The Catch-22 of Negative Feedback aka NFB
 

"Bret Ludwig" wrote in message
oups.com...

Stewart Pinkerton wrote:.
snip

Your problem is that you know I'm right but that you have thirty years
invested in commercially telling people tubes are obsolete.

Jute, you know very little about amplifiers, and you are certainly not
right about this. Tubes have been obsolete for the best part of fifty
years, except for fashion victims who like big shiny toys that glow in
the dark.

Andre Jute



Jute's a ****penis, but the fact is people buy audio equipment like
women buy designer dresses and that isn't going to change. If you want
some booty you let her spend her money the way she wants and don't
balk.

**Irrelevant. Jute lies to get his point accross. If he told the truth, no
one would care either way. When confronted by his obvious lies, he tells
more lies to disguise the fact.


Tubes were the most reliable and best sounding way to build an audio
amplifier up until relatively recent times

**Up 'till around 1968, that is quite true. It's now almost FOUR DECADES on.
Jute is STILL telling people about transistor amps which have not existed
for several decades.

and they still work very
well when correctly designed. Solid state amplifiers that are truly
well built are not much cheaper than tube ones, and if they made more
tube ones the price would come down and quality go up.

**Utter and complete ********. Due to the presence of the (expensive) output
transformers, alone, tube amps are priced well above an approximately
equivalent SS one.


--
Trevor Wilson
www.rageaudio.com.au

The Catch-22 of Negative Feedback aka NFB
 

"Andre Jute" wrote in message
ups.com

How does negative feedback work?
Negative feedback is simply a negative voltage fed back
from the output to the input amplifying device to offset
part of the harmonic distortion which is present as a
positive voltage.

Wrong. The voltage that is fed back in audio power amps is almost always
positive with respect to the input and output of the piece of equipment.
Therefore it is wrong to call it a negative voltage.

Wrong. The voltage that is fed back in audio power amps is simply a fraction
of the output signal. It is not fed back to offset the distortion, but
rather is fed back to offset the foreward-going signal voltage.

It costs nothing except a loss of gain
and a few side effects such as phase shift and possible
instability which are well known in the mathematical
literature and more or less easily guarded against
depending on the level of NFB.

Wrong. Negative feedback always reduces phase shift. If misapplied it can
cause an amplifier to become less stable, but in fact when properly applied,
negative feedback increases stability.

Negative feedback increases stability in the sense that it stabilizes the
amplifiers most important technical parameters. For example consider the
gain of an amplifier. If there is no negative feedback, then the gain of an
amplifier is very much exposed to natural variations in the parameters of
its active devices whether they be tubes or solid state. For example, the
gain of both tubes and transistors can be very sensitive to temperature.
With negative feedback, the important parameters of the amplifier are set
by a pair of resistors, whose properties can be made to be very stable and
independent of temperature.

You should get the idea by wrong - Jute has no clue about what negative
feedback is, how it works, or what its real benefits are.

The Catch-22 of Negative Feedback aka NFB
 

"Ruud Broens" wrote in message


we've been through this 'linearity contest' before, here.
whereas you define it in terms of current amplification,
i define it in terms of voltage amplification.
as real-world interfacing in audio is with *voltages*,
doesn't seem unreasonable...


Negative feedback is generally used to make amplifiers more linear in the
voltage domain. It's a highly sucessful strategy. We sent men to the moon,
partially based on amplifiers that were linearized with negative feedback.

Where's the beef?

The Catch-22 of Negative Feedback aka NFB
 

"Arny Krueger" wrote in message
...
: "Ruud Broens" wrote in message
:
:
: we've been through this 'linearity contest' before, here.
: whereas you define it in terms of current amplification,
: i define it in terms of voltage amplification.
: as real-world interfacing in audio is with *voltages*,
: doesn't seem unreasonable...
:
:
: Negative feedback is generally used to make amplifiers more linear in the
: voltage domain. It's a highly sucessful strategy. We sent men to the moon,
: partially based on amplifiers that were linearized with negative feedback.
:
: Where's the beef?
:
they 'beef' is, your banana needs 1K more straightening' than my banana -
why keep claiming it is "superior" ?

:-)
Rudy

The Catch-22 of Negative Feedback aka NFB
 

: we've been through this 'linearity contest' before, here.
: whereas you define it in terms of current amplification,
: i define it in terms of voltage amplification.
: as real-world interfacing in audio is with *voltages*,
: doesn't seem unreasonable...
:
:
: Negative feedback is generally used to make amplifiers more linear in the
: voltage domain. It's a highly sucessful strategy. We sent men to the moon,
: partially based on amplifiers that were linearized with negative feedback.


Uhhh, power amplifiers work on complex loads in the power domain?

The Catch-22 of Negative Feedback aka NFB
 

On Fri, 24 Mar 2006 12:59:37 +0100, "Ruud Broens"
wrote:

"Arny Krueger" wrote in message
...
: "Ruud Broens" wrote in message
:
:
: we've been through this 'linearity contest' before, here.
: whereas you define it in terms of current amplification,
: i define it in terms of voltage amplification.
: as real-world interfacing in audio is with *voltages*,
: doesn't seem unreasonable...
:
:
: Negative feedback is generally used to make amplifiers more linear in the
: voltage domain. It's a highly sucessful strategy. We sent men to the moon,
: partially based on amplifiers that were linearized with negative feedback.
:
: Where's the beef?
:
they 'beef' is, your banana needs 1K more straightening' than my banana -
why keep claiming it is "superior" ?

Because what matters is the output of the *final* circuit - the banana
is perfectly straight in the opamp, but your tube circuit is still
bendy. The opamp is *designed* to use large amounts of linearising
feedback, something that simply isn't an option with the inherently
much lower open-loop gain of tubes.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

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The Catch-22 of Negative Feedback aka NFB
 

On 24 Mar 2006 00:46:36 -0800, "Andre Jute" wrote:

I must say, Wilson, I don't understand why you're getting your knickers
in a knot. You're like those bolshies I used to know who claimed that
anyone who wasn't willing to kill for "socialism" was only play-acting.
Are you really claiming that someone who merely uses the NFB he finds
lurking in DHTs can't belong to the club until he repents and uses
excessive amounts of loop NFB? Are you really claiming that the use of
lots and lots of NFB is a prerequisite for good audio design? Are you
really claiming that because a little NFB is a good thing, an unlimited
amount must therefore be better, and an infinite amount best of all?
Seems a bit immoderate to me, old chap.

Your hysterical belief that I am "against" NFB is the product of your
unsophisticated literal-mindedness. There is no reason for NFB to be an
act of faith, like an on-off switch. For the record, quite contrary to
your silly claims about what I said, I believe the little NFB that
occurs naturally in triodes and in certain conservatively sanctioned
traditional topologies are A Good Thing. To avoid giving you another
apoplectic fit, I shan't repeat what I think of the excessive amounts
of NFB required to make transistors work at all.

As ever, you have no idea what you're talking about. A modern power
transistor such as the 2SC2922 is *more* linear than a 300B, *without*
any feedback. With feedback, due to its gain of 100, it can achieve
linearity far beyond the wildest dreams of the 'ultrafidelista'.

That, of course, is why KISASS will kick the ass of KISS any day of
the week.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

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The Catch-22 of Negative Feedback aka NFB
 

"Stewart Pinkerton" wrote in message
...
: On Fri, 24 Mar 2006 12:59:37 +0100, "Ruud Broens"
: wrote:
:
: "Arny Krueger" wrote in message
: ...
: : "Ruud Broens" wrote in message
: :
: :
: : we've been through this 'linearity contest' before, here.
: : whereas you define it in terms of current amplification,
: : i define it in terms of voltage amplification.
: : as real-world interfacing in audio is with *voltages*,
: : doesn't seem unreasonable...
: :
: :
: : Negative feedback is generally used to make amplifiers more linear in the
: : voltage domain. It's a highly sucessful strategy. We sent men to the moon,
: : partially based on amplifiers that were linearized with negative feedback.
: :
: : Where's the beef?
: :
: they 'beef' is, your banana needs 1K more straightening' than my banana -
: why keep claiming it is "superior" ?
:
: Because what matters is the output of the *final* circuit - the banana
: is perfectly straight in the opamp, but your tube circuit is still
: bendy.

yeah, right, as in 0.007 % distortion kinda bendy.
must be what they call 'the scottish bend',
then
R.

The opamp is *designed* to use large amounts of linearising
: feedback, something that simply isn't an option with the inherently
: much lower open-loop gain of tubes.
: --
:
: Stewart Pinkerton | Music is Art - Audio is Engineering
:
: Posted Via Usenet.com Premium Usenet Newsgroup Services
: ----------------------------------------------------------
: ** SPEED ** RETENTION ** COMPLETION ** ANONYMITY **
: ----------------------------------------------------------
: http://www.usenet.com

The Catch-22 of Negative Feedback aka NFB
 

The details of transistor amplifiers have changed immensely and the
devices have improved, but the physics are still the same as when John
F. Kennedy was holding up operations at Idlewild while pounding on the
Monroe Doctrine in SAM 26000. Bipolar transistors are still low
impedance, current controlled, current controlling devices.

The Catch-22 of Negative Feedback aka NFB
 

"Stewart Pinkerton" wrote in message
...
: On Fri, 24 Mar 2006 17:57:12 +0100, "Ruud Broens"
: wrote:
:
: : : Where's the beef?
: : :
: : they 'beef' is, your banana needs 1K more straightening' than my banana -
: : why keep claiming it is "superior" ?
: :
: : Because what matters is the output of the *final* circuit - the banana
: : is perfectly straight in the opamp, but your tube circuit is still
: : bendy.
:
: yeah, right, as in 0.007 % distortion kinda bendy.
: must be what they call 'the scottish bend',
: then
:
: Be more specific about the tubed circuit you claim has this level of
: distortion.
:

eehhrrmm,
don't think that earlier suggestion of a scottish detective will
work out,
after all,

thanks for detecting,
not even well above noise level,
lot'sZZ

:-)
Rudy