'Local Feedback and Nonlinearity of Multistage Feedback Amplifiers'

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ppl

ppl

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Joined 2001
Isn’t amusing how the works of over a century ago still influence our lives daily. Consider the influence of Mr. Armstrong and his Insights on regeneration being mealy effectively controlled positive feedback. This brilliant Idea was directly responsible for stability in all systems both Mechanical as well as electrical and Electronic. A moment of silence for the Late EH Armstrong http://users.erols.com/oldradio/

Moving along to our favorite subject of Audio Amplifiers and some observations made in prior posts http://www.diyaudio.com/forums/showthread.php?postid=662129#post662129 A BIBO stable system is often confused with a critically dampened system Requiring no overshoot or ringing what so ever when in reality if the Rise in output stops on its own prior to saturation then in the stick sense the system meets the BIBO Stable requirement because the output while overshooting the input slightly is still bound by a resistance greater than itself ceasing the rise prior to system saturation, In this manner the system speed and agility as stated In http://www.diyaudio.com/forums/showthread.php?postid=669061#post669061 can be optimized over that of an inherently stable system. However also as previously pointed out this is under ideal conditions and Driving a reactive load of unknown parameters can send a marginally stable system into complete chaos. Clipping Do real Audiophile actually Drive there ultra Pure reference Amps anywhere near clipping LOL.

In the 1980’s I Played with what is Known as feed Forward and the system while very fast in the order of 1800 Volts per microsecond slew rate ascending and 700 volts per microsecond descending for a 200 WPC@8 Ohms Power amp. THD@ that power was typically 0.005% 10-40 KHz. In that time the distortion race was hot and I considered this stellar performance in comparison to other similar rated commercial Designs even at the High end. It also did not sound too bad with some Loudspeakers and downright nasty with others like the Martin Logan model I had on loan at that time. With vanderstiens this Amp was marvelous just power it from a dedicated Noise spike free AC mains and or endure the occasional pop when a spike was present. Worked real great as a test bed for Power conditioners The Amp sounded real fast but was subject to loud pops from Line induced transients from a nearby window type air conditioner in the workshop so precautions were taken in the listening room. I decided that in the end inherently stable system ether critically or even slightly over dampened but without over compensation was best overall and in more situations, the technique is still vigorously perused however to this Day http://www.patentstorm.us/class/330/112-Positive_feedback.html
http://www.tfcbooks.com/articles/tws5.htm
http://www.tpub.com/content/neets/14180/css/14180_76.htm
A real interesting tutorial on this technique is in Positive feed back op amp circuits http://www.ibiblio.org/obp/books/socratic/output/opamp4.pdf
 
amplifierguru

amplifierguru

Disabled Account
Joined 2004
members.dodo.com.au/~gregball/guru_001.htm
thanks Dimitri,

The link you gave was the later model, where they used the same Vas current source load (more complex boosted supply cct) at the DC300A. I'm still certain an earlier version existed that used the simple bootstrap arrangement.

At any rate, I think there's reasonable agreement that unconditional stability is achievable with nested NFB, +ve FB, etc..

Cheers,
Greg
 
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ingrast

Member
Joined 2004
suite101.com/welcome.cfm/astronomy_astrophysics
padamiecki said:



...
please alight me,
what problems with Poles?
Click to expand...


Greetings padamieckl !!

Of course it was a words joke. In earlier posts, it was mentioned NASA had scraped the X-29 program because they could not cope with a system pole under certain flight conditions.

Then it looks like Russians brought out a production fighter (S37)essentially equal in concept to the X-29.

So the natural joke was to assume they had no trouble with poles. :clown:

Regards, Rodolfo

PS hope you understand there is no offense intended ...
 
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ingrast

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Joined 2004
suite101.com/welcome.cfm/astronomy_astrophysics
padamiecki said:




;)


... BUT THeY REALY HAVE THE PROBLEMS WITH POLES
especially Putin......
Click to expand...


Seriously now, even as far as we are located in South America, we are well aware of the hardship Poland endured in its long history. To have big and often militarist powers in the neighborhood has been tragic.

And then there is the polish cultural heritage - music particularly for me - is an inescapable reference.

Rodolfo
 
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padamiecki

Member
Joined 2004
ingrast said:



Seriously now, even as far as we are located in South America, we are well aware of the hardship Poland endured in its long history. To have big and often militarist powers in the neighborhood has been tragic.

And then there is the polish cultural heritage - music particularly for me - is an inescapable reference.

Rodolfo
Click to expand...


Rodolfo
Sorry that out of the main theme, but
I am astonished of your history knowledge,
I thought that only we know it ;)
what kind of music do you like, Chopin? Penderecki? Szymanowski?:wave2:
 
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ingrast

Member
Joined 2004
suite101.com/welcome.cfm/astronomy_astrophysics
padamiecki said:



Rodolfo
Sorry that out of the main theme, but
I am astonished of your history knowledge,
I thought that only we know it ;)
what kind of music do you like, Chopin? Penderecki? Szymanowski?:wave2:
Click to expand...


Mostly the spirited, romantic stream best known worldwide through Chopin, spiced in his case with equally strong nationalist influences. I used to play his piano works but it was a long long time ago.

Rodolfo
 
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