Experiences of Class A solid-state ?
 

"Eeyore" wrote in
message
Arny Krueger wrote:

"Eeyore" wrote
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.

In my case my I was comparing the H-H TPA 50 amplifier (
a fairly classic A/B design of its era and quite widely
used in pro-audio - including the BBC ) with ~ 0.1% THD
on the spec sheet with a friend's recently assembled kit
ampliifer using Crimson Elektrik modules. These used a
rather more 'state of the art' design with the then new
high speed Japanese output devices ( the H-H used
Motorola darlingtons ).

Lets just say the difference wasn't subtle !

The H-H sounded gritty by comparison to the much smoother
Crimson.

I had to search high and low to find much out about H-H brand equipment.
Apparently they were popular in the late 70s. I wouldn't try to generalize
very much related to just one sample of such an ancient obscure piece.

Experiences of Class A solid-state ?
 

Trevor Wilson wrote:

**Bull****. Only poorly deisgned Class A/B amps sound significantly worse
than an otherwise identical Class A amp. Pay careful attention to my words:
"Otherwise identical".

Guess who this asshole is.

--
ha

Experiences of Class A solid-state ?
 

Scott Dorsey wrote:

**Bull****. Only poorly deisgned Class A/B amps sound significantly worse
than an otherwise identical Class A amp. Pay careful attention to my words:
"Otherwise identical".

That's not what I said. That is not at ALL what I said.

This is obviously Filly Assilon. It can neither hear nor read with its
head in there.

--
ha

Experiences of Class A solid-state ?
 

Arny Krueger wrote:
"Eeyore" wrote in

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.

If you don't mind non-complementary output stages, there are truly
gargantuan MOSFETs available today for electric motor control applications.
Most aren't designed for linearity, but some careful selection may help.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Experiences of Class A solid-state ?
 

hank alrich wrote:

Scott Dorsey wrote:

**Bull****. Only poorly deisgned Class A/B amps sound significantly worse
than an otherwise identical Class A amp. Pay careful attention to my words:
"Otherwise identical".

That's not what I said. That is not at ALL what I said.

This is obviously Filly Assilon. It can neither hear nor read with its
head in there.

Actually it was another Australian !

You've comitted the cardinal sin now. Prepare to be roasted.

Graham

Experiences of Class A solid-state ?
 

Scott Dorsey wrote:

Arny Krueger wrote:
"Eeyore" wrote in

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.

If you don't mind non-complementary output stages, there are truly
gargantuan MOSFETs available today for electric motor control applications.
Most aren't designed for linearity, but some careful selection may help.

I'm still fond of lateral mosfets. I've got a couple of amps here ( of my own
design in fact ) with 12 Hitachi devices per channel.

Graham

Experiences of Class A solid-state ?
 

"Eeyore" wrote in
message
Arny Krueger wrote:

"Eeyore" wrote
Arny Krueger wrote:
"Eeyore" wrote
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.

Used in some Japanese amps from maybe the late 70s and
early 80s.

I've just generally heard that they hadn't been
brilliantly succesful.

I think the usual phrase used to describe this is
"sliding bias".

Yes.


It seems to me that sliding bias can make power amps
less reliable, by turning minor faults into situations
where lots of power is dissipated in the output stage.
The trick might be to back out the sliding bias feature
when things start going awry, like a shorted load or
some such.

I couldn't comment without seeing a schematic really. I
can't imagine why that should be so.

You haven't come across any then ?

I'm pretty sure I've heard some Technics amps with sliding bias. They sold
them in appliance stores around here in the days of. I seem to recall
their advertising buzzword was "New Class A" or some such.

Experiences of Class A solid-state ?
 

"Eeyore" wrote in
message
Arny Krueger wrote:

"Eeyore" wrote
in
Arny Krueger wrote:

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 !

http://www.dself.dsl.pipex.com/ampins/classg/g.htm

"Class-G is now out and about. So what has changed? This
would be easier to answer if there had been more
published on the technology; as it is I have to rely
pretty much on my own research. I found that Schottky
power diodes have eliminated the commutation-diode
glitching. Having peeled this skin from the distortion
onion, linearity was still signficantly poorer than a
Blameless Class-B design. This proved to be due to Early
effect in the output stage devices, stemming from the
sudden changes in collector voltage they experience in
Class-G operation. I had my own ideas about how to deal
with this, and you can read all in Electronics World for
Dec 2001 and Jan, Feb 2002. There is a fully worked-out
design, and even a PCB available to ease building it."

The "Early Effect" amounts to being an increase in beta
with increased VCE. The happens in a class-G amp when
the power supply voltage is switched to a higher voltage.

I notice that his ideas on the matter can only apparently
be read in the copies of EW mentioned.

His does pontificate a heck of alot !

I believe that Self also added some stuff on his allegedly new Class G
technology in his book.

"Audio Power Amplifier Design Handbook, Fourth Edition" It's about $50 in
paperback from Amazon.

Experiences of Class A solid-state ?
 

"Arny Krueger" wrote in message
. ..
"Eeyore" wrote in
message
Arny Krueger wrote:

"Eeyore" wrote
Arny Krueger wrote:
"Eeyore" wrote
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.

Used in some Japanese amps from maybe the late 70s and
early 80s.

I've just generally heard that they hadn't been
brilliantly succesful.

I think the usual phrase used to describe this is
"sliding bias".

Yes.


It seems to me that sliding bias can make power amps
less reliable, by turning minor faults into situations
where lots of power is dissipated in the output stage.
The trick might be to back out the sliding bias feature
when things start going awry, like a shorted load or
some such.

I couldn't comment without seeing a schematic really. I
can't imagine why that should be so.

You haven't come across any then ?

I'm pretty sure I've heard some Technics amps with sliding bias. They sold
them in appliance stores around here in the days of. I seem to recall
their advertising buzzword was "New Class A" or some such.

If that was sliding bias, then my experience with "New Class A" has been
favorable. My lady friend had a Technics Receiver featuring same from the
early eighties, driving KLH speakers which I'm fairly familiar with. I've
listened to full symphony orchestra with that combo, and I'd have to say the
receivers sound was more "sweet" and lifelike than any other receiver I've
heard from the eighties (including Marantz and Yamaha). It sounded far less
"bright", and far more like a current high-quality amplifier.

Experiences of Class A solid-state ?
 

"Eeyore" wrote in message
...
:
:
: Arny Krueger wrote:
:
: "Eeyore" wrote
: 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.
:
: In my case my I was comparing the H-H TPA 50 amplifier ( a fairly classic A/B
: design of its era and quite widely used in pro-audio - including the BBC )
: with ~ 0.1% THD on the spec sheet with a friend's recently assembled kit
: ampliifer using Crimson Elektrik modules. These used a rather more 'state of
: the art' design with the then new high speed Japanese output devices ( the H-H
: used Motorola darlingtons ).
:
: Lets just say the difference wasn't subtle !
:
: The H-H sounded gritty by comparison to the much smoother Crimson.
:
: Graham
:
The Crimson Elektrik modules with the quad 405 like cooling blocks
yeah, didn't they advertise in the Wireless World ?
Rudy