Hi,

Just to let people know that I've now put up some webpages on Jim Sugden's
original Class A solid state power amps. You can find these via a new link
on the AudioMisc page (URL in my sig below). :-)

I will add more pages on JES as and when I get a chance. Next to be added
will be pages on the Hi Fi News 'home constructor' version of the
amplifiers, and pages on the A41/A51 and their control (pre) amps.

Hope people find the pages of interest.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

On Tue, 04 Sep 2007 18:47:10 +0100, Jim Lesurf
wrote:

Hi,

Just to let people know that I've now put up some webpages on Jim Sugden's
original Class A solid state power amps. You can find these via a new link
on the AudioMisc page (URL in my sig below). :-)

I will add more pages on JES as and when I get a chance. Next to be added
will be pages on the Hi Fi News 'home constructor' version of the
amplifiers, and pages on the A41/A51 and their control (pre) amps.

Hope people find the pages of interest.

Slainte,

Jim

Definitely, thanks for those. Have to say that the biasing methods
have a very fragile look to them; Sugden definitely had a bee in his
bonnet about how an amplifier should work. Unfortunately for him it
wasn't long after all this that people started to suss how to make a
class B amp without the huge distortion rise at low level.

I'm a little surprised he didn't get as far as a long-tail pair for
the input. The technique was well enough known by then. Perhaps a
component count issue? Transistors cost a fortune back then; I can
remember my 30/- OC71.

d

--
Pearce Consulting
http://www.pearce.uk.com

Jim Lesurf wrote:
Hi,

Just to let people know that I've now put up some webpages on Jim Sugden's
original Class A solid state power amps. You can find these via a new link
on the AudioMisc page (URL in my sig below). :-)

I will add more pages on JES as and when I get a chance. Next to be added
will be pages on the Hi Fi News 'home constructor' version of the
amplifiers, and pages on the A41/A51 and their control (pre) amps.

Hope people find the pages of interest.

Slainte,

Jim


Long sold now, but I posted these a while back:

http://patchoulian.googlepages.com/sugdenc51andp51

I've probably got some more photos, should you ever need them.

FWIW they were pretty good, and serviced/repaired by Sugden in 2004.

Rob

In article , Rob

wrote:


Long sold now, but I posted these a while back:

http://patchoulian.googlepages.com/sugdenc51andp51

I'll have a look later this morning. :-)

I've probably got some more photos, should you ever need them.

You sent me PDF copies of the documents IIRC. However I'd welcome any good
colour photos of the amps. I have a pile of documents the people at Sugden
Audio kindly sent to me. This includes things like Jim Sugden's original
notes, etc. But I lack good colour photos of the early units.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

In article , Don Pearce
wrote:
On Tue, 04 Sep 2007 18:47:10 +0100, Jim Lesurf
wrote:

Hi,

Just to let people know that I've now put up some webpages on Jim
Sugden's original Class A solid state power amps. You can find these
via a new link on the AudioMisc page (URL in my sig below). :-)

Definitely, thanks for those. Have to say that the biasing methods have
a very fragile look to them;

Well, it was the mid 1960s and the transistors available at the time were
poor (perhaps a better term would be 'rubbish' compared with nowdays), as
well as people not yet having really learned how to use bipolars in ways
we'd now regard as 'obvious' for giving best results. The bias
stabilisation diodes were a neat trick. These days we'd probable use
something more like a rubber zener, but I don't know when that first came
into use.

I've been told that the need to carefully match the diodes and resistors
into matched sets in boxes was a real PITA. Kept one 'girl' sic working
full time just on that.


Sugden definitely had a bee in his bonnet about how an amplifier should
work. Unfortunately for him it wasn't long after all this that people
started to suss how to make a class B amp without the huge distortion
rise at low level.

Indeed. By about the mid 1970s the early problems had essentially been
sussed. The available power transistors were also much better. As a result
topologies like the 'triples' and the linearised versions of class AB were
in use. JES themselves slowly moved away from Class A into what was either
AB or more like 'high bias' than Class A. In fairness, though, in the days
when a BD121 was the state of the art it would be dubious if these more
familiar arrangements would have worked OK. And although we nowdays take
them as if they appeared in the year dot, they actually had to be invented.
;-

I'm a little surprised he didn't get as far as a long-tail pair for the
input. The technique was well enough known by then. Perhaps a component
count issue? Transistors cost a fortune back then; I can remember my
30/- OC71.

When I get a chance to do the relevant pages, you should find the 'series
3' and later had arrangements that would be more familiar these days. TBH
the thing that makes my hair[1] stand on end with the early JES designs is
the a.c. coupling from one stage to another inside the feedback loop. Alas,
I don't have a circuit for the Si 402 so can only suspect it was similar to
the A21/A41 at present. I can't even determine yet if any were ever sold.
Hence my assumption at present that the Richard Allan amp was the first
Class A SS power amp to go on sale for domestic HiFi.

I found it quite interesting how the designs did evolve as he experimented
and learned. The change was quite rapid during the first couple of years.

I have been told that both Hacker radio and Uncle Clive argued about who
was first. But I've not found any contemporary documents on that as yet.
Found more well-known items by JLH, Williamson, etc, though.

Slainte,

Jim

[1] Not that I have much hair on my head these days to engage in such
reactions. :-)

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

"Jim Lesurf" wrote in message
...
Hi,

Just to let people know that I've now put up some webpages on Jim
Sugden's
original Class A solid state power amps. You can find these via a new
link
on the AudioMisc page (URL in my sig below). :-)

I will add more pages on JES as and when I get a chance. Next to be
added
will be pages on the Hi Fi News 'home constructor' version of the
amplifiers, and pages on the A41/A51 and their control (pre) amps.

Hope people find the pages of interest.


Sugden's current adverting slogan appears to be:

"Rescuing music from technology"

:-)

"Jim Lesurf"

Just to let people know that I've now put up some webpages on Jim Sugden's
original Class A solid state power amps. You can find these via a new link
on the AudioMisc page (URL in my sig below). :-)

I will add more pages on JES as and when I get a chance. Next to be added
will be pages on the Hi Fi News 'home constructor' version of the
amplifiers, and pages on the A41/A51 and their control (pre) amps.

Hope people find the pages of interest.


** Only if they actually ENJOY reading tedious, pseudo technical drivel.

Your page on the A21 is particularly loaded with fallacies and nonsense.

Gullible readers are being expected to believe that 1968 was some kind of
"dark ages" in SS amplifier history, that the available silicon transistors
were of highly inferior quality and designers were all still struggling with
the evil bogey of crossover distortion.

And that class A operation was the answer.


WHAT ******** !!



Eg:

Quad released their famous 303 model way back in 1967 !!

In 1969 it won a Design Council Award.

The 303 delivered 45 watts per channel into 8 ohms loads.

It was short circuit safe.

It used all silicon transistors and exhibited no sign of crossover
distortion.

The power devices used were rugged planar types, RCA 38494s and 40411s.

THD measured at the 1 watt level was circa 0.003% and less than 0.03 % at
rated power - ten times less at both levels than Sugden's woeful A21.

The 303 used regulated PSU and drove the "difficult" ESL57 with ease.

It ran cool with very low idle current in the output devices.

Compared to the Quad 303, Sugden's A21 was a pile of junk.

It is * NO * surprise that a credible magazine like Wireless World failed
to mention its appearance at some 1968 audio fair.

Since it was clearly an embarrassment !!
---------------------------------------------


BTW:

This French page has some good pics of the insides of a Quad 303.

http://cf.geocities.com/quadfranco/a...33/amp303.html

Here is a schematic of the 1970 version.

http://www.geocities.com/quad_esl63/...c/power303.jpg





......... Phil

Quad released their famous 303 model way back in 1967 !!

In 1969 it won a Design Council Award.

The 303 delivered 45 watts per channel into 8 ohms loads.

It was short circuit safe.

It used all silicon transistors and exhibited no sign of crossover
distortion.

The power devices used were rugged planar types, RCA 38494s and 40411s.

THD measured at the 1 watt level was circa 0.003% and less than 0.03 % at
rated power - ten times less at both levels than Sugden's woeful A21.

The 303 used regulated PSU and drove the "difficult" ESL57 with ease.

It ran cool with very low idle current in the output devices.

Compared to the Quad 303, Sugden's A21 was a pile of junk.

It is * NO * surprise that a credible magazine like Wireless World failed
to mention its appearance at some 1968 audio fair.

Since it was clearly an embarrassment !!
---------------------------------------------


BTW:

This French page has some good pics of the insides of a Quad 303.

http://cf.geocities.com/quadfranco/a...33/amp303.html

Here is a schematic of the 1970 version.

http://www.geocities.com/quad_esl63/...c/power303.jpg


Yes thats the better one with the diode-less biasing arrangement. We
used to copy that diagram and made no end of them for mates and other
applications

I'm sure PW wouldn't have really minded after all it was spreading the
good word

I re-furbed a pair for my wife's study room a couple of years ago, new
uprated power, output, and PCB caps. New cermet pots, beefed up a bit
of the output wiring and its as good, possibly a bit better, than new
and will last many, many years yet:-)........

--
Tony Sayer

"tony sayer" wrote in message
...
Quad released their famous 303 model way back in 1967 !!

In 1969 it won a Design Council Award.

The 303 delivered 45 watts per channel into 8 ohms loads.

Performance into 4 ohm loads?

It was short circuit safe.

There are no classic SOA or current limiters. How was the output stage
protected?

It used all silicon transistors and exhibited no sign of crossover
distortion.

Par for the course.

The power devices used were rugged planar types, RCA 38494s and 40411s.

40411s were rugged, indeed.

THD measured at the 1 watt level was circa 0.003% and less than 0.03 % at
rated power - ten times less at both levels than Sugden's woeful A21.

OK, that's at 1 KHz. How about 20 KHz?

The 303 used regulated PSU and drove the "difficult" ESL57 with ease.

It ran cool with very low idle current in the output devices.

Compared to the Quad 303, Sugden's A21 was a pile of junk.

The interest in the Sugden amps mystifies me because they seem to be so
backward.


This French page has some good pics of the insides of a Quad 303.

http://cf.geocities.com/quadfranco/a...33/amp303.html

Here is a schematic of the 1970 version.

http://www.geocities.com/quad_esl63/...c/power303.jpg

It looks to me like there is no loop feedback from the output back to
anyplace near the input. Am I missing something?

Yes thats the better one with the diode-less biasing arrangement. We
used to copy that diagram and made no end of them for mates and other
applications

I'm sure PW wouldn't have really minded after all it was spreading the
good word

I re-furbed a pair for my wife's study room a couple of years ago, new
uprated power, output, and PCB caps. New cermet pots, beefed up a bit
of the output wiring and its as good, possibly a bit better, than new
and will last many, many years yet:-)........

The contemporaneous similar US amp might have been the Dyna ST-120 which had
a far more checkered reputation.

"Arny Krueger"
Phil Allison


** Try answering the right person's post - Arny.

Sayer snipped the original context out of sight and now YOU are asking him
about MY post.

Then you sneakily introduce a NEW context of your own making.

What a posturing ASS you are.



The 303 delivered 45 watts per channel into 8 ohms loads.

Performance into 4 ohm loads?


** Not relevant - ask the same Q about the A21.

( The 303 spec was for 42 watts at 6 ohms. )



It was short circuit safe.

There are no classic SOA or current limiters. How was the output stage
protected?


** The output triples inherently limit at 4.5 amps.


It used all silicon transistors and exhibited no sign of crossover
distortion.

Par for the course.


** Absolutely not the case for domestic SS amps in 1967.

The 303 was non bias critical & output device temp did not affect the
setting.

Go look at the original context for MY post.

Stop being such a PITA smartarse Septic ASSHOLE !!!.



THD measured at the 1 watt level was circa 0.003% and less than 0.03 % at
rated power - ten times less at both levels than Sugden's woeful A21.

OK, that's at 1 KHz. How about 20 KHz?


** The 303 spec was for 0.1 % at any level up to 45 watts at 10kHz.



Compared to the Quad 303, Sugden's A21 was a pile of junk.

The interest in the Sugden amps mystifies me because they seem to be so
backward.


** A quirky, pommy amp only a quirky pommy could love.



Here is a schematic of the 1970 version.

http://www.geocities.com/quad_esl63/...c/power303.jpg


It looks to me like there is no loop feedback from the output back to any
place near the input. Am I missing something?


** You sure have missed it:

R113 (82k) and R 111 (2.2k) divide the output by 38.3 times, then R108 & R
101 ( both 22k) cause the whole amp to act as a unity gain inverter to that
divided down level.

So overall gain is - 38.3 and the input sensitivity = 500mV.


Hey Arny - still not corrected all those STUPID errors on your page about
the Crown amp ?

****ing compewter geek ******.




........ Phil