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Waly
diyAudio Member

Join Date: Jan 2011
Location: moderation crapper
Quote:
 Originally Posted by Bonsai Nonsense. The two are not the same, and TPC is clearly inferior to TMC.
You obviously missed some late discussions on this topic.

Let me put it this way: show me a TMC compensated amp and I'll give you back a TPC compensated version with exactly the same performance metric (loop gain, phase margin, etc...)

It was mathematically proven that TMC is equivalent to TPC plus a lead lag phase correction. Yes, TMC could be considered as a more simple and straightforward 2nd order compensation method compared to TPC, but to claim that TMC is superior in any other way shape or form, that's totally incorrect.

 31st March 2013, 11:23 PM #372 Bonsai   Account disabled at member's request   Join Date: Jul 2003 Location: Europe No.
Dave Zan
diyAudio Member

Join Date: Nov 2010
Quote:
 Originally Posted by Waly Let me put it this way: show me a TMC compensated amp and I'll give you back a TPC compensated version with exactly the same performance metric (loop gain, phase margin, etc...) It was mathematically proven that TMC is equivalent to TPC plus a lead lag phase correction. Yes, TMC could be considered as a more simple and straightforward 2nd order compensation method compared to TPC, but to claim that TMC is superior in any other way shape or form, that's totally incorrect.
I assume you refer to the work by the esteemed "Megajocke"?
This is a very ingenious analysis but not a mathematical proof.
It is based on approximations such as that the IPS has infinite bandwidth and no phase shift.
Probably more important is that it considers only transfer function and not what Bode called "sensitivity" (I think it would be better called desensitivity since it is the factor by which the sensitivity is reduced).
Usually the Return Ratio and the (de)sensitivity are equal but this is not inevitable, which is precisely why Bode created the two distinct terms.
I think they are not equal in this case and that TMC can do better on this metric.
But I would like to learn more. Perhaps after criticism of Mike's repeated assertions without evidence, now Bonsai can contribute his own analysis?

Best wishes
David

ivanlukic
diyAudio Member

Join Date: Jul 2010
Location: Cacak
Quote:
 Originally Posted by Esperado I will just add that, in all analog mixing desks i had modified, there is a great improvement, in the mixing bus input stages, to swap to current feed-back OPAs. .

A number of people noticed great improvement when CF opamps are used for summing amplifiers in mixing consoles.

Bonsai
Account disabled at member's request

Join Date: Jul 2003
Location: Europe
Quote:
 Originally Posted by Dave Zan I assume you refer to the work by the esteemed "Megajocke"? This is a very ingenious analysis but not a mathematical proof. It is based on approximations such as that the IPS has infinite bandwidth and no phase shift. Probably more important is that it considers only transfer function and not what Bode called "sensitivity" (I think it would be better called desensitivity since it is the factor by which the sensitivity is reduced). Usually the Return Ratio and the (de)sensitivity are equal but this is not inevitable, which is precisely why Bode created the two distinct terms. I think they are not equal in this case and that TMC can do better on this metric. But I would like to learn more. Perhaps after criticism of Mike's repeated assertions without evidence, now Bonsai can contribute his own analysis? Best wishes David
Why? Why? Surely I can also just go on pounding away, saying that I am right and then I will have proven my point! Or, do I really have to get busy on the simulator?

michaelkiwanuka
Banned

Join Date: Oct 2010
Location: Chigwell, Essex
Quote:
 Originally Posted by Bonsai A monologue with the occasional word in bold does not constitute proof, as of course we are seeing in that other discussion. Now, repeat after me TPC does not equal TMC TMC is better than TPC VFA does not equal CFA CFA is great for audio
He who knows not and knows not that he knows not is a ......

 1st April 2013, 12:20 PM #377 Bonsai   Account disabled at member's request   Join Date: Jul 2003 Location: Europe Positively Rumsfeldian.
michaelkiwanuka
Banned

Join Date: Oct 2010
Location: Chigwell, Essex
Quote:
 Originally Posted by Waly ...show me a TMC compensated amp and I'll give you back a TPC compensated version with exactly the same performance metric (loop gain, phase margin, etc...)
True!

Waly
diyAudio Member

Join Date: Jan 2011
Location: moderation crapper
Quote:
 Originally Posted by Dave Zan I assume you refer to the work by the esteemed "Megajocke"? This is a very ingenious analysis but not a mathematical proof.
A Canadian good friend of mine (but not so esteemed here) reached exactly the same results using a star-triangle transformation of the TMC feedback network. Now, if that's not mathematical proof, then I don't know what that is.

In fact, my offer to provide a TPC version with exactly the same performance metric is based on his work. Calculating the equivalent TPC network RC values takes about 5 minutes.

Dave Zan
diyAudio Member

Join Date: Nov 2010
Quote:
 Originally Posted by Waly ...friend of mine ...reached exactly the same results using a star-triangle transformation of the TMC feedback network. Now, if that's not mathematical proof, then I don't know what that is.
A star-delta transform seemed more robust to me too, so that's what I used myself.
But our results, or perhaps interpretations, seem to differ a little. Can you post your friend's results?
Quote:
 ...my offer to provide a TPC version with exactly the same performance metric is based on his work. Calculating the equivalent TPC network RC values takes about 5 minutes.
A worked example would help too, can you post one?

Best wishes
David

PS. Nice to read a post with a hint of actual substantiation.

Last edited by Dave Zan; 1st April 2013 at 01:54 PM. Reason: Added P.S.

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