NFB 101 Part Deux

NFB 101 Part Deux

Sorry it has been a while coming but I have just finished part two of
NFB 101. I found I could not describe it properly without diagrams and
proper equations so I had to resort to using a word processor and
converting the result into a pdf, all of which took time. So point your
browser here: http :// www .ianbell.ukfsn.org/data/nfb101.pdf to download it.

Cheers

Ian

Re: NFB 101 Part Deux

Ian Thompson-Bell wrote:
> Sorry it has been a while coming but I have just finished part two of
> NFB 101. I found I could not describe it properly without diagrams and
> proper equations so I had to resort to using a word processor and
> converting the result into a pdf, all of which took time. So point
> your browser here: http :// www .ianbell.ukfsn.org/data/nfb101.pdf to
> download it.
> Cheers
>
> Ian

Thanks, Ian. Just printed it out to read later.

Re: NFB 101 Part Deux



"Ian Thompson-Bell" <ruffrecords@yahoo.co.uk> wrote in message
news:frh1t4$e34$1@energise.enta,net ...
> Sorry it has been a while coming but I have just finished part two of NFB
> 101. I found I could not describe it properly without diagrams and proper
> equations so I had to resort to using a word processor and converting the
> result into a pdf, all of which took time. So point your browser here:
> http :// www .ianbell.ukfsn.org/data/nfb101.pdf to download it.
>
Excellent Ian. I have just printed this out for bedtime reading.
And just as Andre had reported there was nothing happening.
Your timing was impeccable:-)

Iain

Re: NFB 101 Part Deux

Iain Churches wrote:
> "Ian Thompson-Bell" <ruffrecords@yahoo.co.uk> wrote in message
> news:frh1t4$e34$1@energise.enta,net ...
>> Sorry it has been a while coming but I have just finished part two of NFB
>> 101. I found I could not describe it properly without diagrams and proper
>> equations so I had to resort to using a word processor and converting the
>> result into a pdf, all of which took time. So point your browser here:
>> http :// www .ianbell.ukfsn.org/data/nfb101.pdf to download it.
>>
> Excellent Ian. I have just printed this out for bedtime reading.
> And just as Andre had reported there was nothing happening.
> Your timing was impeccable:-)
>
> Iain
>
>

There may be typos in it still. I changed all the text based formulae to
'proper' ones so something may have got lost in translation. There are
certainly some superfluous brackets lying around only because I have not
yet worked out how to get the formula editor to suppress them. And I am
not sure if the figures tie up exactly with the text and of course it is
nowhere near finished yet.

Cheers

Ian

Re: NFB 101 Part Deux



Ian Thompson-Bell wrote:
>
> Iain Churches wrote:
> > "Ian Thompson-Bell" <ruffrecords@yahoo.co.uk> wrote in message
> > news:frh1t4$e34$1@energise.enta,net ...
> >> Sorry it has been a while coming but I have just finished part two of NFB
> >> 101. I found I could not describe it properly without diagrams and proper
> >> equations so I had to resort to using a word processor and converting the
> >> result into a pdf, all of which took time. So point your browser here:
> >> http :// www .ianbell.ukfsn.org/data/nfb101.pdf to download it.
> >>
> > Excellent Ian. I have just printed this out for bedtime reading.
> > And just as Andre had reported there was nothing happening.
> > Your timing was impeccable:-)
> >
> > Iain
> >
> >
>
> There may be typos in it still. I changed all the text based formulae to
> 'proper' ones so something may have got lost in translation. There are
> certainly some superfluous brackets lying around only because I have not
> yet worked out how to get the formula editor to suppress them. And I am
> not sure if the figures tie up exactly with the text and of course it is
> nowhere near finished yet.
>
> Cheers
>
> Ian

Good work Ian.


RDH4 has all this spelled out of course, and uses
µ , "mu" for amplification factor and ß "beta" for fraction of output
voltage
either in series with input voltage for series voltage NFB or in shunt
with applied NFB
as in shunt voltage NFB.

RDH4 lists all the many varieties of feedback, both positive and
negative,
and current and voltage types and whether it is shunt or series.
RDH4 also has a table to show what the effects are of all the different
types
of NFB.

But not every single fascinating aspect of feedback is explored in RHD4.

For example, did you know that positive "series" current feedback will
reduce the output
resistance of any amplifier, but at the cost of reducing bandwidth and
increasing distortions?

If we consider a "normal" amp response of having a reducing output
voltage as the RL becomes lower
as having a POSITIVE output resistance, then the positive CFB can reduce
this amount of Rout
to a lesser value; a typical ultralinear amp with say Ro = 7 ohms with
PCFB
can easily have its Rout reduced to say 1 ohm.
We assume Rout has been reduced from +7 ohms to +1 ohm.
Then the application of the global series voltage "normal" NFB will
reduce it even more to a lower value along with all distortions of the
amp and those
produced by the PCFB applied internally.

We can even apply so much PFFB that the positive Ro becomes a NEGATIVE
output resistance,
and the result is that output voltage rises when RL value is reduced.
So +1 ohm can be reduced further so Rout = ZERO ohms, then even less
than zero ohms, ie
maybe -1ohm.
Obviously, such negative Ro tempts fate and credulity because its
impossible
to get an amp which makes say 16Vrms at clipping into 8 ohms to make
20Vrms into 1 ohm.
But it is possible to make the same amp which makes 1.6V into 8 ohms
deliver 2V into 1 ohms.
But we would find this difficult to live with; once you examine how its
done, and experiment
with it, there are definate stability issues, and the open loop gain (
OLG ) must be reduced or phase tailored
to prevent oscilations, and the application of the PCFB be prevented at
extremities of LF and HF bandwidth.
Very interesting, but don't say I have not warned you.

The maths involved around each different form of feedback will take you
another 20 pages to explain.

I do suggest that all your terms for RL, Ra, and all others be made the
same as in RDH4,
because it was a good standard and everyone should know it, and that
equations be written in the same way.

In your theoretical workings for NFB application, how about showing some
typical
tube power amplifier schematics with NFB applied with all working
voltages with their polarities
so ppl can measure their own amps and understand it all a lot better?

Using a triangle pointing to the right to represent an amp with two
inputs on the
left vertical side and one output at the right point is the text book
way to represent an amp
so people do not have to keep in mind all the complex inner amp topology
which distracts them from the basic idea.
The same model can then be used for a tube amp or an opamp.

However, to include all possible phase shift peculiarities of the open
loop
character of an amp and the equivalent networks in the amp which produce
them
and their interaction when FB is used takes rather a lot of work.

NFB theory and application has already covered in many old books, and
many should be found then read,
and the messages in each will overlap each other books's shortcomings,
and you end up wize while you
remember it all, then dumb again when you forget it all.
Unless of course all you do all day everyday is design and stabilise new
and old amplifiers.
I probably do enough to keep me wize.

I have never seen an online calculator for NFB, where one dials in the
details of the open loop gain and all its phase shift rates and bothers,
and then
ask for 20dB of NFB, and click "calculate", and have the program come up
with the FB network and including all the phase tweaking networks needed
for
unconditional stability into any possible type of reactive loading, R
load, or no load at all.
Such a program could possibly be a boon for the dumbos to whom feedback
is a terrible mystery, and always will be,
and hence hated fiercely, and avoided.
But with a programmed or synthesized solution,
one must ensure it is still a viable solution which works in practice.
Since garbage in = garbage out with simulation programs, expect many
simulated solutions using tubes and OPTs to still be good oscillators
when nobody expected it.
That's because its difficult for anyone to correctly define all the open
loop
gain and phase shift character. Too fucking hard.
Just bulid it, and learn to stabilise it by empirical methods of network
applications and trial and error
and by observation with a CRO. This is a far quicker way than all the
calculations in the world sitting
down at a table when you should be in the workshop achieving something
real.

Models of the single tube amplifier stage should include an extremely
low voltage generator producing output of µ x Vg
with series resistance between the gene output and the anode terminal
should be explained
as equivalent models of the triode or pentode ot any other tube.
Newbies NEED to know the very boring basics before thay can have any
chance of understanding.
Most don't have a clue what a voltage generator is, or what the dynamic
anode resistance is at all!!!

I welcome you to borrow whatever you need from

http :// www .turneraudio,com .au/tube-operation1.html

and

http :// www .turneraudio,com .au/tube-operation3.html

I don't have all the possible various feedback applications mentiuoned
at my site.

It is to be expected that the learning tube crafter will absorb the
basic ideas and
be able to perform all the basic calculations for normal series and
shunt VOLTAGE NFB.

The equations for gain with FB applied are slightly different for the
these two main types of NFB.

Since NOBODY ever dares to apply any positive voltage or current
feedback anywhere anymore to any amp whatsoever,
I have not mentioned exactly how it can be done successfully, because
the risks of
parasitic oscillations are so likely in the hands of ignorant would be
experts.

In general with low µ triode input/drivers, tube amplifiers have only a
mild amount of voltage gain without
any NFB applied, ie, "open loop" gain.
And this "OLG", open loop gain is then reduced by the OPT voltage ratio.

So, to force the amp to have an apparently larger amount of open loop
gain,
some positive voltage FB or positive current FB was applied and the
resulting amp
with mild applications of standard series voltage global negative FB
measured far better than with
just standard global series voltage NFB applied alone.
Its all mentioned in RDH4.

There was classic application of combined forms of FB in a commercial
example in Bogan amps
which had variable positive FB to vary the damping factor of their amps
and it gave better
sounding bass we have been told.

But such fiddles with FB or active manipulations of Rout are to be
treated with utmost caution.

With too much positive current FB, a shorted output can make an amp
oscillate
internally very violently, and cause its demise from thermal runaway
of the output tubes, so too much PCFB is extremely undesirable.
A little dab of PCFB goes a long way and is extremely effective in
reducing Rout a lot though
without increasing the bad artifacts of reduced BW and distortions very
much.

In SS amps, nobody ever would use old fashioned tricks of positive FB
anywhere
because the total including the input LTP, VAS and output BJTs of
mosfets is over 100,000x,
or more than 80dB, so when a TOTAL amount of series voltage NFB is
applied
in the form of say 30dB emitter or source FB in the output stage and
50dB of global NFB,
the gross distortions of crossover and THD and IMD in the OLG
charateristic are reduced
to well below what is ever possible to be heard.

Well, in theory that is, because often some ratbag pissant 20 watt SE
tube amp will
give a clearer rendition of what Motzart or Led Zeppilin intended than
some
100W SS thinge, and despite the fact the SE amp will have very little
NFB and
have 100 times the measured THD/IMD than the SS amp.

Numbers ain't everything.

Patrick Turner.

Re: NFB 101 Part Deux

Patrick Turner wrote:
> Good work Ian.
>
>
> RDH4 has all this spelled out of course, and uses
> µ , "mu" for amplification factor and ß "beta" for fraction of output
> voltage
> either in series with input voltage for series voltage NFB or in shunt
> with applied NFB
> as in shunt voltage NFB.
>

Yes I wanted to use the proper symbols but I took me so long to get my
head around the word processors formula editor that I never got round to
working out how to do special characters. I will revise that aspect
though.

> RDH4 lists all the many varieties of feedback, both positive and
> negative,
> and current and voltage types and whether it is shunt or series.
> RDH4 also has a table to show what the effects are of all the different
> types
> of NFB.
>
> But not every single fascinating aspect of feedback is explored in RHD4.
>
> For example, did you know that positive "series" current feedback will
> reduce the output
> resistance of any amplifier, but at the cost of reducing bandwidth and
> increasing distortions?
>
> If we consider a "normal" amp response of having a reducing output
> voltage as the RL becomes lower
> as having a POSITIVE output resistance, then the positive CFB can reduce
> this amount of Rout
> to a lesser value; a typical ultralinear amp with say Ro = 7 ohms with
> PCFB
> can easily have its Rout reduced to say 1 ohm.
> We assume Rout has been reduced from +7 ohms to +1 ohm.
> Then the application of the global series voltage "normal" NFB will
> reduce it even more to a lower value along with all distortions of the
> amp and those
> produced by the PCFB applied internally.
>
> We can even apply so much PFFB that the positive Ro becomes a NEGATIVE
> output resistance,
> and the result is that output voltage rises when RL value is reduced.
> So +1 ohm can be reduced further so Rout = ZERO ohms, then even less
> than zero ohms, ie
> maybe -1ohm.
> Obviously, such negative Ro tempts fate and credulity because its
> impossible
> to get an amp which makes say 16Vrms at clipping into 8 ohms to make
> 20Vrms into 1 ohm.
> But it is possible to make the same amp which makes 1.6V into 8 ohms
> deliver 2V into 1 ohms.
> But we would find this difficult to live with; once you examine how its
> done, and experiment
> with it, there are definate stability issues, and the open loop gain (
> OLG ) must be reduced or phase tailored
> to prevent oscilations, and the application of the PCFB be prevented at
> extremities of LF and HF bandwidth.
> Very interesting, but don't say I have not warned you.
>
> The maths involved around each different form of feedback will take you
> another 20 pages to explain.
>
> I do suggest that all your terms for RL, Ra, and all others be made the
> same as in RDH4,
> because it was a good standard and everyone should know it, and that
> equations be written in the same way.
>

Clearly RDH4 has covered this material in some detail and I did include
a link to chapter 7 saying I was not going to repeat that chapter. The
question is what is the right balance for RAT readers, especially
noobies as this is supposed to be NFB101 and it is already bogged down
in maths. Personally I like the analysis to be clear without such things
as 'this can be expressed as' without any attendant explanation.
Obviously it needs to be heavily tube related so I thought after the CF
I would do he unbypassed CC followed by shunt derived and applied FB
around a triode of pentode stage mainly because they are easier to
understand and there are no stability problems. Next I thought I would
cover the classic two stage shunt fed series applied circuit which leads
nicely into stability issues.

> In your theoretical workings for NFB application, how about showing some
> typical
> tube power amplifier schematics with NFB applied with all working
> voltages with their polarities
> so ppl can measure their own amps and understand it all a lot better?
>

That sounds like a good idea.

> Using a triangle pointing to the right to represent an amp with two
> inputs on the
> left vertical side and one output at the right point is the text book
> way to represent an amp
> so people do not have to keep in mind all the complex inner amp topology
> which distracts them from the basic idea.
> The same model can then be used for a tube amp or an opamp.
>

I purposely avoided that because its common usage is to represent an
amplifier with infinite gain, zero output resistance and infinite input
impedance and as we both know, tubes only meet one of those criteria. I
was trying to emphasize that tubes fall far short of this ideal which is
why many of the op-amp simplifications just don't apply to tubes.

> However, to include all possible phase shift peculiarities of the open
> loop
> character of an amp and the equivalent networks in the amp which produce
> them
> and their interaction when FB is used takes rather a lot of work.
>
> NFB theory and application has already covered in many old books, and
> many should be found then read,
> and the messages in each will overlap each other books's shortcomings,
> and you end up wize while you
> remember it all, then dumb again when you forget it all.
> Unless of course all you do all day everyday is design and stabilise new
> and old amplifiers.
> I probably do enough to keep me wize.
>
> I have never seen an online calculator for NFB, where one dials in the
> details of the open loop gain and all its phase shift rates and bothers,
> and then
> ask for 20dB of NFB, and click "calculate", and have the program come up
> with the FB network and including all the phase tweaking networks needed
> for
> unconditional stability into any possible type of reactive loading, R
> load, or no load at all.
> Such a program could possibly be a boon for the dumbos to whom feedback
> is a terrible mystery, and always will be,
> and hence hated fiercely, and avoided.
> But with a programmed or synthesized solution,
> one must ensure it is still a viable solution which works in practice.
> Since garbage in = garbage out with simulation programs, expect many
> simulated solutions using tubes and OPTs to still be good oscillators
> when nobody expected it.
> That's because its difficult for anyone to correctly define all the open
> loop
> gain and phase shift character. Too fucking hard.
> Just bulid it, and learn to stabilise it by empirical methods of network
> applications and trial and error
> and by observation with a CRO. This is a far quicker way than all the
> calculations in the world sitting
> down at a table when you should be in the workshop achieving something
> real.
>
> Models of the single tube amplifier stage should include an extremely
> low voltage generator producing output of µ x Vg
> with series resistance between the gene output and the anode terminal
> should be explained
> as equivalent models of the triode or pentode ot any other tube.
> Newbies NEED to know the very boring basics before thay can have any
> chance of understanding.
> Most don't have a clue what a voltage generator is, or what the dynamic
> anode resistance is at all!!!
>


An interesting point. Do you think NFB101 should start with a statement
of what knowledge is assumed along with pointers to references for those
who don't have it?

> I welcome you to borrow whatever you need from
>
> http :// www .turneraudio,com .au/tube-operation1.html
>
> and
>
> http :// www .turneraudio,com .au/tube-operation3.html
>
> I don't have all the possible various feedback applications mentiuoned
> at my site.
>

Thanks for the permission to use ingfo from your site.

Cheers

Ian

Re: NFB 101 Part Deux



Ian Thompson-Bell wrote:
>
> Patrick Turner wrote:
> > Good work Ian.
> >
> >
> > RDH4 has all this spelled out of course, and uses
> > µ , "mu" for amplification factor and ß "beta" for fraction of output
> > voltage
> > either in series with input voltage for series voltage NFB or in shunt
> > with applied NFB
> > as in shunt voltage NFB.
> >
>
> Yes I wanted to use the proper symbols but I took me so long to get my
> head around the word processors formula editor that I never got round to
> working out how to do special characters. I will revise that aspect
> though.
>
> > RDH4 lists all the many varieties of feedback, both positive and
> > negative,
> > and current and voltage types and whether it is shunt or series.
> > RDH4 also has a table to show what the effects are of all the different
> > types
> > of NFB.
> >
> > But not every single fascinating aspect of feedback is explored in RHD4.
> >
> > For example, did you know that positive "series" current feedback will
> > reduce the output
> > resistance of any amplifier, but at the cost of reducing bandwidth and
> > increasing distortions?
> >
> > If we consider a "normal" amp response of having a reducing output
> > voltage as the RL becomes lower
> > as having a POSITIVE output resistance, then the positive CFB can reduce
> > this amount of Rout
> > to a lesser value; a typical ultralinear amp with say Ro = 7 ohms with
> > PCFB
> > can easily have its Rout reduced to say 1 ohm.
> > We assume Rout has been reduced from +7 ohms to +1 ohm.
> > Then the application of the global series voltage "normal" NFB will
> > reduce it even more to a lower value along with all distortions of the
> > amp and those
> > produced by the PCFB applied internally.
> >
> > We can even apply so much PFFB that the positive Ro becomes a NEGATIVE
> > output resistance,
> > and the result is that output voltage rises when RL value is reduced.
> > So +1 ohm can be reduced further so Rout = ZERO ohms, then even less
> > than zero ohms, ie
> > maybe -1ohm.
> > Obviously, such negative Ro tempts fate and credulity because its
> > impossible
> > to get an amp which makes say 16Vrms at clipping into 8 ohms to make
> > 20Vrms into 1 ohm.
> > But it is possible to make the same amp which makes 1.6V into 8 ohms
> > deliver 2V into 1 ohms.
> > But we would find this difficult to live with; once you examine how its
> > done, and experiment
> > with it, there are definate stability issues, and the open loop gain (
> > OLG ) must be reduced or phase tailored
> > to prevent oscilations, and the application of the PCFB be prevented at
> > extremities of LF and HF bandwidth.
> > Very interesting, but don't say I have not warned you.
> >
> > The maths involved around each different form of feedback will take you
> > another 20 pages to explain.
> >
> > I do suggest that all your terms for RL, Ra, and all others be made the
> > same as in RDH4,
> > because it was a good standard and everyone should know it, and that
> > equations be written in the same way.
> >
>
> Clearly RDH4 has covered this material in some detail and I did include
> a link to chapter 7 saying I was not going to repeat that chapter. The
> question is what is the right balance for RAT readers, especially
> noobies as this is supposed to be NFB101 and it is already bogged down
> in maths. Personally I like the analysis to be clear without such things
> as 'this can be expressed as' without any attendant explanation.
> Obviously it needs to be heavily tube related so I thought after the CF
> I would do he unbypassed CC followed by shunt derived and applied FB
> around a triode of pentode stage mainly because they are easier to
> understand and there are no stability problems. Next I thought I would
> cover the classic two stage shunt fed series applied circuit which leads
> nicely into stability issues.
>
> > In your theoretical workings for NFB application, how about showing some
> > typical
> > tube power amplifier schematics with NFB applied with all working
> > voltages with their polarities
> > so ppl can measure their own amps and understand it all a lot better?
> >
>
> That sounds like a good idea.
>
> > Using a triangle pointing to the right to represent an amp with two
> > inputs on the
> > left vertical side and one output at the right point is the text book
> > way to represent an amp
> > so people do not have to keep in mind all the complex inner amp topology
> > which distracts them from the basic idea.
> > The same model can then be used for a tube amp or an opamp.
> >
>
> I purposely avoided that because its common usage is to represent an
> amplifier with infinite gain, zero output resistance and infinite input
> impedance and as we both know, tubes only meet one of those criteria. I
> was trying to emphasize that tubes fall far short of this ideal which is
> why many of the op-amp simplifications just don't apply to tubes.

But even with an opamp with huge open loop gains and supposedly huge
Rin,
the actual OLG and OL BW ( open loop bandwidth ) can be stated as easily
as the BASIC OL BW of a tube amp.
The calculations should always include a drawn model of the amp with
whatever
BASIC resistances/impedances which affect the aplication of NFB.



>
> > However, to include all possible phase shift peculiarities of the open
> > loop
> > character of an amp and the equivalent networks in the amp which produce
> > them
> > and their interaction when FB is used takes rather a lot of work.
> >
> > NFB theory and application has already covered in many old books, and
> > many should be found then read,
> > and the messages in each will overlap each other books's shortcomings,
> > and you end up wize while you
> > remember it all, then dumb again when you forget it all.
> > Unless of course all you do all day everyday is design and stabilise new
> > and old amplifiers.
> > I probably do enough to keep me wize.
> >
> > I have never seen an online calculator for NFB, where one dials in the
> > details of the open loop gain and all its phase shift rates and bothers,
> > and then
> > ask for 20dB of NFB, and click "calculate", and have the program come up
> > with the FB network and including all the phase tweaking networks needed
> > for
> > unconditional stability into any possible type of reactive loading, R
> > load, or no load at all.
> > Such a program could possibly be a boon for the dumbos to whom feedback
> > is a terrible mystery, and always will be,
> > and hence hated fiercely, and avoided.
> > But with a programmed or synthesized solution,
> > one must ensure it is still a viable solution which works in practice.
> > Since garbage in = garbage out with simulation programs, expect many
> > simulated solutions using tubes and OPTs to still be good oscillators
> > when nobody expected it.
> > That's because its difficult for anyone to correctly define all the open
> > loop
> > gain and phase shift character. Too fucking hard.
> > Just bulid it, and learn to stabilise it by empirical methods of network
> > applications and trial and error
> > and by observation with a CRO. This is a far quicker way than all the
> > calculations in the world sitting
> > down at a table when you should be in the workshop achieving something
> > real.
> >
> > Models of the single tube amplifier stage should include an extremely
> > low voltage generator producing output of µ x Vg
> > with series resistance between the gene output and the anode terminal
> > should be explained
> > as equivalent models of the triode or pentode ot any other tube.
> > Newbies NEED to know the very boring basics before thay can have any
> > chance of understanding.
> > Most don't have a clue what a voltage generator is, or what the dynamic
> > anode resistance is at all!!!
> >
>
> An interesting point. Do you think NFB101 should start with a statement
> of what knowledge is assumed along with pointers to references for those
> who don't have it?

Exactly.

NFB is a very tricky and foreign concept to many minds.

Its no use taling about volts and amps to those who don't know what they
are
and how they relate to resistance in the form of Ohm's Laws.

Newbie confusions are 90% due to very poor mental picturing of the very
basic issues.

Instead of making the effort to leaqrn, the silly newbie short cuts to
human commonsense, and such simplistic thinking doesn't work with
electronics very well.

First come the concepts, then the math.

NFB acts in an amp to force it to amplify the difference between an
input signal and an output signal. Distortion at the output
is amplified in such a way to oppose its own production, and people
must see how to easily calculate from what they observe in a given amp
after taking voltage measurements
after calculating gain.

Then in an amp with NFB and OLG of 100, and ß = 0.1, and with 0.1% of
THD at 10Vrms output level,
there will be THD at the output = 10 x 0.1/100 Vrms = 0.01Vrms.

If ß = 0.1, then 0.1 x 0.001Vrms of distortion appears at the negative
feedback terminal of the amp
which is the second of the pair of input terminals able to be found on
every amplifier.

So, with OLG = 100, it only takes 10V / 100 of input sugnal between the
two input terminals for
output of 10V, so the open loop Vin input voltage = 0.1Vrms.

The 0.001Vrms of distortion is also amplified 100 times by the OLG gain
and so hence appears as 0.1V Dn at the output.
But how can this be when we measured Dn = 0.01Vrms???????

It is because the open loop character of the amp tries to make 0.11Vrms
of Dn,
but the amplified distortion fed back of 0.1Vrms subtracts from the
0.11Vrms of Dn to leave the measured
residue of 0.01Vrms.

The action of distortion reduction occurs simultaneously with
distoprtion creation
by the amp without any NFB.

The open loop BW and thus phase of the signals determines how effective
this THD/IMD reduction by NFB actually is.

Even without the official feedback/gain/bandwidth formulas, the above
explains the essence of NFB
application in all cases of simple series voltage NFB, and even in a
cathode follower,
which the newbie must come to understand as the most basic of all
applications of series voltage NFB.

They have to know why the words "series" and "voltage" are used.

One reason is that the type of *LOOP* or global NFB used most is
neither "shunt" nor "current".

Electronics demands we have to consider more than one thing acting
simultaneously, and we have to make fine distinctions.




>
> > I welcome you to borrow whatever you need from
> >
> > http :// www .turneraudio,com .au/tube-operation1.html
> >
> > and
> >
> > http :// www .turneraudio,com .au/tube-operation3.html
> >
> > I don't have all the possible various feedback applications mentiuoned
> > at my site.
> >
>
> Thanks for the permission to use ingfo from your site.

Over the last 2.5 years since I included the NFB descriptions and basic
tube workings
at my website,
nobody has challenged me on the legitimacy.

Let me know if you think I have made any mistakes.

Patrick Turner.

t is
>
> Cheers
>
> Ian

Re: NFB 101 Part Deux

Patrick Turner wrote:
>>> Using a triangle pointing to the right to represent an amp with two
>>> inputs on the
>>> left vertical side and one output at the right point is the text book
>>> way to represent an amp
>>> so people do not have to keep in mind all the complex inner amp topology
>>> which distracts them from the basic idea.
>>> The same model can then be used for a tube amp or an opamp.
>>>
>> I purposely avoided that because its common usage is to represent an
>> amplifier with infinite gain, zero output resistance and infinite input
>> impedance and as we both know, tubes only meet one of those criteria. I
>> was trying to emphasize that tubes fall far short of this ideal which is
>> why many of the op-amp simplifications just don't apply to tubes.
>
> But even with an opamp with huge open loop gains and supposedly huge
> Rin,
> the actual OLG and OL BW ( open loop bandwidth ) can be stated as easily
> as the BASIC OL BW of a tube amp.
> The calculations should always include a drawn model of the amp with
> whatever
> BASIC resistances/impedances which affect the aplication of NFB.
>

I agree the triangle is in common usage. However, the diagram I used
does follow the RDH one and to me rather neatly shows exactly what is
meant by series applied NFB which I find hard to see in the triangle
version but that's just me. Perhaps when I get to multi-stage tube
circuits the triangle will be more appropriate, much as illustrated by
your owm web site.

snip

>>> Newbies NEED to know the very boring basics before thay can have any
>>> chance of understanding.
>>> Most don't have a clue what a voltage generator is, or what the dynamic
>>> anode resistance is at all!!!
>>>
>> An interesting point. Do you think NFB101 should start with a statement
>> of what knowledge is assumed along with pointers to references for those
>> who don't have it?
>
> Exactly.
>
> NFB is a very tricky and foreign concept to many minds.
>
> Its no use taling about volts and amps to those who don't know what they
> are
> and how they relate to resistance in the form of Ohm's Laws.
>
> Newbie confusions are 90% due to very poor mental picturing of the very
> basic issues.
>
> Instead of making the effort to leaqrn, the silly newbie short cuts to
> human commonsense, and such simplistic thinking doesn't work with
> electronics very well.
>
> First come the concepts, then the math.
>

OK, I'll include a 'you must be familiar with' bit at the start along
with pointers to books & web sites with the basics. I'll include a link
to your site if that's OK.

>
> Over the last 2.5 years since I included the NFB descriptions and basic
> tube workings
> at my website,
> nobody has challenged me on the legitimacy.
>
> Let me know if you think I have made any mistakes.
>

The power stuff certainly saves me a lot of work especially as tube
power amps are a complete unknown to me.

Thanks for the input.

P.S I have just been through the pdf and changed all the Bs to betas and
ms to mus (can't work out how to get special characters in my mail app).

Cheers

Ian

Re: NFB 101 Part Deux



Ian Thompson-Bell wrote:
>
> Patrick Turner wrote:
> >>> Using a triangle pointing to the right to represent an amp with two
> >>> inputs on the
> >>> left vertical side and one output at the right point is the text book
> >>> way to represent an amp
> >>> so people do not have to keep in mind all the complex inner amp topology
> >>> which distracts them from the basic idea.
> >>> The same model can then be used for a tube amp or an opamp.
> >>>
> >> I purposely avoided that because its common usage is to represent an
> >> amplifier with infinite gain, zero output resistance and infinite input
> >> impedance and as we both know, tubes only meet one of those criteria. I
> >> was trying to emphasize that tubes fall far short of this ideal which is
> >> why many of the op-amp simplifications just don't apply to tubes.
> >
> > But even with an opamp with huge open loop gains and supposedly huge
> > Rin,
> > the actual OLG and OL BW ( open loop bandwidth ) can be stated as easily
> > as the BASIC OL BW of a tube amp.
> > The calculations should always include a drawn model of the amp with
> > whatever
> > BASIC resistances/impedances which affect the aplication of NFB.
> >
>
> I agree the triangle is in common usage. However, the diagram I used
> does follow the RDH one and to me rather neatly shows exactly what is
> meant by series applied NFB which I find hard to see in the triangle
> version but that's just me. Perhaps when I get to multi-stage tube
> circuits the triangle will be more appropriate, much as illustrated by
> your owm web site.
>
> snip
>
> >>> Newbies NEED to know the very boring basics before thay can have any
> >>> chance of understanding.
> >>> Most don't have a clue what a voltage generator is, or what the dynamic
> >>> anode resistance is at all!!!
> >>>
> >> An interesting point. Do you think NFB101 should start with a statement
> >> of what knowledge is assumed along with pointers to references for those
> >> who don't have it?
> >
> > Exactly.
> >
> > NFB is a very tricky and foreign concept to many minds.
> >
> > Its no use taling about volts and amps to those who don't know what they
> > are
> > and how they relate to resistance in the form of Ohm's Laws.
> >
> > Newbie confusions are 90% due to very poor mental picturing of the very
> > basic issues.
> >
> > Instead of making the effort to leaqrn, the silly newbie short cuts to
> > human commonsense, and such simplistic thinking doesn't work with
> > electronics very well.
> >
> > First come the concepts, then the math.
> >
>
> OK, I'll include a 'you must be familiar with' bit at the start along
> with pointers to books & web sites with the basics. I'll include a link
> to your site if that's OK.
>
> >
> > Over the last 2.5 years since I included the NFB descriptions and basic
> > tube workings
> > at my website,
> > nobody has challenged me on the legitimacy.
> >
> > Let me know if you think I have made any mistakes.
> >
>
> The power stuff certainly saves me a lot of work especially as tube
> power amps are a complete unknown to me.
>
> Thanks for the input.
>
> P.S I have just been through the pdf and changed all the Bs to betas and
> ms to mus (can't work out how to get special characters in my mail app).

When doing plain text emails to the group or anyone else,
I depress Alt while typing 2 3 0 for µ or mu when I release the Alt key.
Alt and 2 2 5 gives ß, or beta.

I used to use u and B for µ and ß and got pulled up about it.
B is reserved for magnetic field strength, not the fraction fed back.
Context makes it obvious though what id meant, but adherance to old
conventions
makes it easier when ppl read something elsewhere and they don't have to
learn another
language, or drive on the other side of the road.

But I don't know what other typing tricks give what.

Anyone like to post the list of possible Alt plus signs and figures?????


Patrick Turner.


>
> Cheers
>
> Ian

Re: NFB 101 Part Deux

Patrick Turner wrote:
>
> When doing plain text emails to the group or anyone else,
> I depress Alt while typing 2 3 0 for µ or mu when I release the Alt key.
> Alt and 2 2 5 gives ß, or beta.
>

Unfortunately that does not seem to work for me. Anyone know how to do
it in Thunderbird?

Cheers

Ian

Re: NFB 101 Part Deux



Ian Thompson-Bell wrote:

> Patrick Turner wrote:
> >
> > When doing plain text emails to the group or anyone else,
> > I depress Alt while typing 2 3 0 for µ or mu when I release the Alt key.
> > Alt and 2 2 5 gives ß, or beta.
> >
>
> Unfortunately that does not seem to work for me. Anyone know how to do
> it in Thunderbird?

It's not related to Thunderbird. It's how to generate 'alternate characters'
generally in Windows but Patrick didn't explain it fully.

Hold down the Alt key *and keep it held down*.

Then press 2, 3 ,0 ON THE NUMERIC KEYPAD.

Then release the Alt key.

Should work on all PCs with Windows.

Graham

µ

Re: NFB 101 Part Deux

Eeyore wrote:
>
> Ian Thompson-Bell wrote:
>
>> Patrick Turner wrote:
>>> When doing plain text emails to the group or anyone else,
>>> I depress Alt while typing 2 3 0 for µ or mu when I release the Alt key.
>>> Alt and 2 2 5 gives ß, or beta.
>>>
>> Unfortunately that does not seem to work for me. Anyone know how to do
>> it in Thunderbird?
>
> It's not related to Thunderbird. It's how to generate 'alternate characters'
> generally in Windows but Patrick didn't explain it fully.
>
> Hold down the Alt key *and keep it held down*.
>
> Then press 2, 3 ,0 ON THE NUMERIC KEYPAD.
>
> Then release the Alt key.
>
> Should work on all PCs with Windows.
>
> Graham
>
> µ
>
>

But I am not using windows, I am using Linux

Cheers

Ian

Re: NFB 101 Part Deux



Ian Thompson-Bell wrote:

> Eeyore wrote:
> > Ian Thompson-Bell wrote:
> >> Patrick Turner wrote:
> >
> >>> When doing plain text emails to the group or anyone else,
> >>> I depress Alt while typing 2 3 0 for µ or mu when I release the Alt key.
> >>> Alt and 2 2 5 gives ß, or beta.
> >>>
> >> Unfortunately that does not seem to work for me. Anyone know how to do
> >> it in Thunderbird?
> >
> > It's not related to Thunderbird. It's how to generate 'alternate characters'
> > generally in Windows but Patrick didn't explain it fully.
> >
> > Hold down the Alt key *and keep it held down*.
> >
> > Then press 2, 3 ,0 ON THE NUMERIC KEYPAD.
> >
> > Then release the Alt key.
> >
> > Should work on all PCs with Windows.
> >
> > Graham
> >
> > µ
>
>
> But I am not using windows, I am using Linux

Then it won't work !

I imagine there may be some equivalent way to do the same.

Graham

Re: NFB 101 Part Deux



Ian Thompson-Bell wrote:
>
> Eeyore wrote:
> >
> > Ian Thompson-Bell wrote:
> >
> >> Patrick Turner wrote:
> >>> When doing plain text emails to the group or anyone else,
> >>> I depress Alt while typing 2 3 0 for µ or mu when I release the Alt key.
> >>> Alt and 2 2 5 gives ß, or beta.
> >>>
> >> Unfortunately that does not seem to work for me. Anyone know how to do
> >> it in Thunderbird?
> >
> > It's not related to Thunderbird. It's how to generate 'alternate characters'
> > generally in Windows but Patrick didn't explain it fully.
> >
> > Hold down the Alt key *and keep it held down*.
> >
> > Then press 2, 3 ,0 ON THE NUMERIC KEYPAD.
> >
> > Then release the Alt key.
> >
> > Should work on all PCs with Windows.
> >
> > Graham
> >
> > µ
> >
> >
>
> But I am not using windows, I am using Linux
>
> Cheers

There must be a way to type greek letters used in science.

Patrick Turner.
>
> Ian

Re: NFB 101 Part Deux

Patrick Turner wrote:
>
> Ian Thompson-Bell wrote:
>> Eeyore wrote:
>>> Ian Thompson-Bell wrote:
>>>
>>>> Patrick Turner wrote:
>>>>> When doing plain text emails to the group or anyone else,
>>>>> I depress Alt while typing 2 3 0 for µ or mu when I release the Alt key.
>>>>> Alt and 2 2 5 gives ß, or beta.
>>>>>
>>>> Unfortunately that does not seem to work for me. Anyone know how to do
>>>> it in Thunderbird?
>>> It's not related to Thunderbird. It's how to generate 'alternate characters'
>>> generally in Windows but Patrick didn't explain it fully.
>>>
>>> Hold down the Alt key *and keep it held down*.
>>>
>>> Then press 2, 3 ,0 ON THE NUMERIC KEYPAD.
>>>
>>> Then release the Alt key.
>>>
>>> Should work on all PCs with Windows.
>>>
>>> Graham
>>>
>>> µ
>>>
>>>
>> But I am not using windows, I am using Linux
>>
>> Cheers
>
> There must be a way to type greek letters used in science.
>

Easy enough in a word processor but not is seems in the mail client.

Cheers

Ian