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|18th May 2012, 07:36 AM||#1|
Join Date: Feb 2012
The Aikido Comedy: Straight Talk
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:
(1) Many 'Aikido' designs and circuits certainly function reasonably wellPerhaps if we begin with this fair overview of the situation,
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.
|18th May 2012, 08:09 AM||#2|
Join Date: Feb 2012
Here was my original thesis, minus the Ace Ventura reference:
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.
Last edited by nazaroo; 18th May 2012 at 08:13 AM.
|18th May 2012, 08:35 AM||#4|
Join Date: Feb 2012
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.
Last edited by nazaroo; 18th May 2012 at 08:41 AM.
|18th May 2012, 09:07 AM||#5|
Join Date: Feb 2012
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?
(1) Is John giving a real analysis, or more of an 'analogy'?I think the answer in 2004, by Mr. Broskie's own admission,
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,We will examine these assumptions / premises and axioms one by one.
Last edited by nazaroo; 18th May 2012 at 09:14 AM.
|18th May 2012, 09:39 AM||#6|
Join Date: Feb 2012
Okay, lets start with number 1:
(1) The first stage is treated as a resistor-divider network,
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.
(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.
Last edited by nazaroo; 18th May 2012 at 09:45 AM.
|18th May 2012, 09:40 AM||#7|
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
|18th May 2012, 09:53 AM||#8|
|18th May 2012, 09:57 AM||#9|
and I actually thought computer software was his real main thing, and the tube amp stuff just a hobby, tho a growing one lately
|18th May 2012, 09:57 AM||#10|
Join Date: Feb 2012
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:
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.
Last edited by nazaroo; 18th May 2012 at 10:00 AM.
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