"Jim Lesurf" wrote in message
...
In article , Iain M Churches
wrote:

"Jim Lesurf" wrote in message
...


The obvious point here is that most of the SET amps I have seen
reviewed in consumer mags have - where a value is given - o/p
impedance of around 1 Ohm even midband at low power.

I seem to recall than Andre told me they sometimes have a DF of 1.

If you mean DF=1 into 8 Ohms, that is a remarkably low (poor) value! With
a
Quad ESL57 I'd expect it to produce changes in the frequency response of
over 10 dB if using the 8 Ohm o/p taps. Having such a poor o/p - LS ratio
might well also affect the distortion and peak power levels quite
markedly.

I don't think we should take this DF=1 as a norm. It is just something that
Andre has mentioned to me, in connected with amplifiers without NFB.
There are several on this, and other groups who use SET amps, so maybe
they can provide us with a more reliable figure.

Yes indeed. I am still intrigued to know how an amplifier with such a
poor test bench specification can sound so good. I have no axe to grind
here. I do not own an SET amp.

From what you say, maybe you preferred the resulting frequency response
which would have been *very* different than when used with an amp with a
nominally flat response and a low o/p impedance.

There are still factors in this equation which we have to mark as unknown.
I can hardly go to the gentleman's house and ask to take his amp to bits to
look for the presence of a feedback loop. It would be a bit like asking
the
owner of a vintage Bentley for permission to strip the engine to measure the
crankshaft:-))

A complication is that the 57 can provoke oscillations in amps that are
not
unconditionally stable. The low and reactive speaker impedance can also
aggravate 'd.c. ducking' effects that can generate off LF effects as well
with musical dynamics. No idea if these have any relevance in this case,
though.

We have now established that the speakers are not type 57 but a later
improved export model known as type 63 Mk II.

The difficulty of estimating amp-speaker interactions is that -
particularly with low-feedback and single rail designs like SET - a lot of
data would be needed to determine what *might* be happening. Alas, your
report, as many magazine ones, does not give the relevant information, so
we can't do more than speculate.

Agreed. You will appreciate that I am unable to give any more relevant
information, just from visiting the gentleman's house, and listening
to a recording. (Bear in mind that I went there to listen to a
performance, not evaulate a system:-)

As with many things Russian, it is difficult to guess the age of the
amplifier simply by looking at it. They still use hammer finish for
metalwork. It may well be that this amplifier is much older than
its pristine condition suggests.


At lowish listening levels, the SET distortion was not even faintly
audible. I daresay that at higher levels it might have been so. I was
not invited to touch the level controls, and did not do so.

OK. At low powers I would expect the distortions to fall and hence what
you
say seems entirely plausible to me.

Andy tells me that the 211 can deliver 20W with lowish THD.
So, if our listen level was 3-5W, this would explain why there was no
audible distortion.

Once again, I stress that I am not suggesting superiority of SET over
any other topology, just saying that my first acquaintance with it has been
most impressive, given the circumstances and the music to which I was
invited to listen.


Cordially,

Iain

Arny Krueger wrote:
"bugbear" wrote in message


Arny Krueger wrote:

"bugbear" wrote in message



On a related note, given the extreme claims
made for human hearing (or audio perception in
its widest sense) has there been a reputable
documented case of a sonic change detectable by a human
under DBT that CANNOT be detected by measurement?


AFAIK no.

Listening tests are at least 10 times less sensitive than the best
measurements.

If that's true, your answer to my question is "yes" (not no).


I don't see it.

You're quite right; I read "less" as "more" in your statement.
My bad.

BugBear

"Jim Lesurf" wrote in message
...
Well, one of the aims of the kind of points I make (e.g. about o/p
impedance) is to see if it may be possible to establish that the 'cause'
of
the preference might be due to an identifiable factor which could then be
replicated - if people so choose - with amp designs that do not share the
power limitations or practical difficulties of a SET.


People who choose and listen to SET amps probably do not realise that
power limitations or practical difficulties which you mention, even exist,
given the type of music to which they listen on these amplifiers.

Iain

"Stewart Pinkerton" wrote in message
...
On Wed, 12 Jan 2005 17:39:18 +0000, Eiron wrote:

Iain M Churches wrote:

The whole object of the excercise was for you to build an SS equivalent
of Andre's SET amp, so that we lesser mortals could build both and
compare
like with like. If your amplifier does not meet the criteria, then you
cannot be credited with even getting to the starting gate.

Yes, but not a *copy* of the KISS. And who gives a flying fart about
'credit', or indeed about *your* opinion of what 'meets the criteria'?

My opinion has little or nothing to do with the case:-)
For your design to be acceptable you have to meet the criteria as
discussed with you by other members of RAT, i.e an equivalent
design in solid state. No more - no less.

It would be amusing to design and build a minimalist amp.

So what is holding you back?
It seems that the odds given are such that a few people stand
to make a considerable sum of money from a very small stake
if you succeed:-)

Iain

"Iain M Churches" wrote in message

"Arny Krueger" wrote in message
...
"Rob" wrote in message



I suppose my chief concern is the way measured
difference/performance is translated to an audible outcome. HiFi
World is a terror for this. As are many on this good NG ...

That's a valid concern. Interpreting the meaning of audio
measurements is still a bit of an art.


This is a very interesting point Arny. I know that you have
considerable experience in subjective testing. I have read the
results published by Olsen
et al, but do you happen to have figures for parameters such a THD to
indicate the threshold beyond which a measured improvement is not
audible. This is something I am very interested to test with a panel
of listeners.

Actually, there are some published graphs for THD and IM. I reprinted them
at

http://www.pcavtech.com/techtalk/THD/2nd_Thrsh.gif

and

http://www.pcavtech.com/techtalk/IM/DifTonTh.gif


The source was:

J. Robert Stuart(Meridian Audio), Digital Audio for the Future, Audio, 3/98
pp 30-37.

They are over-simplifications, but they show some relevant stuff.

On Thu, 13 Jan 2005 13:27:53 +0200, "Iain M Churches"
wrote:


"Stewart Pinkerton" wrote in message
.. .
On Wed, 12 Jan 2005 17:39:18 +0000, Eiron wrote:

Iain M Churches wrote:

The whole object of the excercise was for you to build an SS equivalent
of Andre's SET amp, so that we lesser mortals could build both and
compare
like with like. If your amplifier does not meet the criteria, then you
cannot be credited with even getting to the starting gate.

Yes, but not a *copy* of the KISS. And who gives a flying fart about
'credit', or indeed about *your* opinion of what 'meets the criteria'?

My opinion has little or nothing to do with the case:-)
For your design to be acceptable you have to meet the criteria as
discussed with you by other members of RAT, i.e an equivalent
design in solid state. No more - no less.

It would be amusing to design and build a minimalist amp.

So what is holding you back?
It seems that the odds given are such that a few people stand
to make a considerable sum of money from a very small stake
if you succeed:-)

Iain


I've been the minimalist route for amp design, and the problem is that
it doesn't stay that way. You always end up thinking "if I just do
this, it will work SO much better" and by the time you are done, you
have put in all the buffered current mirrors etc that really make it
work. And in the end, why not? The bits cost bugger all.

d

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

Hello Iain
I did not mention your name
as you had not posted much in the cap testing thread, and I thought perhaps you
wanted to keep a low profile

I have killfiled a small number of people who post on this forum, so I don't
partake in the usual ng sport of endless ridiculous mud slinging. I keep the
profile that befits the subject, and since this is one of the emptiest
newsgroups on audio subjects, that means not many posts.

The test µ-follower is to be built by my BBC pal, to a circuit drawn by
another ex BBC engineer, Morgan Jones.

Ah, Morgan! Good to see you're keeping him off the streets. Andy


=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

"Andy Evans" wrote in message
...
Hello Iain
I did not mention your name
as you had not posted much in the cap testing thread, and I thought
perhaps you
wanted to keep a low profile

I have killfiled a small number of people who post on this forum, so I
don't
partake in the usual ng sport of endless ridiculous mud slinging.

It seems a little better of late. Only one Anglo Saxon expletive in my
direction
this year - today in fact:-) New Years resolutions?

I keep the
profile that befits the subject, and since this is one of the emptiest
newsgroups on audio subjects, that means not many posts.

Understood. I can see from a little archive research that many people
seem to have dropped out from this group. I think I can see why:-((

Ah, Morgan! Good to see you're keeping him off the streets. Andy

It would be refreshing to see him on this NG.
But little chance I fear:-(

Iain

"Don Pearce" wrote in message
...

I've been the minimalist route for amp design, and the problem is that
it doesn't stay that way. You always end up thinking "if I just do
this, it will work SO much better" and by the time you are done, you
have put in all the buffered current mirrors etc that really make it
work. And in the end, why not? The bits cost bugger all.

The cost is not really a factor. The idea was to design and build the
SS equivalent of Andre's simple SET amplifier, so that those
interested could build both for listening comparison.

Iain

On Thu, 13 Jan 2005 14:35:24 +0200, "Iain M Churches"
wrote:


"Don Pearce" wrote in message
...

I've been the minimalist route for amp design, and the problem is that
it doesn't stay that way. You always end up thinking "if I just do
this, it will work SO much better" and by the time you are done, you
have put in all the buffered current mirrors etc that really make it
work. And in the end, why not? The bits cost bugger all.

The cost is not really a factor. The idea was to design and build the
SS equivalent of Andre's simple SET amplifier, so that those
interested could build both for listening comparison.

Iain

I understand that, and it could be an interesting experiment -
although the very different transfer characteristics of a BJT and a
triode would make it of limited value. And of course in SS it is so
much more trivial a task to do all the good stuff.

If only you could get valves that worked on positrons!

d

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