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 28th February 2013, 01:37 AM #211 The Dastardly Dad of Three diyAudio Member   Join Date: Sep 2009 working my way thru this great writeup - meantime, two q) a) is this part of the article correct : ? "A trend line analysis performed in the Excel Chart shows good correlation to a cubic law (R2 = 1.00, where perfect correlation is R2 = 1)." .... Presumably the R2 is less than 1.00 since perfect corr is 1. b) I am probably missing the point, but why the extensive discussion/charts on the 2SC4004 BJT linearity and load-line cancellation instead of doing same on the SJEPs ? Thanks again
 28th February 2013, 02:31 AM #212 The one and only     Join Date: Mar 2001 Nice, Dr. Mike! I think it will keep the audience busy for at least a day...
 28th February 2013, 02:48 AM #213 diyAudio Member   Join Date: Feb 2004 Location: Davis,CA Mike Really clear article You are a natural Best Bob
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Quote:
 Originally Posted by kasey197 working my way thru this great writeup - meantime, two q) a) is this part of the article correct : ? "A trend line analysis performed in the Excel Chart shows good correlation to a cubic law (R2 = 1.00, where perfect correlation is R2 = 1)." .... Presumably the R2 is less than 1.00 since perfect corr is 1. b) I am probably missing the point, but why the extensive discussion/charts on the 2SC4004 BJT linearity and load-line cancellation instead of doing same on the SJEPs ? Thanks again
Thanks for the kind comment.

(a) Good question! I figured somebody would (and should) ask. The actual R^2 is less than one, but not by much. Excel rounded 0.999... to 1.00 when I fixed the number of decimal places to report. So, to answer your question, R^2 = 1 is indeed perfect correlation. R^2 = 1.00 is simply rounding up a number very close to 1.

As for (b), great question given the thread, and worthy of an appropriate answer. I'll make two comments and then let you decide if you would like more clarification.

First, I think a "linear" transistor as a concept is worth discussing, and if one reveals itself in its transfer characteristic, like the 2SC4004, better to talk about it to see if we can understand why. Might be of use to the crowd around here. Very inventive bunch.

Second, the 2SC4004 transfer curve is an indicator of what might be done with an R100 with sufficient curvature in the output characteristics that is in series with extra drain resistance that is itself not in parallel with the load. Would a little extra power dissipation allow the drain current THD to be cleaned up without relying solely on the speaker load for canceling, which is not purely resistive? It's another means for output loop feedback than just source degeneration. I discuss this motivation at the end of that section. More analysis would be needed to answer that question than can be done with the commonly available Spice model of the SJEP120R100, which doesn't model the output curvature very well.

Hope this helps clarify my motivation.

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Quote:
 Originally Posted by Nelson Pass Nice, Dr. Mike! I think it will keep the audience busy for at least a day...
Hey, your the man. BTW, a "fat cab" is heading your way.

 28th February 2013, 12:34 PM #216 diyAudio Member     Join Date: Jul 2005 Location: North East __________________ "It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
 1st March 2013, 12:41 AM #217 The one and only     Join Date: Mar 2001 I have a question about the cubic law component. Like everyone else, I assume that fets are square law devices, and this is supported by the clean second harmonics we get when we are only varying the Ids current with the Vds voltage remaining constant. When Vds is allowed to vary with signal, we start seeing some 3rd harmonic creeping in, and when the gain variation due to Drain resistance matches against variation due to transconductance, we see that "sweet spot" has clean 3rd harmonic with the second having been cancelled. Is this related to what you are talking about? Otherwise I'm somehow missing that in the distortion readings of these devices in ordinary analog use.
 1st March 2013, 01:04 AM #218 diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain even if I read the article in sort of skimp and end fashion ( proper read tomorrow ) , I have some objections : - there is no enough references neither to Zen Mod nor to Jimi Hendrix's work - mentioning "and other specialty SemiSouth JFETs" is not for faint-hearted , as I (by very nature ) am __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
 1st March 2013, 01:19 AM #219 diyAudio Member     Join Date: Oct 2010 Location: Burlington, NC I noticed that too ZM. Was trying notnto bring attention to it, but you runied it. As for the swwet spot, does it always mean second harmonic cancellation. Are we to assume this as the definition. 3rd harmonic is not what i would charcaterize as sweet. ZM, on the other hand __________________ ...Shape the sound , Man!
 1st March 2013, 01:23 AM #220 diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain re-read Beast ....... both article and thread then you'll be confused , for real __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

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