Sound Quality Vs. Measurements

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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.
 
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 .
 
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@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?
 
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".)

feedbacks.gif
 
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 .
 
Wavebourn said:
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.

nigel pearson said:
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.

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).

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.

Does an ECC 81 become a ECC 82 if the gain is equal ?
No, there is more to a valve than gain.
 
Actually, "purple" feedback is nested: it combines feedback by current through emitter of the 1'st transistor (voltage on the resistor is proportional to the emitter current) and by voltage (through the resistor from collector of the 2'nd transistor, proportional to the voltage on it's collector). However, according to Wayne's classification the feedback through that resistor can be called "Current" since currents sum on the emitter, but it is misleading term that I don't use.
 
When at college I was taught about theoretical pentodes . I wish I had kept my notes . It was quickly said no such device existed .

As I understood it the linearity of a triode is by conduction between cathode and anode due to effects of secondary emission or " related " . Admittedly an RAF college so perhaps not top scientists . The words are important . However others will be confused and not understand there is no magic in this . I always saw the pentode as vastly superior .

My speculation about ECC 82 and 81 is that within reason the parts are the same size and current similar . I suspect the distortion and gain to be very similar if shunt feedback is used on an ECC81 . Neither are especially linear . It strikes me that someone adjusts one to get the other when laying down these designs .

I have some of the D series battery valves . Are they worth trying ?
 
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?

When you make yourself clear, yes, I do. No idea why we always have to prod you to make yourself as clear to others as you are to yourself. :D
 
I have no talents to prove neither definitions nor axioms. Sorry. :D

Wave, I'm serious. I love reading your posts most of the time, but every now and then you simply assume the reader perfectly follows your line of reasoning.

Thus, some of the illustrations you provide can be very confusing sometimes, sidetracking one in an irrelevant direction.

But your second time round explanations are usually crystal clear. :nod:
 
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?


Finally an answer ..... :radar:

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".)

feedbacks.gif

Ahhh more, like pulling teeth huh ...... :cheers:
 
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