"Class A" nonsense

[mooreamps]

The point I made applies to all audio amps (not RF which is completely different and way off topic).


You mean for RF? Certainly not for audio.

The point you're making applies to only guitar amplifers, not all audio amplifiers. You're not going to over-drive a stereo audio "home theater" amp until the "bias shifts" , and thus it becomes a "different operating class" or some such. Classes of operation are defined in the data sheets of device in question, and the general definitions in RHA, US Navy NEETS, and such.


-g

[Old Tele man]

...shall we 'take a vote' to confirm that this 'dead horse' has been beaten enough all ready?

...or shall we continue with the beating ad nauseum?

[cminor9]

...shall we 'take a vote' to confirm that this 'dead horse' has been beaten enough all ready?

...or shall we continue with the beating ad nauseum?

Amen. This thread is getting to be a little the the vi versus emacs discussions on the olde timey geek BBS'es.








vi is better than emacs, btw.

[balijukka]

I agree, this is not going anywhere.
Let's rest it, it'll raise it's head again in a couple of years.

As you may have noticed, most of our senior specialists here have retained to make any comments. Been through this too many times already.

jukka

[Merlinb]

The point you're making applies to only guitar amplifers, not all audio amplifiers. You're not going to over-drive a stereo audio "home theater" amp until the "bias shifts" , and thus it becomes a "different operating class" or some such. Classes of operation are defined in the data sheets of device in question, and the general definitions in RHA, US Navy NEETS, and such.


-g

I have no idea what you're on about. If an audio amp is Class AB it makes no difference whether it is hifi, guitar, overdriven or otherwise.

[Enzo]

No one must decide to stop the thread, all one has to do is vote by not posting anymore. It will stop when the last poster is done.

[raiken]

PS. since when you and Randall have been on the same side. Who's the turncoat ?

Merlin is the man. His site is where I go when I want to learn something.

RA

[Alex/Tubewonder]

It seems to me some of you guys are confusing definitions of operating classes with standards which are two very different things.

A definition is what it implies, a set of constraints, or design rules if you wish, that allow an individual "skilled in the art" to design an amplifier of a certain class according to its definition.

A standard or norm is a set of measurable minimum parameters values allowing different realizations of a product to be compared against a common denominator.

For example, an old DIN standard required for an amplifier to be a HiFi one to have a flat frequency response. What flat response is can be a question of dispute therefore a standard or norm was imposed against which you could compare your measurements.

Minimum required "flatness" per old DIN norm was IIRC +-1.5 db within 100Hz to 10kHz band relative to 1kHz point, but nothing said your product couldn't be +-0.2db within 20Hz to 20kHz. It would still comply with the standard but if it measured a response flatness +1/-3db rel 1kHz it would not be within boundaries of the norm.

Note that standards do not tell you how you should go about designing your amp to comply, they tell you what and how to measure it and what the minimum limits of compliance are.

Remember old confusion regarding an amplifiers claimed output power? Music power, speech power, steady sine signal power?

Can an AC15 type amp based on 2 EL84s deliver 35W of power? Yes it can. But this figure is meaningless without telling how you defined and measured it.
I can say so in a marketing brochure and if anyone protests I'll just say: read the small print: peak power of one period of a 10kHz square wave. Is it compliant with any standards? Yes, that's how you would measure output power of a pulse amplifier. Is it relevant to an audio or guitar amp? Not in the least, but looks impressive in the fancy brochure.

Standards and norms don't impose operating classes, that's what definitions are for. Since definitions are to certain extent flexible it has given rise to a number of variations like "extended class A", "deep class AB" and so on.

In conclusion, a class A or AB amplifier, designed per conventional class A or AB definition, when driven into clipping is still a class A or AB design, just overdriven.

[balijukka]

designed per conventional class A or AB definition,

That's the problem.
What is conventional class A or AB definition.
The only definition I have seen has the input ac signal as one of it parameters, which makes amplifier class signal dependent.
I do not like it, but that's the way it is.

jukka

[balijukka]

Merlin is the man. His site is where I go when I want to learn something.

RA

Me too, but he can still be hard headed when not wearing his wizzard hat.

jukka

[Alex/Tubewonder]

That's the problem.
What is conventional class A or AB definition.
The only definition I have seen has the input ac signal as one of it parameters, which makes amplifier class signal dependent.
I do not like it, but that's the way it is.

jukka

Wrong. Input signal magnitude does not change the class of amp. It is a design question. You design for maximum possible undistorted OUTPUT signal amplitude, doesn't mean the amp stops being whatever class it was designed in just because you turned down the volume knob. Your car engine is capable of putting out certain max power BY DESIGN not because you have pedal to the metal. Pedal to the metal can be one of requirements to enable the engine to deliver.
Certain input signal level is required BY DESIGN for the amp to deliver max output level. Input signal does not change the DESIGN.
Just like playing "Purple Haze" on a LP will not change it into a Strat.

[Chuck H]

IM(very)HO...

Input signal could be indicated as a defining parameter for a given class because in most designs it CAN effect the operating class. This doesn't mean that an amp driven into a different class by exceeding any indicated input level is no longer the same class. It only means it is not being operated in that class.

So it follows that input level SHOULD be a defining parameter because it DOES effect the class of operation. Still, just because an amp is designed in a way that allows the user to exceed the max input level for it's indicated class shouldn't mean that an amp can no longer be classed there. Output singnals from the source to be amplified can very greatly. So it only makes sense that any amplifiers volume allow for amplification of even very low source output signals.

As was noted by Steve earlier, there is no reason why how an amplifier is classed and how it is operated shouldn't be independent of each other.

Considering that guitar amplifiers, for example, are typically operated outside of their intended parameters, "I" think trying to define operating class in a finite way only further confuses the issue. As is demonstrated by this thread.

Chuck

[balijukka]

You design for maximum possible undistorted OUTPUT signal amplitude,

Now where is a definition that claims so ??
That's what I have been asking all through this thread.
Everyone seems to know for sure that there is a standard definition that says so, but it reality it looks like another urban myth.

jukka

[R.G.]

How To Ride A Dead Horse

Lakota Sioux tribal wisdom says that when you discover you are riding a dead horse, the best strategy is to dismount. However, in business we often try other strategies with dead horses, including the following:

1. Buying a stronger whip.
2. Changing riders.
3. Changing to another dead horse.
4. Grimly continuing to beat the dead horse while saying things like "This is the way we always have ridden this horse."
5. Appointing a committee to study the horse.
6. Arranging to visit other sites to see how they ride dead horses.
7. Increasing the standards to ride dead horses.
8. Appointing a tiger team to revive the dead horse.
9. Creating a training session to increase our riding ability.
10. Comparing the state of dead horses in today's environment.
11. Revisiting the performance requirements for horses to determine if dead horses might not be acceptable for the immediate needs after all.
12. Changing the definition of "dead" so that the horse does not qualify under it, making the horse not "dead".
13. Hiring contractors to ride the dead horse.
14. Harnessing several dead horses together for increased speed.
15. Hiring or appointing a team of expert consulting riders to see if a highly focused team approach can get the dead horse to work better.
16. Declaring that "No horse is too dead to beat."
17. Providing additional funding to increase the horse's performance.
18. Doing a CA Study to see if contractors can ride it cheaper.
19. Purchasing a product to make dead horses run faster.
20. Declaring that the horse is actually "better, faster and cheaper" or “a better value” if it's dead.
21. Forming a quality circle to find uses for dead horses.
22. Revisiting the performance requirements for horses.
23. Saying that the horse was procured with cost as an independent variable.
24. Promoting the dead horse to a supervisory position.
25. Hiring consultants to review dead horses on other continents to see if riding dead horses can be off-shored.

[Enzo]

In other more or less scientifically oriented forums where I visit, there are lively and equally pointless discussions over whether 0.99999999... and 1 are equal. Oh the mighty arguments that fly supporting either position.