Experiences of Class A solid-state ?
 

"Eeyore" wrote in
message
Don Pearce wrote:

Eeyore wrote:
Don Pearce wrote:
"Bret Ludwig" wrote:
Trevor Wilson wrote:
"Dave Plowman (News)" wrote
in message
Eeyore
wrote:
Have you ever spent any time listening to a true
Class A solid state amplifiers ?

Yes. A mate drove his ESLs with a Sugden. One of
the cleanest sounding systems I've ever heard.
Wouldn't shake the windows, though. ;-)

**Sugdens have never built pure Class A amps
(whatever that means). They have only ever built
high bias Class A/B designs. And, of course, Class A
is only Class A when specified into a particular
load impedance. Usually 8 Ohms. Given the fact that
ESLs vary all over the map, impedance-wise,
suggesting that the amp is Class A is even less
likely.

This is actually true.

High bias AB amps operate in class A through most of
the power range they spend all their time in, giving
the advantage of Calss A operation where it is
needed, and rather than running out of power when
this is exceeded they simply transition into Class B.

So-called experts, and their toadies and asskissers
(such as Jeboo-selling Randy Slone) have pounded on
the idea that Class AB is a poor design methodology
because of "transconductance doubling". Obviously
this is nonexistant in the region of Class A
operation.

Do you mean nonexistent in the region of class B
operation? It is class A that provides the
transconductance doubling because there are two active
devices operating in parallel.

I'm concerned about the transconductance 'modulation'
with signal level since this introduces non-linearity.

Graham

That would be greatest in the transition region between
class A and class B.

Exactly spot-on Don and readily visible when looking at a
distortion analyser's output.

Agreed.

This is why Trevor's ideas baffle me.

The point that Trevor alludes to and Doug Self describes in detail, is the
fact that there are numerous other sources of nonlinear distortion that can
be bigger problems in poorly designed amps.

Don't be proud Graham, go spend some time with Self's article:

http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm

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.

Experiences of Class A solid-state ?
 

"Arny Krueger"


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

Experiences of Class A solid-state ?
 

"Eeyore" wrote in
message

I've browsed it occasionally I don't consider him to be
especially any guru though.

I've read Self's little article about power amp distortion mechanisms
several times, and have been struck by the benefits that I might have
received from it, had it been available about 20 years ago, when I was
trying to design a SOTA power amp.

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

Do tell.

Wannabe Krooger's audio fantasies
 

The Krooborg tries to escape his permanent exile from every avenue and
side street in the audio industry.

Have you ever spent any time listening to a true Class A
solid state amplifiers ?

I've worked with power amps

Let's take a look at that Kroo-klaim, shall we.

Fact: Arnii Krooborg has never been gainfully employed in any aspect of
any audio-related business. The closest Krooger ever came to achieving
his lifelong goal was a short-term gig selling portable Lafayette
systems at Radio Shack in the '70s.

Fact: Arnii Krooborg has never published a single article (let alone a
book) about any aspect of audio design or engineering.

Fact: Arnii Krooborg doesn't even have a real engineering degree.


So when Krooger claims to have "worked with" audio gear, he's talking
out of his ass, as usual. By the same token, anybody who has replaced a
fuse in an amplifier has "worked with" the amp. If you replaced the
binding posts or a vacuum tube, you "worked with" the amp. Thhe closest
poor Arnii Krooger will ever come to attaining any audio credibility is
blathering on Usenet. And not everywhere on Usenet -- only the groups
that haven't banned him for life.





--

"Christians have to ... work to make the world as loving, just, and supportive as is possible."
A. Krooger, Aug. 2006

Experiences of Class A solid-state ?
 

"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.

The idle current flow in one device of a pair increases to double while the
other drops to just under zero at peak level.

That double value current peak flows entirely via the load to the common
point.

Very basic stuff.



We all know that speakers can be capacitive-reactive and can jack the load
current to unexpectedly high levels. A common power amp will have +/- 80
volt DC rails and may need to deliver up to 15 amps peak to the load.


** Such a power stage has a rated output of over 500 watts and so HAS to
use at least 8 large output devices.


So, now the OPT is dissipating 2400 watts per channel just sitting
there, not counting internal losses.


** 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.



Considering that heavy duty electrical room heaters usually top out around
1600 watts, the problem should be self-evident. We're basically talking a
power amp that duplicates the heating function of 3 room heaters and has
to be hooked up to a clothes dryer circuit.


** A 500 watt class A amp has an idle dissipation just over 1000 watts
dropping to around 500 watts at full output.

A 500 watt class AB amp dissipates about 270 watts, worst case, when
operated at half power.

Simple fact.

Not Arny's ********.



........ Phil

Experiences of Class A solid-state ?
 

"Arny Krueger"


I've read Self's little article about power amp distortion mechanisms
several times, and have been struck by the benefits that I might have
received from it, had it been available about 20 years ago, when I was
trying to design a SOTA power amp.



** SOTA = Stupid Over the Top Arny-amp ???


ROTFL !!



......... Phil

Experiences of Class A solid-state ?
 

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 ?

Graham

Experiences of Class A solid-state ?
 

Arny Krueger wrote:

"Trevor Wilson" wrote
"Eeyore" wrote
Trevor Wilson wrote:
"Scott Dorsey" wrote
Trevor Wilson wrote:

**There are plenty of reasons NOT to go pure Class A
and very few to do so.

Other than size and heat?

**Cost, reliability and the fact that high bias Class
A/B is lower in distortion.

Lower ?

**Yup. Self has provided convincing proof of this.

Agreed.

I would hope that this paper would be required reading for any
self-appointed power amp guru:

http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm

Meow !

Experiences of Class A solid-state ?
 

Arny Krueger wrote:

We all know that speakers can be capacitive-reactive and can jack the load
current to unexpectedly high levels.

Entirely calaculable though.


A common power amp will have +/- 80
volt DC rails and may need to deliver up to 15 amps peak to the load.

15 Amps ? I'd design for 40 !

Graham

Experiences of Class A solid-state ?
 

Arny Krueger wrote:

"Eeyore" wrote in

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 ! ).

Graham