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Old 6th January 2010, 03:46 PM   #3371
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Andrew, I am certainly glad that you found some 29ma LSK170's. They have a complement, now in the same range. Anyone who got a p channel data sheet at Burning Amp can prove this. It is a new part designation.
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Old 6th January 2010, 03:48 PM   #3372
pooge is offline pooge  United States
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Originally Posted by syn08 View Post
Sorry, my tired eyes are playing tricks... I still have to get used with these progressive lenses.
Try the Hoya progressive lens. Expensive, but worth every penny. No swimming effect. Closest in similarity to single vision lenses I've ever had.
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Old 6th January 2010, 03:48 PM   #3373
iko is offline iko  Canada
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Any idea how much capacitance vary for different samples of the same device? Also, do you guys use the data sheet values for capacitance or you actually measure the device at hand? If you measure, is the procedure involved?
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Old 6th January 2010, 03:50 PM   #3374
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Looks like the real problem here is, this thread seems to be one of the "not so DIY Audio" pointers thread, where those with commercial interests and products can probe each others IP, sort of like writing a patent such that the examiner will approve it as having legs, but witholding enough info to truly protect the trade secret that makes it unique (and hopefully profitable).

All those DIY'ers not in the industry posting her, raise your hands...
Don't quite get the drift here, I certainly am not in the audio industry. The non-DIY aspect to me is "if you can't get X unobtainable part there is no point in proceeding".
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Old 6th January 2010, 03:51 PM   #3375
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Well, what I have to say is this: I predict that IF you parallel two 2sk389's with an Idss at 8ma, you will have more input capacitance, that one 2sk389 with an Idss of 16ma. Geometry rules, not Idss. You know, twice the surface area in the device's effective geometry gives more input capacitance. Idss is controlled by another variable, does anyone know what it is?
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Old 6th January 2010, 03:53 PM   #3376
SY is offline SY  United States
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If you measure, is the procedure involved?
Apply a square wave via a series resistor. Measure rise time. I'll probably screw the pooch on the constant (away from my references), but I think the capacitance is the time for the square wave leading edge to reach 63% of its max value divided by the series resistance.
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Old 6th January 2010, 04:00 PM   #3377
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First things first. We know that the LSK170 (for example) can have a wide Idss range, even up to 29ma. Why? What is the mechanism for the spread in Idss? It is not geometry, is it? Don't they all look the same under the microscope?
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Old 6th January 2010, 04:02 PM   #3378
Magura is offline Magura  Denmark
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Originally Posted by scott wurcer View Post
Unfortunately some of these might be equally obsolete, I was thinking of things like the old E410 series from Siliconix which might be available from Linear Systems. The noise gets down to 3nV or so and the C's are only 1-3pF. By linearity I mean gos. The input Vgs-Id transfer function is the same square law for all FET's.

EDIT- Hand matched 2SK222's would give you a good go too. 10mS at 1mA and only 8-10pF.
Hmm, they both are about as obsolete as they come. At least the usual suspects didn't have any.
Something tells me that I should just be happy about the stock of 2sk369bl.


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Old 6th January 2010, 04:07 PM   #3379
Magura is offline Magura  Denmark
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Originally Posted by john curl View Post
First things first. We know that the LSK170 (for example) can have a wide Idss range, even up to 29ma. Why? What is the mechanism for the spread in Idss? It is not geometry, is it? Don't they all look the same under the microscope?
John, now look, those who knows don't bother playing your little games, those who don't know, also don't bother playing your little games.

So, guess what?

Either explain what you claim to know, or don't, but really, get a hold of yourself.

Nobody bothers playing your little games.

What can I say? It's a damned shame. You're having a bad day.


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Old 6th January 2010, 04:08 PM   #3380
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Originally Posted by ikoflexer View Post
Any idea how much capacitance vary for different samples of the same device? Also, do you guys use the data sheet values for capacitance or you actually measure the device at hand? If you measure, is the procedure involved?

FYI - Data sheets unfortunately use the concept of Ciss and Crss. The extrapolated zero bias capacitances and formula for C vs V (usually ~1/3 power law) is the way SPICE does it and I find this preferable. In this case Cgs and Cgd are usually about the same value. The main point is that you can compute the correct value for each in your circuit.
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