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Lost'n Found Lost'n Found is offline
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Do you guys like or dislike feedback in amplifiers?

I know it is a question that . . . . -_- sigh

But still, what do you think?

I think we can't live without feedback, so what is ur feedback?


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Patrick Turner Patrick Turner is offline
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Lost'n Found wrote:

Do you guys like or dislike feedback in amplifiers?

I know it is a question that . . . . -_- sigh

But still, what do you think?

I think we can't live without feedback, so what is ur feedback?


Say one forgets to mow the lawns.

Wife says, "lawns are looking a bit ragged dear"

Youse start thinkin, "Hmm, no sex tonight if I don't mow the lawns..."

So you go mow the lawns.

The natural order if for man to not mow lawns as often as the audience
around him wishes, and this is his mistake.

The error is pointed out by someone close to him, and action is taken to

correct the mistake and mow the fukkin lawn.

The lawns which are the signal now looks clean and tidy;
the audience is happy.

However such error corrections in electronic NFB are so fast, and happen

with such rapidity that the corrections of errors occur while errors are
made,
and it as if the wife is intimately in contact with the man's brain and
has him
cutting each blade of grass shorter while it grows longer,
so the apearance of the lawn is always beautiful.

The negativity of such feedback may seem indeed to be horridly negative,

nobody likes to be henpecked that much, but in ampifiers that's what
occurs,
only ithe reality is that the mistakes the amp makes are fed back in
opposite phase to oppose their own creation
as they are created so less of a mistake occurs.

Under such circumstances, and considering that no correction system is
perfect
because it includes the forward path of the misbehaving amp
then there are mistakes in this mistake fixing process and it results in

some ""second order"" harmonic products being formed which under some
circumstances
make the amp sound worse than if no NFB was applied.

But where the distortion is less than 10%, the bandwidth without NFB is
adequate,
phase shift low, and applied NFB
about over 14dB, the reduction of THD is going to sound better than had
nothing been done
and no FB applied.

There are many books on the subject of NFB.
Have you read any?

Patrick Turner.



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Ian Iveson Ian Iveson is offline
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Lost'n Found wrote

Do you guys like or dislike feedback in amplifiers?

I know it is a question that . . . . -_- sigh

But still, what do you think?

I think we can't live without feedback, so what is ur feedback?


Ah, well, erm...we seem to like arguing about it, anyway.

Firstly, on the definition of feedback. Every real dynamic system
contains feedback in the sense of regulation due to load, or dynamic
equilibrium. This sense is trivial for our purposes.

Engineers have a particular meaning, however, which comes from and is
precisely defined by control system theory. One part of this
definition is the "canonical system diagram", which represents a
system as a forward function, whose output is summed with (or
subtracted from) the system input, and whose input is that sum. There
is no function in the feedback path. The implication is that the
forward and feedback paths must be separate and distinct. If there is
in reality only one path from input to output, then the analysis
becomes trivial, and there is no point in considering it as a system
with feedback.

Feedback in the trivial sense cannot be a bad thing because it is in
everything. Hence if it is bad, there is no such thing as good, in
which case bad becomes as trivial as the feedback: it doesn't exist.

Feedback in the engineering sense is a bad thing, IMHO. Often,
however, it is less bad than its absence in a particular real circuit.
Think of it like medicine. Never a good thing, but better than being
sick.

Bad because it is a complication. Because it is problematic and the
problems require solutions at the expense of further complication.
Because the complication is not euphonic and so, because the solutions
are never perfect, the inevitable faults aren't musical.

The issue is strongly linked to another. Some believe that domestic
audio systems should be excluded from the category of musical
instrument, on the grounds that their function is merely to reproduce.
It follows from this premise that performance can be measured in terms
of deviations from some original music that happened somewhere else,
or at a different time, or both. Performance measured by such criteria
is always improved by any reduction in the sum of deviations.
Perfection is guaranteed if every deviation is zero, and hence the sum
of deviations is also zero. Such perfection cannot be achieved without
feedback, and in reality so far feedback has been found necessary to
get even close.

Several problems arise from that view. Such perfection is not actually
possible: deviation is never quite zero. On the simple face of this,
there is no agreed method of combining various deviations, or kinds of
distortion, into a single measure. Hence there is no single measure of
quality. As a simple example, if I can reduce 2H distortion by 20dB at
the expense of creating 3dB of extra 7H and a spot of crossover
distortion, is that an improvement? Or a matter of taste...perhaps
even statistically average taste? Second, rather less simply, it is
close to self-evident to say that the idea of reproducing the sound of
a symphony orchestra or a rock concert in my room is impossible. Two
speakers in this room is just never going to do that. Now, it is
possible to see this in terms of error, as an engineer might, and end
up with another matter of taste.

I believe there is a serious philosophical question behind all this. I
don't actually *want* a reproduction. Music is music...it is
indubitably here in my room...my system is making actual real music.
Judging it by the sum of differences is just not appropriate. Fidelity
is not the same thing as precision. I want my music to be coherent *in
its own right*, to have its own spirit and life. I want to hear the
music the musicians play, not what they measure. That is not a matter
of taste, but one that begs philosophical interpretation.

The same question arises in a different form if I ask whether there is
a single, perfectly right and proper way of playing, say, Beethoven's
5th? Obviously not, so is every performance, regardless of any measure
of quality, of equal merit? Obviously not. How do we define fidelity?
How do we judge performance?

When it seems just right, just now. It is a single feeling, not a sum
of differences. It is unlikely to come from a system with lots of
feedback, which is aimed at the sum of differences. Some report it is
possible, more or less just about nearly, with none. Or very little.
You'll know when, or not.

cheers, Ian










"in message . ..



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Eeyore Eeyore is offline
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Lost'n Found wrote:

Do you guys like or dislike feedback in amplifiers?


It's not really a case of liking or disliking it.

You can't make a very linear amplifier without using it. Case closed.

A LOT of nonsense is talked about feedback, mostly by the uninformed /
foolish / gullible / wannabe crowd.

Graham

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Sander deWaal Sander deWaal is offline
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"Lost'n Found" said:

Do you guys like or dislike feedback in amplifiers?

I know it is a question that . . . . -_- sigh

But still, what do you think?

I think we can't live without feedback, so what is ur feedback?



Every amplifier uses feedback, but us tubies usually only use the
"local feedback" variety.

A cathode resistor is local feedback, and some even argue that a
triode has inherent feedback.

So it's not a matter of liking or not liking, it;s just there.

Now loop feedback, that's something different.
If possible, I try to avoid it in my tube amps, usually because they
apparently don't need it.
But when they do, I don't hesitate to use it with care.

I know of no (commercial) transistor amp that can work without loop
feedback.

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


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Eeyore Eeyore is offline
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Sander deWaal wrote:

A cathode resistor is local feedback, and some even argue that a
triode has inherent feedback.


Strictly speaking that's an *unbypassed* cathode resistor but I know
what you're driving at.

snip

I know of no (commercial) transistor amp that can work without loop
feedback.


It could be done though. It's simply not conventional to do so.

Graham

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John Byrns John Byrns is offline
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In article ,
Eeyore wrote:

Sander deWaal wrote:

A cathode resistor is local feedback, and some even argue that a
triode has inherent feedback.


Strictly speaking that's an *unbypassed* cathode resistor but I know
what you're driving at.

snip

I know of no (commercial) transistor amp that can work without loop
feedback.


It could be done though. It's simply not conventional to do so.


Wasn't it done about a year ago right here in this group, although it
wasn't commercial which I assume is the reason for the disclaimer.


Regards,

John Byrns
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Sander deWaal Sander deWaal is offline
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John Byrns said:


A cathode resistor is local feedback, and some even argue that a
triode has inherent feedback.



Strictly speaking that's an *unbypassed* cathode resistor but I know
what you're driving at.



That's what I meant, sorry.
It's njust not a habit of mine to bypass cathodes ;-)


I know of no (commercial) transistor amp that can work without loop
feedback.



It could be done though. It's simply not conventional to do so.



Wasn't it done about a year ago right here in this group, although it
wasn't commercial which I assume is the reason for the disclaimer.



Yup. I've tried it with BJTs, and even my hybrid (MOSFET out) amps
don't use global feedback for AC (there is a DC servo loop, though).

But commercially, I have not seen it.
Densen claimed they did it, but it turned out there *was* global
feedback in there..........

But we're digressing into silicon again, gentlemen, some readers will
punish us for that ;-)

--
"Due knot trussed yore spell chequer two fined awl miss steaks."
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Eeyore Eeyore is offline
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John Byrns wrote:

Eeyore wrote:
Sander deWaal wrote:

A cathode resistor is local feedback, and some even argue that a
triode has inherent feedback.


Strictly speaking that's an *unbypassed* cathode resistor but I know
what you're driving at.

snip

I know of no (commercial) transistor amp that can work without loop
feedback.


It could be done though. It's simply not conventional to do so.


Wasn't it done about a year ago right here in this group, although it
wasn't commercial which I assume is the reason for the disclaimer.


I'm not sure. It's entirely possible I made the same claim a year ago
though.

I know exactly how to do it. It's almost trivial in fact. I guess it might
actually be commercially viable given the crazy claims being made about
feedback.

Graham

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Andre Jute Andre Jute is offline
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Default The Longears ZNFB Silicon Amp (LZSA or Elzilsa) Feedback


Eeyore wrote:
John Byrns wrote:

Eeyore wrote:
Sander deWaal wrote:
I know of no (commercial) transistor amp that can work without loop
feedback.

It could be done though. It's simply not conventional to do so.


Wasn't it done about a year ago right here in this group, although it
wasn't commercial which I assume is the reason for the disclaimer.


I'm not sure. It's entirely possible I made the same claim a year ago
though.


You're tripping over your ego again, Poopie, thinking everything
everyone says relates to you. But Mr Byrns is referring to an
outstanding solid state amplifier designed by that great post office
engineer Stewart Pinkerton.

I know exactly how to do it. It's almost trivial in fact.


Go for it, Longears. We'll agree the spec and then you can draw,
develop and publish the design, running a thread here all the time with
an account of how you're going. Be a way for you to regain some
respect.

I guess the first parameter should be ZNFB, though we might have to be
a bit flexible about that.

I guess it might
actually be commercially viable given the crazy claims being made about
feedback.


Forget a commercial deal. That's too tough a test to set; designing the
thing to a ZNFB parameter is a tough enough nut to crack.

Graham


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



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Eeyore Eeyore is offline
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Default The Longears ZNFB Silicon Amp (LZSA or Elzilsa) Feedback



Andre Jute wrote:

Eeyore wrote:

I guess it might
actually be commercially viable given the crazy claims being made about
feedback.


Forget a commercial deal. That's too tough a test to set; designing the
thing to a ZNFB parameter is a tough enough nut to crack.


The challenge was no *loop* feedback.

Graham

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Phil Allison Phil Allison is offline
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"Eeyore"


Do you guys like or dislike feedback in amplifiers?


It's not really a case of liking or disliking it.

You can't make a very linear amplifier without using it. Case closed.



** This pommy lass has had some success using class A, mosfets &
transformers.

http://www.susan-parker.co.uk/zeus.htm

Good to see she finally figured out the difference between a "lateral" and
"vertical" mosfet.

http://www.susan-parker.co.uk/zeus-t...9-fft-1khz.htm





........ Phil


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Patrick Turner Patrick Turner is offline
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Ian Iveson wrote:

Lost'n Found wrote

Do you guys like or dislike feedback in amplifiers?

I know it is a question that . . . . -_- sigh

But still, what do you think?

I think we can't live without feedback, so what is ur feedback?


Ah, well, erm...we seem to like arguing about it, anyway.

Firstly, on the definition of feedback. Every real dynamic system
contains feedback in the sense of regulation due to load, or dynamic
equilibrium. This sense is trivial for our purposes.

Engineers have a particular meaning, however, which comes from and is
precisely defined by control system theory. One part of this
definition is the "canonical system diagram", which represents a
system as a forward function, whose output is summed with (or
subtracted from) the system input, and whose input is that sum. There
is no function in the feedback path. The implication is that the
forward and feedback paths must be separate and distinct. If there is
in reality only one path from input to output, then the analysis
becomes trivial, and there is no point in considering it as a system
with feedback.

Feedback in the trivial sense cannot be a bad thing because it is in
everything.


Absolute BS.

NFB is NOT in everything.

Really, Ian, you should wash your brain with soap
because its full of BS.

You cannot accept that NFB exists in a triode, so now NFB is in evrything.

All who read Ian's posts should have their BS detectors turned on,
and air conditioning set to deal with the blast of hot air.

Patrick Turner.

Hence if it is bad, there is no such thing as good, in
which case bad becomes as trivial as the feedback: it doesn't exist.

Feedback in the engineering sense is a bad thing, IMHO. Often,
however, it is less bad than its absence in a particular real circuit.
Think of it like medicine. Never a good thing, but better than being
sick.

Bad because it is a complication. Because it is problematic and the
problems require solutions at the expense of further complication.
Because the complication is not euphonic and so, because the solutions
are never perfect, the inevitable faults aren't musical.

The issue is strongly linked to another. Some believe that domestic
audio systems should be excluded from the category of musical
instrument, on the grounds that their function is merely to reproduce.
It follows from this premise that performance can be measured in terms
of deviations from some original music that happened somewhere else,
or at a different time, or both. Performance measured by such criteria
is always improved by any reduction in the sum of deviations.
Perfection is guaranteed if every deviation is zero, and hence the sum
of deviations is also zero. Such perfection cannot be achieved without
feedback, and in reality so far feedback has been found necessary to
get even close.

Several problems arise from that view. Such perfection is not actually
possible: deviation is never quite zero. On the simple face of this,
there is no agreed method of combining various deviations, or kinds of
distortion, into a single measure. Hence there is no single measure of
quality. As a simple example, if I can reduce 2H distortion by 20dB at
the expense of creating 3dB of extra 7H and a spot of crossover
distortion, is that an improvement? Or a matter of taste...perhaps
even statistically average taste? Second, rather less simply, it is
close to self-evident to say that the idea of reproducing the sound of
a symphony orchestra or a rock concert in my room is impossible. Two
speakers in this room is just never going to do that. Now, it is
possible to see this in terms of error, as an engineer might, and end
up with another matter of taste.

I believe there is a serious philosophical question behind all this. I
don't actually *want* a reproduction. Music is music...it is
indubitably here in my room...my system is making actual real music.
Judging it by the sum of differences is just not appropriate. Fidelity
is not the same thing as precision. I want my music to be coherent *in
its own right*, to have its own spirit and life. I want to hear the
music the musicians play, not what they measure. That is not a matter
of taste, but one that begs philosophical interpretation.

The same question arises in a different form if I ask whether there is
a single, perfectly right and proper way of playing, say, Beethoven's
5th? Obviously not, so is every performance, regardless of any measure
of quality, of equal merit? Obviously not. How do we define fidelity?
How do we judge performance?

When it seems just right, just now. It is a single feeling, not a sum
of differences. It is unlikely to come from a system with lots of
feedback, which is aimed at the sum of differences. Some report it is
possible, more or less just about nearly, with none. Or very little.
You'll know when, or not.

cheers, Ian

"in message . ..


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Patrick Turner Patrick Turner is offline
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Sander deWaal wrote:

John Byrns said:

A cathode resistor is local feedback, and some even argue that a
triode has inherent feedback.



Strictly speaking that's an *unbypassed* cathode resistor but I know
what you're driving at.


That's what I meant, sorry.
It's njust not a habit of mine to bypass cathodes ;-)


I know of no (commercial) transistor amp that can work without loop
feedback.



It could be done though. It's simply not conventional to do so.


Wasn't it done about a year ago right here in this group, although it
wasn't commercial which I assume is the reason for the disclaimer.


Yup. I've tried it with BJTs, and even my hybrid (MOSFET out) amps
don't use global feedback for AC (there is a DC servo loop, though).

But commercially, I have not seen it.
Densen claimed they did it, but it turned out there *was* global
feedback in there..........

But we're digressing into silicon again, gentlemen, some readers will
punish us for that ;-)


There are plenty of people who have used only emitter or source follower
connected output stages which is a localised application of perhaps
anything from 15 to 50 dB of series voltage NFB.

Some of these ppl then try to jump on the bandwagon to gain approval and
sales with ppl who hate global NFB.
By not including global NFB, they try to con us into thinking there isn't
any NFB, but
we know the truth here.

Now providing the output stages are in class A, then the local follower NFB
is enough to render
the silicon output stage to be as linear as any triode output stage of the
same power.
Typically, a single complememntary source follower couple of NPN and PNP
power mosfets
can give less than 1% THD into 16 ohms at 25 watts at clipping in pure class
A.
The THD is a combination of mainly 2H and 3H and fairly benign THD at low
levels where
such an amp would typically be used to make less than a watt of average
power,
and where the THD is typically less than 0.2%.
Using 6 mosfets instead of 2 gives 1/3 of the THD because the load each
mosfet sees in class A rises from
32 ohms to 96 ohms and the amount of follower FB is increased 3 times.
Bias can be reduced to keep the sixpack cool, and the AB transition is
tolerable.

But you have to provide a drive voltage slightly greater than the speaker
voltage.

So the driver amp using BJTs has to be linear, and a ziclai pair with its
own NFB
and a +70V supply is a nice candidate, or else a tubed driver stage
with a couple of triodes and FB loop.

The simplest driver would be say a pair of EL84 in triode in parallel
with choke loading and this should give 20Vrms at less than 0.5%, or a lot
less than the output
stage of mosfets, and the Rout of the triode drive stage will be only about
1k, have
gain at about 18, have no NFB and give sufficient bandwidth in the face of
the
input capacitance of the mosfets which is reduced from the Cg-s stated in
the data due to the
follower connection.

Better results are obtained when the mosfet amp uses an OPT and is driven
with a PP
LTP because the output device symmetry acts to keep the THD much lower than
N and P devices.
The OPT allows load matching.
See my page on class A mosfets with a combination of shunt NFB and global FB
at
http://www.turneraudio.com.au/solids...no-mosfet.html

My intended improvement to my ciruitry is to replace the bjts at the input
with
2SK369 high gm j-fets which then should drive the mosfet output stage
without the bjt N&D of the present set up.

In case you were not aware of what simplicity really was, try having a look
at
the ZEUS amplifier at Sue Parker's website at
http://www.susan-parker.co.uk/zeus.htm

The only problem for us tubies with Sue's amp is the low input resistance
because of the
step up input tranny.

Hence a PP triode LTP driving the mosfet gates should make a lot of sense to
those of us
who are not fond of input trannies, even when they are wide band toroidals.

I am not worried by people wanting yo lynch me on a stout oak tree branch
because
i dare to recommend silicon as a means to an end.

I like blondes, brunettes, AND redheads.

Patrick Turner.





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


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Ian Iveson Ian Iveson is offline
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Daft Patrick blurted

Feedback in the trivial sense cannot be a bad thing because it is
in
everything.


Absolute BS.

NFB is NOT in everything.

Really, Ian, you should wash your brain with soap
because its full of BS.

You cannot accept that NFB exists in a triode, so now NFB is in
evrything.

All who read Ian's posts should have their BS detectors turned on,
and air conditioning set to deal with the blast of hot air.


The whole world, and everything in it, is in a state of shifting
dynamic equilibrium, or dynamic not-quite-equilibrium. Everything
suffers its own consequences, and those of everything else, to some
degree. Even you.

And, incidentally, not all quacking things are ducks, as many ducks
have found to their cost.

Ian




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Peter Wieck Peter Wieck is offline
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Default The Longears ZNFB Silicon Amp (LZSA or Elzilsa) Feedback


Andrew Jute McCoy blathered:

Go for it, Longears. We'll agree the spec and then you can draw,
develop and publish the design, running a thread here all the time with
an account of how you're going. Be a way for you to regain some
respect.


"We" should be discussing Peter Drucker and apologizing for "Our" lies
if "respect" is at stake.

_You_ lie as actual human beings breath.


Peter Wieck
Wyncote, PA

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Patrick Turner Patrick Turner is offline
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Ian Iveson wrote:

Daft Patrick blurted

Feedback in the trivial sense cannot be a bad thing because it is
in
everything.


Absolute BS.

NFB is NOT in everything.

Really, Ian, you should wash your brain with soap
because its full of BS.

You cannot accept that NFB exists in a triode, so now NFB is in
evrything.

All who read Ian's posts should have their BS detectors turned on,
and air conditioning set to deal with the blast of hot air.


The whole world, and everything in it, is in a state of shifting
dynamic equilibrium, or dynamic not-quite-equilibrium. Everything
suffers its own consequences, and those of everything else, to some
degree. Even you.

And, incidentally, not all quacking things are ducks, as many ducks
have found to their cost.

Ian


Ian, you are really trying hard to be the Prince of Fools.

If BS was music, you'd be a brass band.

You have no grip on reality.

Patrick Turner.




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