The reasonable reception of my idea of a critique of the Aikido design concept(s)
has encouraged me to start a new thread discussing it.
I wish of course to start the discussion on a good note,
with a balance of fair, generous allowance to all interested parties,
and an avoidance of any personal attacks on all sides.
To me this should be a sincere information exchange and investigation,
as well as a research project that can advance everyone's understanding of tube circuits,
for the obvious purpose of improving and selecting designs, methods, and strategies.
So before I begin diving in and shredding various design proposals,
I will happily acknowledge some important points:
level headed analysis will prevail in all the exchanges and discussions that follow.
Nothing would be more enjoyable to me than to have Mr. Broskie himself join us in the discussion.
Sincerely,
Nazaroo
has encouraged me to start a new thread discussing it.
I wish of course to start the discussion on a good note,
with a balance of fair, generous allowance to all interested parties,
and an avoidance of any personal attacks on all sides.
To me this should be a sincere information exchange and investigation,
as well as a research project that can advance everyone's understanding of tube circuits,
for the obvious purpose of improving and selecting designs, methods, and strategies.
So before I begin diving in and shredding various design proposals,
I will happily acknowledge some important points:
(1) Many 'Aikido' designs and circuits certainly function reasonably well
and perhaps better than less carefully crafted plans. My purpose here is not
to gainsay or contradict positive experiences of others who have built some
of these circuits, but to advance knowledge and improve all design strategems.
(2) John Broskie has certainly done all DIYers and students of tube
circuits many a service in his public offerings on the internet,
for over a decade. Anyone can benefit from reading his many online
articles and comments. My purpose here is not to in any way attack
the integrity, honesty, or talent of this generous contributor to tube lore.
So it is only in the light of these two statements of fact above,
that anything that follows should be interpreted.
Perhaps if we begin with this fair overview of the situation,and perhaps better than less carefully crafted plans. My purpose here is not
to gainsay or contradict positive experiences of others who have built some
of these circuits, but to advance knowledge and improve all design strategems.
(2) John Broskie has certainly done all DIYers and students of tube
circuits many a service in his public offerings on the internet,
for over a decade. Anyone can benefit from reading his many online
articles and comments. My purpose here is not to in any way attack
the integrity, honesty, or talent of this generous contributor to tube lore.
So it is only in the light of these two statements of fact above,
that anything that follows should be interpreted.
level headed analysis will prevail in all the exchanges and discussions that follow.
Nothing would be more enjoyable to me than to have Mr. Broskie himself join us in the discussion.
Sincerely,
Nazaroo
Here was my original thesis, minus the Ace Ventura reference:
In this quotation, I am referring to a specific,
and I believe integral element in the 'Aikido' design,
which John Broskie has applied across several different preamp/amp circuits,
made for a variety of purposes.
This is a technique whereby John cancels out
power-supply (PS) hum and noise entering a prior stage,
by applying an appropriately scaled copy of the noise signal
(inverted) to an amplifying device in the next stage,
mixing it with the original signal (containing the noise),
and thereby cancelling it out.
The (forward) feedback for this correctional system is near instantaneous,
and providing the DC current/voltage of the sample-point stay as described, (i.e., the prior stage output port),
and the noise/hum signals remain balanced (initial + copy),
cancellation occurs and noise-hum near-disappears.
That is the basic theory.
For it to hold, several things are required, and some are not.
(1) What is NOT required, is that the noise/hum be constant in amplitude or predicable in content.
(2) What IS required, is that the same noise/hum signal be present in both sources
(original and copy) on an instantaneous basis.
(3) What IS required, is that the same Amplitude (adjusted for amplification factors in each stage)
be present, for signals to cancel.
(4) What IS required, is that the same Phase for frequencies of interest is maintained
through the system, so that exact copies of the random noise-wave are reproduced, added and cancelled.
(5) What IS required, is that both (all) stages have the same 'Amplification Curve'
or Compression effects, so that signals remain balanced at all volumes.
That is the opener.
It remains for us to take a few example circuits,
and also trace a bit of the history of John Broskie's ideas,
as this technique has evolved.
Nazaroo said:
In this quotation, I am referring to a specific,
and I believe integral element in the 'Aikido' design,
which John Broskie has applied across several different preamp/amp circuits,
made for a variety of purposes.
This is a technique whereby John cancels out
power-supply (PS) hum and noise entering a prior stage,
by applying an appropriately scaled copy of the noise signal
(inverted) to an amplifying device in the next stage,
mixing it with the original signal (containing the noise),
and thereby cancelling it out.
The (forward) feedback for this correctional system is near instantaneous,
and providing the DC current/voltage of the sample-point stay as described, (i.e., the prior stage output port),
and the noise/hum signals remain balanced (initial + copy),
cancellation occurs and noise-hum near-disappears.
That is the basic theory.
For it to hold, several things are required, and some are not.
(1) What is NOT required, is that the noise/hum be constant in amplitude or predicable in content.
(2) What IS required, is that the same noise/hum signal be present in both sources
(original and copy) on an instantaneous basis.
(3) What IS required, is that the same Amplitude (adjusted for amplification factors in each stage)
be present, for signals to cancel.
(4) What IS required, is that the same Phase for frequencies of interest is maintained
through the system, so that exact copies of the random noise-wave are reproduced, added and cancelled.
(5) What IS required, is that both (all) stages have the same 'Amplification Curve'
or Compression effects, so that signals remain balanced at all volumes.
That is the opener.
It remains for us to take a few example circuits,
and also trace a bit of the history of John Broskie's ideas,
as this technique has evolved.
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To take John Broskie's original 2004 post in hand,
where the "Aikido Amplifier" name was coined,
we can see John's own understanding of how the circuit operates.
We will only quote for review what is necessary for understanding the concepts:
Nor has he felt it necessary to edit his post in nearly 8 years.
where the "Aikido Amplifier" name was coined,
we can see John's own understanding of how the circuit operates.
We will only quote for review what is necessary for understanding the concepts:
Certainly John's description is virtually enclosed, and self-explanatory.New Tube Circuit: The Aikido Amplifier
"...this amplifier sidesteps power supply noise by incorporating the noise into its normal operation. As a result, in terms of distortion and output impedance and PSRR, the following circuit works at least a magnitude better than the equivalent SRPP or grounded-cathode amplifier. The improved PSRR advantage is important, for it greatly unburdens the power-supply design and it helps prevent the signal from recirculating through the power supply."
...
How it works
This circuit eliminates power-supply noise from the output, by injecting the same amount of PS noise at the top and bottom of the two-tube cathode follower circuit. The way it works is that the input stage (the first two triodes) define a voltage divider of 50%, so that 50% of the PS noise is presented to the CF's grid; at the same time the 100k resistors also define a voltage divider of 50%, so the bottom triode's grid also sees 50% of the PS noise. Since both of these signals are equal in amplitude and phase, they cancel each other out, as each triodes sees an identical increase in plate current (imagine two equally strong men in a tug of war contest).
If the output connection is taken from the the cathode follower's cathode, then the balance will be broken. The same holds true if the cathode follower's cathode resistor is removed. (Besides, this resistor actually makes for a better sounding cathode follower, as it linearizes the cathode follower at the expense of a higher output impedance.)
Note also the absence of any cathode resistor bypass capacitors; these caps are very much in the signal path and very few do not damage the sound, unless high quality capacitors are used. If a cathode resistor bypass capacitor is used on the input stage's bottom triode, then the two resistor voltage divider ratio must be changed from 50% to match the new AC noise divider ratio imposed by the input stage. In other words, much less PS noise noise will need to be injected into the cathode follower's bottom triode's grid. "
Nor has he felt it necessary to edit his post in nearly 8 years.
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John's banter is so reasonable and pleasant,
its hard to imagine there could be any fundamental flaw
in his reasoning process.
But we are compelled to look closer at analysis.
The first thing we must ask, is,
What really is happening here?
is that his understanding of this circuit was naive,
but intuitively 'lucky'.
Also, as the story unfolds, John reveals that he himself was surprised,
at the glowing reports given of the performance of a few of his designs.
Thus his interest and explanation may have been in part ad hoc,
a quick attempt to explain for himself and others why the circuits sounded so good.
His personal mathematical expertise and ability was perhaps
not fully developed at this time, as he confesses in several posts,
that he is not up to the math, and indeed enlists a friend
to assist him piece together several equations to describe
a number of his more exotic circuits.
In any case, John Broskie must be commended for taking the
brave and daring step of publishing his circuits and openly
sharing this thoughts, leaving him open to criticism.
If we move on toward John's own explanation,
we see several assumptions, reductions, simplifications present:
its hard to imagine there could be any fundamental flaw
in his reasoning process.
But we are compelled to look closer at analysis.
The first thing we must ask, is,
What really is happening here?
(1) Is John giving a real analysis, or more of an 'analogy'?
(2) Is John knowingly oversimplifying the explanation?
I think the answer in 2004, by Mr. Broskie's own admission, (2) Is John knowingly oversimplifying the explanation?
is that his understanding of this circuit was naive,
but intuitively 'lucky'.
Also, as the story unfolds, John reveals that he himself was surprised,
at the glowing reports given of the performance of a few of his designs.
Thus his interest and explanation may have been in part ad hoc,
a quick attempt to explain for himself and others why the circuits sounded so good.
His personal mathematical expertise and ability was perhaps
not fully developed at this time, as he confesses in several posts,
that he is not up to the math, and indeed enlists a friend
to assist him piece together several equations to describe
a number of his more exotic circuits.
In any case, John Broskie must be commended for taking the
brave and daring step of publishing his circuits and openly
sharing this thoughts, leaving him open to criticism.
If we move on toward John's own explanation,
we see several assumptions, reductions, simplifications present:
(1) The first stage is treated as a resistor-divider network,
as an explanation of how the Power Supply hum/noise enters,
and is found in the 1st stage output.
(2) The noise is assumed to come from the B+ power-supply.
For intents and purposes, John does not distinguish various sources of noise
in the first stage, but assumes it can be treated / removed simply.
(3) The hum/noise creeping in from both stages is assumed to be the same
as a copy of the noise that can tapped directly from the B+ supply.
(4) The amplitude of the noise signal is assumed to be semi-constant or linear
(or at least proportional), and so a complimentary copy can be bled off
from a real resistor-divider network across the B+ and fed to the following stage.
We will examine these assumptions / premises and axioms one by one.as an explanation of how the Power Supply hum/noise enters,
and is found in the 1st stage output.
(2) The noise is assumed to come from the B+ power-supply.
For intents and purposes, John does not distinguish various sources of noise
in the first stage, but assumes it can be treated / removed simply.
(3) The hum/noise creeping in from both stages is assumed to be the same
as a copy of the noise that can tapped directly from the B+ supply.
(4) The amplitude of the noise signal is assumed to be semi-constant or linear
(or at least proportional), and so a complimentary copy can be bled off
from a real resistor-divider network across the B+ and fed to the following stage.
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Okay, lets start with number 1:
At first sight, John's idea seems quite reasonable:
The tube and its Anode load are in series across the power supply,
and each is a resistance.
As a result, part of the B+ noise (hum, hiss) is dissipated
in the load, and part of this noise-signal appears across the tube.
If we reference ground, then it is the portion appearing across the tube
that we find on the output terminal and in the signal path.
The trouble is, at least some, perhaps a significant amount,
of PS noise is coming in from other directions:
(a) Heater-circuit to cathode bleeding. This source comes from another (often unrectified 60 cycle) output in a multi-part supply. Although it has a phase relation to the main transformer, there is no way of predicting its phase in relation to the 120 cycle full wave B+ supply. What is worse, two more factors come into play:
(b) Electromagnetic field hum pickup. This source again will not vary with input-tube anode current signal swings, except in as much as some of it may be caused by them directly. Most likely the bulk of such noise will be being injected into the 1st stage via the grid leads, independently of the amplitude of the input signal, and this constant source will be amplified by gain of the tube.
(c) Random Noise Produced in Various Components. This noise will be individual and unique to each circuit component, and cannot be accurately tracked or canceled by a similar type of 'white-noise' or 'pink-noise' generated in the B+ supply.
Even if John's method of injecting PS noise into the following stage was effective, it would only work for the hum component of the noise, and it would only work for a constant amplitude hum-component of the total hum in the first stage. Fluctuating hum components in the first stage cannot be mimicked by a resistor-divider network across the B+, unless the other fluctuating components are also being injected backwards into the Power Supply circuit in significant quantities!
This would be only the first caveat to the Voltage-Divider treatment of the first stage.
Noise from other sources in the 1st stage cannot be
tracked, copied or cancelled by the proposed method.
(1) The first stage is treated as a resistor-divider network,
as an explanation of how the Power Supply hum/noise enters,
and is found in the 1st stage output.
as an explanation of how the Power Supply hum/noise enters,
and is found in the 1st stage output.
At first sight, John's idea seems quite reasonable:
The tube and its Anode load are in series across the power supply,
and each is a resistance.
As a result, part of the B+ noise (hum, hiss) is dissipated
in the load, and part of this noise-signal appears across the tube.
If we reference ground, then it is the portion appearing across the tube
that we find on the output terminal and in the signal path.
The trouble is, at least some, perhaps a significant amount,
of PS noise is coming in from other directions:
(a) Heater-circuit to cathode bleeding. This source comes from another (often unrectified 60 cycle) output in a multi-part supply. Although it has a phase relation to the main transformer, there is no way of predicting its phase in relation to the 120 cycle full wave B+ supply. What is worse, two more factors come into play:
i) Its amplitude will go up and down with cathode current interactions, not in sync with the voltage dividing effect of the tube/load at the output.
ii) Its amplitude is likely to remain almost constant in comparison to B+ hum coming in through the Anode current.
iii) Its amplitude could be in any arbitrary proportion to the B+ sourced hum/noise.
iv) The "noise" component of the heater and B+ will have no correlation at all.
ii) Its amplitude is likely to remain almost constant in comparison to B+ hum coming in through the Anode current.
iii) Its amplitude could be in any arbitrary proportion to the B+ sourced hum/noise.
iv) The "noise" component of the heater and B+ will have no correlation at all.
(b) Electromagnetic field hum pickup. This source again will not vary with input-tube anode current signal swings, except in as much as some of it may be caused by them directly. Most likely the bulk of such noise will be being injected into the 1st stage via the grid leads, independently of the amplitude of the input signal, and this constant source will be amplified by gain of the tube.
(c) Random Noise Produced in Various Components. This noise will be individual and unique to each circuit component, and cannot be accurately tracked or canceled by a similar type of 'white-noise' or 'pink-noise' generated in the B+ supply.
Even if John's method of injecting PS noise into the following stage was effective, it would only work for the hum component of the noise, and it would only work for a constant amplitude hum-component of the total hum in the first stage. Fluctuating hum components in the first stage cannot be mimicked by a resistor-divider network across the B+, unless the other fluctuating components are also being injected backwards into the Power Supply circuit in significant quantities!
This would be only the first caveat to the Voltage-Divider treatment of the first stage.
Noise from other sources in the 1st stage cannot be
tracked, copied or cancelled by the proposed method.
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hmm, the schematic I have got from manual looks slightly different, with a few more resistors 
can't what difference it makes
but I guess the exstra resistors have been added for a reason
well, I can say they are 1Mohm, two coupling to ground, and other two coupling to B+
ehh, now I see yet a few other changes/differences
can't what difference it makes
but I guess the exstra resistors have been added for a reason
well, I can say they are 1Mohm, two coupling to ground, and other two coupling to B+
ehh, now I see yet a few other changes/differences
maybe because noone reads it
Im not even sure I could find that one
actually I seached a lot on aikido
and didn't find much other than chit chat on other forums
ehh, I thought he was using his computer software to do this
and I actually thought computer software was his real main thing, and the tube amp stuff just a hobby, tho a growing one lately
hmm, the schematic I have got from manual looks slightly different, with a few more resistors
can't what difference it makes
but I guess the exstra resistors have been added for a reason
well, I can say they are 1Mohm, two coupling to ground, and other two coupling to B+
oh, and there's a cap less(removed)
Yes, needless to say, the "Aikido Amplifier" has evolved through
several modifications over the years, to further correct for noise and improve performance.
And also, John Broskie has also applied the "Aikido" branding
to several circuits/amps that have quite diverse topologies
and additional devices to improve sound, such as Constant Current Sources
in the Anode loads or cathode circuits of various incarnations, including transistors.
This simply reflects John's own growth and learning-curves
in his understanding of tube circuits and noise control.
We will be discussing some of these 'mods' and John's comments on them later.
Right from the start however, many of the items you refer to
were added back in 2004, not for the purpose of 'Aikido PSRR',
but for safety reasons, likely as a result of some unfortunate accidents:
This was the final page of the 2004 Introductory article.
Safer version of the Aikido Amplifier
"In the schematic above, safety resistors have been added. The two 1M resistors save the second stage should the input tube be yanked from its socket or its heater opened. The two added 100k resistors save the power amplifier should the cathode follower tube be yanked from its socket, as the same DC voltage will be presented to the coupling capacitor. "
Many of John's modifications were possibly tried much earlier,
and his own personal journey is not available in detail.
However, most of these mods do not at all take away
John's claim or his own perception of the essence of
the "Aikido Amplifier".
For many years he has maintained that the unique and universal feature,
(of "Aikido") has been his own special noise reduction technique,
as described above.
Lately he has tried to extend the "Aikido" branding to
anything and everything that he has published online,
whether original or not.
Is this an attempt to extend his personal "Aikido Empire"?
Or just an opportune absorption of ideas as his learning curve progresses?
We will bring up this issue again as we examine the history.
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I don't know what all the fuss is about. I thought it was obvious that all Broskie is claiming is that supply rail noise is cancelled; to a first approximation it is. To say that other noise sources are not cancelled is true, but no claim about them has been made. The OP seems to be tilting at windmills.
It depends on what you mean by "real life". Valve audio circuit design is a branch of applied physics (or it ought to be). Note that I said circuit design; determining the requirements for that design takes us well outside physics into psychoacoustics etc. As a branch of physics it should be possible to estimate how a circuit will behave using mathematics.
I suspect the main issue with the Aikido in "real life" is that the effect of an external load has not been considered. This means that the circuit-theoretic model needs to be improved, not discarded.
I suspect the main issue with the Aikido in "real life" is that the effect of an external load has not been considered. This means that the circuit-theoretic model needs to be improved, not discarded.
True dat.
Short answer: No.
Sure, it is important to consider the presence and interaction of the circuit with varying loads on the output.
But the failure here is not in too much isolation from real-world applications,
or over-optimistic modeling of an 'ideal' circuit.
There are several fundamental and catastrophic failures,
in both the model, and in Broskie's understanding of how this and indeed all tube circuits work.
And ultimately, according to known physical principles,
the circuit simply cannot do what is being claimed for it.
I will go back to my initial statement, as a reminder,
which sums up the essential behavior of the circuit,
and why Broskie's method is a failure:
It effectively cancels power supply noise when there is no signal.
When there is an actual signal, it no longer cancels power supply noise!
This has nothing at all to do with loading on the output of any stage,When there is an actual signal, it no longer cancels power supply noise!
or the output loading on the design as a whole.
It has everything to do with the addition of an INPUT signal.
Broskie's method minimizes hum/noise from the power-supply
ONLY when there is no signal.
When a model of operation or explanation is so wrong that
it fails to realistically describe any of the actual circuit behavior,
its time to discard it in favor of sound analysis.
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Agreed.
I have done some research into the Aikido circuit and IMO nazaroo is disputing things that were never claimed to be true.
Also, the assumption that there is no ps noise cancelling when a signal is present is not true AFAIK.
IMO Broskie has an intuitive understanding of how circuits work that is beyond most people, whether he is an expert at doing the math or not.
No, its actually a lot more than this.
This is true as far as it goes, but,
Lets look again at why his circuits actually perform reasonably well:
(1) Mr. Broskie recommends appropriate tubes and other parts for specific functions, these have low-noise features built-in. For instance,
a) He suggests the right tube for the right job, whether its voltage amplification or impedance matching.
b) He recommends the right kind of caps for signal paths, vs. PS smoothing.
c) He suggests low-noise resistors for low-signal applications.
(2) Mr. Broskie follows well known and generally well-accepted design procedures. Thus,b) He recommends the right kind of caps for signal paths, vs. PS smoothing.
c) He suggests low-noise resistors for low-signal applications.
a) He eliminates both parts and topologies when they interfere with impedance matching, or add noise or distortion, instead of reducing it, such as bypass caps.
b) He generally follows sensible and well-understood rules for setting idle-current and bias-points to get the best out of tubes for a given function or context.
c) He identifies weaknesses in circuits and procedures, and refines them for better performance.
For all his skill and expertise here, Mr. Broskie should be praised, not least for bothering to explain his procedures in a teaching atmosphere, and in an 'open' environment. b) He generally follows sensible and well-understood rules for setting idle-current and bias-points to get the best out of tubes for a given function or context.
c) He identifies weaknesses in circuits and procedures, and refines them for better performance.
And the application of tried and true methods generally gives the desired results: Better sounding circuits, at least better than off-the-shelf examples.
But these ideas don't originate with Mr. Broskie.
---------------------------------------
However even with the "Aikido Amplifier" topology/design/ethos,
I think John Broskie will himself admit that most of all this
is not original to him, but simply encompass well-known
design procedures already in the public domain.
What is "original" or unique to Broskie's Aikido topology,
is his novel noise-cancelling circuit added usually to the following stage,
in an attempt to remove the B+ ('rail noise') from the signal path,
which was added in the previous stage.
The whole point then, is:
Is this novel idea actually doing what Broskie says it is?
If it doesn't even effectively cancel the 'rail noise',
then your statement that it DOES, "to a first approximation",
is in essence incorrect,
and so is Broskie's circuit.
Well, IMO I'm sticking carefully to things that ARE claimed to be true.
There in fact IS some noise-cancelling,
So there is no 'untrue assumption' on my part.
I'm sticking to scientific facts.
My opening claim is quite different,
and also very relevant to noise-control in tube circuits:
The noise-cancelling effects of Broskie's circuit are inconsistent and unreliable
when a varying signal is being passed by the circuit.
We are not here to promote legends, but do a scientific analysis.
I'm sure Houdini and Evil Kenival were a great stunt-men,
but much of there technique remains proprietary, hypothetical and legendary.
The bottom line is, what is the circuit really doing?
What did Broskie think it was doing or claim it was doing,
is also a necessary part of the investigation, but not the focus.
The 'legend' of Broskie is completely irrelevant.
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Precisely.
The circuit and also previous analysis/claims about it
can be analyzed and both the circuit and a description of how it functions
can be significantly improved.
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The Aikido input stage is the classic voltage mirror configuration. Not a well known circuit by the way in either SS or Vacuum state land. It provides a tracking non-linear active load for the non-linear driver, resulting in linear gain with no real R load attached. Its main point of interest is to provide linear gain (simple 3/2 power tube models, with no actual load), where as a resistor to B+ does not.
It does seem that in order to get signal gain with a real R load attached, it would need unequal dynamic AC resistances to ground and to B+ to provide the load current. So violating the 50% B+ noise divider ratio.
But with no extra load, both tubes have the same plate current and so the same AC plate resistance: Rp = 2u/3G[Vg +Vp/u]^.5 or Rp = 2u/3G[Ip]^.333 So it would seem to provide a 50% B+ noise divider at all signal levels (outside of saturation and with no loading).
A subsequent cathode follower would then seem a good idea to avoid output loading, as the Aikido does indeed use. For a real power output stage, one might want to consider a VT current mirror to get linear current out, with a real load. Also not a well known circuit in VT land.
Don
It does seem that in order to get signal gain with a real R load attached, it would need unequal dynamic AC resistances to ground and to B+ to provide the load current. So violating the 50% B+ noise divider ratio.
But with no extra load, both tubes have the same plate current and so the same AC plate resistance: Rp = 2u/3G[Vg +Vp/u]^.5 or Rp = 2u/3G[Ip]^.333 So it would seem to provide a 50% B+ noise divider at all signal levels (outside of saturation and with no loading).
A subsequent cathode follower would then seem a good idea to avoid output loading, as the Aikido does indeed use. For a real power output stage, one might want to consider a VT current mirror to get linear current out, with a real load. Also not a well known circuit in VT land.
Don
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