Chris Hornbeck wrote:
On Fri, 22 Sep 2006 16:06:35 -0400, "Henry Pasternack"
wrote:
Brilliant analysis, saved, but snipped 'cause you've
already read it.
I've skimmed Plodnick's exhaustive -- and exhausting! -- summary of the
60 or so posts, many of them long, in the thread "Negative Feedback in
Triodes: The Logical and Experimental Proof" which I started on 15
August 2006:
http://groups.google.ie/group/rec.au...dff8d8ed263a35
Leaving only two questions: if it's feedback, where's
the change in bandwidth and input-referred noise?
And B: what do we gain from pretending that it's true?
IOW, what insights arise from stretching this analogy
into an assumption?
The first is a metaphysical question that Plod has answered
surprisingly well: "Negative feedback is a model. The system operates
the same regardless of the model."
The answer to your second question arises from acceptance of the
qualities of a model as an operational tool in a practical design, and
also as a weapon in our hand against the barbarians at the gate of RAT.
One model, yours, models the triode according to Thevenin or Norton, or
whatever turns up your wick, without the feedback. This model is liable
to frivolous attack from the sort of engineers and hangers-on who have
NFB signs in their eyeballs. It simply gets boring listening to them,
and watching Patrick actually make a serious argument (the same one)
every time I tweak their noses.
One model, among several that Patrick and I have described and other
parties have elaborated, models the pentode as a triode with the
internal feedback removed, the pentode requiring the negative feedback
to be reapplied externally in order to function, the rationale being
that something invisible is happening inside the triode which resembles
NFB as applied to pentodes to a large enough extent to be called NFB
and so to be modelled (see the second part of my original exposition
referenced above). This is a useful model for non-electronic purposes
as well in that it preempts some arguments particularly against SET
amps made by the NFB neanderthals.
Electronically it is irrelevant whether or not you believe, as Patrick
appears sincerely to do, that actual NFB takes place inside the triode,
or whether you believe, as I do, that the net effect at the output end
of the triode is similar enough to view the process inside as so close
to NFB as to be calculable as NFB, indeed to be shorthanded (at least
in the privacy of our fractious family on RAT) without qualification as
"xdB NFB". It's a black box effect and arguments in the dark inside the
box about who's got the torch do not affect the electrical outcome. Or,
as Plod bluntly puts it for those of duller mind than you, "Negative
feedback is a model. The system operates the same regardless of the
model."
I'm very sorry to be so hard-assed about such a trivial
subject, but fuzzy thinking has become palpably dangerous
in the modern world.
Of course I agree with you.The Fuzzy Thinking and Arrogant Hubris of a
minority pressure group that led to the banning of DDT, which in turn
caused an ongoing genocide by starvation and the return of a previously
eradicated wasting disease (malaria) of those poor black people least
able to defend themselves, is matter of principle for which it is worth
standing up and offending or even losing friends.
But whether inside a triode there is negative feedback or some other
mechanism with the same net effect on the sound-- is, as you say, "a
trivial subject", not worth fighting about, except if we can use it as
a club to beat the enemies of fidelity around the ears.
Fight the power. Fuzziness is great,
even if it gets in yer teeth, in some other circumstances,
of course.
Deliberate fuzzy thinking is a major tool of the enemies of society and
should be stomped wherever it is encountered.
Much thanks, as always,
Chris Hornbeck
Andre Jute
Habit is the nursery of errors. -- Victor Hugo