The Aikido Comedy: Straight Talk

[nazaroo]

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 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,
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

[nazaroo]

Here was my original thesis, minus the Ace Ventura reference:

Originally Posted by Nazaroo

The comedy is in this:

It effectively cancels power supply noise when there is no signal.

When there is an actual signal, it no longer cancels power supply noise!

Its the perfect comedy, because the louder your music, the more it drowns out the power supply noise.

Effectively, you have what is called 'masking',
and it works very well.

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.

[tinitus]

nazaroo, you certainly have a way with words, I give you that

[nazaroo]

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:

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. "

Certainly John's description is virtually enclosed, and self-explanatory.
Nor has he felt it necessary to edit his post in nearly 8 years.

[nazaroo]

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'?

(2) Is John knowingly oversimplifying the explanation?

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,
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.

[nazaroo]

Okay, lets start with number 1:

(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.

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.

(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.

[tinitus]

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

[tinitus]

Originally Posted by nazaroo

Nor has he felt it necessary to edit his post in nearly 8 years.

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

[tinitus]

Originally Posted by nazaroo

The first thing we must ask, is,
What really is happening here?[INDENT] [B](1) Is John giving a real analysis, or more of an 'analogy'?

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

[nazaroo]

Originally Posted by tinitus

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:

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. "

This was the final page of the 2004 Introductory article.

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.