The Aikido Comedy (pt 7): Historical Perspective

..moving along...

Another important historical factor in explaining how and why
this circuit became such a darling of amateur DIYers,
was of course the aggressive promotion of it by John Broskie.

Broskie was careful to hedge his promises, leaving pages of friendly anecdotes,
even create something of an artificial "mystery" surrounding the circuit.

The "Aikido" branding is a perfect example of the technique.
With parts, boards, and prepackaged kits, Broskie's sales hype
was near irresistable to vulnerable DIYers who trusted his analysis.

The best barometer of Broskie's own understanding of tube circuits,
besides his repeated admissions and attempts at a kind of innocent neutrality,
was how he handled the Mu-Follower / Mu-Stage question.

Broskie began back in the early 2000's dismissing the Mu-Follower,
because he did not understand real PSRR, or the effectiveness
of the Mu-Follower circuit in virtually eliminating PS noise.

Its a testament, not to his analytical skills, but to his irrational stubbornness,
that he continued to dismiss the Mu-Follower in favour of his pet (adopted) invention,
i.e., PS noise injection as a solution to PS noise until 2006.

However, unlike some of the posters here,
it is also a testament to John Broskie's self-revelation
that the Mu-Follower after all was the best PSRR circuit.
After nearly 6 years, he incorporated it instead of an SRPP
for the first stage of his preamp,
in the 2005-2006 article, "Aikido meets Mu Follower".

That is, finally Broskie quietly (almost silently!) admitted
that the Mu-Follower was the best solution to PSRR
in a small-signal input stage (better than his first choice).

That Broskie had after 2006 abandoned his early unbridled enthusiasm
for the original Aikido circuit
has been clearly noted by DualTriode:

Quote:

Originally Posted by Dual Triode 1. John evolved his view from the 50 50 voltage divider to an adjustable division based on the mu of the buffer triodes. 2. The Aikido Cathode Follower circuit has a formula in the instruction manual based on the mu of the installed triodes. This is only the buffer half. The input section is not part of the ACF circuit. 3. The full-on Aikido circuit instruction manual has a different formula for the selection of the buffer divider values. I assume that the different selection formula has to do with the contribution for the first stage. Odd to my way of thinking is that there is no consideration for tube selection or operation point of the input stage. 4. I agree that there should be an adjustment on test to best null the noise output. 5. Considering items 2 and 3 above some of the "if then" conclusions by nazaroo perhaps could be evolved. 6. John has nothing to do with the input stage. The first place I saw this stage is in the post WWII, this is how we did it texts. It was not then and is not now push pull. The top triode acts as a active resistor that can be replaced with a resistor of value rp + (u + 1)Rk, think of this as the DC condition for the AC condition the functional value of the top triode rp varies equally and in opposite direction to the bottom triode providing “cancellation” of harmonics. My simulations show cancellation of both even and odd harmonics. This needs to be confirmed in the real world. 7. Nazaroo lighten up you are battling the Tar Baby left behind by John,he is laughing. 8. Remember most users use well filtered and regulated PS's with the Aikido DT

I can agree wholeheartedly with DualTriode's observations here.

The Aikido circuit is indeed a 'tar-baby',
as its stubborn defenders have demonstrated,
and it has indeed been significantly modified/abandoned
by Broskie himself, as his updated manual and
own posts on Tubecad show.

In my view, the combination of Broskie's dismissive treatment of the Mu-Follower,
followed by his 6-year refusal to acknowledge its remarkable PSRR features,
along with his shameless self-promotion of his "Aikido" branded line,
show that Broskie is not the "tube-god" many would hype him as.
His analytical skills re: tube circuits have evolved,
but he began in the early 2000's on an amateur level,
and his inability to correctly assess the Mu-Follower
show an incredible density and stubbornness,
not a 'magical' intuitive insight into tube circuits.

Broskie's own opinion of himself is thankfully more modest
than his hysterical defenders.

Quote:

Nazaroo lighten up you are battling the Tar Baby left behind by John, he is laughing.

He certainly is!

It causes me to recall the famous remark by Liberace,
when someone had tried to humiliate him,
by referencing his sexual orientation and effeminate flamboyancy:

"I'm really hurt by it.
I cried, .........all the way to the bank."

 ---------------------------------------------------------------

Originally Posted by SY: 

"You have yet to specify what experiment would be appropriate.
Your only suggestions involved changing circuit conditions and looking around inside the circuit rather than where it counts- input versus output in the unmodified circuit. "
 

One more empty post, no experiments performed, no results posted.
For someone who insists on experiment, you do damn little of it. ...
I would have performed about 30 experiments by now (a night's work),
if I thought experimenting would clarify the circuit operation.

What I don't understand is why a clever and competent experimenter wouldn't just go ahead and construct their own experiments.
I already explained why testing the output is useless for understanding what is going on inside it.

As someone who honestly believes he understands the circuit quite well,
(and it is awfully simple after all),
I just don't feel the need for any experiments.

If I thought there was some remarkable secret,
other than the mistakes in the documented historical analysis,
I suppose I'd think of one, but really there isn't much to discover.

The original Aikido circuit has relatively poor PSRR during signal amplification.
The Mu-Follower circuit has far better, real PSRR at all times,
and it has less stages.

End of story.

The Aikido Comedy (pt 6): Thinking/Testing Failures

Here's my suggestion if you want to test my point:

First leave the circuit as is, but:

(1) lower the B+ for safety reasons, then

(2) set the 1st tube idling with plate at half the B+ (balancing the load resistance)

(3) inject a 120 Hz exaggerated PS hum signal, say 10 volts,

(4) measure the voltage of this PS hum signal at the plate
(this will give an idea of the AC impedance of the tube as viewed by the PS,
if it differs from that of a simple resistor (it won't significantly differ, but go ahead).

You should easily be able to pull this up on your scope.

(5) Now add a 6-10 Hz input signal on the grid.

My prediction is that you will see the PS hum signal being AM modulated by the input signal:



This is enough to test the first assertion,
namely that PS noise is modulated by the input signal.

What happens when you raise the frequency of the input signal above the frequency of the 'carrier' (PS 120 Hz)?
Essentially the "Ring Modulator" sound effect.
Its non-musical and also an unwanted intrusion into the input signal (the music).

Although the 'real life' situation involves much smaller voltages (signal and noise), the type of artifacts produced are the same.


If you have the equipment, display an FFT in the frequency domain of this output.

Of course one is free to calculate what you think is PSRR any way you like.

That is precisely how absurd claims about impossibly naive techniques are perpetuated. 

Recall again Broskie's own explanation:

Quote:

... 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.

One source of PS noise is coming from the 1st stage,
the other from his added resistor-divider.

The top tube in the 2nd stage is fed the PS noise from the 1st stage (along with the signal).

The bottom tube in the 2nd stage is fed the independent copy.

The bottom tube however is not a cathode-follower:
Its signal is inverted.
The two triodes in the 2nd stage are equally matched,
(same cathode resistors, same DC current, same gain),
so the two noise signals are supposed to cancel.

Quote:

The way it works is that the input stage (the first two triodes) defines 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 triode sees an identical increase in plate current (imagine two equally strong men in a tug of war contest).

Broskie could have explained the opposing tube configurations better (see my note above),
but the point ends the same: opposite signals (phases) cancel.

Note his perception of the operation of the 1st stage however.
Clearly Broskie himself perceives the SRPP as a simple voltage divider in regard to the AC noise.
He is concerned to avoid bypass caps, for just this reason,
because they would imbalance the AC resistance,
"add distortion", and complicate the noise-biasing.

CONTRA DF96's assertion that
"Nazaroo doesn't know the difference between static and dynamic resistance",
we find that it is Broskie who treats the SRPP as a simple DC circuit,
even eliminating capacitors to "make it so".



------- SIDEBAR ---- Flashback to 2002 ---

The above is actually an SRPP stage, one Broskie(?) has analyzed before,
in Tube Cad Journal (2002).


There he describes it as "controversial", because there were
several varied analyses of this circuit available.
Part of the reason that controversy brewed,
was because Broskie himself was so unfamiliar with Mu-Stages,
that he confused the two, and blurred their distinction.
In a very convoluted series of manipulations,
he ends up with Alan Kimmel's Mu Stage from 1993,
but he deliberately fails to acknowledge this,
and to cover his tracks,
he misnames the circuit an "SRPP Amplifier with an Internal Coupling Cap"
and he tries to re-name the circuit an "SRSE",
and even tries to describe it as a kind of Loftin-White circuit.

After stirring up a lot of fuss and muddying the waters,
in regard to the operation of both the SRPP and the MU-stage,
leaving the reader with the impression that Mu-Followers
have poor CSS characteristics (another gross error by Broskie),
we have come full circle.

Now Broskie makes some more modifcations,
resulting in a "Mu-follower + Cathode-follower".
Finally, he finishes by eliminating the Mu-follower,
and restoring the SRPP as a 1st stage + Cathode-follower,
complete with a capacitor 'voltage-divider' to inject PS noise,
back into the 2nd stage, just as in the later "Aikido" design.
Presumably he discovered that two caps don't make a reliable voltage divider,
especially if they are frequency-sensitive,
alter the phase of the noise-signal, and short it to ground
instead of presenting it to the 2nd stage lower input!

All of this was just a long-way-round way of
crapping all over the Mu-follower/Mu-Stage,
(actually a far superior circuit to his own 'brilliant' concoction),
to setup the selling of the soon-to-be "Aikido" preamp.
--------------------------

Clearly Broskie believes that the PS noise coming from stage 1
is constant in amplitude, to match the signal he taps
from the B+ through his resistor-divider.

Further, he perceives the the PS noise in the 1st stage
as coming from the B+ through the 1st stage as a voltage divider.

Quote:

If the output connection is taken from 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.)

Here again Broskie is concerned with matching the gain
of the two triodes in the 2nd stage.
Why? because only then will the two signals match in amplitude and cancel at the output.
This again presumes that PS hum from stage 1 is a constant amplitude and shape.

But is any of Broskie's analysis valid?

(1) First in regard to the source of noise in the 1st stage,
its amplitude will be affected by several factors, including
the real sources from which it comes.
And we dare suggest more hum is coming from the grid inputs
and possibly the heaters (depending on the tube) than from the B+
directly across the tubes acting as a voltage divider.

This part of his "theory" is already very suspicious,
and is disproved by experience with hum problems
re: input and heaters.

But so what?
Even if Broskie is wrong about the source of PS hum in stage 1,
surely his method will cancel it out regardless.
To an extent this must be true,
provided it remains constant in amplitude,
and he has adjusted his hum-injection right.
This is where again however, Broskie's methodology fails:

(2) Why should the PS hum magically be exactly 50%
of total PS hum found in the common supply?
There is no logical reason for this, especially when we can
pinpoint several different sources combining to create it.

This is nonsense, and we'd be far better off with a simple
adjustment resistor in his voltage-divider,
to nail the right amount of hum in any version actually built,
by LISTENING to it.

(3) Provided the actual wave-shape of the hum coming from stage 1
is the same as the hum directly tapped,
We should be able to eliminate 90% of it, or at least minimize it.

The reason for this is not in Broskie's analysis,
but in the simple fact that:
IF the PS hum is coming from tube heaters or grid-pickup,
it is likely to be constant, whatever value it is.
(of course this doesn't preclude improving the stage 1 hum,
by for instance moving heater-lines or adding shielding,
in which case we would also have to ADJUST AGAIN the
injected PS noise amplitude.

 here's the simplest experiment possible.

Replace Broskie's voltage-divider with an adjustable one that has a wide swing (like 30% to 70%).
i.e., keep the 100k grid-resistor, and add a 100k linear pot bypassed by another 100k resistor. so you can swing the injection-signal amplitude significantly.

Now listen, and set to minimum hum if possible.
Disconnect and take a reading from the pot, and see if 50% of
the B+ hum was the minimum balance-point.

This isn't rocket-science.

Next try something even more daring:
use a strong sine-wave input signal on stage 1.
Take a copy of this, and put it too on the grid of the lower tube of stage 2.
Adjust that to completely if possible cancel out the sine-signal.

NOW measure the A.C. hum/noise and see if it has increased.

 -------------------------------------
 Lets talk about why the Broskie noise-injection would work, and when it won't.

List of things necessary for it to work as described:

(1) PS hum/noise coming out of stage 1 must be 50% of raw PS hum/noise.

(2) gain of both triodes in stage 2 must be closely matched.

(3) voltage-divider for injection must be accurately 50%/50%, i.e., matched 1% resistors.

(4) Both stage 1 and voltage-divider must be feeding off same PS / point.

(5) PS hum/noise at either sample point must not be influenced by input signal in first stage.

(6) PS hum/noise at either sample point must not be influenced by input signal in second stage top triode.

(7) Phase of complex PS hum/noise signal must not shift in any significant frequency band.


List of some things that could go wrong:

(1) PS hum/noise varies in output of stage 1.

(2) PS hum/noise amplitude does not match that of voltage divider.

(3) PS hum/noise varies in power-supply itself.

(4) Gain varies between tube-triodes in either stage, either out of box or over time.

(5) Stage 1 generates no significant PS hum/noise, in which case Stage 2 simply injects noise!

(6) quiescent operating points of tubes involved shifts based on signal amplitude (non-linear Rp etc.).

(7) Hum/noise injected into circuit from other causes shifts phase of either PS hum/noise signal.


Things going wrong caused by DIY circuit-builder:

(1) Failing to set tube-bias correctly,

(2) Failing to match tube-gains.

(3) Running each stage off different PS.

(4) Running voltage-divider off different PS or section.

(5) Eliminating noise from stage 1 by rectifying heaters or shielding grids.

(6) Eliminating PS hum/noise in one part of PS but not others.

(7) Failing to adjust the circuit for minimum hum/noise.

 -------------------------

"Why you shouldn't just test the output?"  

Its obvious.
The whole point as stated right from the start,
was that the circuit does not operate as claimed.

It has been conceded repeatedly that the circuit is indeed low noise,
when powered by a well-designed power supply and good tubes.

That the circuit can cancel some hum is acknowledged.
Testing the output however tells us nothing about what is going on
inside the stages, which is what the thread is about.

Its like this:

(1) Stage 1 adds some hum/noise from various sources in a real-world build.

(2) Stage 2 also adds some hum/noise from various sources, including amplifying hum/noise from previous stages.

(3) Broskie's circuit indeed eliminates most of the small amount of hum/noise present, if adjusted properly.

(4) This leaves sweet F.A. at the output to measure and analyze,
and tells us nothing about how the circuit(s) really operate,
where the noise is coming from, or how much noise was generated and cancelled.

(5) Its the worst method for trying to determine what is happening in the circuits.


Here's an analogy.

(1) I take a can of white paint.

(2) Jerry Lewis adds an unknown color to it.

(3) Broskie shuts the lights off.

(4)  try to figure out the color that was added.

(5) I analyze the paint-shelf instead and notice the green can has been used.

------------

This is an Information Theory type problem.

When you shuffle a deck of cards properly,
there is no way to establish exactly how the cards were shuffled,
by examining the deck after shuffling.
There are a near-infinite number of ways it could have happened.

Put even straighter,
There is no real way to tell what you wrote in the sand,
after you erase it.

Certain processes are 'lossy';
they lose information permanently.
For instance, once a picture is reduced or compressed using a 'lossy' process,
there is no way to recover the original exactly.

Trying to guess what the distortion process was after the circuit has removed 90% of it,
is like trying to guess what the dog ate after he poops it out.
You are far better just watching what he ate.
The output is all but useless for detailed analysis
of a complex but lossy process with internal interactions,
like a multi-stage amplifier system with various kinds of
noise sources and cancelling feedback loops.

The Aikido Comedy (pt 5): How tests go wrong

From Aikido User Guide:

PSRR: "The Aikido circuit sidesteps power supply noise by incorporating the noise into its normal operation. The improved PSRR advantage is important, for it greatly unburdens the power-supply. With no tweaking or tube selecting, you should easily be able to get a -30dB PSRR figure (a conventional grounded-cathode amplifier with the same tubes and current draw yields only a -6dB PSRR); and with some tweaking of resistor R1’s value, -60dB—or more—is possible. Additionally, unless regulated power supplies are used for the plate and heater, these critical voltages will vary as the power line’s voltage falls and climbs with your house’s and neighbors’ house’s use, usually throwing the supposedly fixed wall-voltage askew. Nevertheless, the Aikido amplifier will still function flawlessly, as it tracks these voltage changes symmetrically."


 "PSRR is almost invariably measured in the absence of signal." - SY

"I am an expert, and I can assure you that PS ripples depend on signal, both their form and amplitude, since the load discharges filter capacitors. Without load there is no ripples theoretically. That means, ripples are not superimposed on the signal. They are modulated by signal. Especially when the amp is loaded such a way that peak output current almost equals to an idle current of output cathode follower (like in case of power amp)." - Wavebourn

--------------------------------------------

"...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..."


No, this is incorrect: The fundamental flaw in this analysis here is simple:

The algebraic equations used for AC analysis of tube circuits
are not 'real', in that they express AVERAGES, not absolute impedances.

Thus any equation for Plate Resistance Rp) is not a factual statement of a fixed value, but rather an average, based on a range of instantaneous values and impedance slopes exhibited by the tube during a cycle, or a number of cycles
of an example sine wave input.

That is, the number you get when you calculate Rp
is an average value based on the size of input and voltage swing
at the plate against a load resistance with a fixed B+ voltage.

This is exactly the kind of thinking that caused Broskie to
fundamentally misunderstand the action of the first stage,
and subsequently model it as a voltage divider.

See further down for more details on real circuit behavior.


Certainly some noise reduction is achieved at times by the Broskie Aikido technique here.  And as noted, one very effective trick is to remove noise in the time-span between  musical signals.

But if that were all the Aikido circuit did, it would really be just a cheap trick,
and not a serious noise-reduction technique. Ideally we would want a design or method that removes noise consistently at ALL times.

That is, or ought to be the real definition of PSRR.




Certainly non-linearity of the tube amplification also is a significant source
of intermodulation, sidebands, noise and non-musicality, but its not the only one.

But operating a tube in its most linear region is no guarantee
that there will be no IM distortion, or unwanted products.

The power supply too is well-recognized as another source of modulation
and distortion components, which brings us back to Broskie's claim.


This is the very crux of the claim concerning Broskie's technique.

I would re-formulate the question as a fact of life this way:

Its very difficult to remove PS sourced distortion during a music signal,
while using ordinary resistive loads.

Only high impedance CSS based isolation from the power-supply noise
can keep it out of the signal path, along with its horrendous and undesirable side-effects.


"...That means, ripples are not [merely] superimposed on the signal.
They are modulated by signal."  - Wavebourn


This nails the scientific facts of the case on the head.

I am continually surprised by the penetrating insight Wavebourn shows.

He alone has seen the light, and probably guess very accurately
what I will be posting in the way of analysis.

 Let me recap what this thread is NOT about:

(1) theory vs. experiment in science (they are both essential: one doesn't trump the other).

(2) criticizing Broskie or his amps. They are as reasonably well designed and function as well as most other designs.


Now lets recap what the thread IS about:

(1) Why Broskie's 'Aikido' B+ noise cancelling circuit is a failure.

(2) Why the circuit doesn't and cannot do what is claimed for it.

I intend to demonstrate my thesis on theoretical grounds, not experimental.

The reason this is more than adequate,
is that the theoretical grounds I am using are well-understood,
and non-controversial.

I'm not claiming any secret insights or magical effects.
I'll be instead going over familiar ground,
in a way that shows exactly why the Broskie technique is ineffective.

I will also repeat what I said previously, in case it was missed:
There is no indication from the responses so far,
that anyone except Wavebourn has a clue what is wrong
with both the circuit and the historical analysis/claims for it.


To make my point clearer, and in fact simple enough for all,
lets suppose Broskie's first premise is actually true:

(1) The first stage acts like a voltage-divider.

(2) The Powersupply hum (and noise also) can be viewed as an (unwanted) signal voltage.

(3) This voltage (Vps) appears across the load-resistor and tube (in series).

A percentage of this noise-signal appears at the output terminal of the 1st stage.

(4) We can ignore the issue of the non-linearity of the first tube stage entirely.

We can concede for argument's sake that additional components (harmonics, sidebands, IM distortion etc.) added by stage 1 directly during idle are even smaller relative to Vps than Vps. Thus for instance, if Vps were 10 mV, the additional internally generated noise components might be only 1 mV. This effect will not be significant, because Broskie's circuit would presumably still cancel out 90% of the B+ noise.

(5) However, the tube stage is still a VARIABLE voltage-divider, not a static one.

The tube internal resistance fluctuates according to the AMPLIFIED input signal.  ...
At each peak in the sine wave input signal, the noise signal is being divided across a different voltage-divider:

The Power Supply noise is being Amplitude-Modulated
by the input signal, as only Wavebourn perceived and noted.

Since in a typical musical signal the frequency (frequencies)
vary widely over the entire music spectrum,
what we have is a Ring Modulator, with no musical relation to the input signal.

The simple resistor-divider network of Broskie is is incapable of cancelling out this AM signal, and only (by clumsy design and adjustment) cancels out the PS hum and noise when the circuit is in idle (not amplifying an input signal).

(6) The fact that the Plate Current in either or both stages only fluctuates mildly or even in unison or in a complimentary fashion has no relevance to the AM voltage signal generated in each tube by power-supply noise reacting with an input signal.

Even virtual constant-current Class-A circuits will AM modulate power supply noise and result in a deteriorated music signal. Each stage will AM modulate the same noise-signal independently and in a random fashion in relation to the noise signal, and they cannot cancel out. Remember, it is not the current that is being amplified in these input stages but the voltage that appears at the output of the previous stage. The criss-crossing of the voltages of each stage (signal inversion) guarantees there can be no alignment or canceling except at two instantaneous time-points when the signals cross their idle-voltage lines.

This is why it is so important to isolate amplifying stages from power-supply noise and other noise sources.

(7) Broskie's Voltage-divider/sampler of the B+ noise-signal is a STATIC divider.

No experiments are necessary, contra SY and others.
This is simply Ohm's Law in operation.

Broskie's circuit as first described and presented achieves no reliable signal-cancellation except during idle.
If the overall circuit performs well,
it is for reasons of good tube choice/general circuit design,
all in spite of Broskie's innovation.

This analysis is based on Broskie's own claim that
the first stage acts like a voltage-divider to the PS noise-signal. (hence the irony)
 -----------------

Some however are still making the same analytical mistakes:

(1) The Rp published in a datasheet is an approximation and an average. Its not hard data, but the centerline of a range of values presented by tubes coming off the assembly line.

(2) Also, the Rp has little to do with the actual resistance presented to the power-supply connection, which here is functioning as a secondary "input" for AC hum and noise.

(3) The Rp value is given by the maker for the purpose of calculating algebraic approximations for AC impedances AS SEEN BY Grid Input and Anode Output circuits, its not meant for calculating impedances for signals presented across the power-supply connections.

(4) The Rp value is based on Class-A amplification in which a true (full cycle) AC signal is superimposed upon the voltage at the plate below the load from inside the tube, through the grid.

(5) The powersupply "input" (from ground to top of load connection)
is neither a true AC impedance, nor is it a DC resistance:

It can only be properly modeled in an equivalent circuit as a fixed resistor, a diode, and a variable resistor in series. This is critically important for understanding how the 'diode' characteristic of the tube chops PS A.C. signals in half, effectively multiplying their harmonic content by an order of magnitude.

When people reach a certain level of expertise at circuit analysis,
typically by taking electronics technology 'degrees' or studying 1st year electromagnetism, they think they understand what they are doing,
because they have gained a certain skill in manipulating some algebraic equations.*

Electronics courses however, very rarely cover the real physics behind the algebraic equations and their 'variables'.
Nor do they sufficiently impress upon the students that the algebraic equations themselves are just convenient approximations, and cannot be relied upon as if they were Newtonian Laws of physics.

As indicated above, you can't just use the published "Rp" value
as if it were the actual impedance seen by signals originating in the powersupply and appearing across the cathode-tube-load circuit-path.

____________________________________

 *(Few people know for instance that virtually all of modern electronics came from Heavyside's brilliant breakdown of Hamilton's Quaternions into 3 and 2 dimensional components, pretty much inventing all of modern 'vector calculus' and circuit analysis. )

The Aikido Comedy (pt 4): Key Flaw?

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 can be 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,
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.

------------------------

"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."

 

 

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,

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.
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 the statement that it DOES, "to a first approximation",
is in essence incorrect,
and so is Broskie's circuit.

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.


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.


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 Comedy (pt 3): Essence of Aikido

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:

Quote:

A 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.

The Aikido Comedy (pt 2)

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:

Quote:

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.

 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.

 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.

The Aikido Comedy (pt 1)

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.


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

Quote:

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.