Richard,
You are obfuscating. The issue is simple. You stated that the HF signal travels essentially only on the edge of a trace. That is wrong. We don't want people here to be misled by a wrong statement whatever the larger context.
On a typical PWB trace, most of the HF current travels on the flat surface. Simple as that.
Cheers,
Bob
Well, perhaps I cant explain what was done without a lot more dialog and drawings.... your statement is true enough in general. So, in that case I accept easily to not confuse anyone. However, as soon as two wires are used, close to each other, the HF is concentrated on the inside closest to the other wire... so it all depends on geometry of what you/I are talking about.
If you think about the gap bridged by large C, you will understand that at low freqs it was one large piece and not two strips until the freq increases such that the cap Ls starts to makes itself known. One side of the caps is grounded. Have to see the phases in all this. It was a way to demonstrate edge created delay at high audio freqs.... Its very cool, I still think.
Unfortunately, I cant give details of the LLNL experiment [used ground plane which is not the same here] because it involves nuc device trigger design... no, really. Just thats where the edge effect came from.... not pcb's. Someday It will become more clear. Dont fret about it. Nothing has been done which defies the laws... quit the contrary.
THx-RNMarsh
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Bob c;
Will you be installing a chapter on CFA design -- pro/con and maybe an example in your next revision? maybe examples from here would be nice.
THx-RNMarsh
Will you be installing a chapter on CFA design -- pro/con and maybe an example in your next revision? maybe examples from here would be nice.
THx-RNMarsh
probably hasnt been the last time. 
Surfaces ?
And don't it depends a lot of the electromagnetic fields around ?
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Power Factor Correction & CFA
Here's an example of PFC @ work in a High Power Amp. Some interesting info in the PDF, including mention of them utilising CFA techniques as well !
Unfortunately it "appears" they had issues with the design, & they are no longer made. Their latest range is the PowerLight™ 3 Series, Class H & D. It seems they have dropped @ least the PFC in these offerings.
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I realise that other manufactures now have PFC High Power Amps available, but back in the 90's QSC were the first, to my knowlege.
Here's an example of PFC @ work in a High Power Amp. Some interesting info in the PDF, including mention of them utilising CFA techniques as well !
Unfortunately it "appears" they had issues with the design, & they are no longer made. Their latest range is the PowerLight™ 3 Series, Class H & D. It seems they have dropped @ least the PFC in these offerings.
*************
I realise that other manufactures now have PFC High Power Amps available, but back in the 90's QSC were the first, to my knowlege.
I disagree. PMA has already given the right answer.
One definition that defines CFA is low impedance at inverting node, nothing to do with the feedback network or its loadings. In A CFA the inverting input is always lower impedance than the non inverting, irrespective of whether Jfets or Bjts are used.
You may not agree but its the way the industry decided to discribe it, as is the case the reason J Curl s design is a VFA.
If you still have problems with that then I suggest you argue your case with National Semiconductor, Analog Devices, Linear technology etc.
Really? You need to read a few posts down...
So, in your opinion, if the input jfets are replaced in the JC topology by bipolar devices, then suddenly the amplifier (since the inverting input impedance would decrease) changes from a VFA to a CFA?
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We can discus the name for the topologi from now on and to the end of the world, It will lead us nowhere, For me it's a current modulation below the JFET, So in my book it qualifies as current feedback, even if what you do is to demodulate the node(s) with opposing signal(s).
Youve got to be kidding.
Read again this sentence. " In A CFA the inverting input is always lower impedance than the non inverting, irrespective of whether Jfets or Bjts are used.
Why is that manso, here your inputs are really High impedance, the FB pint is set by the feedback resistor to a point around zero potential, but not referenced to GND, essentially a low impedance node, thus current feedback.
Which is also a correct view, although I prefer as a fundamental criteria for a CFA to check if the AC open loop gain can be modulated/controlled by the feedback network (see the formula I posted above). Which, in this particular case, is - hence it's a CFA. Otherwise, it can be pretty hard to define "low impedance", how low is "low"?
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Aint it fun to reinvent the definition of CFA to your own liking?
We started this discussion with What Is CFA and then went on to design/SIM/build CFA. Pls go back to beginning and catch up. Cause this is boring the ones who followed this from its beginning.
THx-RNMarsh
We started this discussion with What Is CFA and then went on to design/SIM/build CFA. Pls go back to beginning and catch up. Cause this is boring the ones who followed this from its beginning.
THx-RNMarsh
Classic CFA topology - vs Simplified CFA
This is the accepted CFA topology being built and described: Its unique characteristics are well described by IC mfr and tech literature... some referenced back towards the beginning here.
View attachment CFA-1.pdf
I have been hinting for awhile that fewer parts could work well and I first published my idea for it about 35 years ago. This is where the CFA topology got bleared. If high Z values are used it may behave more like a VFA. Low Z values give some of the similar characteristics of the classic CFA, shown above. Instead of a simplified CFA, I have since called it a complimentary push-pull to differentiate it from the classic CFA topology.
Thx-RNMarsh
This is the accepted CFA topology being built and described: Its unique characteristics are well described by IC mfr and tech literature... some referenced back towards the beginning here.
View attachment CFA-1.pdf
I have been hinting for awhile that fewer parts could work well and I first published my idea for it about 35 years ago. This is where the CFA topology got bleared. If high Z values are used it may behave more like a VFA. Low Z values give some of the similar characteristics of the classic CFA, shown above. Instead of a simplified CFA, I have since called it a complimentary push-pull to differentiate it from the classic CFA topology.
Thx-RNMarsh
At CFA cross-roads
At CFA cross-roads ---
This is my simplified CFA. It really didnt ever get simplified - it started this way to use some of the inherent cancellation which might apply. Later I embellished it with cascode and ccs. You can also..... if we want to take this CFA in a slightly different direction to see what happens... difference... pro-con; CFA vs "Simplified" CFA/ compl p-p?
View attachment CFA-3.pdf
This basic topology is now extreamly advanced in IC form. For example, see AD8001 thru AD8011.
[Note: mfr of consumer audio... like Marantz use the CFA and not the simplified or compl p-p.]
Thx-RNMarsh
At CFA cross-roads ---
This is my simplified CFA. It really didnt ever get simplified - it started this way to use some of the inherent cancellation which might apply. Later I embellished it with cascode and ccs. You can also..... if we want to take this CFA in a slightly different direction to see what happens... difference... pro-con; CFA vs "Simplified" CFA/ compl p-p?
View attachment CFA-3.pdf
This basic topology is now extreamly advanced in IC form. For example, see AD8001 thru AD8011.
[Note: mfr of consumer audio... like Marantz use the CFA and not the simplified or compl p-p.]
Thx-RNMarsh
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So you think that anything not matching that particular topology is not a CFA? Why am I not surprised? You don't seem to grasp the difference between a particular topology and the concept and properties of a CFA.
While the schematic you posted is a possible (actually, very common) CFA implementation, it is not the only possible, take a look at this, under Section 3. To add insult to injury, not all implementations of that topology are true CFAs (in particular true for audio amplifiers, where only perhaps 5-10% of the CFA characteristics are preserved).
With a little research (I'm here to help if in trouble) you may find that my definition of CFA as a feedback network OLG modulated amplifier is not at all original. It is found in many articles found in the online libraries, it is taught at graduate level here (not sure about the US). It is though (and unfortunately) obfuscated by the marketing jargon language noise around the CFA (which you, and others, seem to be captive).
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you assume too much. we also covered here the characteristics of Classic CFA topology that are unique.... and what contributed to those characteristics. Those also describe the CFA.
I am just not including and going over old material again now.... so you can pick at it. So, I dont include it again as I did already. I am not saying yours or any one elses may not have similar or same characteristics... the ones I showed do have those characteristics... and they are classic designs and used today as CFA in audio amps around the world. What better to compare with VFA?
Does your amp being discussed have CFA characteristics - I dont know. Tests... data? You say it does.... Where's the beef? We werent even sure what your schematic was for a long time... still not sure with what you have shown to date... so how can I say it is or isnt. Are you now argueing about what JC amp design would be classified? Need data to determne that also. Maybe you are right. Is it relevent here. How so?
THx-RNMarsh
I am just not including and going over old material again now.... so you can pick at it. So, I dont include it again as I did already. I am not saying yours or any one elses may not have similar or same characteristics... the ones I showed do have those characteristics... and they are classic designs and used today as CFA in audio amps around the world. What better to compare with VFA?
Does your amp being discussed have CFA characteristics - I dont know. Tests... data? You say it does.... Where's the beef? We werent even sure what your schematic was for a long time... still not sure with what you have shown to date... so how can I say it is or isnt. Are you now argueing about what JC amp design would be classified? Need data to determne that also. Maybe you are right. Is it relevent here. How so?
THx-RNMarsh
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Can we stop this semantic pedantic sh*t?
It serves NO useful purpose. It only reduces the S/N which makes it difficult to see the real gems among the BS.
This thread is about how to design amps without LTP i/ps which might be loosely called CFAs or even other topologies which might have some of their desirable characteristics.
Equally noisy and useless is posting performance figures without actual circuits that might help someone build a better amp.
If you want to wank, please start another thread titled "My d*ck is bigger than yours" or similar.
____________________
Welcome to the real world.
In case its not obvious, its MUCH simpler to ensure good layout, wiring, grounding etc with very simple circuits so 'real life' is close to SPICE world.
If you achieve 1ppm THD20k @full power with 2 x bc184s and a piece of wet string in SPICE world, you are FAR more likely to get single digit ppm in the practical device (assuming a reasonable level of competence) .. than with a zillion or even 56 devices .. even with zillion layer PCBs.
Again, in case it isn't obvious, my aim is to equal or better da zillion device amps with much simpler topologies, NOT to accept a lower level of performance.
an engineer is someone who can do for 2 bob what any fool can do for a quid - Anon