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Old 1st March 2013, 02:47 PM   #231
49 - for the 18th time
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Originally Posted by Nelson Pass View Post
Thanks for the explanation. Its been 22 years since I operated at the
Threshold (that's a joke, son!) it explains why I don't see much cubic.

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Old 1st March 2013, 03:07 PM   #232
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Originally Posted by buzzforb View Post
I will be starting on extensive F6 amp thingie and will be doing a lot of variation with the r100 and its operating points. I would argue that Nelson's points of operation are probably a pretty safe bet to work with. I have 8 transistors and will test them all for Yfs and leakage before putting them in the circuit and playing with rail voltage and bias.
Thanks buzzforb. Your results will be valuable. You will be dedicate fun time and energy to determine their sweet spot. A small risk of inadvertent burnouts is probable for this valuable semi. I hope that you publish the findings.



The sweet spot of R100A in diy F6 is approximately: [Vds = 23 V, Idss =1.4 A, and Vgs ~1.2 V]. Thanks to Mr. Pass, lhquam, Zen Mod, buzzforb, flochinni, generg, and countless others for disclosing and practicing this valuable characteristic. Some of you may need to know the sweet spot for R085A!.
  • Can I deduce the "average sweet spot" from published data sheets of typical performance. Variability?
  • Is the sweet spot of a single R100A important; or use an average value for the R100A family due to the unavoidable intrinsic variability of their characteristics?.
  • Is there a mathematical expression emanating from the Physics of the device which one could use to determine the average sweet spot.
  • The sweet spot methodology is also applicable to MOSFETs e.g. [IRFP240], and BJTs e.g. [2SC4004]. How do I arrive at their average sweet spots.
Not knowing the sweet spot of a device is a barrier to practice/use it.

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Old 1st March 2013, 03:20 PM   #233
Zen Mod is offline Zen Mod  Serbia
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all you need is THD measuring shebang , along with few braincells dedicated to it's use

I'm always lacking in at least one of these two

when your F6 is going to sing ?
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Old 1st March 2013, 03:27 PM   #234
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Originally Posted by Semisouthfan View Post
Hmmm, two of my favorite topics, women and wine. I'm now old enough that I can't remember which comes first.
Mike
Remember that being associated with a university skews the curve. Those in your classroom and labs keep you thinking young. For me, at some point, it didn't matter which came first.
Best
Bob

Last edited by flocchini; 1st March 2013 at 03:30 PM. Reason: added word
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Old 1st March 2013, 04:02 PM   #235
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Originally Posted by flocchini View Post
Mike
Remember that being associated with a university skews the curve. Those in your classroom and labs keep you thinking young. For me, at some point, it didn't matter which came first.
Best
Bob
Ha Ha! You got that right. The average age of this town plummets every August. But the risks for not practicing defensive driving are in anti-phase.

I do have a dim memory of those days. I seem to recall the latter (wine) helped with the former (women), but then I got married.
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Old 1st March 2013, 04:22 PM   #236
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Nothign helps at that point.
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Old 1st March 2013, 04:30 PM   #237
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Old 1st March 2013, 04:31 PM   #238
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Quote:
Originally Posted by Zen Mod View Post
all you need is THD measuring shebang , along with few braincells dedicated to it's use

I'm always lacking in at least one of these two

when your F6 is going to sing ?
Thanks Zen Mod. I am still collecting parts for my diy F6; I am the slow diy step; but thanks to Mr. T and Mr. b for the high caliber of their service and offerings.

The published idle operating points and junction temperature of each semiconductor in [for examples] BA3 Front End, F5 and F5T, L'Amp a simple SIT etc., are their sweet spots. I believe that you are saying not to bother with the sweet spot of the individual device; but rather with the net outcome %THD of the resulting [multi-semiconductor] amplifier; regardless of the potential variability of their intrinsic sweet spots.

Mr. T and Mr. b. and others supply audio DIYers with matched power devices for FW amps. I'll go back to a past E-mail and determine whether the matching of R100A was done at the sweet spot. I vaguely remember the answer to be yes. I'll post the results.

The buzz is the sweet spot.

N.B. The following are the results for matching the R100A

The Semisouth R100A transistors have been sorted. They are ready to ship.

They were measured at 1.55-1.60A @ 23V on a heatsink that varied from 54-56c. This is the assumed voltages and current for both the J2 and F6.


Last edited by Antoinel; 1st March 2013 at 04:41 PM.
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Old 1st March 2013, 05:04 PM   #239
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My simplistic understanding of certain points made in Mike's article boils down to this: I still don't understand why he spent all that time on the BJT?
Certainly the area of operation around the threshold is a non-linear area. Looking at the "You Won't Find a Linear Transistor Hear" box I see Gate/Base voltage as it relates to Id/Ic with constand Vd/Vc. A rising bias I, correlates to a higher Gate voltage and a change in the fx. In a typical transistor (IRF240) we apply enough bias to get good linear "sound" wich ussually means .5A to 1.5A or higher. Just as the paper points out. The first area to avoid is low threshold. Does this come down to the relative "size" of the device? If we use a 100A transistor we are cutting our throat from the begining because we wont be far enough up on that Vgs threshold curve operating at 1.5A Iq? N.P. always says we want that bias as high as we can stand it. Or is it, above that knee in the Vgs vs Ids curve?
When N.P. asked about the fx being measured as a square law funtion, I thought 2SK170, well Hell, we are operating at .1Vgs, way up on the curve from pinch-off (threshold) it's a nice strait line up there. Trying to do that with an output part is different... I guess that explains his answer
These ideas were all with the Drain Voltage held constant. I beleive N.P. was eluding to and interaction with the drain behaviour that allows for 2nd order H cancelation I didn't really get that from this article
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Old 1st March 2013, 07:42 PM   #240
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In all fairness, Dr. Mazzola presented new and valuable [measured] data for R100 in his paper as shown in the Figure which is entitled "You won't find a linear transistor here". The like Figure 4 of the attendant datasheet of R100 is of lesser value to DIYers; but shows clearly that Vgs is ~1.1 V. Also, Figure 1 of the attendant datasheet [Id vs. Vds with variable Vgs] did not show the region of interest for audio.

Dr. Mazzola. Please consider generating a Figure 1 and a Figure 4 like in the official data sheet; but for audio application. Noting that the approximate sweet spot for R100A is [Vds ~ 25 V, Idss~1.5 A and Vgs ~1.2 V]. Thank you.

NB. The curves like in the Figure of the paper are tremendously valuable. This Figure has data for sweet spots. For example, the last curve to the right: [Vds constant ? [cascode] , Ids = 0.5-0.6 A, and Vgs ~ 1.4 V].

Last edited by Antoinel; 1st March 2013 at 07:59 PM.
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