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Old 16th July 2012, 11:11 PM   #6741
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Like, Diesel VS Sedan? Which is better: Diesel, or Sedan?

You did not answer MY question.

What is nested feedback, how it realy works and some examples...
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Old 16th July 2012, 11:17 PM   #6742
a.wayne is offline a.wayne  United States
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Wave I'm not following you are you saying it's effect is the same ...?
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Old 16th July 2012, 11:27 PM   #6743
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Originally Posted by a.wayne View Post
Wave I'm not following you are you saying it's effect is the same ...?
I am saying it is like "Diesel or sedan". Sedan can be Diesel, can be not. The same way feedback by whatever can be nested, or single. Irrelevant question.
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Old 17th July 2012, 08:13 AM   #6744
dvv is offline dvv  Serbia
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@Wayne

I'd answer your question by saying whichever works best for your and whichever you're most comfortable with.

@Wave
A better comparison is whether your car uses a petrol or a diesel engine. Both do exactly the same thing, but are technically rather different, and, as ever, each has its pros and cons. Just about every sedan made in Europe will most probably be available with both, so it's your choice.
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Old 17th July 2012, 10:17 AM   #6745
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Originally Posted by Wavebourn View Post
I am saying it is like "Diesel or sedan". Sedan can be Diesel, can be not. The same way feedback by whatever can be nested, or single. Irrelevant question.

Please guys don't give this one up . A proper debate on feedback would be wonderful . My strongest affection is for shunt voltage feedback . Only because Bob Stuart taught me about it . To quote Bob circa 1978 " I have had in my book a circuit sketched for some years now using input shunt feedback . Now I find the components exist to do it properly " . It was NE 5534 in shunt . He left me to research it .

Diesel has more explosive power ( good ) . It has a long burn time ( less good for revs ) . Although not isothermal the diesel engine can be close to non automobile gas turbines for efficiency due to safety factors limiting aero-jets . Axial automobile gas turbines are more efficient . The axial is not greatly more complicated than a turbocharger . It can have air bearings ( no oil to change ) . It can also become a home generator set . I look forward to when I can own that . Before I am 70 please , that gives it 14 years . The Jag costs too much for me .

Last edited by nigel pearson; 17th July 2012 at 10:20 AM.
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Old 17th July 2012, 05:24 PM   #6746
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Quote:
Originally Posted by dvv View Post
@Wave
A better comparison is whether your car uses a petrol or a diesel engine. Both do exactly the same thing, but are technically rather different, and, as ever, each has its pros and cons. Just about every sedan made in Europe will most probably be available with both, so it's your choice.
No. The question is like whether you car uses diesel engine, or it is green in color. Because green car can use both engines. Nested feedbacks mean more than one loop, with loops inside loops. Current feedback is description of a single loop: whether the designer calculates feedback current, or feedback voltage. As you see, the question is irrelevant: nested feedbacks can include either current feedbacks, or voltage feedbacks. You can't answer the question, what is better, nested or current feedback, because the question is irrelevant, like what is better, green car, or diesel car.

Do you hear me now?
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Old 17th July 2012, 05:29 PM   #6747
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Quote:
Originally Posted by nigel pearson View Post
Please guys don't give this one up . A proper debate on feedback would be wonderful . My strongest affection is for shunt voltage feedback . Only because Bob Stuart taught me about it . To quote Bob circa 1978 " I have had in my book a circuit sketched for some years now using input shunt feedback . Now I find the components exist to do it properly " . It was NE 5534 in shunt . He left me to research it .
Here is the chart that I drew for students long time ago. I hope it helps. What Bob taught you, is parallel feedback by voltage (output voltage applied to input in parallel with the signal).

(The typo in the 3'rd picture description, should read "Parallel feedback" instead of "parallel input".)

Click the image to open in full size.
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Old 17th July 2012, 06:51 PM   #6748
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No1 . No additional feedback . There is " re " which is usually small ( 10 to 50 ohms ) . Some people do not realize that a triode is still a transition resistance device like a transistor or pentode . It's greater or lesser linearity is the result of secondary emission , a very excellent type of negative feedback . This can be manipulated for varying mu . A pentode is a wonderful device as there are so many options . A " theoretical pentode " requires zero drive current . It has a perfectly exponential curve . It can convert voltage to current without requiring current . Capacitance is the death of that concept . I guess the only way to get linearity without feedback is infinite resistance and voltage where an exponential becomes a straight line . Does an ECC 81 become a ECC 82 if the gain is equal ? Graphs not ears in this question . I suspect it does ?

I saw your diagrams before . They are very good . The purple one great . I use purple for feedback loops .
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Old 17th July 2012, 07:12 PM   #6749
DF96 is offline DF96  England
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Quote:
Originally Posted by Wavebourn
Here is the chart that I drew for students long time ago.
Where is the fourth option: shunt application of current feedback? Would raise output impedance and reduce input impedance - I admit I can't think of a useful purpose for it.

Quote:
Originally Posted by nigel pearson
Some people do not realize that a triode is still a transition resistance device like a transistor or pentode . It's greater or lesser linearity is the result of secondary emission , a very excellent type of negative feedback . This can be manipulated for varying mu .
No. In a triode secondary electrons end up at the anode again fairly quickly. The triode's linearity is caused by the anode electric field, not secondary emission.

Quote:
A " theoretical pentode " requires zero drive current . It has a perfectly exponential curve .
You may be confusing a normal ideal pentode (3/2 law) with an ideal remote-cutoff pentode (exponential law).

Quote:
I guess the only way to get linearity without feedback is infinite resistance and voltage where an exponential becomes a straight line .
If you have near-ideal characteristics (e.g. BJT) then you can make some progress with pre-distortion or balancing. Some precision analogue circuits work this way.

Quote:
Does an ECC 81 become a ECC 82 if the gain is equal ?
No, there is more to a valve than gain.
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Old 17th July 2012, 07:24 PM   #6750
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No, there is more to a valve than gain.
of course... it has soul.
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