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Andre Jute Andre Jute is offline
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Default Explanation still required for triode superiority

In an effort to be agreeable, I tried hard to give you negative
feedback inside the tube as an explanation of the overwhelming
superiority of triodes (or trioded pentodes) for audio reproduction,
among other reasons because NFB is accessible to many who belong on RAT
and is a genetic deformity of the silicon scum whose only purpose on
RAT is dissension. NFB is what the silicon slime abuse to make their
inadequate components sound passable, and what even tubies inspired by
the age of sophisters and cost-accountants use to linearize pentodes.
NFB thus has a base level of familiarity which gives it a head start in
any black box model intended to explain something to diplomaed
quarterwits among the silicon slime as well as the better-educated
kibbitzers in my own camp.

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.

Despite my cracks about the metaphysics of tubes, there *has* to be an
electrical reason for the superiority of triodes. But sure, all kinds
of input is welcome.

Andre Jute

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Peter Wieck Peter Wieck is offline
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Default Explanation still required for triode superiority


Andrew Jute McCoy wrote its usual fallacious arguments:

Called "begging the question".

Triodes are neither "superior" nor "inferior" when it comes to
amplifiers. However, they do have many difficulties. Not the least of
which a

Flea Power.
Expensive to create.
Difficult to make operational (as your model so clearly illustrated).

So, if one suspends belief sufficiently to actually beg said question,
then further discussion is optional. Just like any given
Science-Fiction movie/novel/premise.

Oh, RIGHT!! McCoy failed in this venue as well. Silly me. Never mind.

Peter Wieck
Wyncote, PA

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[email protected] Desdemona@ramadanadingdong.com is offline
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Default Explanation still required for triode superiority

On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:

In an effort to be agreeable, I tried hard to give you negative
feedback inside the tube as an explanation of the overwhelming
superiority of triodes (or trioded pentodes) for audio reproduction,
among other reasons because NFB is accessible to many who belong on RAT
and is a genetic deformity of the silicon scum whose only purpose on
RAT is dissension. NFB is what the silicon slime abuse to make their
inadequate components sound passable, and what even tubies inspired by
the age of sophisters and cost-accountants use to linearize pentodes.
NFB thus has a base level of familiarity which gives it a head start in
any black box model intended to explain something to diplomaed
quarterwits among the silicon slime as well as the better-educated
kibbitzers in my own camp.

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.

Despite my cracks about the metaphysics of tubes, there *has* to be an
electrical reason for the superiority of triodes. But sure, all kinds
of input is welcome.

Andre Jute



I know the answer!

It's distance!!

In a triode, there is a great distance between elements, forcing the electrons
to be linear!

In a transistor, things are so close and crowded that any electron going through
has to grab a few buddies to take along... and the more going through, even more
extras tag along - clearly exponential!

And in ICs, which sound even worse then discrete transistors, things are even
closer, so sound lots worse because they are even more exponential!!

Simple.

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Chris Hornbeck Chris Hornbeck is offline
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Default Explanation still required for triode superiority

On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.


If, by "you", you mean the newsgroup in general, who "must"
offer a reason, then prepare yourself for quite a...
what's the word? Anyway, Caveat Emptor (Latin for "take
a flashlight into the supposedly empty cave") and
Habeas Corpus (Latin for "habanero sauce is good on the
corpse"). Lotsa misinformation abounds.

But if by "you" you mean "me", who's been the bitchiest
about the topic, then, no, I don't have any pat answers.
I can offer a couple topics for possible discussion, but
the topic doesn't lend itself to pat answers.

And, I would generally agree about your conclusion, at
least in appropriate circumstances. Not all circumstances
are appropriate, YMMV, yadayada. But, yeah.

Much thanks, as always,

Chris Hornbeck
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22/7 22/7 is offline
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Default Explanation still required for triode superiority

Soundhaspriority wrote:
Of course. "Distance makes the heart grow fonder."


A minor correction. The saying actaully is: " Distance makes heart
grow yonder."

22/7



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Phil Phil is offline
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Default Explanation still required for triode superiority

Andre Jute wrote:

In an effort to be agreeable, I tried hard to give you negative
feedback inside the tube as an explanation of the overwhelming
superiority of triodes (or trioded pentodes) for audio reproduction,
among other reasons because NFB is accessible to many who belong on RAT
and is a genetic deformity of the silicon scum whose only purpose on
RAT is dissension. NFB is what the silicon slime abuse to make their
inadequate components sound passable, and what even tubies inspired by
the age of sophisters and cost-accountants use to linearize pentodes.
NFB thus has a base level of familiarity which gives it a head start in
any black box model intended to explain something to diplomaed
quarterwits among the silicon slime as well as the better-educated
kibbitzers in my own camp.

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.

Despite my cracks about the metaphysics of tubes, there *has* to be an
electrical reason for the superiority of triodes. But sure, all kinds
of input is welcome.

Andre Jute

Andre, I think you are too quick to dismiss the idea that feedback
transforms amplitude distortions into phase-smearing, like Otala claimed
in his talk/paper (assuming a paper ever followed the talk!). When
Patrick was defending feedback, he mentioned that poorly designed amps
sound like crap when they have lots of feedback, but that if you fix
them up a bit, meaning get rid of much of their excessive nonlinearities
-- read, *amplitude* nonlinearities -- then adding feedback sounds okay.
Now, if we eliminate the idea that feedback produces random noise -- and
we *know* that it reduces amplitude non-linearities -- then the only
distortion mechanism left, I believe, is phase-shifting. However, I want
to describe the usual "constant 20 degrees phase lag at 40 KHz" as
"phase-shifting," and a dynamic, microsecond to microsecond shifting
back and forth of one frequency relative to another as "phase-smearing,"
or "time-smearing."

What Otala was saying is that applying feedback to circuits with lots of
open-loop distortions, which are (I believe) almost always amplitude
distortions, converts these distortions into a back and forth smearing
of the high frequencies relative to the low frequencies (and it may
smear both in terms of the delay through the amp). Nor can we assume
that this time-smearing is a simple function of the low frequency
amplitude, because it is probably proportional to the magnitude of the
distortions, as well as the LF amplitude: VERY non-musical. When enough
feedback is applied to badly designed amps, the amplitude distortions
become quite small, so why did Patrick find that they sounded much worse
than the same amp sounds when touched up enough to reduce the larger
open-loop amplitude distortions? As you say, *something* is wrong, and
if it isn't high amplitude distortions (it can't be), and if feedback
doesn't produce spurious noises, then the only thing left is exactly
what Otala said, time-smearing.

In essence, feedback *connects* two things that are normally separate in
an amp, namely amplitude distortions, and phase-smearing. It achieves a
balance between these two, a balance which is determined by the speed of
the amp, the amount of feedback, and the amount of amplitude distortion.
Contrary to what you say, Otala was *not* referring to TIM, and
transistors did not become so much faster after 1980 than the ones used
in his '73 article to make the problem he described go away. Yes, the
amps had to be designed well enough to avoid TIM, but that was not a
real problem even in '73 *if* you knew what you were doing. The problem
he described in '80 was quite different, and even high MHz tubes are
subject to it.

The interesting things, assuming that feedback problems are indeed
time-smearing (regardless of whether this comes from the conversion of
amplitude distortions), are one, a single tone will reveal nothing of
this, giving very low THD numbers, and two, multiple tones should show
something, although looking at it in the amplitude realm will only show
higher than expected IMD. There should be a fairly easy way to test to
see if this really produces time-smearing. In general, we put a 4 volt
60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of
feedback, preferably using non-linear sections of the amplifying devices
(say, use two 12AX7 type triodes where the plate curves vary from widely
spaced to closely spaced, and use about 60 to 80 dB of feedback to get
the overall gain down to 1). Use a high pass filter to see only the 20
KHz signal, and use the 20 KHz signal from the generator to trigger the
'scope. If time-smearing exists, then the 20 KHz signal will appear
"fuzzy" on the scope, since it is being shifted back and forth. Repeat
without the 60 Hz signal to make sure the time-smearing isn't coming
from somewhere else, and then also divide the output from each tube down
so that you get the same amplitude output *without* using feedback, and
see if the time-smearing goes away. Finally, if possible test over a
region where the curves are fairly linear, to see if that also reduces
the time-smearing. If so, you have proof that feedback transformed the
amplitude distortion into time-smearing. I will try to do this, but I
have little time, less energy, and not the best test bench in the world,
so it may be a while! If you or someone else both can and wants to try
this, I suspect we will get an answer much faster than if I do it. Note
that we can use pentodes or transistors, too, but using solid state has
the disadvantage of possibly introducing other complications due to the
poor quality silicon parasitic capacitances. Also, I am suggesting the
use of very different magnitudes as well as frequencies for the two
signals, in case equal magnitudes somehow avoids this problem, or at
least masks it from this test. And again, contrary to what Patrick said,
the idea that *if* this were true, then by now someone would have
already tries it, and the results would have become widely know, is just
naive. The human race simply isn't that intelligent, at least not yet.

An interesting conclusion, assuming this feedback time-smear mechanism
exists, is that the output of a feedback amp does *not* match the input
when multiple signals exist! However, our normal tests cannot see this,
since they tend to focus on one frequency at a time. I believe that
Patrick, as well as Otala, said that using local feedback to achieve
good open loop linearity, combined with some global feedback, tends to
sound pretty good. This makes sense for two reasons, first because
although the local feedback will produce phase-smearing, it does so at
*very* high speed, which I believe directly reduces the amount of
smearing (common sense says that as the speed of devices approaches
infinity, feedback becomes "perfect"). Second, the result does contain
some mis-match between input and output, even given the high speed of
local feedback, but now the global feedback will not only reduce the
remaining "normal" amplitude distortions, it should also reduce the
time-smearing produced by the local feedback, since this time-smearing
will still produce an error signal for the global feedback. Of course,
this reduction in time-smearing will itself produce more time-smearing,
but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of
time-smearing is reduced by "dividing up" the total feedback into local
plus global.

Finally, you saw the review of Otala that Phil Allison gave, and I think
you were as impressed by it as I was (although it looked bad to PA).
When a man who was as talented, knowledgeable, and honest as Otala
produces a PROOF that negative feedback *always* transforms the
amplitude distortions of the open loop into phase smears of the closed
loop, we should not dismiss it as simply a problem of "old devices," a
problem that a slight increase in speed can make go away, especially
when the discussion that led to his analysis (the Audio Critic BS
session) included a lot of talk about vacuum tubes, and how their speed
advantage made it easier to use them with feedback. We really should do
at least one or two tests before dismissing his conclusions. Again, I
will try to do so, but if you want to know anytime soon, you should
probably rely on someone else.

Phil
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Andre Jute Andre Jute is offline
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Default Explanation still required for triode superiority


22/7 wrote:
Soundhaspriority wrote:
Of course. "Distance makes the heart grow fonder."


A minor correction. The saying actaully is: " Distance makes heart
grow yonder."

22/7


I think you're right, No. 22. But if you used a spelling checker your
meaning would be so much clearer: "Distance makes the heart thunder."

That we can all agree to. Long rooms, permitting greater separation of
ears and speakers, definitely do have better bass, and deep bass
increases the respiration rate; it is an ur-instinct reaction to
threat.

Hope this explains everything including the price of fish beyond Alpha
Centauri (1).

For this insight I have recommended that you be promoted to No. 21.

Andre Jute


(1) Once after lunch with a lady from our publishers, Douglas Adams and
I walked up four floors of a narrow stairwell behind her. She wore a
transparent plastic raincoat over a skintight flesh coloured body
stocking. We discussed the price of fish beyond Alpha Centauri. I swear
that's what we discussed.

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Andre Jute Andre Jute is offline
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Default Explanation still required for triode superiority


Chris Hornbeck wrote:
On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.


If, by "you", you mean the newsgroup in general, who "must"
offer a reason, then prepare yourself for quite a...
what's the word? Anyway, Caveat Emptor (Latin for "take
a flashlight into the supposedly empty cave") and
Habeas Corpus (Latin for "habanero sauce is good on the
corpse"). Lotsa misinformation abounds.


I'd say "****'em" but their minds are clearly syphiclically degenerated
(the NFB of the immoral) so touching them physically may expose one to
contamination.

As for "must", sure thing. The most amazing thing about the amateur
flamers on RAT is not their incompetence in both electronics and
polemics but there blind hypocrisy, best seen in their pretension of
being "scientific".

But if by "you" you mean "me", who's been the bitchiest
about the topic, then, no, I don't have any pat answers.
I can offer a couple topics for possible discussion, but
the topic doesn't lend itself to pat answers.


Bring on your topics, Chris. We could do with some fresh air in RAT.

And, I would generally agree about your conclusion, at
least in appropriate circumstances. Not all circumstances
are appropriate, YMMV, yadayada. But, yeah.


Which conclusion? That "triodes sound better" or that "there must be an
electrical explanation"?

Much thanks, as always,

Chris Hornbeck


Andre Jute
"Take the money and run" -- Len Deighton

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David R Brooks David R Brooks is offline
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Default Explanation still required for triode superiority

22/7 wrote:
Soundhaspriority wrote:
Of course. "Distance makes the heart grow fonder."


A minor correction. The saying actaully is: " Distance makes heart
grow yonder."

22/7

Or "absinthe makes the heart grow fonder", as Crowley put it
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Eeyore Eeyore is offline
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Default Explanation still required for triode superiority



Andre Jute wrote:

Which conclusion? That "triodes sound better"


That's your opinion.

or that "there must be an electrical explanation"?


Of course there must be. Added low order distortion of course. It's
basically an 'effect' like SRS or BBE 'sound enhancement'. With toobs you
can't turn if off though

Graham



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Andre Jute Andre Jute is offline
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Default Explanation still required for triode superiority


Andre Jute wrote:
Chris Hornbeck wrote:
On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.


If, by "you", you mean the newsgroup in general, who "must"
offer a reason, then prepare yourself for quite a...
what's the word? Anyway, Caveat Emptor (Latin for "take
a flashlight into the supposedly empty cave") and
Habeas Corpus (Latin for "habanero sauce is good on the
corpse"). Lotsa misinformation abounds.


I'd say "****'em" but their minds are clearly syphiclically degenerated
(the NFB of the immoral) so touching them physically may expose one to
contamination.

As for "must", sure thing. The most amazing thing about the amateur
flamers on RAT is not their incompetence in both electronics and
polemics but there blind hypocrisy, best seen in their pretension of
being "scientific".


And down with IBM's ViaVoice too for that "there" for "their". In the
same sentence as "pretension" too! -- AJ

But if by "you" you mean "me", who's been the bitchiest
about the topic, then, no, I don't have any pat answers.
I can offer a couple topics for possible discussion, but
the topic doesn't lend itself to pat answers.


Bring on your topics, Chris. We could do with some fresh air in RAT.

And, I would generally agree about your conclusion, at
least in appropriate circumstances. Not all circumstances
are appropriate, YMMV, yadayada. But, yeah.


Which conclusion? That "triodes sound better" or that "there must be an
electrical explanation"?

Much thanks, as always,

Chris Hornbeck


Andre Jute
"Take the money and run" -- Len Deighton


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Andre Jute Andre Jute is offline
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Default Explanation still required for triode superiority

I've read your arguments, Phil. Their subtext is methods to make NFB
more usable, less damaging to reproduced sound. That is a legitimate
outlook for Otala, who has to fit into an existing industrial
environment where NFB is an ineradicable part of that dominant
electronics cost-accounting system in which the explicit purpose of NFB
is to make cheap parts tolerable.

But that has buggerall to do with me as a DIYer. I can afford to take
the far simpler, more fundamental course of making my amps so superior
in design and components right from the start -- that I can do without
NFB and without the damage that NFB does. So I design amps without NFB,
period. I shortcut the problem of NFB and eliminate it before it
arises. My amps are ultra-silent without NFB; they do not need NFB for
any purpose whatsoever. Since one of my ZNFB amps is capable of 80W
when in its PSE mode, more than enough to drive electrostatic panels to
power-rivetter volume, I take the view that any designer who requires
NFB to make his hi-fi amps work has either permitted cost-accountants
to bully him, is an impressionable fashion victim, or is too thick to
put his mind in gear, tick one or more boxes.

The rest is interesting speculation but not of such consuming interest
to me that I will spend a morning setting up bench experiments to prove
the details of something I already know: that NFB smears the sound. A
complete summary of my view on NFB can be found here
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm
and here
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm

I haven't changed my mind one jot or tittle over the recent discussion.
I have heard absolutely nothing that proves a contrary case. That is
not to say you may not be right, that the psycho-acoustic effect which
gives Class A1 ZNFB (or very low NFB) amps their distinct superiority
is a subliminal reaction to the HF phase- smearing in NFB amps that you
say Otala posits. I just haven't seen any proof yet, and know that,
when I do see such proof, I will consider it of intellectual interest
-- and continue to build the sort of ZNFB amps I have always built, in
which NFB is excluded for its amplitude smearing at frequencies
starting below 100c/s, so that HF phase smearing, if it exists in NFB
tube amps, is no danger to my sound.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Phil wrote:
Andre Jute wrote:

In an effort to be agreeable, I tried hard to give you negative
feedback inside the tube as an explanation of the overwhelming
superiority of triodes (or trioded pentodes) for audio reproduction,
among other reasons because NFB is accessible to many who belong on RAT
and is a genetic deformity of the silicon scum whose only purpose on
RAT is dissension. NFB is what the silicon slime abuse to make their
inadequate components sound passable, and what even tubies inspired by
the age of sophisters and cost-accountants use to linearize pentodes.
NFB thus has a base level of familiarity which gives it a head start in
any black box model intended to explain something to diplomaed
quarterwits among the silicon slime as well as the better-educated
kibbitzers in my own camp.

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.

Despite my cracks about the metaphysics of tubes, there *has* to be an
electrical reason for the superiority of triodes. But sure, all kinds
of input is welcome.

Andre Jute

Andre, I think you are too quick to dismiss the idea that feedback
transforms amplitude distortions into phase-smearing, like Otala claimed
in his talk/paper (assuming a paper ever followed the talk!). When
Patrick was defending feedback, he mentioned that poorly designed amps
sound like crap when they have lots of feedback, but that if you fix
them up a bit, meaning get rid of much of their excessive nonlinearities
-- read, *amplitude* nonlinearities -- then adding feedback sounds okay.
Now, if we eliminate the idea that feedback produces random noise -- and
we *know* that it reduces amplitude non-linearities -- then the only
distortion mechanism left, I believe, is phase-shifting. However, I want
to describe the usual "constant 20 degrees phase lag at 40 KHz" as
"phase-shifting," and a dynamic, microsecond to microsecond shifting
back and forth of one frequency relative to another as "phase-smearing,"
or "time-smearing."

What Otala was saying is that applying feedback to circuits with lots of
open-loop distortions, which are (I believe) almost always amplitude
distortions, converts these distortions into a back and forth smearing
of the high frequencies relative to the low frequencies (and it may
smear both in terms of the delay through the amp). Nor can we assume
that this time-smearing is a simple function of the low frequency
amplitude, because it is probably proportional to the magnitude of the
distortions, as well as the LF amplitude: VERY non-musical. When enough
feedback is applied to badly designed amps, the amplitude distortions
become quite small, so why did Patrick find that they sounded much worse
than the same amp sounds when touched up enough to reduce the larger
open-loop amplitude distortions? As you say, *something* is wrong, and
if it isn't high amplitude distortions (it can't be), and if feedback
doesn't produce spurious noises, then the only thing left is exactly
what Otala said, time-smearing.

In essence, feedback *connects* two things that are normally separate in
an amp, namely amplitude distortions, and phase-smearing. It achieves a
balance between these two, a balance which is determined by the speed of
the amp, the amount of feedback, and the amount of amplitude distortion.
Contrary to what you say, Otala was *not* referring to TIM, and
transistors did not become so much faster after 1980 than the ones used
in his '73 article to make the problem he described go away. Yes, the
amps had to be designed well enough to avoid TIM, but that was not a
real problem even in '73 *if* you knew what you were doing. The problem
he described in '80 was quite different, and even high MHz tubes are
subject to it.

The interesting things, assuming that feedback problems are indeed
time-smearing (regardless of whether this comes from the conversion of
amplitude distortions), are one, a single tone will reveal nothing of
this, giving very low THD numbers, and two, multiple tones should show
something, although looking at it in the amplitude realm will only show
higher than expected IMD. There should be a fairly easy way to test to
see if this really produces time-smearing. In general, we put a 4 volt
60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of
feedback, preferably using non-linear sections of the amplifying devices
(say, use two 12AX7 type triodes where the plate curves vary from widely
spaced to closely spaced, and use about 60 to 80 dB of feedback to get
the overall gain down to 1). Use a high pass filter to see only the 20
KHz signal, and use the 20 KHz signal from the generator to trigger the
'scope. If time-smearing exists, then the 20 KHz signal will appear
"fuzzy" on the scope, since it is being shifted back and forth. Repeat
without the 60 Hz signal to make sure the time-smearing isn't coming
from somewhere else, and then also divide the output from each tube down
so that you get the same amplitude output *without* using feedback, and
see if the time-smearing goes away. Finally, if possible test over a
region where the curves are fairly linear, to see if that also reduces
the time-smearing. If so, you have proof that feedback transformed the
amplitude distortion into time-smearing. I will try to do this, but I
have little time, less energy, and not the best test bench in the world,
so it may be a while! If you or someone else both can and wants to try
this, I suspect we will get an answer much faster than if I do it. Note
that we can use pentodes or transistors, too, but using solid state has
the disadvantage of possibly introducing other complications due to the
poor quality silicon parasitic capacitances. Also, I am suggesting the
use of very different magnitudes as well as frequencies for the two
signals, in case equal magnitudes somehow avoids this problem, or at
least masks it from this test. And again, contrary to what Patrick said,
the idea that *if* this were true, then by now someone would have
already tries it, and the results would have become widely know, is just
naive. The human race simply isn't that intelligent, at least not yet.

An interesting conclusion, assuming this feedback time-smear mechanism
exists, is that the output of a feedback amp does *not* match the input
when multiple signals exist! However, our normal tests cannot see this,
since they tend to focus on one frequency at a time. I believe that
Patrick, as well as Otala, said that using local feedback to achieve
good open loop linearity, combined with some global feedback, tends to
sound pretty good. This makes sense for two reasons, first because
although the local feedback will produce phase-smearing, it does so at
*very* high speed, which I believe directly reduces the amount of
smearing (common sense says that as the speed of devices approaches
infinity, feedback becomes "perfect"). Second, the result does contain
some mis-match between input and output, even given the high speed of
local feedback, but now the global feedback will not only reduce the
remaining "normal" amplitude distortions, it should also reduce the
time-smearing produced by the local feedback, since this time-smearing
will still produce an error signal for the global feedback. Of course,
this reduction in time-smearing will itself produce more time-smearing,
but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of
time-smearing is reduced by "dividing up" the total feedback into local
plus global.

Finally, you saw the review of Otala that Phil Allison gave, and I think
you were as impressed by it as I was (although it looked bad to PA).
When a man who was as talented, knowledgeable, and honest as Otala
produces a PROOF that negative feedback *always* transforms the
amplitude distortions of the open loop into phase smears of the closed
loop, we should not dismiss it as simply a problem of "old devices," a
problem that a slight increase in speed can make go away, especially
when the discussion that led to his analysis (the Audio Critic BS
session) included a lot of talk about vacuum tubes, and how their speed
advantage made it easier to use them with feedback. We really should do
at least one or two tests before dismissing his conclusions. Again, I
will try to do so, but if you want to know anytime soon, you should
probably rely on someone else.

Phil


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Phil wrote:

Andre Jute wrote:

In an effort to be agreeable, I tried hard to give you negative
feedback inside the tube as an explanation of the overwhelming
superiority of triodes (or trioded pentodes) for audio reproduction,
among other reasons because NFB is accessible to many who belong on RAT
and is a genetic deformity of the silicon scum whose only purpose on
RAT is dissension. NFB is what the silicon slime abuse to make their
inadequate components sound passable, and what even tubies inspired by
the age of sophisters and cost-accountants use to linearize pentodes.
NFB thus has a base level of familiarity which gives it a head start in
any black box model intended to explain something to diplomaed
quarterwits among the silicon slime as well as the better-educated
kibbitzers in my own camp.

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.

Despite my cracks about the metaphysics of tubes, there *has* to be an
electrical reason for the superiority of triodes. But sure, all kinds
of input is welcome.

Andre Jute

Andre, I think you are too quick to dismiss the idea that feedback
transforms amplitude distortions into phase-smearing, like Otala claimed
in his talk/paper (assuming a paper ever followed the talk!). When
Patrick was defending feedback, he mentioned that poorly designed amps
sound like crap when they have lots of feedback, but that if you fix
them up a bit, meaning get rid of much of their excessive nonlinearities
-- read, *amplitude* nonlinearities -- then adding feedback sounds okay.
Now, if we eliminate the idea that feedback produces random noise -- and
we *know* that it reduces amplitude non-linearities -- then the only
distortion mechanism left, I believe, is phase-shifting. However, I want
to describe the usual "constant 20 degrees phase lag at 40 KHz" as
"phase-shifting," and a dynamic, microsecond to microsecond shifting
back and forth of one frequency relative to another as "phase-smearing,"
or "time-smearing."

What Otala was saying is that applying feedback to circuits with lots of
open-loop distortions, which are (I believe) almost always amplitude
distortions, converts these distortions into a back and forth smearing
of the high frequencies relative to the low frequencies (and it may
smear both in terms of the delay through the amp). Nor can we assume
that this time-smearing is a simple function of the low frequency
amplitude, because it is probably proportional to the magnitude of the
distortions, as well as the LF amplitude: VERY non-musical. When enough
feedback is applied to badly designed amps, the amplitude distortions
become quite small, so why did Patrick find that they sounded much worse
than the same amp sounds when touched up enough to reduce the larger
open-loop amplitude distortions? As you say, *something* is wrong, and
if it isn't high amplitude distortions (it can't be), and if feedback
doesn't produce spurious noises, then the only thing left is exactly
what Otala said, time-smearing.

In essence, feedback *connects* two things that are normally separate in
an amp, namely amplitude distortions, and phase-smearing. It achieves a
balance between these two, a balance which is determined by the speed of
the amp, the amount of feedback, and the amount of amplitude distortion.
Contrary to what you say, Otala was *not* referring to TIM, and
transistors did not become so much faster after 1980 than the ones used
in his '73 article to make the problem he described go away. Yes, the
amps had to be designed well enough to avoid TIM, but that was not a
real problem even in '73 *if* you knew what you were doing. The problem
he described in '80 was quite different, and even high MHz tubes are
subject to it.

The interesting things, assuming that feedback problems are indeed
time-smearing (regardless of whether this comes from the conversion of
amplitude distortions), are one, a single tone will reveal nothing of
this, giving very low THD numbers, and two, multiple tones should show
something, although looking at it in the amplitude realm will only show
higher than expected IMD. There should be a fairly easy way to test to
see if this really produces time-smearing. In general, we put a 4 volt
60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of
feedback, preferably using non-linear sections of the amplifying devices
(say, use two 12AX7 type triodes where the plate curves vary from widely
spaced to closely spaced, and use about 60 to 80 dB of feedback to get
the overall gain down to 1). Use a high pass filter to see only the 20
KHz signal, and use the 20 KHz signal from the generator to trigger the
'scope. If time-smearing exists, then the 20 KHz signal will appear
"fuzzy" on the scope, since it is being shifted back and forth. Repeat
without the 60 Hz signal to make sure the time-smearing isn't coming
from somewhere else, and then also divide the output from each tube down
so that you get the same amplitude output *without* using feedback, and
see if the time-smearing goes away. Finally, if possible test over a
region where the curves are fairly linear, to see if that also reduces
the time-smearing. If so, you have proof that feedback transformed the
amplitude distortion into time-smearing. I will try to do this, but I
have little time, less energy, and not the best test bench in the world,
so it may be a while! If you or someone else both can and wants to try
this, I suspect we will get an answer much faster than if I do it. Note
that we can use pentodes or transistors, too, but using solid state has
the disadvantage of possibly introducing other complications due to the
poor quality silicon parasitic capacitances. Also, I am suggesting the
use of very different magnitudes as well as frequencies for the two
signals, in case equal magnitudes somehow avoids this problem, or at
least masks it from this test. And again, contrary to what Patrick said,
the idea that *if* this were true, then by now someone would have
already tries it, and the results would have become widely know, is just
naive. The human race simply isn't that intelligent, at least not yet.

An interesting conclusion, assuming this feedback time-smear mechanism
exists, is that the output of a feedback amp does *not* match the input
when multiple signals exist! However, our normal tests cannot see this,
since they tend to focus on one frequency at a time. I believe that
Patrick, as well as Otala, said that using local feedback to achieve
good open loop linearity, combined with some global feedback, tends to
sound pretty good. This makes sense for two reasons, first because
although the local feedback will produce phase-smearing, it does so at
*very* high speed, which I believe directly reduces the amount of
smearing (common sense says that as the speed of devices approaches
infinity, feedback becomes "perfect"). Second, the result does contain
some mis-match between input and output, even given the high speed of
local feedback, but now the global feedback will not only reduce the
remaining "normal" amplitude distortions, it should also reduce the
time-smearing produced by the local feedback, since this time-smearing
will still produce an error signal for the global feedback. Of course,
this reduction in time-smearing will itself produce more time-smearing,
but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of
time-smearing is reduced by "dividing up" the total feedback into local
plus global.

Finally, you saw the review of Otala that Phil Allison gave, and I think
you were as impressed by it as I was (although it looked bad to PA).
When a man who was as talented, knowledgeable, and honest as Otala
produces a PROOF that negative feedback *always* transforms the
amplitude distortions of the open loop into phase smears of the closed
loop, we should not dismiss it as simply a problem of "old devices," a
problem that a slight increase in speed can make go away, especially
when the discussion that led to his analysis (the Audio Critic BS
session) included a lot of talk about vacuum tubes, and how their speed
advantage made it easier to use them with feedback. We really should do
at least one or two tests before dismissing his conclusions. Again, I
will try to do so, but if you want to know anytime soon, you should
probably rely on someone else.

Phil


I have seen no evidence of the time smearing you are talking about.

The essence of time smearing you speak of when testing say 5kHz
with 60Hz present as a larger signal is that the 60Hz affects the devices as
a changing
reactance load on the devices so that the phase of the 5kHz waves are phase
advanced
and phase lagged alternatively 60 times persecond.

Phase modulation and FM modulation was gained deliberately in
reactance tube modulators which exploited the change in gm with Ia in
a tube thus shifting the F of an oscillator or the phase of an RF carrier.
There is much about thei is old books.

But dynamic phase shift of a fraction of a 5kHz wave I have not seen due to
dynamic action by a lower F.
The NFB reduces ALL artifacts and such phase shifting is reduced in the open
loop
character of an amp where it allegedly should exist.

I repeatedly gave the conditions needed where the application of NFB didn't
make any improvement
to the sound, and made little difference to the measured THD artifacts
especially when weighted
for audibibilty, and increased the number of artifacts significantly.
Far greater minds than I have spelled it all out in Wireless World years ago.

I suggest you read all your local university library archives containing the
magazine with its brilliant audio
articles between when it first appeared in 1917 to now.
( I assume your local uni isn't full of football magazines in the archives ).

I have only read and copied out the audio stuff up to about 1996.
In all of this literature on the effects NFB there wasn't much about
FB causing dynamic phase shift that I can recall.
Perhaps if you read what I read you'll find something I missed.
Seriously, methinks you NEED to do some real study.

Perhaps you'd like to re-iterate what I said to all about open loop bw,
phase shift, and the amount of applied NFB and the amount of open loop THD.

The fuzziness you say is observed when viewing the HF wave in a cascaded
12AX7
amp where the gain has been reduced to 1 is hard to believe.
A cascaded pair of 12AX7 would have an open loop gain = at least 3,000,
and applying FB to reduce gain to 1.0 = 70dB of applied NFB.

Any dynamic phase shifting in any signal before FB is applied should be
easily
visible / measurable / quantifiable before NFB is connected,
but after a reduction of 70dB it would most definately be invisible on a CRO.

Do offer my sincerest respects to Mr Otala and ask him to
tell you all about what you appear to maybe not understand as well as he may.

I suspect you instead remain delighted
by the jargon and terminology around the subject rather than staying
with the cold hard facts about applied NFB and its effects and the conditions
under which it is applied,
all of which cannot easily be dealt with without being
utterly precise at all times, which seems right considering the books and
magazine articles
which have been written about NFB so far.

Patrick Turner.






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Arny Krueger wrote:

"Phil" wrote in message
...

Andre, I think you are too quick to dismiss the idea that feedback
transforms amplitude distortions into phase-smearing,


There is no reliable theoretical or measurable support for this idea.
There's no support based on reliable listening tests.

In contrast, there are zillions of examples of equipment with tons of
negative feedback that has marvelous phase accuracy, both measured and
heard. Proven theory says this is exactly as it should be.

How thoroughly does something need to be disproved to be abandoned?


Furthermore it can easily be shown to be yet another myth by the
application of mathematics !

Graham


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Default Explanation still required for triode superiority


"Phil" wrote in message
...

Andre, I think you are too quick to dismiss the idea that feedback
transforms amplitude distortions into phase-smearing,


There is no reliable theoretical or measurable support for this idea.
There's no support based on reliable listening tests.

In contrast, there are zillions of examples of equipment with tons of
negative feedback that has marvelous phase accuracy, both measured and
heard. Proven theory says this is exactly as it should be.

How thoroughly does something need to be disproved to be abandoned?




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Eeyore wrote:

Andre Jute wrote:

Which conclusion? That "triodes sound better"


That's your opinion.

or that "there must be an electrical explanation"?


Of course there must be. Added low order distortion of course. It's
basically an 'effect' like SRS or BBE 'sound enhancement'. With toobs you
can't turn if off though

Graham


I am not sure triodes are superior.

They are just 3 terminal devices with inbuilt NFB.

In the 1950s and 60s in many recording studios, gear was used that was mostly
designed by cloth eared
engineers with 100% regard only for numbers and such gear had SHIRTLOADS of
pentodes and beam tetrodes
and transformers and NFB.

We hear the results today on well recorded and preserved vinyl recordings.
Not a digit or PN junction used anywhere.

Great stuff when it turned out right. Was it dependant on triodes?
maybe, but also maybe not.
Why would any engineer use 3 triodes where two pentodes would do?

The final link for us lesser latterday mortals is from recording to speaker,
and triodes are a good choice.
Not necessarily superior IMHO, and i say that after trying
such tubes as the 13Ei SEUL with mild NFB that I believe will give ANY triode
amp some real competion,
providing the power ceiling is the same.

As a later SE amp development I tried a quad of humble cheap EH 6CA7,
actually Sovtek prettied up,
to get 35 watts SE with CFB, and again the measurements were NOT typically
inferior to PP designs and the sound was detailed, sparkling and natural
sounding
and all that anyone may wish for.

I have built SET amps with 2A3 or 300B, and found they gave the best 8 and 4
watts
i have ever heard with 7 db of NFB to reduce Rout compared to tubes like a
single EL84 in pentode
or a single EL34 in pentode, respectively, but with 20dB of NFB needed to get
the same Rout.

The CFB connection transcends the UL connection which transcends pentode.
Triode is somewhere in their between CFB and UL IMHO.

Experimenters may experiment to verify/discount my opinions.

See my web pages for more on such matters.
http://www.turneraudio.com.au

Patrick Turner.








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Stuart Krivis wrote:

On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.


First we would have to accept these things as true. :-)


In the face of overwhelming evidence that as far as accuracy is concerned,
triodes are really quite flawed.

The simple explanation being that for some, accuracy of reproduction is
not what they seek, they simply seek what they consider to be 'a nice
sound'. Which is all fine and well but accuracy ain't part of it.

Graham


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Stuart Krivis wrote:

On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig"
wrote:

Peter Wieck wrote:
Andrew Jute McCoy wrote its usual fallacious arguments:

Called "begging the question".

Triodes are neither "superior" nor "inferior" when it comes to
amplifiers. However, they do have many difficulties. Not the least of
which a

Flea Power.
Expensive to create.
Difficult to make operational (as your model so clearly illustrated).


Triodes are cheaper to build than beam power tubes of a given size,
simpler, and can be used for amplifiers of any size. Most 50 kW AM
broadcast transmitters had two triodes in their modulators giving 30 kW
audio power in Class B.


AM transmitters are a bit orthogonal to the topic at hand. :-)


The toobies don't care though !

Graham


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Stuart Krivis wrote:

On Mon, 25 Sep 2006 14:06:16 +0100, Eeyore wrote:
Arny Krueger wrote:
"Phil" wrote:

Andre, I think you are too quick to dismiss the idea that feedback
transforms amplitude distortions into phase-smearing,

There is no reliable theoretical or measurable support for this idea.
There's no support based on reliable listening tests.

In contrast, there are zillions of examples of equipment with tons of
negative feedback that has marvelous phase accuracy, both measured and
heard. Proven theory says this is exactly as it should be.

How thoroughly does something need to be disproved to be abandoned?


Furthermore it can easily be shown to be yet another myth by the
application of mathematics !


Don't mention math! You'll get them all confuzzled. :-)


They would seem to be confuzzled already with their talk of 'HF smearing' !

Graham


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Eeyore said:


The simple explanation being that for some, accuracy of reproduction is
not what they seek, they simply seek what they consider to be 'a nice
sound'. Which is all fine and well but accuracy ain't part of it.



You won't hear me say anything else, regarding my own hobby designs.

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


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Sander deWaal wrote:

Eeyore said:

The simple explanation being that for some, accuracy of reproduction is
not what they seek, they simply seek what they consider to be 'a nice
sound'. Which is all fine and well but accuracy ain't part of it.


You won't hear me say anything else, regarding my own hobby designs.


That because you're honest Sander ! :~) Unlike some here.

Graham

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Bret Ludwig wrote:

Stuart Krivis wrote:
On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig"
wrote:

Triodes are cheaper to build than beam power tubes of a given size,
simpler, and can be used for amplifiers of any size. Most 50 kW AM
broadcast transmitters had two triodes in their modulators giving 30 kW
audio power in Class B.


AM transmitters are a bit orthogonal to the topic at hand. :-)


Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else
you would have had nothing but Morse code.


And since when was AM 'hi-fi' ?

Graham


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Bret Ludwig wrote:

Eeyore wrote:
Bret Ludwig wrote:
Stuart Krivis wrote:
On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig"
wrote:

Triodes are cheaper to build than beam power tubes of a given size,
simpler, and can be used for amplifiers of any size. Most 50 kW AM
broadcast transmitters had two triodes in their modulators giving 30 kW
audio power in Class B.

AM transmitters are a bit orthogonal to the topic at hand. :-)

Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else
you would have had nothing but Morse code.


And since when was AM 'hi-fi' ?


That would be before VHF FM became dominant. On days with little
electrical storm activity in the hemisphere and in the right locations
very fine broadcast fidelity was possible. Even today, at a place I
visited in north central Missouri I heard KXTR from Kansas City through
a passive Millen tuner (essentially a crystal radio) in astonishing
fidelity at an elderly hi-fi buff's house. Shame everything they play
is by the appalling Sir Neville Marriner at the Academy of
St-Martin-in-the-Fields. Vintage Toscanini and other classic
conductors' recordings would be so much better, but instead they play
that LOAD continually.

They say LF transmissions in England and Germany were even more
impressive.


The problem with AM AUIU was always one of bandwidth for one part and of course
that any interference was directly demodulated.

Those old valve sets did sound rather good though ( I had one myself - an EKCO !
) but that for the most part was mainly due to the excellent design of the RF
circuitry.


Graham


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Chris Hornbeck wrote:

1. Unweighted THD is useless as an indicator of quality.


So why do you think I regularly mention the order of the distortion ?

Graham

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On 25 Sep 2006 03:09:39 -0700, "Andre Jute" wrote:

Bring on your topics, Chris. We could do with some fresh air in RAT.


Some folks who I'd hoped to be refreshing have turned out
to be terminally boring. Sorry for having encouraged 'em.
We live and don't learn... or something. Again, sorry, all.


No time this week to give any adequate or deserving response
to yours or Henry's provocative posts, but, if I may, a few
possibilities:

1. Unweighted THD is useless as an indicator of quality.

2. Unweighted IMD " " "

3. We make totally unwarranted assumptions of monotonicity.
This is a fatal flaw in our thinking, and we all do it, all
the time.

4. We make often unwarranted assumptions about input signal
bandwidth.

5. We *always* *without exception* forget to properly weight
the importance of simply being upstream in the signal path.
Always.

6. Loud voices will say that everything (that doesn't include
the dreaded vacuum valve, scourge of nations) sounds the same.
This has recently been expanded to include transistor amplifiers
from the early 1970's, by certain especially vocal ideologes,
in another thread, this very week.

Against such a religious fervor, nothing can stand.

Been reading about weaponry this week; no real purpose;
haven't needed a weapon since discharged from the Army
in 1972; just looking, ya know?

It seems that the US military converted from the Colt .45
caliber pistol in standard issue since 1911(!) to a Berreta
of some NATO gauge in the mid 1980's. But it seems it doesn't
work, despite all the high powered analysis. Ya shoot
sombody with it, but they keep comin'.

What's so sadly wrong with the story is that the US military
went through the whole exact same hand-wringing back 100+
years ago in the Phillippines, leading to the adoption
of, wait for it, the .45 caliber.


Modeling and analysis are essential; but the map is not
the world.


Which conclusion? That "triodes sound better" or that "there must be an
electrical explanation"?


Strong agreement with the former; strong disagreement ('cause
that ain't science!) with the latter.

"Take the money and run" -- Len Deighton


And also... who? Bob Segar? Somebody like that, anyway.

Much thanks, as always,

Chris Hornbeck


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On Tue, 26 Sep 2006 05:07:55 +0100, Eeyore
wrote:

1. Unweighted THD is useless as an indicator of quality.


So why do you think I regularly mention the order of the distortion ?


Wanna *not* be a major disappointment? Post something
positive and educational on the topic.

Right here; right now.

Lord knows you're capable, and all the latterday endless cheap
shots are beneath you. Step up to the plate and take a swing!

This *could* be a very interesting newsgroup again someday.
Gonna take everybody; no slackers.

As always,

Chris Hornbeck
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Eeyore wrote:

Stuart Krivis wrote:

On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.


First we would have to accept these things as true. :-)


In the face of overwhelming evidence that as far as accuracy is concerned,
triodes are really quite flawed.

The simple explanation being that for some, accuracy of reproduction is
not what they seek, they simply seek what they consider to be 'a nice
sound'. Which is all fine and well but accuracy ain't part of it.

Graham


Graham, you may not realise it, but you speak with a flawed reasoning ability
on this issue, IMHO.

Its easily possible to build a class A triode PP amp with say a pair of KT90
strapped as triodes fo 30 watts at about 0.7% thd with no global NFB.
If 26dB of global NFB is connected (as it used to be done so often in 1955),
THD at 30 watts drops to 0.035% and at normal average listening levels of a
watt
the THD is quite negligible at around 0.01% and accuracy is what would be
heard in your ears
and accuracy is what you want and it depends on the
measuable artfacts being audible or not. Since artifacts of 0.01% are
inaudible,
mainly a tiny amount of 3H and without any crossover distortions etc, the
music is accurate, no?

Perhaps you need to buy a pair of Halcros made in Sth Aust and they give only
0.0001% at 200 watts at 20 kHz.

All the accuracy anyone might crave for.

Meanwhile, many ppl don't mind THD being 0.1% or more, and are flat out trying
to
determine if that is audible or not.

Patrick Turner.


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Eeyore wrote:

Bret Ludwig wrote:

Stuart Krivis wrote:
On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig"
wrote:

Triodes are cheaper to build than beam power tubes of a given size,
simpler, and can be used for amplifiers of any size. Most 50 kW AM
broadcast transmitters had two triodes in their modulators giving 30 kW
audio power in Class B.

AM transmitters are a bit orthogonal to the topic at hand. :-)


Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else
you would have had nothing but Morse code.


And since when was AM 'hi-fi' ?

Graham


The best transmissions here have 9kHz of audio modulation.

In 1999 I built a tubed AM radio with a flat AF bw of 10Hz to 10kHz, which meant
the
IFT had to be carefully contructed for a wide pass band of about 17kHz,
and some treble boosting compensates for the sideband cutting.

So although 10khz is missing from the 20kHz of AF bw needed for true hi-fi, my
AM
radio is unsurpassable compared to all other AM radios I have ever worked on.
All brand name AM tuners and radios have less AF bw than my set because they
were
designed to give about 7kHz max of IF bw so AF is restricted to 3.5kHz if one is
very lucky
and with many SS AM sets the AF is about 2kHz, and the distortion is much
higher.

The audio amp in the radio is an EL34 in triode with 12AX7 driver and with 12 dB
of NFB.
There is a full range two way speaker in a floor standing reflex box under the
radio set.
The radio provides truly wonderful, musical, undistorted and non tiring
listening.

Patrick Turner.





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Eeyore wrote:

Bret Ludwig wrote:

Eeyore wrote:
Bret Ludwig wrote:
Stuart Krivis wrote:
On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig"
wrote:

Triodes are cheaper to build than beam power tubes of a given size,
simpler, and can be used for amplifiers of any size. Most 50 kW AM
broadcast transmitters had two triodes in their modulators giving 30 kW
audio power in Class B.

AM transmitters are a bit orthogonal to the topic at hand. :-)

Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else
you would have had nothing but Morse code.

And since when was AM 'hi-fi' ?


That would be before VHF FM became dominant. On days with little
electrical storm activity in the hemisphere and in the right locations
very fine broadcast fidelity was possible. Even today, at a place I
visited in north central Missouri I heard KXTR from Kansas City through
a passive Millen tuner (essentially a crystal radio) in astonishing
fidelity at an elderly hi-fi buff's house. Shame everything they play
is by the appalling Sir Neville Marriner at the Academy of
St-Martin-in-the-Fields. Vintage Toscanini and other classic
conductors' recordings would be so much better, but instead they play
that LOAD continually.

They say LF transmissions in England and Germany were even more
impressive.


The problem with AM AUIU was always one of bandwidth for one part and of course
that any interference was directly demodulated.

Those old valve sets did sound rather good though ( I had one myself - an EKCO !
) but that for the most part was mainly due to the excellent design of the RF
circuitry.

Graham


Most AM tube radios were built down to a price rather than up to a quality.

Most are just examples of poor performing junk.

Worse are 95% of SS radios.

But AM could have been wonderful but having many stations spaced at
9kHz apart thus limiting the AF bw due to side band interference was more
important than ****ing fidelity.

One would require 40kHz of RF bw for 20kHz of AF bw, so there would be much fewer
AM stations on the band if this had been used for the standard.

With FM, the problems were reduced, but even then they settled for second rate specs
of only 15kHz of bw for audio, pilot at 19kHz and a subcarrier F for stereo at 38kHz
when it should
have been at 100kHz, thus allowing the pilot tone to be at say 25kHz.

Now we are supposed to be getting better when digital broadcasting gets started
but I never see exactly what the specs are for that...

Patrick Turner.



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Chris Hornbeck wrote:

On Tue, 26 Sep 2006 05:07:55 +0100, Eeyore
wrote:

1. Unweighted THD is useless as an indicator of quality.


So why do you think I regularly mention the order of the distortion ?


Wanna *not* be a major disappointment? Post something
positive and educational on the topic.

Right here; right now.

Lord knows you're capable, and all the latterday endless cheap
shots are beneath you. Step up to the plate and take a swing!

This *could* be a very interesting newsgroup again someday.
Gonna take everybody; no slackers.


It's a subject that truly intruiges me.

Where I suspect I'd differ with you is that I'd expect a DSP simulation to
sound just the same as the beloved triode.

It is something that I'm looking into btw.

As for the effect of the order of the distortion, does anyone recall who
wrote that thesis about it and the weighting thereof ?

Graham



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Phil wrote:

As frustrated as I sometimes get with this guy's arguments, this is why
I love the guy ...


Patrick's post are regularly most interesting indeed.

Graham

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As frustrated as I sometimes get with this guy's arguments, this is why
I love the guy ...

Admiring Phil

Patrick Turner wrote:


Eeyore wrote:


Bret Ludwig wrote:


Stuart Krivis wrote:

On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig"
wrote:

Triodes are cheaper to build than beam power tubes of a given size,
simpler, and can be used for amplifiers of any size. Most 50 kW AM
broadcast transmitters had two triodes in their modulators giving 30 kW
audio power in Class B.

AM transmitters are a bit orthogonal to the topic at hand. :-)

Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else
you would have had nothing but Morse code.


And since when was AM 'hi-fi' ?

Graham



The best transmissions here have 9kHz of audio modulation.

In 1999 I built a tubed AM radio with a flat AF bw of 10Hz to 10kHz, which meant
the
IFT had to be carefully contructed for a wide pass band of about 17kHz,
and some treble boosting compensates for the sideband cutting.

So although 10khz is missing from the 20kHz of AF bw needed for true hi-fi, my
AM
radio is unsurpassable compared to all other AM radios I have ever worked on.
All brand name AM tuners and radios have less AF bw than my set because they
were
designed to give about 7kHz max of IF bw so AF is restricted to 3.5kHz if one is
very lucky
and with many SS AM sets the AF is about 2kHz, and the distortion is much
higher.

The audio amp in the radio is an EL34 in triode with 12AX7 driver and with 12 dB
of NFB.
There is a full range two way speaker in a floor standing reflex box under the
radio set.
The radio provides truly wonderful, musical, undistorted and non tiring
listening.

Patrick Turner.





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Andre Jute wrote:

I've read your arguments, Phil. Their subtext is methods to make NFB
more usable, less damaging to reproduced sound. That is a legitimate
outlook for Otala, who has to fit into an existing industrial
environment where NFB is an ineradicable part of that dominant
electronics cost-accounting system in which the explicit purpose of NFB
is to make cheap parts tolerable.

But that has buggerall to do with me as a DIYer. I can afford to take
the far simpler, more fundamental course of making my amps so superior
in design and components right from the start -- that I can do without
NFB and without the damage that NFB does. So I design amps without NFB,
period. I shortcut the problem of NFB and eliminate it before it
arises. My amps are ultra-silent without NFB; they do not need NFB for
any purpose whatsoever. Since one of my ZNFB amps is capable of 80W
when in its PSE mode, more than enough to drive electrostatic panels to
power-rivetter volume, I take the view that any designer who requires
NFB to make his hi-fi amps work has either permitted cost-accountants
to bully him, is an impressionable fashion victim, or is too thick to
put his mind in gear, tick one or more boxes.

The rest is interesting speculation but not of such consuming interest
to me that I will spend a morning setting up bench experiments to prove
the details of something I already know: that NFB smears the sound. A
complete summary of my view on NFB can be found here
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm
and here
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm

I haven't changed my mind one jot or tittle over the recent discussion.
I have heard absolutely nothing that proves a contrary case. That is
not to say you may not be right, that the psycho-acoustic effect which
gives Class A1 ZNFB (or very low NFB) amps their distinct superiority
is a subliminal reaction to the HF phase- smearing in NFB amps that you
say Otala posits. I just haven't seen any proof yet, and know that,
when I do see such proof, I will consider it of intellectual interest
-- and continue to build the sort of ZNFB amps I have always built, in
which NFB is excluded for its amplitude smearing at frequencies
starting below 100c/s, so that HF phase smearing, if it exists in NFB
tube amps, is no danger to my sound.


Be fair now, you didn't ask, "Why should I build high feedback pentode
amps," you asked, "Why do do [no feedback] triode amps sound better?" I
merely attempted to give you an answer. You believe that triodes have an
internal feedback mechanism, and you wondered why they (still) sound
better. The basic core of my response/answer is that (1) negative
feedback transforms relatively benign amplitude distortion into much
less musical phase distortion, and (2) either triodes do *not* have this
distortion mechanism, or it occurs at such staggeringly high frequencies
that triodes can "get away with it," since the amount of phase
distortion produced decreases as the high frequency limit increases.

And I proposed a test, which may not work anyway, and which apparently
only I have any interest in performing! However, I believe you when you
say you already know that feedback smears the sound somehow, and don't
need a test to "justify" your decisions, which is a stand I do respect.
For a while there, all of us had to face serious criticisms for saying
that in our own experience, cables do sound different, and it really is
a mark of character to stand up and say something that is true, but
"officially" stupid. If only the "official" beliefs didn't so often turn
out to be the ones that are actually stupid, we could all be mindless
sheep, and be better off for it! ;-)

However, there are sometimes good reasons for more fully understanding
something. If we assume for a moment that my analysis -- which is
basically my attempt to guess at the rest of what Otala was saying,
since I have yet to see the full text -- is correct, then several
interesting things follow. First, since a threshold below which we
cannot hear phase distortion realistically *must* exist -- and again,
for Patrick's benefit, this is phase-smearing, and *not* the simple
phase shifting which feedback does correct -- we should be able to add
some feedback and get "all gain, no pain." Patrick said that he added 6
dB to lower output Z, and it sounded fantastic, as opposed to a 20 dB
version of the same amp. Well, maybe this is completely true, but if we
*know* that it is true, then, for example, amps that use high-mu
transmitter tubes with positive grid drive and a bit of feedback to get
the Zout down begin to make sense, especially when the feedback is used
in a two-stage configuration that does not include the output
transformer, meaning that it can have a *very* high upper frequency
limit (you don't need to "dumb down" a stage like you often need to do
with a three-stage to prevent oscillation), which limits the damage
feedback can do to sub-threshold levels. Many people report that they
LOVE the sound of these things, but an unjustified, in this case, bias
against *any* use of feedback could prevent us from even trying one.

Or, let's look at the home builder who wants to make a solid state amp
-- what the hell -- or at least one with a SS output stage. There are
basically two forms of feedback, the normal one, and the "active-error"
version described by J. R. MacDonald and others. The active-error
version only "corrects" the output when an actual error exists, whereas
the standard version has to correct the open-loop gain even when the
load is a steady resistance and the devices are behaving with perfect
linearity. If tests show more phase-smearing with the standard version
than with the active-error version, well, I know which version I would
want to use, or have in a new television. As a bit of a side note, with
better sounding SS output stages, maybe we can more easily hear the
advantage, assuming one exists, of using a tube to produce the error
signal (a tube doesn't have poor quality parasitic capacitances to
potentially mess up the low level information).

All of this may sound like something only of interest to home builders,
but at least some manufacturers actually would be happy to produce
noticeably better sounding products, if they could do so for about the
same money! If EE's in general become aware of the full characteristics
of feedback -- and if home builders start to do this, many EE's and high
end manufacturers will indeed follow, eventually -- then we might
actually see better products in cars and TV's. No, I'm not saying do
this so that we will get better products, but a good understanding of
what is needed to make better audio products does tend to help everyone,
sooner or later. Low output Z triodes are in fact the theoretically best
audio devices at this time, sound-wise, but they require an expensive,
heavy, big, high quality output transformer, and that will always limit
their use.

Or, maybe someone just wants to write an article for AudioXpress about
the true nature of feedback, and how to best use it, if its use cannot
be avoided!

Phil


Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
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containing vital gems of wisdom"
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Phil wrote:

Andre Jute wrote:


In an effort to be agreeable, I tried hard to give you negative
feedback inside the tube as an explanation of the overwhelming
superiority of triodes (or trioded pentodes) for audio reproduction,
among other reasons because NFB is accessible to many who belong on RAT
and is a genetic deformity of the silicon scum whose only purpose on
RAT is dissension. NFB is what the silicon slime abuse to make their
inadequate components sound passable, and what even tubies inspired by
the age of sophisters and cost-accountants use to linearize pentodes.
NFB thus has a base level of familiarity which gives it a head start in
any black box model intended to explain something to diplomaed
quarterwits among the silicon slime as well as the better-educated
kibbitzers in my own camp.

But fine, you want to reject my explanation, then you must offer a
better reason to explain why triodes are such superior amplification
devices to anything else, so much more pleasing to the ear, so much
more accurate to the cultivated taste.

Despite my cracks about the metaphysics of tubes, there *has* to be an
electrical reason for the superiority of triodes. But sure, all kinds
of input is welcome.

Andre Jute


Andre, I think you are too quick to dismiss the idea that feedback
transforms amplitude distortions into phase-smearing, like Otala claimed
in his talk/paper (assuming a paper ever followed the talk!). When
Patrick was defending feedback, he mentioned that poorly designed amps
sound like crap when they have lots of feedback, but that if you fix
them up a bit, meaning get rid of much of their excessive nonlinearities
-- read, *amplitude* nonlinearities -- then adding feedback sounds okay.
Now, if we eliminate the idea that feedback produces random noise -- and
we *know* that it reduces amplitude non-linearities -- then the only
distortion mechanism left, I believe, is phase-shifting. However, I want
to describe the usual "constant 20 degrees phase lag at 40 KHz" as
"phase-shifting," and a dynamic, microsecond to microsecond shifting
back and forth of one frequency relative to another as "phase-smearing,"
or "time-smearing."

What Otala was saying is that applying feedback to circuits with lots of
open-loop distortions, which are (I believe) almost always amplitude
distortions, converts these distortions into a back and forth smearing
of the high frequencies relative to the low frequencies (and it may
smear both in terms of the delay through the amp). Nor can we assume
that this time-smearing is a simple function of the low frequency
amplitude, because it is probably proportional to the magnitude of the
distortions, as well as the LF amplitude: VERY non-musical. When enough
feedback is applied to badly designed amps, the amplitude distortions
become quite small, so why did Patrick find that they sounded much worse
than the same amp sounds when touched up enough to reduce the larger
open-loop amplitude distortions? As you say, *something* is wrong, and
if it isn't high amplitude distortions (it can't be), and if feedback
doesn't produce spurious noises, then the only thing left is exactly
what Otala said, time-smearing.

In essence, feedback *connects* two things that are normally separate in
an amp, namely amplitude distortions, and phase-smearing. It achieves a
balance between these two, a balance which is determined by the speed of
the amp, the amount of feedback, and the amount of amplitude distortion.
Contrary to what you say, Otala was *not* referring to TIM, and
transistors did not become so much faster after 1980 than the ones used
in his '73 article to make the problem he described go away. Yes, the
amps had to be designed well enough to avoid TIM, but that was not a
real problem even in '73 *if* you knew what you were doing. The problem
he described in '80 was quite different, and even high MHz tubes are
subject to it.

The interesting things, assuming that feedback problems are indeed
time-smearing (regardless of whether this comes from the conversion of
amplitude distortions), are one, a single tone will reveal nothing of
this, giving very low THD numbers, and two, multiple tones should show
something, although looking at it in the amplitude realm will only show
higher than expected IMD. There should be a fairly easy way to test to
see if this really produces time-smearing. In general, we put a 4 volt
60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of
feedback, preferably using non-linear sections of the amplifying devices
(say, use two 12AX7 type triodes where the plate curves vary from widely
spaced to closely spaced, and use about 60 to 80 dB of feedback to get
the overall gain down to 1). Use a high pass filter to see only the 20
KHz signal, and use the 20 KHz signal from the generator to trigger the
'scope. If time-smearing exists, then the 20 KHz signal will appear
"fuzzy" on the scope, since it is being shifted back and forth. Repeat
without the 60 Hz signal to make sure the time-smearing isn't coming
from somewhere else, and then also divide the output from each tube down
so that you get the same amplitude output *without* using feedback, and
see if the time-smearing goes away. Finally, if possible test over a
region where the curves are fairly linear, to see if that also reduces
the time-smearing. If so, you have proof that feedback transformed the
amplitude distortion into time-smearing. I will try to do this, but I
have little time, less energy, and not the best test bench in the world,
so it may be a while! If you or someone else both can and wants to try
this, I suspect we will get an answer much faster than if I do it. Note
that we can use pentodes or transistors, too, but using solid state has
the disadvantage of possibly introducing other complications due to the
poor quality silicon parasitic capacitances. Also, I am suggesting the
use of very different magnitudes as well as frequencies for the two
signals, in case equal magnitudes somehow avoids this problem, or at
least masks it from this test. And again, contrary to what Patrick said,
the idea that *if* this were true, then by now someone would have
already tries it, and the results would have become widely know, is just
naive. The human race simply isn't that intelligent, at least not yet.

An interesting conclusion, assuming this feedback time-smear mechanism
exists, is that the output of a feedback amp does *not* match the input
when multiple signals exist! However, our normal tests cannot see this,
since they tend to focus on one frequency at a time. I believe that
Patrick, as well as Otala, said that using local feedback to achieve
good open loop linearity, combined with some global feedback, tends to
sound pretty good. This makes sense for two reasons, first because
although the local feedback will produce phase-smearing, it does so at
*very* high speed, which I believe directly reduces the amount of
smearing (common sense says that as the speed of devices approaches
infinity, feedback becomes "perfect"). Second, the result does contain
some mis-match between input and output, even given the high speed of
local feedback, but now the global feedback will not only reduce the
remaining "normal" amplitude distortions, it should also reduce the
time-smearing produced by the local feedback, since this time-smearing
will still produce an error signal for the global feedback. Of course,
this reduction in time-smearing will itself produce more time-smearing,
but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of
time-smearing is reduced by "dividing up" the total feedback into local
plus global.

Finally, you saw the review of Otala that Phil Allison gave, and I think
you were as impressed by it as I was (although it looked bad to PA).
When a man who was as talented, knowledgeable, and honest as Otala
produces a PROOF that negative feedback *always* transforms the
amplitude distortions of the open loop into phase smears of the closed
loop, we should not dismiss it as simply a problem of "old devices," a
problem that a slight increase in speed can make go away, especially
when the discussion that led to his analysis (the Audio Critic BS
session) included a lot of talk about vacuum tubes, and how their speed
advantage made it easier to use them with feedback. We really should do
at least one or two tests before dismissing his conclusions. Again, I
will try to do so, but if you want to know anytime soon, you should
probably rely on someone else.

Phil



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Stuart Krivis wrote:

On Tue, 26 Sep 2006 10:01:18 +0100, Eeyore wrote:
Chris Hornbeck wrote:
On Tue, 26 Sep 2006 05:07:55 +0100, Eeyore wrote:

1. Unweighted THD is useless as an indicator of quality.

So why do you think I regularly mention the order of the distortion ?

Wanna *not* be a major disappointment? Post something
positive and educational on the topic.

Right here; right now.

Lord knows you're capable, and all the latterday endless cheap
shots are beneath you. Step up to the plate and take a swing!

This *could* be a very interesting newsgroup again someday.
Gonna take everybody; no slackers.


It's a subject that truly intruiges me.

Where I suspect I'd differ with you is that I'd expect a DSP simulation to
sound just the same as the beloved triode.

It is something that I'm looking into btw.

As for the effect of the order of the distortion, does anyone recall who
wrote that thesis about it and the weighting thereof ?


Hamm?


He wrote that joke of a paper purporting to compare tubes and transistors.

It's something quite recent I have in mind.

Graham


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Eeyore said:


As for the effect of the order of the distortion, does anyone recall who
wrote that thesis about it and the weighting thereof ?


Hamm?


He wrote that joke of a paper purporting to compare tubes and transistors.


It's something quite recent I have in mind.



Daniel Cheever:
http://www.next-power.net/next-tube/...b_menu_item=99

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


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Chris Hornbeck wrote:
On 25 Sep 2006 03:09:39 -0700, "Andre Jute" wrote:

Bring on your topics, Chris. We could do with some fresh air in RAT.


[various snips]

if I may, a few
possibilities:

1. Unweighted THD is useless as an indicator of quality.

2. Unweighted IMD " " "


No argument about points 1 and 2; I just normally put it more
emotively.

3. We make totally unwarranted assumptions of monotonicity.
This is a fatal flaw in our thinking, and we all do it, all
the time.

4. We make often unwarranted assumptions about input signal
bandwidth.

5. We *always* *without exception* forget to properly weight
the importance of simply being upstream in the signal path.
Always.


When you find the time, please elaborate on points 3, 4 and 5.

6. Loud voices will say that everything (that doesn't include
the dreaded vacuum valve, scourge of nations) sounds the same.
This has recently been expanded to include transistor amplifiers
from the early 1970's, by certain especially vocal ideologes,
in another thread, this very week.

Against such a religious fervor, nothing can stand.


This relates back to points 1 and 2, where for judgement has been
substituted the belief that when the master tape is reproduced with
under-x per cent of THD, the engineer has faithfully performed his
service. In human terms, elevating a single measure of goodness so high
is inspired by fear, a desire to control events (can't let a bunch of
arty-farties substitute taste for what engineers "know"), which is also
a form of fear, and of course the largest fear-reflex of them all is
religion, the defense against fear of the unknown darkness.

Modeling and analysis are essential; but the map is not
the world.


Actually, the only °essential* is having some method of deciding where
you want to arrive. High fidelity went wrong long before Mr Leak's
inspired marketing terminology (Point One) became an engineering
article of faith, but that set the seal on the decline.

Which conclusion? That "triodes sound better" or that "there must be an
electrical explanation"?


Strong agreement with the former;


That's why we are here.

strong disagreement ('cause
that ain't science!) with the latter.


Eh? Surely a thermionic valve is nothing but a bunch of electrical
impulses created by vacuum, wire and electricity? Whatever happens in
there, regardless of whether we can see it or not, regardless of what
we call the result, *must* perforce have an *electrical* explanation.
°That* is science. Anything else would make me uncomfortable -- and me
a certified witchdoctor!

"Take the money and run" -- Len Deighton


And also... who? Bob Segar? Somebody like that, anyway.


Woody Allen. From of an early movie about a hapless bank robber. Len
Deighton, one of the best novelists ever to work in the thriller genre,
was referring to a novelist's relationships with "moom pitcher pipple".

Much thanks, as always,

Chris Hornbeck


Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
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containing vital gems of wisdom"
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Sander deWaal wrote:

Eeyore said:

As for the effect of the order of the distortion, does anyone recall who
wrote that thesis about it and the weighting thereof ?


Hamm?


He wrote that joke of a paper purporting to compare tubes and transistors.


It's something quite recent I have in mind.


Daniel Cheever:
http://www.next-power.net/next-tube/...b_menu_item=99


Thanks Sander. That's the one.

Graham

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Andre Jute wrote:

This relates back to points 1 and 2, where for judgement has been
substituted the belief that when the master tape is reproduced with
under-x per cent of THD, the engineer has faithfully performed his
service.


What master tape ? There's sod all tape used these days !

Graham

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Stuart Krivis wrote:

What's so sadly wrong with the story is that the US military
went through the whole exact same hand-wringing back 100+
years ago in the Phillippines, leading to the adoption
of, wait for it, the .45 caliber.


Theoretically, they can use hotter loads in the 9mm because all of the
pistols are newer. But I still prefer the 45 ACP. :-)


Me too : ) Why use two rounds when you only need one?
Bob H.

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On 26 Sep 2006 18:57:28 -0700, "Bob H." wrote:


Stuart Krivis wrote:

What's so sadly wrong with the story is that the US military
went through the whole exact same hand-wringing back 100+
years ago in the Phillippines, leading to the adoption
of, wait for it, the .45 caliber.


Theoretically, they can use hotter loads in the 9mm because all of the
pistols are newer. But I still prefer the 45 ACP. :-)


Me too : ) Why use two rounds when you only need one?


A major justification for the larger calibers in modern
personal confrontations is simply the size of the bore;
anybody who's ever looked at the receiving end of a
pistole seems to remember (and mentally inflate) the bore.

And, worst case, ya still gotta knock the ****er down
enough to allow ya to do some serious kicking. Real
people don't just lay down and play dead like in the
movies.

What a gruesome topic. Who started this?

Much thanks, (I think, Arf!)

Chris Hornbeck
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