Classes of operation vs. sound quality

[freedom]

Hi All

I´m under the impression that "non-hifi-nerds" eg. everyday peoble generally believe that Class A sounds better than B, B better than C, C better than D and so forth.

Everyone (in here) knows that the indexes only refers to the collector current angle, for class A, B and C, and that Class D is PWM. We also know that class AB can be made to sound as good, and maybe even better than class A... know this is an issue to be discussed beyond the end of time.

But: Am i right when saying that not-so-well-informed users of common hifi-equipment generally believes that the index of classes is reverse proportional to sound quality?


Thanks in advance

 

[Upupa Epops]

Not - so - well - informed - users are here also, so you will get many oportunity informations . Class of amp tell anything about real quality. I have heard many " A ", which was s...s and several " AB " which was excellent .

 

[MikeB]

I think, a well designed ClassA should always outperform any ClassAB,
but a well designed ClassAB will always outperform a "standard" ClassA.
It's just that ClassA can't have crossoverdistortion and should always
be more linear, especially for higher freqs.
The quality of an amp mainly comes from how good the design is,
not topology or class.

For example, my own ClassAB outperforms my MF-A1, a commercial ClassA.

 

[NUTTTR]

I've heard good Class a/b's and good class A's, but the day you show me a good sounding class b...!!! A class b i had sounded like ****!!! It was horrible...
But i don't know about class a/b vs a, as any very well designed amp will sound good, a very good class a vs very good class a/b the difference should be so minimal you shouldn't be able to tell....
However "technically" i'd say the class a would be 'better' in this case... however i cannot tell you why or how, but cool factor alone
Aaron

 

[Upupa Epops]

With boxes with average efficiency ( cca 90 dB/w or less ) you need minimally 100 W/ ch for preservation of natural sound dynamic. On this look is funny amp with output power 10 W. With typical efficiency of class A ( cca 25 % ) you get by amp 2*100 W of output power 600 W of continuous heat. I don't like " good sounding " stove .

 

[Mr Evil]

In an ideal world with ideal transistors, all amplifier classes give identical outputs. In practice, all can give similarly good performance (except class C, since it isn't possible to build a pure class C audio amp), but class A starts off with the advantage of lacking crossover distortion.

Class A amps are not so common because of the ridiculously low efficiency which overrides any possible distortion advantage.

I have a feeling that technology advances, class D will give the best performance, since it is theoretically capable of both extremely low distortion and near 100% efficiency at the same time.

...but the day you show me a good sounding class b...!!!

I've heard plenty of good sounding class B amps. In fact a properly biased class B has lower distortion than class AB, it's just more difficult to get right.

 

[jam]

A simple test would be to take a class A amp and reduce the bias to class AB and compare the differences.

Most people would choose the amp in class A. There are differences in the sound that occur that cannot be attributed to distortion alone.

 

[djQUAN]

Class A sounds better than B, B better than C, C better than D and so forth.

class B is definitely better than class C. but class D is so much better for audio than class C.

 

[moamps]

...... a properly biased class B .......

What does it exactly mean?

Regards,
Milan

 

[MikeB]

A simple test would be to take a class A amp and reduce the bias to class AB and compare the differences.

Most people would choose the amp in class A. There are differences in the sound that occur that cannot be attributed to distortion alone.

Typically, ClassA use a different topology that is not able to properly
work in ClassAB. Escpecially the singleended versions can't work ClassAB.

"Biasing in ClassB" ???

I thought ClassB has a biasing of 0ma ?

Mike

 

[Upupa Epops]

Is not so far time, when all owners of " Class A " amp will be declared as crime , 'cos they damage " Health of Gaia " , remember on it .

 

[MikeB]

Yes, and all owners of ClassD-Amps go to the EMI-Hell...

 

[Rudy]

To MikeB

as far as i know

Class C = bias current is 0 and vbe off outputpair = 0
Class B = bias current is nearly 0 and vbe off outputpair = 0.6 , they or JUST conducting.

Rudy

 

[MikeB]

Yes, ClassC is obviously not usefull for more than beeping,
and the definition of ClassB is as i remember, that always only one
side is conducting.
But, i think it's much easier to build a ClassAB than a working ClassB.

 

[jam]

MikeB,

I ment in a typical class A amplifier that used complementary outputs as an example to illustrate the differences. See Nelson Pass's articles on the A40 and A75.

Singled ended circuits are generally class A and the comparison would be difficult.

The excersise would be to compare class A operation with class AB operation with the minimum number of variables. Turning up the bias on an amplifer can bring some remarkable differences providing there is adequate heatsinking and the power supply is up to the task.

Regards,
Jam

 

[mr_push_pull]

With boxes with average efficiency ( cca 90 dB/w or less ) you need minimally 100 W/ ch for preservation of natural sound dynamic. On this look is funny amp with output power 10 W. With typical efficiency of class A ( cca 25 % ) you get by amp 2*100 W of output power 600 W of continuous heat. I don't like " good sounding " stove .

What about that Zen version that delivers 10W with a consumption of 400W, if I recall correctly? Anyway, I'm sure that I remember the efficiency (4%) correctly. This should be considered a felony.

 

[Mr Evil]

...What does it exactly mean?..

"Proper" biasing for class B means that each transistor is conducting for exactly half the cycle. A simple complementary pair of output transistors with no biasing will conduct for slightly less than half a cycle each and hence will not technically be class B, but class C.

...I thought ClassB has a biasing of 0ma ?...

Related to the above answer. The definition of class B is that each transistor is conducting for exactly half a cycle. With no biasing at all, there is a place where neither transistor is conducting. Thus you need a little biasing. There will be a little bit of quiescent current flowing because of this, but less than what would normally be considered class AB.

 

[newkirklabs]

Singled ended circuits are generally class A and the comparison would be difficult.

I thought ALL single ended had to be class A. If not, then you would have severe distortion.

Matt

 

[darkfenriz]

biasing class A amp down to class AB is not proper because most A -clacc amps have topologies , which "assume" never swithing off.
but biasing an AB class up to A - that shouldn't make the sound worse unless overheating
cheers

 

[maylar]

"Proper" biasing for class B means that each transistor is conducting for exactly half the cycle. A simple complementary pair of output transistors with no biasing will conduct for slightly less than half a cycle each and hence will not technically be class B, but class C.

That's a sticky point with some engineers. In most classic definitions, Class C is defined as "Significantly less than 180 degrees" and only applies to tuned RF circuits.

Related to the above answer. The definition of class B is that each transistor is conducting for exactly half a cycle. With no biasing at all, there is a place where neither transistor is conducting. Thus you need a little biasing. There will be a little bit of quiescent current flowing because of this, but less than what would normally be considered class AB.

Again, a sticky point. Class B is normally defined as "approximately" 180 degrees per output device, not ~exactly~ 180 degrees. As such, a zero biased bipolar pair would be Class B. Adding enough bias current to eliminate the resulting crossover distortion makes it Class A/B.

The textbook example is a bull horn, where bias is not used because it adds drain to the battery and the distortion you get is not noticeable anyway. They're always referred to as Class B, not C.

That's the definition I learned in Engineering school. Seems it's a bit different around here.