[Andre Jute]

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

[Peter Wieck]

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

[Dominique Michel]

Le 25 Sep 2006 12:51:12 -0700,
"Bret Ludwig" a écrit :


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.

The common 811 available under $20, though not an ideal tube, can give
200 easy watts for a pair. As can 211s, 845s, etc. The GEC book shows
a 1 KW audio amp with a pair of largish glass triodes.

Difficult to use? Just give them a filament supply of several amps,
preferably from a filament transformer with shunts designed for that
tube, a few kV on the plate and enough drive and they work fine.


Audio is not only about power and characteristics on the paper, but about
sound. Most if not all high power tubes are designed for high frequency
transmitters, not for high-fidelity, and they will sound very poorly when used
for an audio amp.

You will get a much better sound when using 4, 6 or 8 EL34 or 300B as only 2
more powerful tubes.

Now, the controversy between pentode and triode is not new. If you look, most
of the so called pentodes used in high fidelity audio are in fact beam-tetrodes.
The main problem with the pentode is its high output impedance. The main
problem with the triode is its low sensibility. The beam tetrode try to get most
of the advantages of the triode as its relatively low output impedance and most
of the advantages of the pentode as its high sensibility. And the result is a
very good tube for power amplification.

But if you want to get a good result in audio with a beam tetrode, you must be
very careful with the design. A triode design is easier because you don't have
the g2. A good practice, if you are using a fixed g2 voltage, is to stabilize
it. Just be doing it, the amp will archive at least a 2 time better dynamic at
the output. But how many amps on the market are using a stabilized Vg2?

Almost no one because it cost more money to build.

Another issue, and not only with the beam tetrode, is the quality of the
tubes. Take the 6L6. It is hundred of different brands, but only a little part
of those brands have a really good quality of manufacturing. It is in theory
the same tube as a 807. Make an amp with 2 x 807, 600V DC on the middle of the
output transformer when the amp is at full output, 300 V DC on the g2, and
replace the 807 by 6L6 tubes. Most of them will just glow up at full output. And
already at low level, they will arc inside the tube because of a too high Va,
and this will sound like hell in the loudspeaker.

Take a preamp tube as the ECC83-12AX7. Buy a few tubes of different brands. You
will get as many sound at the output as brands. In fact even more, because with
the cheaper brands, different tubes will sound differently.

So, when you want to compare tubes, you must not only say the type of the
tubes, but the brand too. And when comparing tubes as different as a triode and
a pentode, you must talk about the topology of the circuits. A good quality
pentode will sound better as a poor quality triode. And a pentode used in a
deign that have a good topology will sound better as a triode of the same
quality but used in a circuit with a poor design.
--
Dominique Michel

[Andre Jute]

Hi, Dominique. Welcome to RAT. I'm Andre Jute. This is my thread.

You say:
The main problem with the triode is its low sensibility.

Actually, the great advantage of the triode (or trioded pentodes like
the EL34) is its *high* sensibility with the music, that is the
natural, unaffected way it reproduces it.

You probably mean "low power". That mainly bothers people who haven't
put their minds in gear. Once you have sensitive speakers, 300B are
overkill on Lowther horns already. Alternatively, when I wanted a
triode single-ended amp to drive Quad ESL63, I built it with
transmitting triodes to give 80W from a standard 2Vrms CD output
(417A::300B::PSE SV572-3 or -10 does the biz in only three ZNFB
stages). If you're willing to pay the price, everything is possible and
nothing is a barrier.

As examples of why the low power of the commoner triodes is not a
problem, here are some bicor horns I built for Lowther drivers:
http://members.lycos.co.uk/fiultra/K...20T91HWAF3.jpg
to use with either of these 300B
http://members.lycos.co.uk/fiultra/T...trafi-crct.jpg
http://members.lycos.co.uk/fiultra/T44bis-'Populaire'-crct.jpg
but here is 0.3W quality amp that drives the Lowthers very pleasingly
indeed:
http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg
http://members.lycos.co.uk/fiultra/t...17acircuit.jpg
http://members.lycos.co.uk/fiultra/t68bismzlayout.jpg
or if you want good quality and more power for less money, here is a 2W
trioded EL34 amp I designed for students:
http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg
to use with this inexpensive but very sensitive (and sensible!)
speaker:
http://members.lycos.co.uk/fiultra/K...Impresario.jpg

All becomes clear when you give up being a fashion-victim of people who
think more power is better power because they are too lazy or stupid to
design within the parameters of the best-sounding components; some are
too thick even to work out that it is the sound that matters, not the
engineering, and of those we have a surplus already on RAT. You might
enjoy "The myth of the Watt:", or then again, not, as the case might
be:
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm

More on my main site, URL under my sig.

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


Dominique Michel wrote:
Le 25 Sep 2006 12:51:12 -0700,
"Bret Ludwig" a écrit :


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.

The common 811 available under $20, though not an ideal tube, can give
200 easy watts for a pair. As can 211s, 845s, etc. The GEC book shows
a 1 KW audio amp with a pair of largish glass triodes.

Difficult to use? Just give them a filament supply of several amps,
preferably from a filament transformer with shunts designed for that
tube, a few kV on the plate and enough drive and they work fine.


Audio is not only about power and characteristics on the paper, but about
sound. Most if not all high power tubes are designed for high frequency
transmitters, not for high-fidelity, and they will sound very poorly when used
for an audio amp.

You will get a much better sound when using 4, 6 or 8 EL34 or 300B as only 2
more powerful tubes.

Now, the controversy between pentode and triode is not new. If you look, most
of the so called pentodes used in high fidelity audio are in fact beam-tetrodes.
The main problem with the pentode is its high output impedance. The main
problem with the triode is its low sensibility. The beam tetrode try to get most
of the advantages of the triode as its relatively low output impedance and most
of the advantages of the pentode as its high sensibility. And the result is a
very good tube for power amplification.

But if you want to get a good result in audio with a beam tetrode, you must be
very careful with the design. A triode design is easier because you don't have
the g2. A good practice, if you are using a fixed g2 voltage, is to stabilize
it. Just be doing it, the amp will archive at least a 2 time better dynamic at
the output. But how many amps on the market are using a stabilized Vg2?

Almost no one because it cost more money to build.

Another issue, and not only with the beam tetrode, is the quality of the
tubes. Take the 6L6. It is hundred of different brands, but only a little part
of those brands have a really good quality of manufacturing. It is in theory
the same tube as a 807. Make an amp with 2 x 807, 600V DC on the middle of the
output transformer when the amp is at full output, 300 V DC on the g2, and
replace the 807 by 6L6 tubes. Most of them will just glow up at full output. And
already at low level, they will arc inside the tube because of a too high Va,
and this will sound like hell in the loudspeaker.

Take a preamp tube as the ECC83-12AX7. Buy a few tubes of different brands. You
will get as many sound at the output as brands. In fact even more, because with
the cheaper brands, different tubes will sound differently.

So, when you want to compare tubes, you must not only say the type of the
tubes, but the brand too. And when comparing tubes as different as a triode and
a pentode, you must talk about the topology of the circuits. A good quality
pentode will sound better as a poor quality triode. And a pentode used in a
deign that have a good topology will sound better as a triode of the same
quality but used in a circuit with a poor design.
--
Dominique Michel

[Patrick Turner]

Dominique Michel wrote:

Le 25 Sep 2006 12:51:12 -0700,
"Bret Ludwig" a écrit :


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.

The common 811 available under $20, though not an ideal tube, can give
200 easy watts for a pair. As can 211s, 845s, etc. The GEC book shows
a 1 KW audio amp with a pair of largish glass triodes.

Difficult to use? Just give them a filament supply of several amps,
preferably from a filament transformer with shunts designed for that
tube, a few kV on the plate and enough drive and they work fine.


Audio is not only about power and characteristics on the paper, but about
sound. Most if not all high power tubes are designed for high frequency
transmitters, not for high-fidelity, and they will sound very poorly when used
for an audio amp.

I doubt this is correct. There are many examples where a tube can be used
equally appropriately for RF or AF.
The 211 makes a nice transmit tube and can be superlative as an audio tubes.
813 is another.....



You will get a much better sound when using 4, 6 or 8 EL34 or 300B as only 2
more powerful tubes.

Ain't necessarily so...



Now, the controversy between pentode and triode is not new. If you look, most
of the so called pentodes used in high fidelity audio are in fact beam-tetrodes.
The main problem with the pentode is its high output impedance. The main
problem with the triode is its low sensibility.

Perhaps you mean sensitivity, or voltage gain. Its a very sensible choice for an
output device....

The beam tetrode try to get most
of the advantages of the triode as its relatively low output impedance and most
of the advantages of the pentode as its high sensibility. And the result is a
very good tube for power amplification.

???



But if you want to get a good result in audio with a beam tetrode, you must be
very careful with the design. A triode design is easier because you don't have
the g2. A good practice, if you are using a fixed g2 voltage, is to stabilize
it. Just be doing it, the amp will archive at least a 2 time better dynamic at
the output. But how many amps on the market are using a stabilized Vg2?

The use of a slow time constant with RC filter used for g2 supply is all that is
required for
AB audio amps with multi grids because in fact the Eg2 variation at average power =
1/10
of clipping power is very small.



Almost no one because it cost more money to build.

I shunt regulate my screen supplies. A few 75V x 5 watt zener diodes and a power
resistor of 10W is usually
all that is needed.



Another issue, and not only with the beam tetrode, is the quality of the
tubes. Take the 6L6. It is hundred of different brands, but only a little part
of those brands have a really good quality of manufacturing. It is in theory
the same tube as a 807. Make an amp with 2 x 807, 600V DC on the middle of the
output transformer when the amp is at full output, 300 V DC on the g2, and
replace the 807 by 6L6 tubes. Most of them will just glow up at full output. And
already at low level, they will arc inside the tube because of a too high Va,
and this will sound like hell in the loudspeaker.

Maybe depends which type of 6L6 one uses....



Take a preamp tube as the ECC83-12AX7. Buy a few tubes of different brands. You
will get as many sound at the output as brands. In fact even more, because with
the cheaper brands, different tubes will sound differently.

So, when you want to compare tubes, you must not only say the type of the
tubes, but the brand too. And when comparing tubes as different as a triode and
a pentode, you must talk about the topology of the circuits. A good quality
pentode will sound better as a poor quality triode. And a pentode used in a
deign that have a good topology will sound better as a triode of the same
quality but used in a circuit with a poor design.
--
Dominique Michel

Tubes brands do make different sound amoung the same type number
and using pentodes in lieu of triodes ditto.

Tubecraft involves many variables around simple ideas.

Its all so much easier than class D DIY PWM amps....

Patrick Turner.

[[email protected]]

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.

[Chris Hornbeck]

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

[Andre Jute]

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

[Andre Jute]

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

[Eeyore]

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

[Patrick Turner]

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.

[Chris Hornbeck]

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

[Eeyore]

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

[Chris Hornbeck]

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

[Andre Jute]

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
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

[Eeyore]

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

[Chris Hornbeck]

On 26 Sep 2006 15:30:25 -0700, "Andre Jute" wrote:

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.

elaborate on points 3, 4 and 5.

We're always fighting the last war. In my on-war-footing and yet
war-unravaged country, this seems particularly unwise, but
still unavoidable.

Progress in any sufficiently mature technology is less a matter
of perfecting the existing technology than in identifying the
flaws in the model by which the technology was created.

Any second rate modern military power could have ruled the world
of even only a hundred years ago. And, conversely, the Number One
Military Might Big Kahuna in the contemporary world can't defeat
a determined insurgency in a militarily defeated and occupied
country. (Or two).

Defining the problem is everything. Defining the problem in the
context of the last war is foolish, but seemingly unavoidable.
Failure to recognize this trap is potentially fatal militarily,
and a blind alley technically.


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

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!

Gotta be more careful with my phraseology. It really depends on
what "be" be. Arf!

Have I heard a technically compelling explanation for ..some.. of
the things that I nonetheless believe to be both true and ultimately
explainable to me in terms that I can accept as real? No.

Do I believe that explanations acceptable to me exist and are
awaiting discovery? Yes.

Science is the quest(ion) itself, so we really aren't in disagreement.
And, I'll try to work up some more keystrokes about my favorite
bete noirs, monotonicity and operating level later, 'gator.

Much thanks, as always,

Chris Hornbeck

[Patrick Turner]

Somebody said, and Andre replied.....



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.


So what happened before Leak that was the beginning of the fidelity decline?
Invention of pentodes and bean tetrodes? Beginning of FB use?
Indirect heating of cathodes?


Patrick Turner.

[robert casey]

"Impedance is futile, you will be simulated into the triode of the
Borg"... :-)

[Phil]

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

[Andre Jute]

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

[Phil]

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/
"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

[Andre Jute]

Phil wrote:
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,"

But I do build pentode amps, if without the "high feedback". The best
amp I ever designed, my Type 114 "Triple Threat" is a PP EL34 with a
pentode/ultralinear/triode switch and NFB tunable from zero to about
6dB in the latest iteration but up to 20dB in some early versions. Of
course, it is my "best" amp only when operated in the trioded ZNFB
mode, but the choice is in the hands of the builder.

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.

My point is a little more subtle. I see an effect which looks like NFB
happening between the terminals of a triode; I'm happy to call it
internal or natural NFB until someone else offers an explanation that
justifies giving it another name; no one offers such an explanation,
merely negative objections to naming it NFB; until they pull their
finger from their arse and say something positive (and more cogent)
than Patrick, who *does* have a case, I shall not change my mind just
because they're "agin". You should also understand that some of these
clowns are agin not for any good reason but only because it is *me*
saying so; Pasternack, for instance, and the usual sockpuppets of the
Magnequest Scum, whose disruptive presence on RAT I dispensed with
wholesale a few years ago ("Jute is wrong even if he is right, isn't
he?" one of them, Ron Bales, complained pitifully!). Pasternack, for
instance, has been repeatedly caught out lying on professional matters
"in my zeal to flame Andre" -- which is his own sickening excuse in his
own words.

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.

I don't need to go that sophisticated. By far the most popular of my
loudspeaker designs (of the published ones; an expensive licensed speak
sells amazingly well in the Far East considering the wretchedly high
price dictated by the cost of the drivers) is an economy fullranger
using a guitar driver, in most installations that I know of with the
tweeter disconnected or, on my advice, never fitted.
http://members.lycos.co.uk/fiultra/K...Impresario.jpg
It has been years since I have been impressed with bandwidth as measure
of audio goodness, and I don't just mean excessive bandwidth, I mean
the upper end of what is commonly called the "audio spectrum". Most
people can't hear it even when they're young. Most people into hi-fi
are over middle age; they're lucky if they can hear past 12kHz. In any
event, Top C on a piano is a frequency of 4186c/s; over 70% of the
energy of that note (over half the decibel value referred to the
fundamental's energy) will be in the 2nd and 3rd harmonics, which takes
you just past 12kHz. (Try an experiment: filter out everything below
the 3rd harmonic of top C, 12558c/s, and listen to what remains. It is
horrid, just white noise.) By the way, the same argument of harmonic
weight in the production of sound applies to the bass end and well into
the midbass: an open G string on a violin played with medium intensity
has only 0.1 per cent of its energy in the fundamental -- which is
196c/s; this is the basis for my thesis that the human ear
reconstitutes the fundamental from the dominant harmonics, where the
energy is. The upshot is that the lower extension of the so-called
"audio range" is another engineering chimera that has nothing
whatsoever to do with music and everything to do with a bunch of
arrogant engineers sitting in a room feeding of each other's
testosterone while setting standards that should instead have been set
by psychologists or musicologists or, in fact, anyone but engineers. In
practice, it means that you can roll speakers off quite high, where the
bass will "measure" modestly but sound very, very clean, and they will
sound better over the long term than those one-note boof-boff big-bass
abominations so beloved of "audiophiles" and "engineers" alike. Peter
Walker didn't build his ESL63 any bigger than 45c/s bass (the last pair
I measured was 8dB down at 32c/s) because to the ear even a 16c/s organ
note, if on the recording at all, will sound startlingly precise
because all the energy are in the first two harmonics above the
fundamental.

More, drivers with a natural high frequency mechanism, like the classic
Lowther driver, can sound screechy in the treble precisely because it
is not a fundamentally natural noise
http://members.lycos.co.uk/fiultra/K...20T91HWAF3.jpg
Lowthers with the whizzer tweaked by the insertion of cotton wool
behind it or by stiffening with C37, always sound more "natural" even
as the measurements start looking less impressive. (I prefer the
waterfall anyway, but only after I have run it through a smoothing
program because the small glitches are a distraction to the eye but not
the ear.)

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.

Hang on a minute. I have demonstrated smearing in the frequency band
I'm interested in. I've done it again and again and again,
theoretically by mathematics, by measurement with instruments,
graphically, and by placebo listening tests (what the pretentious call
ABX).
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm
I have no problem standing by my taste when taste is the question (for
about ten years I was the most widely read music critic in the world
with a column syndicated to 9.2m readers every week) but when science
has an answer I am as keen as the next man (and clearly keener than the
diplomaed quarterwits on RAT) to find the correct answer by the proper
scientific method.

For a while there, all of us had to face serious criticisms for saying
that in our own experience, cables do sound different,

Sure, I believe you can hear cables, under two very specific
conditions. Again, my conclusion is based on a scientific test. I flew
to a different country and in a warehouse spliced huge reels of cable
until I had the several of different construction of a length that an
engineer (a proper one, not one of the local clowns) calculated for me
should be audible by the laws of physics. They were, barely. The other
condition under which cables are audible also answers to the laws of
physics: when components in the audio chain are mismatched, the
resistance and capacitance on a particular cable can make the
combination sound better or worse, hence "cable is audible". I
personally use Cardas golden section multi-diameter cable because the
concept appeals to me: my Impresario speak is designed on Phi, the
formulaic base of the golden section.
http://members.lycos.co.uk/fiultra/K...Impresario.jpg

and it really is
a mark of character to stand up and say something that is true, but
"officially" stupid.

Man, you got enough problems already. You really don't want my
character as well: I was sent into exile from my motherland for saying
the statistical basis of apartheid was flawed (everyone could see it
only twenty years after I said it), and later twice hunted by assassins
sent by the apartheid government for a couple of my books.
http://members.lycos.co.uk/fiultra/THE%20WRITER'S%20HOUSE.html
As an economist I was academically haunted by being the only monetarist
in keynesian countries in a keynesian age, as a psychologist in a
Freudian age thought very odd, most unreliable, a loose cannon on deck
for saying that Freud was a literary giant but didn't know **** about
human character. Today, of course, everyone knows I am right and was
right then. That was nothing to the filth heaped on me for saying the
Common Agricultural Policy of the European Community was a wasteful
abomination, or pointing out that the case against DDT was and is
unproven, or that "global warming" is an official lie (I've been saying
it since the 1960s when I had a running joke in a satarical newspaper
column about the missing hole in the ozone layer).

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! ;-)

Nah, I like being "the most dangerous class", as Lenin called
reformers. Sure, the price has been high, but the alternative would
have been dull.

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

There is no *must* about any threshhold. We're discussing the known
preference for Class A1 triode sound by an important niche of
knowledgeable audiophiles -- despite the known fact that it measures
worse than the alternatives on quite a few parameters. Even if those
parameters are at present driven to ludicrous lengths by the engineers,
it is clear that the highest level of triodes -- DHT, ZNFB, SE or Class
A1 trioded ZNFB PP pentodes -- will never come within a magnitude of
current technology, at least not on the meter. The preference must be
explained by some subliminal effect. The problem with subliminal
effects is that they recede with experience, that is, that they're
educable; for instance, the limit at which distortion now becomes
audible is lower than it was when Olsen first studied the subject 70
years ago.

-- 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."

You're still on someone else's agenda, trying to make NFB usable. My
amps started sounding brilliant the day I rejected NFB on principle.

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.

Hang on a minute. Patrick said that he found that 6dB of NFB didn't
degrade the sound audibly -- a matter of taste for him and his client
which we must permit them to enjoy in peace; I shall just say I tend to
believe that 6dB is very likely a common audibility limit. Patrick also
made the point that the NFB lowers the output impedance, on which he
puts a high priority *because he builds amps for sale, often to be used
with unknown speakers". Anyone who can design his speakers first can
also design them so that output impedance and the consequent need for
NFB is less; amps can be designed to be speaker-friendly without NFB as
long as you know from the beginning that NFB will be excluded.

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,

Been there, done that. You're still on someone else's agenda, this time
"mo' powa' is betta powa'". It's bullcrap. Even at the lower end of the
same argument, a 211 doesn't sound nearly as good as an 845 when both
are built to give the same power, simply because the 211 must be driven
across the 0V bias line into A2 while the 845 stays strictly in A1.
It's another example of a subliminal effect on the ear when very little
difference shows on the measuring instrument.

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.

No. This isn't a bias against NFB. This is a preference for staying in
Class A1.

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.

Sander swears by his hybrid amps. I play SS amps often; the one I like
best is the Quad 405 Mk II, because it is so livable. You might check
Google for the threads when Stewart Pinkerton, a Poopie Stevenson type
clown but with a smidgin more class, challenged me to a design contest.
In theory he was supposed to design a silicon amp to beat my 300B SE
amp, or at least produce something that sounded close to it.
http://members.lycos.co.uk/fiultra/T...trafi-crct.jpg
http://members.lycos.co.uk/fiultra/T44bis-'Populaire'-crct.jpg
Even with months of help and coaching from John Byrns and Patrick
Turner, what Pinko produced was such a botch that not even he wanted to
build it. Bored with waiting for the interminable process to run its
fractious course, I designed my own simple SS amp and showed how it
could be developed to sound something like a good tube amp by driving
it into class A. I'm playing it right now. Thanks for reminding me to
plug it in and try it again; for the cost it can't be beat!
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm
http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm
http://members.lycos.co.uk/fiultra/K...20mGBschem.jpg
http://members.lycos.co.uk/fiultra/K...%20mGBmatr.jpg
http://members.lycos.co.uk/fiultra/K...%20NoBleed.jpg

Basically, I'm saying that, if there is phase-smearing as you claim, I
also think you're right, that it will be inaudible. I am more
interested in what is audible, even if only subliminally. The rest is
of theoretical interest and my time is limited. Thanks for the
entertainment.

Andre Jute
More at http://members.lycos.co.uk/fiultra/JUTE%20ON%20AMPS.htm
and http://members.lycos.co.uk/fiultra/T...mp%20INDEX.htm

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/
"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

[HP]

"Andre Jute" wrote in message ups.com...
My point is a little more subtle. I see an effect which looks like NFB
happening between the terminals of a triode; I'm happy to call it
internal or natural NFB until someone else offers an explanation that
justifies giving it another name; no one offers such an explanation,
merely negative objections to naming it NFB; until they pull their
finger from their arse and say something positive (and more cogent)
than Patrick, who *does* have a case, I shall not change my mind just
because they're "agin".

The effect you see is the change in plate current with plate voltage. This
is exactly the definition of plate resistance, which is both the name and
the explanation that have been in standard use for the past seven decades
or so.

In actual fact there is no external observation you can make of the triode
that proves, or even suggests, there is internal negative feedback at work
inside the tube. Everything you see can be more simply and economically
explained by the Thevenin or Norton models.

Thevenin, Norton, and the NFB conjecture are all just fictional models
that help to describe or predict the tube's external behavior. None of
them represents the actual physical processes at work inside the tube,
and it is a mistake to claim otherwise. The Child-Langmuir equation,
which is based on the distribution of electric fields and charge density
inside the tube is another model, and arguably as good an explanation
of tube behavior as we need. There's nothing in it that depends on
negative feedback, either.

This is fundamentally an engineering debate and the arguments are
necessarily framed in engineering terms. The fact that technical language
is used to express a point doesn't make the point true by default. The
assumptions and inferences have to be grounded in fact and logic to be
valid. The challenge is to define who's qualified to decide what is factual
and logical in an engineering argument. An engineer perhaps?

I would be delighted to debate this subject, point by point, in front of
a qualified and neutral judge (or panel of judges) from the tube audio
engineering community. How about Steve Bench, John Atwood, Lynn
Olson, or Morgan Jones?

-Henry

[Patrick Turner]

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.

[Arny Krueger]

"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?

[Eeyore]

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

[Andre Jute]

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

There are now 136 messages in the thread I started with the post above.

In all that bandwidth, all that shouting, all that bad temper, no one
has taken up the challenge to
offer a better reason [than internal negative feedback]
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

All that we have seen is that Patrick Turner and I have solidified our
faith in our transconductance model substantially and that John Byrns,
arriving late to the thread (a wise man to absent himself from this
boring round about the mulberry bush), has further emphasized the
native appeal of the transconductance model graphically.

None of us deny there may be another explanation. We just say that NFB
inside the triode seems a logical explanation, and the easiest to
assume since we are already familiar with the mechanism and math, and
because it so readily relates the triode to the less attractive
pentode. That's a whole bunch of persuasive practical reasons already.
We don't need faith for our explanation, just the knowledge that it
works for us.

Against that, you mantra-chanting gaggle of naysayers offer us what
precisely? Some basic principles that Plodnick, having regaled us with
unlikely tales of being Terman's annointed successor, can't even copy
out right and refuses to transform into any useful form, probably
because he doesn't know how.

That's hardly a productive use of so much bandwidth and time.

The depth of the supporting arguments for our position, and the
experience backing it, is also very striking when compared to the thin,
unnourishing broth of half-digested and, in some cases halfbaked or
even plain perverse, theories you're throwing against our solid
bulwark.

Andre Jute
Habit is the nursery of errors. -- Victor Hugo