of amplifier classes until I read an article lately. Now i'm  kind of wondering what class is this amplifier that I bought. I haven't peak on the inside and I don't have a circuit yet and it's under warranty so I can not open it. Does anyone know what class this amplifier is?
You are right Brett I rush into buying this amp and did'nt consult first 

Thanks,
Roger 

[d95err]

Here's a simple way to identify the class of mass-produced amplifiers:

How many power tubes?

1: Class A  (can't be anything else with just a single power tube)
2 or more: Class AB (regardless of what the marketing mumbo-jumbo says)

Anything with 2 or more power tubes markeded as Class A is with 95% certainty be class AB with cathode bias. What is cathode bias? Well, that's another topic...

[Joe Kramer]

Class B seem to be efficient as per your analogy co'z its using two amplifying device which would share the load unlike Class A. What about A/B class how or what concept design is this? Using the same analogy.

I think "efficiency" in terms of amplifiers is simply an evaluation of how much power is "wasted" when there's no signal present.  A Class A amp is called inefficient because the output tube (lightbulb) is biased halfway on all the time, so power is being used (and heat is being generated) even when it's just sitting without any input signal.  A Class B amp avoids this problem because we use almost no bias power, and the tubes are virtually off (lightbulbs blacked out) when there's no signal present.  So a Class B amp is "efficient" because it doesn't waste much power when sitting idle.

Class A/B in terms of the lightbulb: we have two bulbs like Class B, and they are biased to be somewhat lit up at rest, but less than 50% as in Class A.  At low signal levels, both bulbs behave like Class A, and reproduce the entire swing of our sinewave signal, but as the sinewave gets bigger (outside the region of the bias point), the two lightbulbs each begin to handle the negative and positive halves of the waveform separately, as in Class B.  So Class A/B behaves like a Class A amp with low level signals, and like a Class B amp with higher level signals.  It's more efficient than Class A (wastes less power), but somewhat less efficient than Class B.  I think that's generally how it works. . . .

Hope that helps.

Regards,
Joe
   

[rogeryu_ph]

Again Joe, you hit the mark once again. I'm now getting the concept more clearly. One last question, is classes A,B, A/B are not for tube amp only and applied even for solid state amp? Like power transistor?
This amp I recently bought without anyone consultation 
http://i186.photobucket.com/albums/x139/rogeryu_ph/PICT0320.jpg
Fender FM65 DSP it's not tube, it's a solid state amp and only 65watts. Could anyone help me classify this?
 
Thanks,
Roger

[rogeryu_ph]

Anyone? 

[Pedal love]

Probably a transistor, complimentary symmetry output. Either that or an output in an IC package.  Don't get too hung up on bias classifications.

[Joe Kramer]

Hey Roger,

I'm back from vacation.   

Solid state and tube amps can have nearly identical configurations, at least as far as classifications A, A/B, and C go.

Pedallove is probably right about yours being an integrated amp chip.  Older SS amps often use discrete, but the newer ones (like a Line 6 I recently looked into) use amps chips.

It's possible to build some great-sounding class A solid state amps though.  If you're interested, look at Nelson Pass's Zen amps here:

http://www.passdiy.com/amps.htm

I've never heard of anyone using these for guitar, but I bet they'd work well. . . .

Regards,
Joe