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"Dave Plowman (News)" wrote in message
...

Anyone with any real life experience of valve amps when they were common
will remember having to have them repaired. And I'd include, Radford, Quad
and Leak in this as I've owned them all. I've got several decent quality
SS amps here that are probably in use far more than the valve ones ever
were, and only one failure I can think of - an input coupling cap on a
home built Lindsey Hood.

True. so true. But don't forget that component technology was not at
the level it is today. The only fault I have ever seen on a Quad II was a
burnt
cathode bias resistor, which for some reason was only rated at 3W.

Jim Kerr at Decca used to joke that the Radford STA100 failed
with monotonous regularity. He had repaired one, in twenty one years:-))


Iain

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Stewart Pinkerton wrote:

Yes, but you have to remember that Patrick earns his living by
repairing valved gear. That makes for very narrow blinkers, a
conveniently selective memory, and a certain economy with the truth.


I thought he designed and built tube, sorry, valve, amps ...

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In article , Iain M Churches
wrote:

"Jim Lesurf" wrote in message
...
As an aside he Can you give me a reference for the AES standard? I
don't have this to hand and I'd be interested to see what they
specifically say.

I can find the reference for you from the AES index. You could probably
do this yourself immediately by going to the website.

OK. I'll have a look on the website, and if I can't find it I'll ask for
help. I tend only to use the website to 'nick' PDF versions of the latest
issue of articles in JAES. (Have the CDROMs up to about 2 years ago.) I
avoid spending a long time online from home as I only have a POTS/modem
here, and want to spend more time on 'real life' and less online. ;-

I can recall reading things about the LS standards many moons ago, but
can't really recall where, or what the details were.



I am also curious as to what value they would accept for 'unusual'
speakers like the old Quad 57's whose impedance varies all over the
shop. :-)

It may well be that the recommendations were not in place at that time.
Another possibility, is that Peter Walker, being the man he wasm, had
special dispensation from the Pope:-)

LOL. Yes, and if so, entirely justified IMHO. :-)

He also carefully designed the QUAD amps to suit the QUAD speakers. :-)

I am less sure than yourself that an o/p impedance of 0.4 Ohms would
only be noticable on sweep tones. However the only tests I've done on
this sort of thing in the past involved music, so I can't comment on
the relative audibility music versus tones.

I too cannot be sure. That is why I have asked the broadcast company to
do some tests with/for me.

If you can, check with more than one type of speaker and make a note of
their impedance-frequency profiles. Traditionally, people tend to think of
this effect in terms of 'damping factor' and the effect around the bass
resonance (in 'mechanical' terms). However many speakers have two (or more)
input impedance peaks. One below 100Hz somewhere associated with the bass
unit. Another somewhere around 2kHz associated with the mid/treble. This
second peak means that the presence region and its surrounding frequencies
can have their frequency balance altered by source resistance.

FWIW My experience of this in the distant past was that quick switching in
and out would sometimes show effects clearly with some music/speakers/room,
but long period listening would also slowly show up differences, but in a
way that was harder to check. Problem here being the variability of
hearing, movements of the head in the room acoustics, etc. All the usual
problems of trying to decide about audible changes. :-)

Perhaps if Arny is interested we could make up some 'ABX' type tests
that apply the kind of modification a 0.4 Ohm (or 1 Ohm) o/p would
impose on some typical speaker(s) and then invite people to judge for
themselves? It seems to me this would be an interesting experiment.

Indeed it would. That is exactly what I propose to do. Can we take a
typical SS amp Ro to be 0.1 Ohms? What do you think? If so, then a
0.39 Ohm resistor would do nicely.

I'm not sure what to regard as typical as these things vary. However I
would agree that something like 0.1 Ohms or less could be taken to be
representitive of 'low o/p impedance' and something like 0.4 or 0.5 could
be said to represent 'high o/p impedance'. However I have seen amps that
have values well below 0.1 Ohm, and reported measurements of others with
impedances of 1.5 Ohms or more!

Two other snags which we would probably need to ignore for the sake of
practicality (and sanity ;-] ) a

1) the possible reactive component with some designs with high output
impedance.

2) Cables (sigh). Ideally just use low series resistance and inductance
cables fairly short.

How much information should the panel of listeners have before hand?

Not sure on this. The main thing is that, ideally, they are given no info
as to when the o/p impedance is 'high' or 'low'. ABX would nominally deal
with that. They could be given to think that "A and B may be different, and
X equals one of them".

Beyond that it might be nice to start in total ignorance of what specific
'cause' (o/p resistance interaction) was being tested. Then after some
tests, let them know this. Then later, suggest possible audible changes -
but never identifying which setting 'X' might be. However this may be too
impractical and convoluted. So, I am not sure what would be best.

Slainte,

Jim

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

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2 tablespoons each:
salt
black, white and cayenne peppers
celery salt
garlic powder
parsley flakes
brown sugar
1 teaspoon sage
2 onions
6 cloves garlic
bunch green onions, chopped

Cut the children?s butts and the beef roast into pieces
that will fit in the grinder.
Run the meat through using a 3/16 grinding plate.
Add garlic, onions and seasoning then mix well.
Add just enough water for a smooth consistency, then mix again.
Form the sausage mixture into patties or stuff into natural casings.



Stillborn Stew

By definition, this meat cannot be had altogether fresh,
but have the lifeless unfortunate available immediately after delivery,
or use high quality beef or pork roasts (it is cheaper and better to
cut up a whole roast than to buy stew meat).

1 stillbirth, de-boned and cubed
¼ cup vegetable oil
2 large onions
bell pepper
celery
garlic
½ cup red wine
3 Irish potatoes
2 large carrots

This is a simple classic stew that makes natural gravy,
thus it does not have to be thickened.
Brown the meat quickly in very hot oil, remove and set aside.
Brown the onions, celery, pepper and garlic.
De-glaze with wine, return meat to the pan and

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325.
Fill the pie with stew, place top crust and with a fork, seal the crusts together
then poke holes in top.
Return to oven and bake for 30 minutes, or until pie crust is golden brown.



Sudden Infant Death Soup

SIDS: delicious in winter, comparable to old fashioned Beef and Vegetable Soup.
Its free, you can sell the crib, baby clothes, toys, stroller... and so easy to
procure if such a lucky find is at hand (just pick him up from the crib and
he?s good to go)!

SIDS victim, cleaned
½ cup cooking oil
Carrots
onions
broccoli
whole cabbage
fresh green beans
potato
turnip
celery
tomato
½ stick butter
1 cup cooked pasta (macaroni, shells, etc.)

Remove as much meat as possible, cube, and brown in hot oil.
Add a little water, season, then add the carcass.
Simmer for half an hour keeping the stock thick.
Remove the carcass and add the vegetables slowly to the stock,
so that it remains boiling the whole time.
Cover the pot and simmer till vegetables are tender
(2 hours approximately).
Continue seasoning to taste.
Before serving, add butter and pasta,
serve piping with hot bread and butter.



Offspring Rolls

Similar to Vietnamese style fried rolls, they have lots of meat
(of course this can consist of chicken, beef, pork, or shrimp).
Who can resist this classic appetizer; or light lunch served with
a fresh salad? Versatility is probably this recipe?s greatest virtue,
as one can use the best part of a prime, rare, yearling, or the
morticians occasional horror: a small miracle stopped short by a

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celery, green onions, and parsley.
Place roast on top with fat side up.
Place uncovered in 500° oven for 20 minutes, reduce oven to 325°.
Bake till medium rare (150°) and let roast rest.
Pour stock over onions and drippings, carve the meat and
place the slices in the au jus.



Bisque à l?Enfant

Honor the memory of Grandma with this dish by utilizing her good
silver soup tureen and her great grandchildren (crawfish, crab or
lobster will work just as well, however this dish is classically
made with crawfish).

Stuffed infant heads, stuffed crawfish heads, stuffed crab or lobster shells;
make patties if shell or head is not available
(such as with packaged crawfish, crab, or headless baby).
Flour
oil
onions
bell peppers
garlic salt, pepper, etc.
3 cups chicken stock
2 sticks butter
3 tablespoons oil

First stuff the heads, or make the patties (see index)
then fry or bake.
Set aside to drain on paper towels.
Make a roux with butter, oil and flour,
brown vegetables in the roux, then add chicken stock and
allow to simmer for 20 minutes.
Add the patties or stuffed heads, and some loose crawfish,
lobster, long piglet, or what have you.
Cook on low for 15 minutes, then allow it to set for at leas

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On Wed, 22 Dec 2004 14:03:20 +0200, "Iain M Churches"
wrote:


"Stewart Pinkerton" wrote in message
.. .
Your Beeb pal might like to consider that many modern speakers have
impedances which dip to 3 ohms or so, somewhere around the crossover
frequency, which is often in the region where the ear is most
sensitive.

Please refer to the AES recommendations for speaker impedances
(which are followed by reputable manufacturers) They do not allow
a speaker of nominal impedance of 8 Ohms to fall to 3 Ohms.

Or were you talking about a 4 Ohm speaker?
You did not say so.

I was talking about modern speakers in general, most of which would
not meet the DIN/AES requirement for 8-ohm nominal impedance (indeed,
very few new speakers are rated at 8 ohms nominal). I note from the
above that you don't consider B&W, Quad, Martin-Logan or Wilson to be
'reputable' manufacturers.......................

A difference in Ro of 0.5 ohms will give a change of volume
of about 1.5dB in the area of that dip, which most speaker engineers
would consider very likely to be audible.

I don't know from where you got the "difference of 0.5 Ohms". We were
originally talking about a amplifier with an Ro of 0.4 Ohms. So the
difference is perhaps 0.3 Ohms.

Patrick Turner raised the 0.5 ohms figure, but the general principle
applies, whether it's 0.3 ohms or 1 ohm (or indeed 3 ohms, as in the
case of some SET amps). And why would you try to shave it to 0.3 ohms,
unless you were aware that it's a real-world problem? I note that you
always prefer semantics to reality.

So your "change of volume of about 1.5dB" is no longer valid,
being reduced to a value which could possibly be perceived
on sweep tones (this will be an interesting thing to test in
the New year) but probably not with music.

My figure is entirely valid for the numbers I quoted, which are
realistic parameters. Not my fault if you're unfamiliar with modern
loudspeakers and their impedance curves. As far as whether it's
aidible on music, note that this violent impedance swing will often
occur in the very area to which the ear is most sensitive. Also, I
would suggest that any piano tuner who couldn't voice within 1.5dB
across a couple of octaves, wouldn't last long.....................
--

Stewart Pinkerton | Music is Art - Audio is Engineering

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"Stewart Pinkerton" wrote in message
...
On Wed, 22 Dec 2004 14:03:20 +0200, "Iain M Churches"
wrote:


"Stewart Pinkerton" wrote in message
. ..
Your Beeb pal might like to consider that many modern speakers have
impedances which dip to 3 ohms or so, somewhere around the crossover
frequency, which is often in the region where the ear is most
sensitive.

Please refer to the AES recommendations for speaker impedances
(which are followed by reputable manufacturers) They do not allow
a speaker of nominal impedance of 8 Ohms to fall to 3 Ohms.

Or were you talking about a 4 Ohm speaker?
You did not say so.

I was talking about modern speakers in general, most of which would
not meet the DIN/AES requirement for 8-ohm nominal impedance (indeed,
very few new speakers are rated at 8 ohms nominal).

Yes. I see. For an engineer, your terms were rather vague:-)

I note from the
above that you don't consider B&W, Quad, Martin-Logan or Wilson to be
'reputable' manufacturers.......................

This has got nothing at all to do with what *I* consider to be reputable
manufacturers.

You will find that all the above makers, and the great majority of
the others, conform to IEC/EN/BS EN 60268-5

It stipulates that impedance may fall to 80% of the nominal rated value,
i.e. 6.4 ohms for an '8 ohm' product.
A manufacturer may specify the nominal impedance

There is no limit on the amount that it may exceed the rated value.
Normally, there would be no point in such a limit, because the
loudspeaker gives its designed frequency response with constant applied
voltage. The impedance is relevant only for determining whether the
loudspeaker can demand more current than the amplifier can supply.


A difference in Ro of 0.5 ohms will give a change of volume
of about 1.5dB in the area of that dip, which most speaker engineers
would consider very likely to be audible.

I don't know from where you got the "difference of 0.5 Ohms". We were
originally talking about a amplifier with an Ro of 0.4 Ohms. So the
difference is perhaps 0.3 Ohms.

Patrick Turner raised the 0.5 ohms figure, but the general principle
applies, whether it's 0.3 ohms or 1 ohm (or indeed 3 ohms, as in the
case of some SET amps). And why would you try to shave it to 0.3 ohms,
unless you were aware that it's a real-world problem? I note that you
always prefer semantics to reality.

This is one of several experiments I want to carry out in a controlled
studio environment. Jim Lesurf, has given me some excellent pointers.
A dealer who carries JBL, B+W, Tannoy and Altec (professional products)
has promised to provide loudspeakers.


My figure is entirely valid for the numbers I quoted, which are
realistic parameters.

I am told otherwise. An engineer with whom I worked at RCA Records,
who is now a designer with JBL, has promised to send me some
impedance curves for their professional products. He tells me that
the recommendation of "a minimum of within 80% of nominal
impedance" is usually regarded as a "worst case scenario" and
thinks that the most good manufacturers can do quite a lot better.


Not my fault if you're unfamiliar with modern
loudspeakers and their impedance curves.

:-)))))


Cordially,


Iain

Tube amplifiers
 

In article , Iain M Churches
wrote:



I note from the above that you don't consider B&W, Quad, Martin-Logan
or Wilson to be 'reputable' manufacturers.......................

This has got nothing at all to do with what *I* consider to be reputable
manufacturers.

You will find that all the above makers, and the great majority of the
others, conform to IEC/EN/BS EN 60268-5

It stipulates that impedance may fall to 80% of the nominal rated value,
i.e. 6.4 ohms for an '8 ohm' product. A manufacturer may specify the
nominal impedance

There is no limit on the amount that it may exceed the rated value.
Normally, there would be no point in such a limit, because the
loudspeaker gives its designed frequency response with constant applied
voltage. The impedance is relevant only for determining whether the
loudspeaker can demand more current than the amplifier can supply.

Alas, the problem is slightly different....

I'd agree that when makers like B&W, etc, specify nominal speaker
impedances they will follow the standards. The snag is that this does notr
mean that all speakers are '8 Ohm'. Nor does it mean that people only buy
'8 Ohm' speakers for domestic use. Indeed, many reviews in magazines, and I
suspect sales/listening sessions in shops, do not mention impedance or give
useful values.

Hence an undetermined number of people will be buying and using speakers
for domestic use which would not be classificiable as '8 Ohms' and they
have no idea of this, nor will it have occurred to them as an issue.

Having read your posting my curiousity got the better of me and I looked
through the reviews in a few issues of HFN. I chose these 'at random'
purely on the basis that they were the first few issues I picked up. The
following summarises the results I found in the reviews:

Feb 2005 issue

Eclipse TD712z (4000 UKP) No plot of impedance. Just told "6 Ohm nominal"

Castle Richmond 3i (320 UKP) Stated "8 Ohm nominal"

Revolver RW33 (499 UKP) No info on impedance

Audio Physic Tempo (2200 UKP) Plot. Min 3.5 Ohms Max 22 Ohms


May 1998 issue

Mission 700 (130 UKP) stated 8 Ohm nomimal

Tannoy M1 (130 UKP) stated 8 Ohm nominal

Electa Amator II (3000 UKP) Plot min 6 Ohms max 20 Ohms

TDL Cotswold CF200 (700 UKP) stated 8 Ohm nominal


April 1997

B&W DM305 (350 UKP) Plot min 4 Ohms max 30 Ohms

Sonus Faber Concerto (1244 UKP) stated 8 Ohm nominal

Acoustic Energy AE2/II (1295 UKP) nominal 6 Ohm stated

Tannoy Mercury M2 (140 UKP) stated has min 6.5 Ohms


Aug 1993

B&W DM600.1 (180 UKP) Plot min 4 Ohms max 30 Ohms

B&W DM620.1 (400 UKP) Plot min 5 Ohms max 20 Ohms

KEF K160 (329 UKP) Plot min 5 Ohms max 20 Ohms

KEF Q80 (549 UKP) Plot min 4 Ohms max 14 Ohms

Klipshorn No info. Just waffle about the sound

JBL Ti2000 no price. Only impedance comment 4 Ohms nominal

ATC SCM20T (2000 UKP) no info given


Sep 1990

Monitor Audio 7 Plot min 7 Ohms max 12 Ohms

Shan Shimna Plot min 8 Ohms max 17 Ohms

Tannoy Mercury Plot min 6 Ohms max 25 Ohms

I would assume the above are reasonably 'typical', but would need to look
at many more reviews to know with reliability.

Looking at the above we can see that many can be assumed to be '8 Ohms'
according to the AES spec. However some reviews simply make a statement
which I assume just reports the maker's claim, so might be incorrect or
'optimistic'. And some speakers either have a nominal value of less that 8
Ohms stated, or have no nominal value given, but have a min value below 6.4
Ohms.

I have no idea what the relative numbers of speakers out in use have
various impedance specs, but I would assume that some of them show minima
that go somewhat below 6.4 Ohms. They probably do so with the user (and
saleperson!) being unaware of this in many cases.

Hence the problem here is not that reputable makers or sellers may be
fibbing, but that this is an area where many reviewers/salespeople/buyers
simply proceed in blissful ignorance. :-)



My figure is entirely valid for the numbers I quoted, which are
realistic parameters.

I am told otherwise. An engineer with whom I worked at RCA Records, who
is now a designer with JBL, has promised to send me some impedance
curves for their professional products. He tells me that the
recommendation of "a minimum of within 80% of nominal impedance" is
usually regarded as a "worst case scenario" and thinks that the most
good manufacturers can do quite a lot better.


As indicated above, my personal concern here is not with professional users
and professional monitors. I expect in that situation those involved will
know the specs, and know what they are doing. I am, however, much less
confident about this for many domestic setups. My main interest here in
what effect this may have when people listen to consumer domestic audio
equipment at home.

Slainte,

Jim

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

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

You will find that all the above makers, and the great majority of the
others, conform to IEC/EN/BS EN 60268-5

It stipulates that impedance may fall to 80% of the nominal rated value,
i.e. 6.4 ohms for an '8 ohm' product. A manufacturer may specify the
nominal impedance

There is no limit on the amount that it may exceed the rated value.
Normally, there would be no point in such a limit, because the
loudspeaker gives its designed frequency response with constant applied
voltage. The impedance is relevant only for determining whether the
loudspeaker can demand more current than the amplifier can supply.

Alas, the problem is slightly different....

I'd agree that when makers like B&W, etc, specify nominal speaker
impedances they will follow the standards. The snag is that this does notr
mean that all speakers are '8 Ohm'. Nor does it mean that people only buy
'8 Ohm' speakers for domestic use.

The critical factor here is not the nominal impedance, which can be anything
the
manufacturer states it to be, but the deviation in a downward direction
from that nominal impedance.

Indeed, many reviews in magazines, and I
suspect sales/listening sessions in shops, do not mention impedance or
give
useful values.

Caveat Emptor:-)
This explains why Tannoy, JBL, B+W have a professional division. You
can bet your bottom Euro that the products they produce for professional
use meet the standard.

Hence an undetermined number of people will be buying and using speakers
for domestic use which would not be classificiable as '8 Ohms' and they
have no idea of this, nor will it have occurred to them as an issue.

Then one would have thought that the onus would be upon the hifi press
to dig a little deeper in review. Professional magazines such as Studio
Sound
certainly do this.

Having read your posting my curiousity got the better of me and I looked
through the reviews in a few issues of HFN. I chose these 'at random'
purely on the basis that they were the first few issues I picked up. The
following summarises the results I found in the reviews:

(snip)

Looking at the above we can see that many can be assumed to be '8 Ohms'
according to the AES spec. However some reviews simply make a statement
which I assume just reports the maker's claim, so might be incorrect or
'optimistic'. And some speakers either have a nominal value of less that 8
Ohms stated, or have no nominal value given, but have a min value below
6.4 Ohms.

Interestingly enough,. Tannoy, B+W and JBL all meet the requirements
relative
to their specified nominal impedance.

As indicated above, my personal concern here is not with professional
users
and professional monitors. I expect in that situation those involved will
know the specs, and know what they are doing. I am, however, much less
confident about this for many domestic setups. My main interest here in
what effect this may have when people listen to consumer domestic audio
equipment at home.

Yes indeed. This makes in-depth review and evaluation from the popular
hifi press even more important.

Cordially,


Iain