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Thursday, June 14, 2012

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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