Output classes A and AB
 

Please note the interpolations.

On Oct 24, 3:42 pm, flipper wrote:

This is what I meant. People seem to be losing track of who said and
meant what.

I am not so sure that losing track is the correct description of what
is going on. It more-or-less started with a statement that a Certain
Amp was a Model for various reasons amongst which was an apparent
broad Class A operational range before it went to AB.

So, an amplifier *may* operate in Class A mode for some range based on
its design.

I may have missed something but as far as I can tell *that* is the
'argument'.

I don't think anyone would disagree even for a hummingbird heartbeat
that some AB amps have some range of A operation before they go AB. It
is how one would describe and represent the amp overall that is at
issue.

But it cannot, must not, nor should it be classified as a
Class A amp if it does not operate in Class A at all ranges.

I haven't seen anyone claim that a Class AB amp is 'actually' a Class
A amp, or should be 'classified' as an 'A' something, or any variation
of the theme.

Otherwise, what we have is a marketing ploy because as previously
stated: Class A = Good Class AB = Not So Good

I think you're worrying about something that no one in here is guilty
of and, near as I can tell, the 'argument' revolves around the claim
by Multi-grid:

"That both tubes are conducting does not mean it is
A. Have some respect...:) AB amps don't have any A power, that is why
there is a separate classification."

It would seem to me that with your comment above saying "an amplifier
*may* operate in Class A mode for some range" that you are disagreeing
with Multi-grid.

I do not necessarily agree with Douglas. I just find the rebuttals to
his statements mostly either technically inept (as from Andre) or
technically elegant (as from John) but beside the point.

Btw, just as a matter of discussion, I see where you're trying to go
with the V8 analogy but I don't think it holds, as given, because 2,
4, 6, and 8 cylinder operation is not a 'natural' consequence of the
'engine class V8' while 'A' and 'B' (loosely defined) are for 'Class
AB'.

Actually, it was John that postulated a series of controls on an AB
amp that would force it (hold it in) to A class only. So, the analogy
of an 8 held to 4 or 6 cylinders only holds under that description.

I think a closer, albeit still 'stretched' quite a bit, analogy would
be if we defined 'engine classes' 4, 8 and "4-8," and then pondered if
a 'Class 4-8' engine was operating 'Class 4' during the times when
only 4 of the cylinders were firing. If the definition for 'Class 4'
was "4 cylinders firing" then one might say it was, despite some
differences, since 4 cylinders are firing under those conditions; Akin
to 'Class A' being the tubes conducting 360 degrees, a situation that
occurs in Class AB amps under certain conditions.

Oh, the entire engine analogy is stretched more than taffy on a hot
day in Atlantic City. But for all that, it is as valid as any other
points made along the line in this particular thread - again excepting
the direct contributions from Patrick which are right into the nitty-
gritty of the situation.

And one might wish to talk about under what conditions the 'Class 4-8'
engine makes the transition from 'Class 4' to 'Class 8' operation
because if it did so at the slightest hint of needing more power it
might make for 'zippy' performance at the expense of fuel efficiency
while a 'Class 4-8' engine reluctant to do so might be more efficient
at the expense of 'zippy' throttle response. But, IMO, saying "it's
Class 4-8, period, there is no Class 4 power" simply serves to obscure
it's operation for no useful purpose.

Well, it ain't nohow a "4-only" and it ain't nohow an "8-only", so it
must be something else. The only accurate label would be a "4-8". That
it operates in either mode is a function of its design. But it belongs
to neither unique class.

It might also be useful to point out, as you did, that 'Class 4'
operation of a 'Class 4-8' engine is not '100% equivalent' to 'Class
4' operation in a true 'Class 4' engine (depending on how well
designed each is) because you're dragging along dead cylinders, a
necessary consequence of it being a 'Class 4-8' engine, and, by the
same token, 'Class A' operation in a Class AB amp is not '100%
equivalent' to a true Class A amplifier (depending on how well
designed each is) for the same reason: the 'Class A' region of a Class
AB amp is compromised by the necessities of it being a Class AB amp.

Yep. And that is contributory to the point but not critical to it.

However, there's nothing in the 'Class' definitions that speaks to
'optimal', 'well designed', or 'equivalencies'.

Amen to that! There is quite a bit of ineffable crap out there. Some
of it is very expensive and uses very expensive boutique-type tubes
for no other reason than that they are expensive boutique tubes -
certainly not for the quality of the signal coming out of them. Why,
even their makers and defenders will wax poetic about how these amps
"add coloration" to the signal that makes them an "instrument in their
own right" and such twaddle. It is those sorts who will wax poetic
about that little bit of "Class A" operation in an AB-designed amp as
some great virtue. In point of fact, this would necessarily require
that the AB operation of the same amp is somehow faulty. Otherwise a
properly designed amp would be A only and t'h*ll with the headroom.

Once again, unless we are dealing in an Orwellian world, it just isn't
necessarily so.

Peter Wieck
Wyncote, PA

Output classes A and AB
 

In article . com,
Peter Wieck wrote:

It is those sorts who will wax poetic
about that little bit of "Class A" operation in an AB-designed amp as
some great virtue. In point of fact, this would necessarily require
that the AB operation of the same amp is somehow faulty. Otherwise a
properly designed amp would be A only and t'h*ll with the headroom.

I don't see how the one follows from the other, could you please explain
the logic you used in arriving at this conclusion?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

GM V8-6-4 (was Output classes A and AB)
 

In article .com,
Peter Wieck wrote:

Point being that the GM V8 remains a V8 even though it is *capable* of
operating in 4 or 6 cylinder modes - albeit at much a much reduced PtW
ratio. And it could also be modified with a suitable network of
controls to remain in either 4 or 6 cylinder mode at all times - and
therefore *technically* be described as a 4 or a 6. It is certainly
not anyone's idea of a V8 anymore - nor what should be a good idea of
a 6 or 4.

Which, of course, would be a 100% marketing ploy, wouldn't it? To call
it a 4 or a 6 by virtue of the modifications?

I'm not sure it was a pure marketing ploy, especially given that I have
seen ads for a current model car that uses this same idea today,
unfortunately I forget what car it is, it might even be a Cadillac,
although I would think they would be too gun shy to try it again. At
any rate the reason I started this sub thread was to ask if anyone more
knowledgeable about engines than you or I knows the theory of the 8-6-4
engine and how it was supposed to improve gasoline mileage, which as I
remember it was what the hype said it was supposed to do? The only
potential efficiency gain that I can see is that it would presumably
reduce throttling losses a bit, but there must be more to it than just
that, does anyone know? I guess I should ask Google.

As a purpose-built 4 or 6 would be a much better solution, wouldn't
it?

Better solution for what problem?

And that same purpose-built 4 or 6 could be made with the same
displacement, potential output HP and torque as a V8, couldn't it?

Yes, but a 4 cylinder engine with the power of a V8 might be a little
rough for many Cadillac buyers.

And that would, of course, cost a pretty penny - more than a similar
displacement & output V8?

I would expect that a V8 would cost more than a 4 of similar
displacement, simply based on the parts count, but what do I know. The
4 would probably require some more expensive drive train parts than the
V8, at least in manual transmission applications.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

Output classes A and AB
 

In article .com,
Multi-grid wrote:

Well Andre, you've stepped in it this time...:) AB operation cannot
effectively cancell *ANYTHING*.

Odd sums anyway.

Thanks for that clarification.

Not second HD( or the even of any order ) because each phase is biased
where the characteristics are changing too rapidly with plate current.
This is the rest of the Class A definition that is implied, the finals
are biased so that the change in characteristic for the opposing
phases approximately cancells( and thus the even HD ).

That's a bunch of nonsense and drivel, if the cancellation were simply
the result of "the finals are biased so that the change in
characteristic for the opposing phases approximately cancels", then the
amount of odd order distortion could also be changed by PP connection.
The fact is that the even order cancellation is not dependent on the
biasing of the tubes, beyond the requirement that the two tubes are
identical and are both biased the same.

Check your High School Trigonometry book to understand why the even
harmonics cancel while the odd ones don't, it's a simple bit of math
that doesn't depend on bias, only that the two sides of the PP circuit
are identical. IIRC even PP class C amplifiers cancel even order
distortion, this was made use of in early FM broadcast transmitters to
minimize interference with high band VHF Television stations, without
the need for a harmonic filter in the output of the FM transmitter.

It is why the
AB amp can't be labled A while both phases of the finals are
conducting( or that that single definition is not enough to describe
Class A ).

It isn't obvious by what logic you arrived at that conclusion?

The x power in A, and XXX power in AB is just serving notice that
marketing had its way with the ad copy.

You aren't by any chance one of Peter Wieck's sock-puppets are you?

AB was an obvious means of minimizing cross-over distortion

Class AB simply moves the crossover notch up to a higher amplitude point
on the signal waveform, if you really want to minimize the crossover
notch you should have Patrick design and wind you an OPT designed
specifically to minimize the crossover notch, or go with a McIntosh
design.

and maximizing power.

Class B operation would be even better for maximizing power.

It works just as well for directly heated triodes
with no NFB as it does for pentodes like the KT88 running a lot of
it...:)

Yep, it sure is great stuff!


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

Output classes A and AB
 

On Oct 24, 10:48 am, John Byrns wrote:
In article .com,
Andre Jute wrote:

Historically, the original purpose of Class AB was to annihilate the
second harmonic which before made up such a very large part of the
THD, while still allowing beam tubes and pentodes to give much larger
power than available before.

Andre, why was Class AB necessary to annihilate the second harmonic,
didn't Push Pull operation already annihilate the second harmonic
irrespective of the class of operation?

Well, yes, but who would want a strictly Class B tube amp? It'll be
harsh and nasty and the THD will be grim. On the other hand, there was
an urgent demand (possibly only from the marketing department,
possibly from speaker manufacturers -- these things are very rarely
consumer-led) for more output than available from SE or even Class A
triodes. Class AB, a natural for the new multi-grid tubes, was for the
time a perfect compromise between the "waste" of Class A and the (at
the time) incredible power available from push-pull operation of beam
tubes and pentodes, *and* Class AB had a lower NFB requirement than
Class B, all others things being equal of course, and thus better
stability margins. All of this happened at the same time ever-lower
THD numbers became the chief marketing tool; it followed in turn that
the THD should be attacked where it was most vulnerable and where it
would give the biggest fix in the least time for the lowest cost, and
that was at the second harmonic. So, you don't want Class B because it
is crude, you can't have Class A because it is too expensive for the
power you want, you must have a lot of stable power with low THD,
bingo, Class AB saves your butt. You have to look at the entire
package of elements that drove the general swing towards Class AB.

Having looked, from a closer vantage point than ours, at the package
of elements, Langford-Smith himself tells us in the RDH4 (Newnes
1997) on p 545 that:
"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."

In Langford-Smith's eyes, therefore, it seems that what drove the
choice of Class AB was the ability to retain most of the power
available in Class B while reducing THD a very big chunk, without the
instability that would follow on the heels of the amount of NFB to
achieve the same task in Class B.

The "invention" of Class AB as a hi-
fidelity amp is what spurred part of a Olsen's work on perception;
before it wasn't known that odd harmonics are proportionately much
more disturbing than even harmonics. It seems to me that AB amps with
largish parts of their output in Class A is a relatively modern trend,
possibly related to ever less-sensitive speakers.

I'm not sure I would agree with that, class AB amps were common even in
the days of efficient speakers, I don't see it as "a relatively modern
trend", if anything is a modern trend, I would think it is the return to
"pure" class A amplifiers on the part of many audiophiles.

Sure, Class A1 amplifiers, as in SE 300B amps, are big since say the
mid-80s. But I think if you go into the history of how much of the
total power of typical Class AB amps at every period was available in
Class A, I think you will find that in the days of sensitive speakers,
when the first watt truly was everything that mattered, the Class A
benefice was quite low, a handful of watts perhaps. It is only in fact
since the 1950s that it was known to specialists that third and higher
odd harmonics are disproportionately more disturbing than the even
harmonics; you can still see the willful resistance, arising from
ignorance, to my practice of designing amps to shape the residual
harmonic artifacts so that the odd residuals are miles below the
fractional remaining second harmonic. Again, those tubes like 807s
when operated in triode were naturals for Class AB, with a naturally
beneficial harmonic spectrum; these things fell out naturally without
the obsessive thought we put into the tiniest detail these days,
bedevilling retrospective analysis.

Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

Of course I could be wrong. I wasn't there, I don't have twenty-twenty
hindsight, and the few amps whose histories I know about are not
exactly in the mainstream. One has to read very carefully between the
lines to understand what someone like Langford-Smith tell you when he
speaks of motives driving commercial choices rather mere engineering
facts: his milieu and assumptions were very far from ours.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Output classes A and AB
 

Eeyore wrote:

Andre Jute wrote:

In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie
Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1
amps would be impossible, and all other classes would produce zero
music -- in fact all other classes would produce 100 per cent pure
noise by being operated at all sonic peaks at either max current and
zero voltage or zero current and voltage plate overvoltage. All of
that follows logically from Poopie's absurd redefinition of Class A as
a Class in which "the output device(s)never cease conducting *under
any signal condition*," (emphasis added). It's ludicrous.

It's actually the only accurate definition.

I've already demonstrated several times that your words "under
any signal condition" make your definition grossly inaccurate. I have
already told you, Poopie Stevenson, three times that your definition
is grossly inaccurate and why. Worse, you, Poopie Stevenson, have
already admitted that your definition should be rewritten as I told
you to rewrite it, three times in all:
******
Poopie wrote:
Do please, if you desire, change it to 'any valid signal
condition for which the amplifer is rated'.
******
Nah, Poopie, we don't only desire it, we demand it, because this kind
of ignorance that you display so stubbornly reflects badly on all of
us.

Any amp can be driven out of class by excessive signal voltage.

Overdriving to cut-off is merely gross abuse and a complete red herring /
irrelevance.

Precisely. That is what I explained to you, three times in all, plus
once more from Flipper, before you finally understood and stopped
following along behind Dougles Zero-sound like a fat little lost lamb.
You are a very slow learner, Poopie.

You really should constrain yourself to talkind about stuff you understand.
Which would seem not to be very much going by your posting history.

Me? Come on, Poopie, I'm not the one who claimed for several days that
a Class A stage is one in which "the output device(s)never cease
conducting *under any signal condition*." You're the one who committed
that stupidity, and so many others. *You* really should constrain
yourself to talking about stuff you understand -- which would seem not
to be very much going by your posting history.

Graham

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Output classes A and AB
 

Poopie Stevenson aka Eeyore
wrote:
John Byrns wrote:
Andre Jute wrote:

Historically, the original purpose of Class AB was to annihilate the
second harmonic which before made up such a very large part of the
THD, while still allowing beam tubes and pentodes to give much larger
power than available before.

Andre, why was Class AB necessary to annihilate the second harmonic,
didn't Push Pull operation already annihilate the second harmonic
irrespective of the class of operation?

Yes, you are right. It does.

The SOLE purpose of AB is to produce larger power outputs using the same tubes.

Now this poor dumb slow learner Poopie Stevenson, an embarrassment to
everyone who comes into contact with him, claims to know more than the
RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this
nugget of authoritative information by F. Langford-Smith B.Sc. B.E.
himself:

"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."

You're a fool, Poopie. You should have taken a tip from John Byrns and
asked a question rather than made a statement you cannot back up.

The dissipation in the output tubes is very considerably lower than that in
Class A.

You're blowing smoke out of your arse, Poopie. I'm clearly talking
about output power but you try to muddy the water with "dissipation in
the output tubes". You're not only a clown, you're a transparent
clown.

Or are you perhaps, in line with the ignorance generally displayed in
your posting history, trying to claim that more output power is
available from Class A than from Class AB? That would be a new nadir
of stupidity even for a man who just claimed that Class A devices
should conduct 360 degrees "under any signal condition".

Graham

Andre Jute
The trouble with Poopie Stevenson is not what he doesn't know, but
what he knows for certain that isn't true. --- with apologies to Mark
Twain

Output classes A and AB
 

That's a bunch of nonsense and drivel, if the cancellation were simply
the result of "the finals are biased so that the change in
characteristic for the opposing phases approximately cancels", then the
amount of odd order distortion could also be changed by PP connection.
The fact is that the even order cancellation is not dependent on the
biasing of the tubes, beyond the requirement that the two tubes are
identical and are both biased the same.

So then John, when one is cut off, what is cancelling?

and on this: "The fact is that the even order cancellation is not
dependent on the biasing of the tubes, beyond the requirement that
the two tubes are identical and are both biased the same.

And how are two tubes 'the same' when one is in the traditional AB
bias piont? Further, as one starts cutting off( not far from its idle
point ), how is this remotely like what is going on in the other
phase?

I'll give you a hint.....nah, you'll get it eventually.

Do try and keep your answer out of the Nonsense&Drivel category.
cheers,
Douglas







Check your High School Trigonometry book to understand why the even
harmonics cancel while the odd ones don't, it's a simple bit of math
that doesn't depend on bias, only that the two sides of the PP circuit
are identical.

No kidding. Where would one get these magical identical tubes?

Getting a class A amp to cancel its 2nd HD is not a trivial exercise.
I suggest you try it on your AB amps, just for kicks.
cheers,
Douglas

GM V8-6-4 (was Output classes A and AB)
 

At
any rate the reason I started this sub thread was to ask if anyone more
knowledgeable about engines than you or I knows the theory of the 8-6-4
engine and how it was supposed to improve gasoline mileage, which as I
remember it was what the hype said it was supposed to do?

Internal combustion efficiency is determined by the compression ratio.
High-vacuum conditions reduce the effective compression ratio. Going
to smaller displacement( through de-activating cylinders) meant
operation at higher manifold pressure, and thus higher
compression( from a given cam timing and combustion chamber geometry).

Unfortunately, you were dragging along other cylinders. There were a
few means of reducing the pumping losses, some worked better than
others. Also, the inactive cylinders were rotated in order to maintain
operating temperatures.

There's more to it, but those are the broad strokes.
cheers,
Douglas

Output classes A and AB
 

In article .com,
Multi-grid wrote:

That's a bunch of nonsense and drivel, if the cancellation were simply
the result of "the finals are biased so that the change in
characteristic for the opposing phases approximately cancels", then the
amount of odd order distortion could also be changed by PP connection.
The fact is that the even order cancellation is not dependent on the
biasing of the tubes, beyond the requirement that the two tubes are
identical and are both biased the same.

So then John, when one is cut off, what is cancelling?

The even order spectral components of the distortion products produced
in each of the two tubes, including cutoff effects.

and on this: "The fact is that the even order cancellation is not
dependent on the biasing of the tubes, beyond the requirement that
the two tubes are identical and are both biased the same.

And how are two tubes 'the same' when one is in the traditional AB
bias piont?

Both tubes must be at the same bias point, be it "traditional AB" or
whatever other bias point floats your boat.

Further, as one starts cutting off( not far from its idle
point ), how is this remotely like what is going on in the other
phase?

Because both tubes are doing exactly the same thing over a complete
cycle, except out of phase.

I'll give you a hint.....nah, you'll get it eventually.

No, I don't think I will ever get "it" unless you give me a hint.

Do try and keep your answer out of the Nonsense&Drivel category.

Done.

Check your High School Trigonometry book to understand why the even
harmonics cancel while the odd ones don't, it's a simple bit of math
that doesn't depend on bias, only that the two sides of the PP circuit
are identical.

No kidding. Where would one get these magical identical tubes?

To the extent that you can't get magical identical tubes you will have
to settle for less than complete even order distortion cancellation.

Getting a class A amp to cancel its 2nd HD is not a trivial exercise.

It's easy enough, trivial even, to adjust the differential bias so a
single even order harmonic is canceled, even with non-identical tubes.

I suggest you try it on your AB amps, just for kicks.

My amp operates class A.

Are you saying that getting a class A amp to cancel its 2nd HD is more
difficult than getting a class AB amp to cancel its 2nd HD, or vice
versa, or neither?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/