Eeyore said:


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.


If you're referring to Hitachi 2SK135/2SJ50s, they are *vertical*
MOSFETs.
My hybrid designs use them exclusively (yep, still have a stash of the
originals.)

Beware of Chinese copies BTW!

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

Eeyore said:


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


Technics used something like that, named class AA or somesuch.

Even after hours of operation, they were useful as champagne coolers.

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

tony sayer said:


Anyone ever made a good commercially viable class D amp?...


www.hypex.nl

http://www.powersoft.it/index.php?_view_lang=en

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

In article , Arny Krueger
writes
"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.



I recall them and they did sound very rough. But they were mainly used
for PA and such applications......
--
Tony Sayer

Harry Lavo wrote:

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

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.

That sounds encouraging. I can imagine it might have that effect.

Graham

Ruud Broens wrote:

"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 ?

They did indeed Rudy.

Graham

tony sayer wrote:

Arny Krueger writes
"Eeyore" wrote in

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.


I recall them and they did sound very rough. But they were mainly used
for PA and such applications......

Many were indeed used in rock PAs simply because they were few British high
power amplifiers of that era but far from exclusively. There was even a special
BBC version of the TPA25.

" There's also a photo of one of the many AIR studio consoles, in their Oxford
Street control rooms. I was interested in the rack of power amplifiers that you
can see to the right of the console. These silver faced units were HH
Electronic TPA100 power amps and what looks like three smaller TPA25 amps at
the bottom of the rack. "

http://www.auroraaudio.net/cgi-bin/d...m=DCForum ID1

Graham

There also wasn't very much of a measurable difference and the
differences weren't all positive for class A. For example, running
an output stage in class A can increase distortion, because the
output devices have to run at higher current levels, where the
output transistors might be far less linear.

Might be. Are they? A well-known designer, a friend of mine, is emphatic on
this point -- they aren't. They're more linear. Or rather, less non-linear.

As my distortion measuring gear progressed to residuals 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.

Probably so, but what types of distortion?

I'm going to try to get Clay Barclay to write something about Crown's
null-testing system. He probably won't, but it's worth a try.

William Sommerwerck wrote:

There also wasn't very much of a measurable difference and the
differences weren't all positive for class A. For example, running
an output stage in class A can increase distortion, because the
output devices have to run at higher current levels, where the
output transistors might be far less linear.

Might be. Are they? A well-known designer, a friend of mine, is emphatic on
this point -- they aren't. They're more linear. Or rather, less non-linear.

As my distortion measuring gear progressed to residuals 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.

Probably so, but what types of distortion?

I'm going to try to get Clay Barclay to write something about Crown's
null-testing system. He probably won't, but it's worth a try.

A key factor here is that crossover distortion is quite high order, hence more
unpleasant to hear.

Graham

Sander deWaal wrote:

Eeyore said:

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.

If you're referring to Hitachi 2SK135/2SJ50s, they are *vertical*
MOSFETs.
My hybrid designs use them exclusively (yep, still have a stash of the
originals.)

I think you got confused there Sander.

Graham