Bob,
Indeed you can look at these circuits from different perspectives (as you can for most circuits!). This is one reason why the discussion about what it is or not is cannot be resolved; in a way, it can be many things at the same time.
I remember Norton amplifiers as having a current differencing input. The LM3900 is an example.
jan
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Strict strategy applies for CFA -
It probably Does confuse the matter. Because there are very particular feedback strategies, such as the application of current-feedback on a high gain transimpedance amplifier connected as a closed loop voltage gain stage, a degree of gain bandwidth independence can be achieved. [It holds for gains <20.]
Likewise, voltage feedback on a high gain transconductance amplifier connected as a closed loop current will give a similar result.
This is what confuses many and causes the eyes to cross.
Only a very specific strategy is being applied here and when done correctly, you get amazing high speed/bandwidth and linearity. Last i heard we are well past 50Ghz. Cant do it with VFA strategy.
Thx-RNMarsh
It probably Does confuse the matter. Because there are very particular feedback strategies, such as the application of current-feedback on a high gain transimpedance amplifier connected as a closed loop voltage gain stage, a degree of gain bandwidth independence can be achieved. [It holds for gains <20.]
Likewise, voltage feedback on a high gain transconductance amplifier connected as a closed loop current will give a similar result.
This is what confuses many and causes the eyes to cross.
Only a very specific strategy is being applied here and when done correctly, you get amazing high speed/bandwidth and linearity. Last i heard we are well past 50Ghz. Cant do it with VFA strategy.
Thx-RNMarsh
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Other than in semantic assumptions nobody so far did brought
any point about an eventual relevancy of thoses CFB for audio
purposes , much less about any theorical advantage in any way
if we except marginal gains in the already high enough slew rates
provided by VFAs.
I m afraid that the CFB mania has nothing to do with supposed
"good sound" but all with some people/manufacturers willing
for something that would yield market differentiation as a mean
to escape the usual market laws dictature and as such will help
to prop up the margins.
any point about an eventual relevancy of thoses CFB for audio
purposes , much less about any theorical advantage in any way
if we except marginal gains in the already high enough slew rates
provided by VFAs.
I m afraid that the CFB mania has nothing to do with supposed
"good sound" but all with some people/manufacturers willing
for something that would yield market differentiation as a mean
to escape the usual market laws dictature and as such will help
to prop up the margins.
First you/we want to understand what a CMA IS. We'll get to the sound.... that is a bit of a leap from where we are now and not about the topology characteristics. So, at this point, we wont be able to design CMA's if we dont understand what we are doing or talking about clearly when it comes to the CMA case.
Right now, we dont know if it offers any advantages or what they may be because we dont even know what it is or how it is defined nor understand the strategy of it. I think its best advantage will show in high level amps at higher audio freqs. That would mean line level into low Z loads and power amps for audio. But, we arent there yet on this forum.
Thx-RNMarsh
Right now, we dont know if it offers any advantages or what they may be because we dont even know what it is or how it is defined nor understand the strategy of it. I think its best advantage will show in high level amps at higher audio freqs. That would mean line level into low Z loads and power amps for audio. But, we arent there yet on this forum.
Thx-RNMarsh
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Ok Good to know. I dont have a long running discourse with any of them. I'll take that under advisement.
[Note: I am trying to K.I.S.S. for all to benefit.]
Descriptions of a topology/design Can be viewed a number of ways, of course. However, it must still meet the strategy or characteristics of the CMA in the end. Otherwise, we are talking about something else. Relate anything one is talking about in terms of how it makes a better or more ideal CMA, please.
Thx-RM
[Note: I am trying to K.I.S.S. for all to benefit.]
Descriptions of a topology/design Can be viewed a number of ways, of course. However, it must still meet the strategy or characteristics of the CMA in the end. Otherwise, we are talking about something else. Relate anything one is talking about in terms of how it makes a better or more ideal CMA, please.
Thx-RM
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Linearity is the stronghold of VFAs , one has yet to prove
that CFBs can do as well , let alone better.
That is a purely misleading statement audio amps wise as you re
inducing that such topology reach thoses frequencies with through
hole or SMD components while in fact it is only possible with sub micron
level processes , to give a perspective , current higher perfs CPUs
that have 4Ghz clock frequencies have devices whose Ft is in the
300-350Ghz ballpark using 32nm process , so we can imagine that
thoses past 50Ghz require 65-130nm process , all things that render
your sayings irrelevant when it comes to qualify a CFB for audio usage.
I may sound harsh but it s just striking that such exemples can be used
to show a topology in a good way while the exemple itself is totaly
inadequate , i will even add that if such high frequency process were
available we could perfectly do a VFA that do thoses 50GHZ.
Then just strike that troublesome/flippent line if it pushed your button and understand the rest - what is CMA and how does it work best?
Personally, I dont care about VFA anymore. Thats a done deal. Well understood.
Levels well below -100dB are desired and both can do it. I alluded to power amp's can benefit with CMA.
I have already designed and built high power CMAmps with great results. And, VFA also. I prefer the results I get from CMA (and I know why i prefer it).
Thx-RNMarsh
Personally, I dont care about VFA anymore. Thats a done deal. Well understood.
Levels well below -100dB are desired and both can do it. I alluded to power amp's can benefit with CMA.
I have already designed and built high power CMAmps with great results. And, VFA also. I prefer the results I get from CMA (and I know why i prefer it).
Thx-RNMarsh
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As I understand it, it's the difference between 'Current Mode' and 'Current Feedback'. Where 'Current Mode' depicts an amplifier where all 'internal' stages are working as 'Current Amplifiers', this is not needed for a 'Current Feedback Amplifier', in the case of the CFA all internal stages could be 'Voltage Mode'.
(edit: And I can always be corrected when wrong
).
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Yet a symmetrical differential input stage has basicaly 20db
less distorsion at 10KHz than your CMA input stage , so much
for linearity or speed as a cure for high frequency distorsion.
I wonder what was the first push-pull currently-called-CFB input stage.
This one is due to James J. Davidson (USA) from year 1965 :
AES E-Library A Low-Noise Transistorized Tape Playback Amplifier
Nothing new under the sun.
This one is due to James J. Davidson (USA) from year 1965 :
AES E-Library A Low-Noise Transistorized Tape Playback Amplifier
Nothing new under the sun.
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Wahab,
Lets drop the continual sniping about CFA. This thread is about exploring this topology and gaining a better understanding. It's a learning thread.
Please go and start your own VFA thread. If you want to bash CFA, do it in that thread, but not here.
forr, I'd like to join Wahab also in your own dedicated VFA thread as well.
OK?
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Where do you see sneeping.?..
Is pointing the better linearity of a symmetrical differential IPS
in respect of a CMA IPS sneeping.?.?
If i follow you , nothing bad must be said about CFBs in this thread ,
and pointing claimed innacuracies about thoses topologies is just plain bashing.?.
As is apparent i m not convinced at all by this topology when
it comes to audio usages and this is for technical reasons
but now if you can explain us where would be the advantages
i m all ears if this has technical grounds.
Why not to start with one example on good designed(schematic) CFA and then explain each stage and how to choose components value, important design considerations and so on. Then variations and improvements and so on.
This talk about 50GHz circuit is not important for audio or I am wrong?
BR Damir
This talk about 50GHz circuit is not important for audio or I am wrong?
BR Damir
I thought that the history of the input stage using push-pull current feedback is not off topic and that people should know that its invention is not at all recent.
Bob C touched on something which to me was a very valid point... and that is that the CFA architecture being discussed is I think symetrical push pull which is just one particular form. If you are trying to understand differences in sound quality you should also look at more traditional single ended CFB designs that hark back to the very early days of SS amplifiers, and why, whatever technical shortcomings they may have, can achieve the sonic appeal that they do. Everything seems based on visual symmetry these days, not just circuitry but PCB layouts too.
Just a sayin'
Haven't seen this posted before but here's another great resource with understandable diagrams.
http://www.ti.com.cn/cn/lit/an/snaa004/snaa004.pdf
Just a sayin'
Haven't seen this posted before but here's another great resource with understandable diagrams.
http://www.ti.com.cn/cn/lit/an/snaa004/snaa004.pdf
There is absolutely no way your amp. can have 80dB of loop gain at 20KHz and be stable. No way at all.
It is yes way
It has multiple feedback 3 chain at least. It also sounds yummyy.Jfet input Hexfet outputs and bjt at the middle. Work as voltage follower class B.
In the past (previous versions) I can't reach 80dB 20k with VFA.
The forum is moving fast