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Old 25th August 2014, 08:15 PM   #441
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Thank you Dr. Mazzola for your revealing answers. I see devices, and their schematics as mere symbols which oversimplifies their reality; unlike your inherent abilities [and those of many others] to " be there and in touch" which enables(d) you to invent, develop and use semis in circuits, plus teach students all about them like you see them.

It may be plausible to suggest that Schade understood the value attendant to this "internal inverse voltage feedback"; now absent or negligible in his beam tetrode, which spurred him to enable it externally as in Fig. 33c of his paper. It may follow that he was simultaneously advertising his Beam Power Tetrode [as you suggested], and also expanding its value as a new Beam Power Triode [with emphasis on power absent in mere triodes] which truly satisfied his 5 requirements of the Ideal Power Tube.

Please include in part III like you already started doing in Part II, the marriage of the couple: the Sweet Spot and Schade Feedback. Is R100A a better or worse switching device than the same R100A utilizing external Schade Feedback? Is Schade Feedback even used or has value in switching circuits?

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Old 26th August 2014, 06:01 PM   #442
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Originally Posted by Antoinel View Post
Thank you Dr. Mazzola for your revealing answers. I see devices, and their schematics as mere symbols which oversimplifies their reality; unlike your inherent abilities [and those of many others] to " be there and in touch" which enables(d) you to invent, develop and use semis in circuits, plus teach students all about them like you see them.

It may be plausible to suggest that Schade understood the value attendant to this "internal inverse voltage feedback"; now absent or negligible in his beam tetrode, which spurred him to enable it externally as in Fig. 33c of his paper. It may follow that he was simultaneously advertising his Beam Power Tetrode [as you suggested], and also expanding its value as a new Beam Power Triode [with emphasis on power absent in mere triodes] which truly satisfied his 5 requirements of the Ideal Power Tube.

Please include in part III like you already started doing in Part II, the marriage of the couple: the Sweet Spot and Schade Feedback. Is R100A a better or worse switching device than the same R100A utilizing external Schade Feedback? Is Schade Feedback even used or has value in switching circuits?

Best regards.
This is great. I have been working toward this moment for two years in crafting these three articles, namely the insight that you are showing to me in your posts.

Yes, it is my interesting opportunity to link internal device properties with the terminal characteristics that we know (or think we know) about our favorite devices and show how the circuit and the device influence each other to achieve linearity through negative feedback. One thing I might say differently: Schade feedback, if it is what is drawn precisely in Schade's article, is in my opinion not absent or negligible in the beam tetrode or pentode, or any other practical controlled electronic "valve" (i.e., transistor) that I am aware of. It's really about how well the designer uses it. "Ultra-linear" and "sweet spot biasing" are examples of that use.

In fact, at this point, I can't help but point out that anyone that read my Part I should have anticipated the coming discussion of this in Part III. In the concluding section of Part I "Searching for the linear transistor Straightening the Curve" internal negative feedback is explicitly discussed and shown in the "Electrokinesis!" box to be observed in the transfer curve of the 2SC4004 BJT. To put it simply, it's internal Schade feedback sampled by the internal resistance of the collector drift region of the BJT. The lesson of Part II was that external resistance (i.e., the load) does the same thing. What's left? To wrap it all up in the general formalism of negative feedback. After we do that, we will be empowered to understand how to view device characteristics as properties influenced by how they were measured and to experimentally explore some features about our devices that perhaps we didn't know they have. It's gonna be fun.

Again, thanks for following along so well. I introduced negative feedback to my students in our intermediate electronics circuits course this morning. I can see it is going to take awhile for it to sink in with the students. It always does because this is a challenging subject even for engineers.
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Old 26th August 2014, 07:25 PM   #443
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Old 26th August 2014, 10:49 PM   #444
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Old 28th August 2014, 03:16 AM   #445
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Since I got no response to post #419, let me suggest a hint to thuart the na sayers. You say you have so much gain, and you can afford to "throw some away" for use as distortion lowering global feedback? Or even local? What does the harmonic spectrum look like? What does your Gain Bandwidth product look like? What is the feedback at lower frequencies vs. higher frequencies? With and without feedback?
The excess gain can easily lower low order distortion at low frequencies but, you don't have the same gain (read feedback, you probably still have the same gain) at high frequency. So you have less feedback at high frequencies??? Causing a trend towards the same distortion as an amp without feedback at higher frequencies. So, what does the harmonic spectrum look like now? You've lowered the THD numbers but only in the region of the very tolerable consonant frequencies and not the intolerant dissonant region.
These philosophies have been studied and published. Where did I get this from? But, without going into psycho hearing etc. etc. The simple stages vs. the multi stages, produce a different harmonic spectrum. Our ears/brain are very acute. -90db of 7th harmonic might as well be 1% of 2nd or 3rd according to some. How much 7th harmonic does a descent SE stage produce? How much 7th harmonic does a 3 or 4 stage amp produce? And how much does that 7th harmonic get corrected by just applying feedback to a 3 or 4 stage amp...
I'm just babeling now... Well ZM might like it but...
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Old 28th August 2014, 04:31 AM   #446
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I did publish a piece which addresses some of this

2008 "Audio Distortion and Feedback"

FIRST WATT ARTICLES

I got some static on this because I used "coffee table" values to
get some pretty pictures, but I think I made my point, and its not
about feedback so much as cascaded complexity.

(I think my critics were just jealous because I know how to make Excel
do this and they don't )

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Old 28th August 2014, 06:48 AM   #447
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Old 28th August 2014, 11:58 AM   #448
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Thanks for chiming in Nelson. To be honest, I probably got much of this understanding from you! I just wanted to give Dr. Mike an angle to experiment and prove feedback is not as good as some would lead us to believe. I think you can see this phenomena in simulation. He has only up to now focused on a single stage and the gain device contributions though and that is an important starting place.
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Old 28th August 2014, 01:54 PM   #449
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Originally Posted by Nelson Pass View Post
I did publish a piece which addresses some of this

2008 "Audio Distortion and Feedback"

FIRST WATT ARTICLES

I got some static on this because I used "coffee table" values to
get some pretty pictures, but I think I made my point, and its not
about feedback so much as cascaded complexity.

(I think my critics were just jealous because I know how to make Excel
do this and they don't )

Thanks for this reminder. The students of Dr. Mazzola who are just learning about NFB, and audio DIYers have an opportunity to benefit from reading this easy-style technical article.
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Old 28th August 2014, 03:24 PM   #450
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