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Current Feedback Amplifiers, not only a semantic problem?
Current Feedback Amplifiers, not only a semantic problem?
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Old 11th January 2019, 11:51 PM   #2401
forr is offline forr  France
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Quote:
Originally Posted by Bonsai View Post
If Chris and Scott can’t convince you then I can’t help you forr.
Thank you. You answer is absolutely counterconstructive regarding your wish :

Quote:
I’d be quite happy frankly if we could all just agree on how these damn CFA’s work . .
Precise references to posts of this thread would be very useful to establish an overview of the topic.
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Old 12th January 2019, 05:21 AM   #2402
N101N is offline N101N
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Revealing untold truths by tautologous circularity, vanishing derivatives, indefinite integration and algorithmic randomness of infinite sequences.

Functional analysis is fraudulently defined as a mathematical model to find the response of a physical system to a given excitation. It is based on the bold assumption that complex system response can be given by a linear superposition of logical constants, under ideal conditions and at a minimum of functionals, that is, absolute, uneffected states can be added together and the result will be another valid state.

Now, it is not possible to express a response mathematically, response defined as a reaction to influence. It is, to put it mildly, frivolous to call fixed-valued relationships a response. The "stimulus" does not stimulate anything, does not act as a loading and does not excite any response; there is no receptive mechanism for influence and no evaluation mechanism for response artifacts. Distortion is attributed to linear elements having linear relationships, the analytical system "responding" exactly the same way to all "impulses". The independent "dynamic entries" (coefficients) must be chosen arbitrarily, calculated separately and inserted manually in a veritable static fashion.

Mathematics can only handle resolved, settled relationships with no connection to anything external, not producing more information than what is implicitly contained in the independently applied initial data and premises. The same amounts are shifted back and forth. A state never evolves to another state. The arbitrarily chosen values are not the attribute of electrical quantities. There are not any new "properties" to derive from self-contained data, the repetitive tautologies do not give any factually new information but psychologically new information. The measured outcome (aggregate statistical mean or expectation value) is predetermined. Events are not representable. Electrical quantities are not properties of physical things or events. Functional analysis is an investigation of mathematical properties.

Functional analysis does not describe behavior. Functional analysis does not measure performance. Functional analysis does not predict anything. The prophetic faculty consists in telling most enigmatically how the terms are related to themselves definitionally by the unsexy methodology of linear probabilistic approximation.

Although linear theory cannot deal with and explain nonlinear phenomena, the empirical data based arguments (propositional variables) associated with a function and determining its value ensure good simulation matches with anticipated behavior and established beliefs. What is computed is the expectation whereby the self-fulfilling prophecy as dull statistical average comes true. The premises, assertions and assumptions applied in the form of preexisting values make the measurements "realistic". Otherwise it is necessary to go back and suitably modify the assumptions. Even though the outcome is nothing but arrant nonsense, as long as it meets the expectations why care?
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Old 12th January 2019, 08:18 AM   #2403
Bonsai is offline Bonsai  Europe
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Quote:
Originally Posted by forr View Post
Thank you. You answer is absolutely counterconstructive regarding your wish :

Precise references to posts of this thread would be very useful to establish an overview of the topic.
We have spent the last few hundred pages trying to to sort this out.

The divide between the accepted engineering principles of CFA operation and your single dimensional view on how they operate is too wide to bridge at this juncture.
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Old 12th January 2019, 09:36 AM   #2404
Max Headroom is online now Max Headroom  Australia
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Of the manufacturing designers present here, some of you have released CFA designs in addition to VFA designs.
What prompted you to to utilise CFA typology, and what advantages do CFA designs have in the speaker cable/loudspeaker real world.


RNM, you have commented that you prefer VFA for bass, CFA for mids (something like that)...can you elaborate please.


Dan.

Last edited by Max Headroom; 12th January 2019 at 09:44 AM.
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Old 12th January 2019, 10:34 AM   #2405
forr is offline forr  France
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Quote:
Originally Posted by Bonsai View Post
The divide between the accepted engineering principles of CFA operation and your single dimensional view on how they operate is too wide to bridge at this juncture.
For most participants of the thread accepted engineering principles of CFA is a sad joke, just as it was thirty five years ago for the greatest names of the audio engineering (by the way, two of them have been published by a CFA defender !). There is a large consensus :

- that, even among the defenders of the concept, CFA is badly named. In this context, your attempt to restrict the label of CFA to push-pull inputs makes your analysis more than strange.

- that the intepretation of the intimate mechanism suggested by the current feedback expression is wrong. This mechanism firstly involves voltage and transconductance.

Concerning my single dimensional view, the total lack of arguments to support the criticism it received and many posts here had the unilateral effect to reinforce it.

Note :

- nobody had his mind changed by the thread. The art of convincing is decidely not on the CFA's side.

- the fundamental fact, which escaped to many, that the low impedance of in(-) does not load the feedback network has been largely highlighted by me.
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Old 12th January 2019, 10:41 AM   #2406
traderbam is offline traderbam  Europe
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Quote:
Originally Posted by Max Headroom View Post
What are the subjective differences, anybody ?.
Dan.
Iím anybody. There is a premise in your question, that there are consistent subjective differences between all instances of CFA and VFA circuits. There is a further problem of defining the boundaries of what a VFA and CFA are. I suggest the premise is false and therefore there is no answer to your question.
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Old 12th January 2019, 12:03 PM   #2407
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by forr View Post
Note :

- nobody had his mind changed by the thread. The art of convincing is decidely not on the CFA's side.

- the fundamental fact, which escaped to many, that the low impedance of in(-) does not load the feedback network has been largely highlighted by me.
Forr,

You have certainly opened a pot of worms when starting this CFA thread.
At the same time you were well aware of the fact that there was a great controversy between the many links you gave in posting #1, not in the least also in the academic world.
So far it was a very vivid discussion, but the chance that "Audio Mortals" could come to a united vision was very small indeed right from the start.

In one of your links I read this interesting comment:

regarding the Truth about CFA,
I sense an "either" vs "or" goal.
Either "Voltage" or"Current" as the controlling entity.
From Philosophy, I have come to see the possibility
that neither inifinity nor zero actually exist.
From Math, I have come to see that
we have "agreed" on methods of handling infinity and zero.
In Practice I have come to see that
both Voltage "and"Current are always present ( OHMs Law ),
so "both" are always parts of a controlling entity.

What makes this comment interesting is that it clearly shows that you can look at the subject from at least 3 different perspectives, all using their own language.
A Babylonian confusion as the outcome is guaranteed.

Your conclusion on the other hand that nobody changed his mind, comes out of the blue.
It has certainly made may people more aware of what's going on in a so called CFA and for those who didn't have a firm opinion, I assume they look at it now in a more differentiated way.

I think what is undisputed is that a CFA has a clever engineered topology of its own in which transimpedance is one of the key factors.
And therefore this topology has been given a name, and as long as everybody understands what being meant with this name, it serves its purpose well.

Outside a magnetic field, no current can flow without first applying a voltage difference. So I can only repeat the above comment that both are always part of a controlling entity.

Whether in a feedback situation the voltage is steering the current or vice versa is to me the chicken and the egg problem, who was first.
So don't put everybody camps. Many of us see the dualism and accept that.
And that the art of convincing is "not on the CFA's side" is therefore an unjustified conclusion and can just as well be accounted to the way you have failed to convince people of your vision.
I'm sorry to say that.


Hans
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Old 12th January 2019, 12:11 PM   #2408
Max Headroom is online now Max Headroom  Australia
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Quote:
Originally Posted by traderbam View Post
I’m anybody. There is a premise in your question, that there are consistent subjective differences between all instances of CFA and VFA circuits. There is a further problem of defining the boundaries of what a VFA and CFA are. I suggest the premise is false and therefore there is no answer to your question.
I ask for real world experiences from which can be drawn trends.....perhaps.
RNM indicates preference for different topologies for different applications, it would be interesting to hear the experiences of others.
Of course the schematics upholding the individuals subjective findings would be useful, and fine examination of these schematics is required to help to understand the basis of these findings/preferences.
My understanding of the general definition of CFA (Current Feedback Amplifier) is that the return/feedback signal (significant current) acts directly at a point in the amplifier input/driver stage causing modulation of the gain of that stage (by significant current injection into emitter circuit)
VFA operation generally depends on a input differential pair to derive the drive signal, and could be described as a secondary correction as opposed to CFA direct/immediate correction.
This difference in fundamental operation will alter intrinsic/excess noise production and properties/consequences.
I expect these noise behaviours are likely the basis for preferences.
Anyone else have real world experience/findings ?.


Dan.

Last edited by Max Headroom; 12th January 2019 at 12:15 PM.
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Old 12th January 2019, 02:23 PM   #2409
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by N101N View Post
Revealing untold truths by tautologous circularity, vanishing derivatives, indefinite integration and algorithmic randomness of infinite sequences.

Mathematics can only handle resolved, settled relationships with no connection to anything external, not producing more information than what is implicitly contained in the independently applied initial data and premises.

The arbitrarily chosen values are not the attribute of electrical quantities.
There are not any new "properties" to derive from self-contained data.
The repetitive tautologies do not give any factually new information.

The measured outcome (aggregate statistical mean or expectation value) is predetermined. Events are not representable.
Functional analysis is an investigation of mathematical properties.

What is computed is the expectation whereby the self-fulfilling prophecy as dull statistical average comes true.

The premises, assertions and assumptions applied in the form of preexisting values make the measurements "realistic".

Otherwise it is necessary to go back and suitably modify the assumptions.
Even though the outcome is nothing but arrant nonsense...
N101N is my new Hero.

Funny, I would have thought that the Electric Universe theory would have appealed to Electrical and Electronic Engineers... It certainly appeals to me, since it predicts with accuracy some facts that the "accepted" theories were not capable to predict...

Cheers,
M.
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Old 12th January 2019, 02:30 PM   #2410
forr is offline forr  France
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Quote:
Originally Posted by Hans Polak View Post
Forr,
You have certainly opened a pot of worms when starting this CFA thread.
At the same time you were well aware of the fact that there was a great controversy between the many links you gave in posting #1, not in the least also in the academic world.
So far it was a very vivid discussion, but the chance that "Audio Mortals" could come to a united vision was very small indeed right from the start.
There seems to be an impossibility to clearly define by a few words what is the Current Feedback concept in a CFA
Quote:
In one of your links I read this interesting comment:
regarding the Truth about CFA,
I sense an "either" vs "or" goal.
Either "Voltage" or"Current" as the controlling entity.
From Philosophy, I have come to see the possibility
that neither inifinity nor zero actually exist.
From Math, I have come to see that
we have "agreed" on methods of handling infinity and zero.
In Practice I have come to see that
both Voltage "and"Current are always present ( OHMs Law ),
so "both" are always parts of a controlling entity. What makes this comment interesting is that it clearly shows that you can look at the subject from at least 3 different perspectives, all using their own language.
The idea of a predominant factor has been introduced here. If there is one at the input stage in a CFA, it can only be a differential voltage at least at small signals and low frequencies.
A voltage can exist without current. At normal temperatures, a current can't exist without voltage.
The basic effet of current reduction in the input stage by the application of feedback is as fundemantal as often forgotten.
Quote:
Your conclusion on the other hand that nobody changed his mind, comes out of the blue. It has certainly made may people more aware of what's going on in a so called CFA and for those who didn't have a firm opinion, I assume they look at it now in a more differentiated way.
So the thread can be as recognized as of some use.
Quote:
I think what is undisputed is that a CFA has a clever engineered topology of its own in which transimpedance is one of the key factors.
The topology of current conveyors, diamond inputs or even simple complementary inputs belong to the CFA category, they do not define what is CFA (Bonsai's confusion on this point).
As far as I analyse, the transimpedance effect, conversion current to voltage is not done in the input stage but at its output, after the current mirrors in a current conveyor.
Quote:
And therefore this topology has been given a name, and as long as everybody understands what being meant with this name, it serves its purpose well.
Everybody understands what a CFA does, the same as a VFA, But persons who understand how a CFA works are more rare.
Quote:
Whether in a feedback situation the voltage is steering the current or vice versa is to me the chicken and the egg problem, who was first.
So don't put everybody camps. Many of us see the dualism and accept that.
And that the art of convincing is "not on the CFA's side" is therefore an unjustified conclusion and can just as well be accounted to the way you have failed to convince people of your vision. I'm sorry to say that.
Do not worry, "my" vision has clarified facts for some people. Would it be invalid, it would have been be torn down since long. It is not the case.
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