Experiences of Class A solid-state ?
 

"Eeyore" wrote in
message
Arny Krueger wrote:

"Eeyore" wrote
Phil Allison wrote:
"Eeyore"

In fact I've a sort of grudge to bear in fact.

** So THAT is what " Eeyore " really is -

a bear with some sort of grudge ??

Long story. Only a small grudge really. I must learn
to lie in job interviews too.

** Oh - that job Doug got with Soundcraft ?

Uhuh.


He did the power amp stage of their "PowerStation".

Joke isn't it ?

What's wrong with it?

Do tell!

It's fairly 'routine'. That's the joke.

IOW, despite the use of a "big name" designer, the wine came out tasting
pretty ordinaire.

Is it class G?

I notice that Self makes some heavy claims about a proprietary implemention
of class G.

Experiences of Class A solid-state ?
 

"Eeyore" wrote in
message
Arny Krueger wrote:

As my distortion measuring gear progressed to residuals
in below 0.01% there was always a mixed bag of
measurable differences. But they were arguably quite
small, given that its often darn hard to hear distortion
below 0.1% or so.

I had a 'revalation' that blew away that idea about 30
years ago.

Do tell.

I made my last try at making small amounts of nonlinear distortion audible
about 5 years ago, and the 0.1% number was the fruit of that effort. My
results aren't that dissimilar from those found in J. Robert Stuart
(Meridian Audio), "Digital Audio for the Future", Audio, 3/98 pp 30-37.
Stuart isn't exactly conservative on this topic. I know of nobody credible
who has claimed lower thresholds for audibilty.

Experiences of Class A solid-state ?
 

"Arny Krueger"
"Eeyore"

In your opinion Graham, what would the quiescent
dissipation of a traditionally-designed output stage
like this be?

Phil's already covered that and I'm in accord with what
he says.

I see no numbers, just a lot of fussing and fuming.



** Open your bloody eyes - asshole.

Fools like YOU only see what they want to.




........ Phil

Experiences of Class A solid-state ?
 

"Phil Allison" wrote in message

"Eeyore"
Arny Krueger wrote:

"Phil Allison"

Yes, there are two problems with class A - both
related to the fact that with class A, the output stage always
has far more current flowing in it. (1) Power
transistors tend to be less
linear at high
currents - the beta falls off. Running an output
stage class A approximately doubles the current that the
output stage has to handle. So, you move the operating
point way out on the output devices. (2) Less SOA
from the perspective of
the load, because
the output devices are pulling so hard against each
other.


** What a load of complete DRIVEL !!!!

Arny - leave commenting on power amp design to people
who know something about it cos they spend their lives
dealing with it at component level.
Cos YOU do not have a bloody clue.

Phil, its real handy for that you seem to be so
mentally incapable of framing a proper technical
reply. Everybody is going to dismiss your ranting.

I'd personally like to see you claim that power
transistors get more linear
when run at very high currents and that there is no
such thing as beta fall-off at high currents.

Oh there is but since a classic Class A output has such
high standing dissipation you use more devices in
parallel and you're actually working them at
lower currents than in A/B.



** Correct.

Arny has made the same ASININE error in FOUR posts.

And as is your style, you've done nothing but posture about it, Phil. Why
not show us a worked-out example? You're capable of it, I've seen you do it.

A "class A amplifer" is one DESIGNED to work correctly
in that mode.

Whatever that means.

His wacky claim about peak device currents being higher
in class A is FALSE.

It's not wacky at all - I've seen it on the bench. It makes perfect sense.
The maximum current through an output device at peak current is increased
when you increase the quiescent current. Something about Kirchoff's law as
applied to the junction of the top and bottom of the output stage, and the
load.

Experiences of Class A solid-state ?
 

Arny Krueger wrote:

"Eeyore" wrote in
Arny Krueger wrote:
"Eeyore" wrote
Phil Allison wrote:
"Eeyore"

In fact I've a sort of grudge to bear in fact.

** So THAT is what " Eeyore " really is -

a bear with some sort of grudge ??

Long story. Only a small grudge really. I must learn
to lie in job interviews too.

** Oh - that job Doug got with Soundcraft ?

Uhuh.


He did the power amp stage of their "PowerStation".

Joke isn't it ?

What's wrong with it?

Do tell!

It's fairly 'routine'. That's the joke.

IOW, despite the use of a "big name" designer, the wine came out tasting
pretty ordinaire.

Is it class G?

The one I saw was just A/B.


I notice that Self makes some heavy claims about a proprietary implemention
of class G.

I haven't heard that. I'd be curious to know how it can be made proprietary !

Graham

Experiences of Class A solid-state ?
 

Arny Krueger wrote:

"Eeyore" wrote in
Arny Krueger wrote:
"Eeyore" wrote

My intention is to entirely eliminate this with a kind
of 'hybrid' output stage.

How? Other than class-A you'd need to come up with some
kind of Gm-halving circuit.

It is a 'form' of Class A that indeed meets the classic
definition but without the very high idle current. It
involves quite a radical rethink of the output stage.

In the past the usual approach to this has been to use a bias circuit that
keeps the output devices from ever turning fully off.

It's that kind of thing.

What do you know about previous examples of this. I've just generally heard
that they hadn't been brilliantly succesful.

Graham

Experiences of Class A solid-state ?
 

"Eeyore" wrote in message
...
:
:
: Arny Krueger wrote:
:
: "Eeyore" wrote
: Arny Krueger wrote:
: "Eeyore" wrote
:
: I'm concerned about the transconductance 'modulation'
: with signal level since this introduces non-linearity.
:
: Again, covered in
: http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm
:
: Which is what I'm designing out.
:
: Although I'd hoped this thread might be more about any
: audible benefits of Class A rather than a discussion of
: design principles ( I'm quite au-fait with those ! ).
:
: Like I said before, I've never done any DBTs involving Class-A amps. This is
: partially because I've never seen a true Class A amp that was capable of
: interesting power levels, in real life.
:
the Manley 500 W monoblocks, using 10 KT90's, do 275 W in triode mode,
500W in penthode mode, presumably very substantially class A
it *does* use a staged power switch on
at steal at about 150 USD/kilo
hehe
(over on RAT, Patrick Turner reported working on a 6*GM70 design,
that could definitely do 100 % class A all the way to 275 W :)

Rudy

: Fair enough.
:
: I've heard enough positive comment on them to pursue my line of thinking on the
: matter already btw.
:
: Graham
:
:

Experiences of Class A solid-state ?
 

"Phil Allison" wrote in message

"Arny Krueger"


Agreed again. Building a truely Class A power amp that
can deliver significant amounts of power output is
really a pretty awesome thing. The OPT stage quiescent
current has to be equal to the *peak* current that is
delivered to the load.

** Absolutely FALSE.

The peak load current is *exactly* double the idle
current for an amp operating in class A.

Agreed.

** Self contradiction - right here.

Oh, I get it, this time.

Yeah, Phil I had things wrong.

Had you not been so extreme and violent in your initial response, I would
have probably gotten it, the first time.

Experiences of Class A solid-state ?
 

Arny Krueger wrote:

"Eeyore" wrote
Arny Krueger wrote:

I'd personally like to see someone claim that power
transistors get more linear when run at very high
currents and that there is no such thing as beta
fall-off at high currents.

Oh there is, but since a classic Class A output has such
high standing dissipation you use more devices in
parallel and you're actually working them at lower
currents than in A/B.

I think I saw the effects of beta fall-off in my testing. I was working
with 8 devices up and 8 devices down. VCC was about 80 volts. The devices
were complements from the MJE 1502x series.

Admittedly, one go add enough devices so that beta fall-off wouldn't be an
issue.

Those devices start showing significantly reduced beta @ around 3A.

In any case the output topology I have in mind is quite insensitive to beta.

Graham

Experiences of Class A solid-state ?
 

Arny Krueger wrote:

"Phil Allison" wrote in message

snip


Arny has made the same ASININE error in FOUR posts.

And as is your style, you've done nothing but posture about it, Phil. Why
not show us a worked-out example? You're capable of it, I've seen you do it.

A "class A amplifer" is one DESIGNED to work correctly
in that mode.

Whatever that means.

I think it means "A "class A amplifer" is one DESIGNED to work correctly in
that mode. "


His wacky claim about peak device currents being higher
in class A is FALSE.

It's not wacky at all - I've seen it on the bench. It makes perfect sense.
The maximum current through an output device at peak current is increased
when you increase the quiescent current. Something about Kirchoff's law as
applied to the junction of the top and bottom of the output stage, and the
load.

Obfuscation.

Graham