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Andre Jute
 
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Default The Catch-22 of Negative Feedback aka NFB


Arny "I spoke in error" Krueger next tries hairsplitting:

"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.


If you can't win the argument, redefine the standard terms.

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.


If you can't win the argument, redefine it so narrowly that you can
split hairs about a single tiny piece.

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.


If you can't win the argument on the specifics, shift ground to the
generality. State that misapplication will always be misapplication, as
if you have just discovered the dull truism.

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.


If you can't win the argument on its merits, drag in a lot of
extraneous considerations and pretend that each of them is the main
problem.

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.


"You should get the idea by wrong" -- duh, Arny? Another Freudian slip?
It tells us poor little Arny, an old man, is still so childish that,
regardless of the facts, he insists on being right and everyone else
being wrong. What a moron.

If you want to be a hairdresser, Krueger, first you should realize that
the purpose of hairdressing is not to promote and increase split ends
but to prevent them. The same in audio with distortion. I thought you
claimed to be an engineer...

Andre Jute
In audio less is hedonism