Current Feedback Amplifiers, not only a semantic problem?

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#2,381
Dan,

From what I see, VFA employs differential voltage stage to derive ops drive signal voltage, CFA (effectively) employs feedback energy directly to the input energy point to control the derived ops drive signal voltage.
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VFA is much more efficient hence preferred for voltage regulation, but I do not recommend it to friends as an audio amplifier.
 
#2,382
vzaichenko,

In an inconsistent formal system comprising multilayered abstraction, full of logical, syntactical and semantical paradoxes, it can be tricky to decide off the cuff or maybe even when you are focused, what is nonsense and what is not. Truth is elusive. Check it out for yourself from trusted sources if you do think it's worth the hassle. I doubt you do. As a matter of fact, I rather dissuade you from udertaking that epic adventure.

Which statement do you find most disturbing?
 
#2,383
syn08 said:
We must certainly live in parallel universes. Draw the schematic after breaking the loop and see what you get. Read any application note about the CFA closed loop gain, for example http://www.ti.com/lit/an/sloa021a/sloa021a.pdf and check out the closed loop gain at pp. 3-4

To add insult to injury, if Rg||Rf=1k and Rf=1k then arithmetic says this is nonsense, something like 0=1, or Rf/Rg=oo
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Parallel universe is certainly the most likely explanation.
Can you show me where I wrote Rg||Rf=1k and Rf=1k please ?
Anyway, as Scott says, there is no Rg. Rf = 1k , closed loop gain is ~1.
 
#2,385
Max Headroom said:
Hi Rodor, thanks for the clarification,I haven't followed this thread closely.....this has become very long thread with much arguing over fine points.
One point that is not widely discussed is the subjective differences between the topologies, and sound reproduction qualities is of course the final goal.


What are the subjective differences, anybody ?.


Dan.
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I see no technical reasons why a CFA would be better than a properly designed VFA when it comes to sound reproduction. Personally I prefer H-bridge VFA for technical reasons.
On the other hand I see some reasons that would make a properly designed VFA better than a CFA, but that is only technical reasons and not subjective "sound quality" reasons.
I'm not afraid of PIM or TIM and if one think that a flat Aol up to several kHz is important one can always use the Otala way.
When it comes to hand waving arguments, I'll leave it to others.
 
#2,388
N101N said:
In an inconsistent formal system comprising multilayered abstraction, full of logical, syntactical and semantical paradoxes, it can be tricky to decide off the cuff or maybe even when you are focused, what is nonsense and what is not. Truth is elusive. Check it out for yourself from trusted sources if you do think it's worth the hassle. I doubt you do. As a matter of fact, I rather dissuade you from udertaking that epic adventure.
Click to expand...
This is pure poetry, current driven and larded with high voltage feedback.


Hans
 
#2,391
herve00fr said:
Thank you Hans,

I have questions/comment on your setup :

- a VFA with a resistor connected to the 2 inputs is detected as a CFA.
- how to conclude on the feedback operation mode while the DUT is in open loop ?
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Just use the test as it is meant to be.
Insert a circuit without any form of external feedback or resistors between the inputs.
All and nothing else it will tell you, whether this circuit has a CFA or a VFA topology with a high probability.

See below the outcome of a test with a single transistor. Has it a CFA topology in this setting ? The test confirms this with a yes.
Is therefore every transistor in every application a CFA ? Of course not.


Hans
 

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#2,392
Science as subsitute for religion.

The logical, conceptual, procedural and number system problems involved in Mathematical Analysis are huge and plenty. The unpalatable discoveries made in the twentieth century have generated tons of literature, but not harmed the authenticity and credibility of Mathematical Analysis. Mathematical Realism established in science, which is not a theory but a religious doctrine, holds the indispensability of numbers to true knowledge and a reliable model of reality. Mathematical Realism adds a miraculous semantic dimension to the scientific worldview, incorporating the numinous believe that numbers have a concrete mind-independent existence with perceptible spatiotemporal properties that anyone can aquire knowledge of without smoking anything. Like every religion of dignity, Physical Theory too has a poetic creation myth, depicting a dramatic moment of birth out of the infinite void of nothingness - some abstract notions gracefully converted to matter - and an ever since growing bubble, all duly calculated and validated in accord with the global cosmological constants, the dark energy parameter, and spiced up with some superimposed Hamiltonian stationary zero saddle point vacuum energy eigenvalues. Theories not formulated mathematically allowing easy computational solutions deserve no attention.
 
#2,393
I mostly agree with that, but would like to add that operators on infinite-dimensional Hilbert spaces need not have eigenvalues. However, all routine quantum mechanical calculations can be done using the physical formulation which means that the audibility of room resonances is basically an Hermitian function.

Jan
 
#2,398
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