Pure Class A Push Pull

megasat16

I am bored! So, Let's hear it. I quoted a few uber amps (not to be confused with tuber amps) that claims Pure Class A amps. They don't use Single Ended output stage. All of the ones I quoted below utilize multiple Push-Pull output transistors pairs. Some of them even have enough reserve current to double output power whenever load impedance is halved while maintaining Pure Class A output.

Traditionally, only SE amps are qualified to be called Pure Class A. So, What gives? Is it marketing strategy or pure ploy to rake in your money? Or is it that they invented sort of new Class A? Or is it that these amps are Biased and designed in a way for each half of the parallel transistors pairs acting as SE- and SE+ and summation at the output so essentially all N side pairs and all P side pairs are always in pure Class A state?

References :

1. From Pass Labs XA series Power Amp Series

X.5 and XA.5 amplifiers utilize the same basic circuit topology and gain devices. They differ in the sizes of the power supplies, the chassis and heat sinks, and the number of output devices. The output stages of the X.5 series are operated in heavily biased Class AB, with an idling dissipation similar to the rated output. The XA amplifiers operate pure Class A with idling dissipation more than twice the rated output.

2. From Luxman Integrated Amp

We have reviewed L-590A, the memorial model for 80th anniversary of our foundation, from its basic performance, refined it, and finally developed the second version, that is L-590AII. The separation performance has attained to the level of high-end models by carefully examining all the circuits including introduction of the pure class A operation with 30W + 30W (8Ω) to acquire condensed sound reproducibility and the high sound quality selector switch IC used in the top-end control amplifier, C-1000f. L-590AII is a top-end model of our integrated amplifier with pure class A amplification method, which is refined to the details by increasingly pursuing strong drive force and condensed sound.

3. From Accuphase A65 Power Amp

Pure Class A operation delivers quality power: 60 watts ? 2 into 8 ohms m Power MOS-FET output stage features 10-parallel push-pull configuration and delivers linear high power progression to ultra-low 1-ohm impedances

quadzilla

Nothing in a class A design says you can't use push pull.

fishbones

Wish I could afford one of those Luxman Integrated's, they're beautiful!

<shakes his head out of daydreaming> - uh, back to the OP's subject...

stuwee

Yamaha

■ Hyperbolic Conversion Amplification Circuit
■ Advanced Power Supply Circuitry (APS)
■ High Dynamic Power
■ Three-Pair Speaker Support
■ LCD (Liquid Crystal Display) Power Level Meters
■ Overload Protection Circuitry






Hyperbolic Conversion Amplification Circuit
This new kind of circuitry, developed by Yamaha, eliminates the only serious drawback of previous Class A operation amplifiers. These had to switch to non-linear class AB operation above a certain load current, causing a slight deterioration in the otherwise excellent sound quality. The new Hyperbolic Conversion Amplification Circuit does away with this problem, allowing your Yamaha MX-800/U to deliver superior performance constantly, without switching or cut-off, over its entire power range.

Advanced Power Supply Circuitry (APS)
An amplifier is only as good as its power supply = this simple truth has prompted Yamaha to develop the APS circuitry incorporated in your new MX-800/U. The problem with conventional power sources was their tendency to produce pronounced voltage ripples during medium to large amplitude music signals, particularly under low impedance loads, together with voltage fluctuations in the power transistors. APS solves this problem by providing an active power source that ensures stable voltage in the final transistor stage under all operating conditions, thus greatly improving power supply to the amplifier.

heiney9

stuwee wrote: »

Yamaha

■ Hyperbolic Conversion Amplification Circuit
■ Advanced Power Supply Circuitry (APS)
■ High Dynamic Power
■ Three-Pair Speaker Support
■ LCD (Liquid Crystal Display) Power Level Meters
■ Overload Protection Circuitry






Hyperbolic Conversion Amplification Circuit
This new kind of circuitry, developed by Yamaha, eliminates the only serious drawback of previous Class A operation amplifiers. These had to switch to non-linear class AB operation above a certain load current, causing a slight deterioration in the otherwise excellent sound quality. The new Hyperbolic Conversion Amplification Circuit does away with this problem, allowing your Yamaha MX-800/U to deliver superior performance constantly, without switching or cut-off, over its entire power range.

Advanced Power Supply Circuitry (APS)
An amplifier is only as good as its power supply = this simple truth has prompted Yamaha to develop the APS circuitry incorporated in your new MX-800/U. The problem with conventional power sources was their tendency to produce pronounced voltage ripples during medium to large amplitude music signals, particularly under low impedance loads, together with voltage fluctuations in the power transistors. APS solves this problem by providing an active power source that ensures stable voltage in the final transistor stage under all operating conditions, thus greatly improving power supply to the amplifier.

That's the kind of marketing crap I was referring to in the last thread about class A. The above is one of the examples of trying to capitalize on the class A buzz and twisting around so severely that it becomes a completely new definition (which is not class A)..........I sold similar Yamaha amps when new and it was all marketing and no substance.

It's like Monarchy (oops the cat is out of the bag) marketing their SE-100 mono blocks as pure single ended class A and then when pressed for an explanation stating "the Mosfet operate in the Mhz range, and they are so fast, switching distortion is a non-issue" That's not single ended class A. Still the amps sound very good.........just that kind of marketing really irks me.

H9

P.s. James, I've stated my POV, poorly, in the other thread so I'm not taking the bait here.

steveinaz

fishbones wrote: »

Wish I could afford one of those Luxman Integrated's, they're beautiful!

<shakes his head out of daydreaming> - uh, back to the OP's subject...

Me too, I'm looking HARD at the L-505U.

mhardy6647

quadzilla wrote: »

Nothing in a class A design says you can't use push pull.

Exactly so.

Class A has nothing to do with output topology (SE vs. PP) and everything to do with bias (the operating points of the output device or devices). Basically class A means "on" all the time; the output devices are dissipating full power all the time. Basically 100% of this output power is dissipated as heat when there is no signal; the amps provide power to the load (speakers) when signal is present, so in theory, at least, they actually generate less heat when amplifying signal than at idle. It is terrifically inefficient, but it eliminates distortion and nonlinearities related to turning the devices "on" and "off" as in class B.

It's easier to understand in the context of vacuum tubes than it is in terms of solid state devices (isn't everything?!); I like this page's explanation.
http://www.duncanamps.com/technical/ampclasses.html

You might want to look at this one, too:
http://sound.westhost.com/class-a.htm

Single-ended amps have to be Class A; Push-pull amps can be Class A, Class AB (intermediate bias points), or Class B (Class C is of no interest for hifi, but is an important, and efficient, operating point for transmitter outputs).

Yes, in intervening decades a bunch of sliding-bias quasi-Class A designs have appeared, flourished, died, or become endemic in the hifi game. They're "hyperbolic" (as in hyperbole), all right :-)

megasat16

Thanks fellas for the replies. But I think I didn't stress enough the word "PURE" or the meaning of the word. I understand there are lots of Class A variations and everyone has their own things.

PURE Class A.

Class A output waveforms can be designed with many kinds of clever biasing scheme but this is not what I am talking about.

PURE is such a reserve word in all of the Class A fantasy and it's only allowed to use for the SE design by the Purists traditionally. It's an equivalent to the SE Triode Class A for the tubers.

Now, it can't be right coz the word Pure is now used with Push-Pull output stages. I know Brock is not taking the bait but at least I tried.

Yamaha Parabolic Class A is another kind of quasi Class A and cleverly thought out Class A biasing scheme while yamaha attempted to boost Class A amp efficiency. But it's been only partially successful in marketing to the Class A folks.

megasat16

For the folks who is interested in the Luxman L-505U, here is a nice one for not a bad price. No affil...

http://cgi.ebay.com/LUXMAN-L-505U-INT-AMP-115V-60Hz-/260754032078?pt=LH_DefaultDomain_0&hash=item3cb626c5ce


But it is not Class A. It is Class A/B Integrated.

fishbones

He has a listing on A'gon too, but at $2,800obo.

strider

megasat16 wrote: »

Thanks fellas for the replies. But I think I didn't stress enough the word "PURE" or the meaning of the word. I understand there are lots of Class A variations and everyone has their own things.

PURE Class A.

Class A output waveforms can be designed with many kinds of clever biasing scheme but this is not what I am talking about.

PURE is such a reserve word in all of the Class A fantasy and it's only allowed to use for the SE design by the Purists traditionally. It's an equivalent to the SE Triode Class A for the tubers.

Now, it can't be right coz the word Pure is now used with Push-Pull output stages. I know Brock is not taking the bait but at least I tried.

Yamaha Parabolic Class A is another kind of quasi Class A and cleverly thought out Class A biasing scheme while yamaha attempted to boost Class A amp efficiency. But it's been only partially successful in marketing to the Class A folks.

Are you saying there are sub types of Class A?

heiney9

strider wrote: »

Are you saying there are sub types of Class A?

Yes, there has long been a debate about what the definition of class A is much like the debate about whether or not negative feedback should be used.

The term class A is so watered down because it can mean a hundred different things that their really is no clear or stated definition. My definition or as I understand it from my resources differs greatly with others definitions and the marketing departments at a lot of the mainstream manufacturer's leverage the term class A to the hilt.

It's a buzz word like "new and improved" and one has to really read between the lines or ask the right questions to understand they aren't always getting what they think they are getting.

Many of these sound good and a few sound great. Monarchy being my current prime example of using marketing misnomers to classify an amp to compete with higher end amps. But when pressed about the design admits it's not really as advertised but then plays it down like it doesn't matter anyway.

But, the amps sound really good and they are affordable so in the end if the consumer purchases based on sketchy marketing terms they are still happy. But that isn't always the case.

H9

mhardy6647

megasat16 wrote: »

Thanks fellas for the replies. But I think I didn't stress enough the word "PURE" or the meaning of the word. I understand there are lots of Class A variations and everyone has their own things.

PURE Class A.

Class A output waveforms can be designed with many kinds of clever biasing scheme but this is not what I am talking about.

PURE is such a reserve word in all of the Class A fantasy and it's only allowed to use for the SE design by the Purists traditionally. It's an equivalent to the SE Triode Class A for the tubers.

No, it's not. Nelson Pass has been designing "pure" class A push-pull (and, in fairness, single-ended) soiled state amplifiers longer than many folks on this forum have been able to construct sentences. And, yeah, he's been responsible for some "impure" ones, too.

Class A is Class A whether the devices are tubes or transistors. Class A is like virginity. It is or it ain't. The sliding-bias stuff is another kettle of fish.

megasat16

mhardy6647 wrote: »

No, it's not. Nelson Pass has been designing "pure" class A push-pull (and, in fairness, single-ended) soiled state amplifiers longer than many folks on this forum have been able to construct sentences. And, yeah, he's been responsible for some "impure" ones, too.

Class A is Class A whether the devices are tubes or transistors. Class A is like virginity. It is or it ain't. The sliding-bias stuff is another kettle of fish.

Mark, you are saying that coz you are impurist. :eek::biggrin:

Purists will never allow such denomination. There is only the one. i.e. Single Ended Class A is pure Class A and others ain't.

Of coz, I agree with you since I am sort of both purist and impurist too. :eek:

heiney9

To me pure class A is Single Ended and I think many of the top designers would agree, maybe not publically because they would shoot themselves in the foot because so few are even producing single ended class A amps anymore. To costly, heavy and inefficient.

They is only the one. i.e. Single Ended Class A is pure Class A and others ain't.

Yep, I fall into that camp, mostly. I am intrigued by the XA series because it seems to be able to walk the fine line of giving SE performance up to the rated output, but then can give more beyond that if needed, but one would rarely need to go beyond the SE portion of the output stage. And it's totally different than a sliding bias scheme or dynamic bias scheme or straight high bias A/B. But from a strictly purists POV it would be difficult to argue it's Pure Class A.

H9

megasat16

strider wrote: »

Are you saying there are sub types of Class A?

There are variations to Class A amplifier topology in order to increase efficiency. They are not fully ON at all time and biasing is controlled with clever methods.

They are known as Quasi Class A (Victor, JVC, Sony), New Class A (Technics), Class AA+(Technics), Sliding Bias Class A (many including that of ML), Sustaining Plateau Class A (Krell), Hyperbolic Class A (Yamaha), etc.

All of the above uses Push-Pull transistors output.

And then, there are two FULL On type Class A which doesn't use these gimmicky biasing techniques. There is Single Ended (using N Type Only) and then there is Push-Pull Type Full On Class A.

Now, we are talking about the latter type Full On Push-Pull Class A.

There is this purist group which would accept real Pure Class A comes in only one form and that is Single Ended type. They would accept no haggling and allows no other type Class A called Pure Class A.

mhardy6647

on second thought...

FTGV

mhardy6647 wrote: »

Class A is Class A whether the devices are tubes or transistors. Class A is like virginity. It is or it ain't. The sliding-bias stuff is another kettle of fish.

Exactly .

heiney9 wrote: »

To me pure class A is Single Ended.

H9

Still riding that 3 legged horse eh Brock?

megasat16

Mark (mhardy),

I know you changed your mind about the post you made earlier but I happened to read it so here is my answer.

I am sort of Electronics Engineer without Math Skills coz I left EE field a very long time (by my standard) ago.

But it doesn't matter, I still understand the design concepts and technologies (less Math). I also left my precious books somewhere that I don't want to reveal.

Anyway, the view of purists are not distorted. But you can say that they are ancient. It's coz SE is definitely only Real Class A operation in the beginning. And when everyone moves into the improving Class A, they dwell onto this believe that the Class A can't be Pure if not SE.

Preamps and amps are similar in a sense but yet different. You can have all True and Pure Class A preamp using SE topology with differential (balanced) outputs. Or you can have real differential preamp using all differential push-pull circuits (true differential) with balanced outputs.

But you can't have balanced output from an amp to the speakers for the obvious reason.

There are a few here who needs to ponder why Push Pull Class A can't be called Pure Class A or why they only accept Pure Class A applies to the SE.

heiney9

FTGV wrote: »

Still riding that 3 legged horse eh Brock?

Yep, if someone tells me it's pure Class A, I expect it to be single ended. Not saying one is better or that I wouldn't own an amp that wasn't single ended just telling you what the terminology means to me and my expectation if someone uses that term.

H9

heiney9

Is it ok to call a design single ended pure class A and the have it actually be a high biased class A/B that moves out of class A after only a small percentage of the rated output? Meaning it's not a push/pull design that only operates in class A.

That's the problem I have witk some manufacturer's mis-using the term "pure" and "single ended". Where does it end? Where's the cut off before something isn't really pure Class A by your definition?

FTGV

heiney9 wrote: »

Is it ok to call a design single ended pure class A and the have it actually be a high biased class A/B that moves out of class A after only a small percentage of the rated output?

Ofcourse not and never suggested such.

TECHNOKID

heiney9 wrote: »

Is it ok to call a design single ended pure class A and the have it actually be a high biased class A/B that moves out of class A after only a small percentage of the rated output? Meaning it's not a push/pull design that only operates in class A.

That's the problem I have witk some manufacturer's mis-using the term "pure" and "single ended". Where does it end? Where's the cut off before something isn't really pure Class A by your definition?

The OP would have been better off to call is thread "Class A Push Pull" rather than "Pure Class A Push Pull". When you start creating a technology that shares 2 technologies IMO it is called Hybrid and Hybrid is not Pure!

heiney9

FTGV wrote: »

Ofcourse not and never suggested such.

Fred, didn't say you did or James either.......my point is, and always has been, the terminology is abused.......so one just needs to know what they are really looking at in some cases.

H9

megasat16

FTGV wrote: »

Ofcourse not and never suggested such.

Yep! Agreed.

heiney9 wrote: »

Is it ok to call a design single ended pure class A and the have it actually be a high biased class A/B that moves out of class A after only a small percentage of the rated output?

Of coz not. It's never is True. I echo what Fred said.

Meaning it's not a push/pull design that only operates in class A.

That's where you are having a problem. Push Pull or SE has nothing to do with Class A topology. You need to see behind the Class A topology.

That's the problem I have witk some manufacturer's mis-using the term "pure" and "single ended". Where does it end? Where's the cut off before something isn't really pure Class A by your definition?

IMO, I think the term Pure is a double edge sword. It's loosely defined and by Purists. In very simple word, Pure Class A means something that is FULL ON / ALWAYS ON (full 360 degree conduction occurs in a transistor).

So, depending on biasing technique, push-pull transistors can be made to be ALWAYS FULLY ON within Class A region or conducting all 360 degrees of a wave form and it can be called Pure Class A?

The trick is with the driver and the power supply design (for output doubling in the Pure Class A amps)

megasat16

TECHNOKID wrote: »

The OP would have been better off to call is thread "Class A Push Pull" rather than "Pure Class A Push Pull". When you start creating a technology that shares 2 technologies IMO it is called Hybrid and Hybrid is not Pure!

Yeah, you are another one that needs to read this thread. I intentionally named this thread PURE CLASS A PUSH PULL for a reason.

Read the references I give in Post # 1? It's about Pure Class A using Push-Pull output transistors.

heiney9 wrote: »

Fred, didn't say you did or James either.......my point is, and always has been, the terminology is abused.......so one just needs to know what they are really looking at in some cases.

H9

No, you have not said that. But someone abusing the terminology doesn't make that Pure Class A only comes in SE form.

TECHNOKID

megasat16 wrote: »

Yeah, you are another one that needs to read this thread. I intentionally named this thread PURE CLASS A PUSH PULL for a reason.

Read the references I give in Post # 1? It's about Pure Class A using Push-Pull output transistors.



No, you have not said that. But someone abusing the terminology doesn't make that Pure Class A only comes in SE form.

What you don't understand, from it birth class A has been single eneded, from its birth Class AB has been push pull. Class A Push Pull is hybrid, it uses part of the 2 technolgies so it not pure. If you want to call it pure, give it another name. Pure lab mixed with pure husky is no longer pure, it can become another pure race but it is no longer pure husky nor pure lab. Nothing wrong with hybrid if it makes the best of both world but it can claim to be pure unless you name it pure something else.

megasat16

TECHNOKID wrote: »

What you don't understand, from it birth class A has been single eneded, from its birth Class AB has been push pull. Class A Push Pull is hybrid, it uses part of the 2 technolgies so it not pure. If you want to call it pure, give it another name. Pure lab mixed with pure husky is no longer pure, it can become another pure race but it is no longer pure husky nor pure lab. Nothing wrong with hybrid if it makes the best of both world but it can claim to be pure unless you name it pure something else.

I understand what you are saying alright. In fact, I never doubted the 1st part. :biggrin:

Now, the question is that Push Pull always been a Class AB? Or can push pull only be Class AB and not Class A? Why?

Are you saying Pass Labs oversold the XA series amplifier as Pure Class A amps coz it's not Pure by the sense it's using Push-Pull output stage instead of Single Ended output stage? How about Accuphase and Luxman? Are they all overselling their products as Pure Class A? Why is it called Pure Class A?

It's the theme of this thread! Why can't Pure Class A can't have Push-Pull output transistors? If you read my Post # 1, the question (possibly the answer) is written in there.

FTGV

heiney9 wrote: »

It's like Monarchy (oops the cat is out of the bag) marketing their SE-100 mono blocks as pure single ended class A and then when pressed for an explanation stating "the Mosfet operate in the Mhz range, and they are so fast, switching distortion is a non-issue"

But does it have complimentry pairs of output devices(push-pull).If not it has to be SE thus Class A

heiney9 wrote: »

...my point is, and always has been, the terminology is abused.
H9

OK but I understood your point in this and the other thread to be that Push Pull and Class A were mutually exclusive.

doctor r

Though this is focused on tube output the theory and explaination of this white paper by Kevin Hayes the owner and designer at VAC will touch upon true class A push pull theory and design goals. This can easily be applied to transitor output also in a conceptual way.

Technical Monograph - Class of Operation

Rick

megasat16

Rick (Doc. R)

Very nice article based on Tube output theory. It's the same concept applies to Transistors. It's all about Class A biasing in the pre-driver stage.

In fact, Class A (I don't want to call it Pure coz it's a technical jargon by purists) Push-Pull full on power amps using transistors have been around since the early 70s. But they are a rarity due to size, weight, cost, complexity and many problems / failure with them. So, not many company or people build them. Instead, push-pull were easier to implement for Class AB and everyone build Class AB. I think later everyone seem to think Push-Pull is always Class AB.