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Old 21st December 2008, 12:57 PM   #21
EUVL is offline EUVL  Europe
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Join Date: Oct 2003
> BJTs are so much easier.

Of course.

> If you are comparing numbers from separate test runs then I am beginning to doubt the results of the yield of matching pairs.

I don't, because I take the same JFET and measure them at different times to see how repeatable the measurements are, and they are repeatable to better than 10uA.

Also I have taken random samples of "matched" devices and then run them one after other within minutes, and the readings and degree of matching are repeatable.

I also have a fixture that allows a dual JFET or a matched single pair to run simultaneously and a push button to toggle between one and the other only for current measurement.

And for the most demanding applications, I can run them in diff pair mode and measure distortion. Minimum even harmonics means best match.

But I doubt many people would bother to take the trouble.


Patrick
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Old 21st December 2008, 06:21 PM   #22
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Location: Milan
Default Re: Group Buy ??

Quote:
Originally posted by EUVL
So there are some interest afterall.

I could organise a production batch if someone would be kind enough to organise the GB as follows :

-- Minimum 500 pcs in total, no max but in multiples of 100 pcs.
-- Maximum 3 addresses to post to (e.g. one Europe, one Asia, one America).
-- USD 2.50 per piece including registered post to the said 3 maximum addresses, plus 4% Paypal fees.
-- As shown, wire cut aluminium, black anodised, with 0.1mm gap for silver epoxy.
-- Parts to be ordered when quota is reached. Payment before delivery.
-- The 3 local coordinators are responsible for payment (i.e. I shall get max 3 payments).

Local delivery I shall leave to you to arrange. That way I do not have all the work to do.

Fair deal ?

You can still get a pair of 2SK170s for less than 1USD if you buy enough, and a pair of 2SJ74s for less than 2 (while stock still last). A heatsink plus a drop of silver epoxy, and you have as close as substitute as you can get. For me a better deal than buying 2SK389 / 2SJ109 on Ebay for 10 Euros, with no better than 3% match in 60% of the cases (Believe me, I have measured enough of them).


Patrick

Hi Patrick

my interest is for a fraction of the proposed min batch (500).. of course we need to gather interest from other members.

your offer is fair, let's see how many fellow diyers wants to join the party

anyway thanks for sharing
ciao
Vale
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Old 21st December 2008, 07:25 PM   #23
EUVL is offline EUVL  Europe
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I was never suggesting you to take 500.

But someone has to volunteer to start a GB, and we probably need 20 people each taking 25 to make it work.

I had 20 prototype made as a favour from a friend, but it was a lot of setup work that the friend who did it is not willing to do it again unless he gets his hours compensated, which is of course fair.


Patrick
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Old 21st December 2008, 07:35 PM   #24
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by EUVL
........they are repeatable to better than 10uA.

Also I have taken random samples of "matched" devices and then run them one after other within minutes, and the readings and degree of matching are repeatable.

I also have a fixture that allows a dual JFET or a matched single pair to run simultaneously and a push button to toggle between one and the other only for current measurement.

And for the most demanding applications, I can run them in diff pair mode and measure distortion. Minimum even harmonics means best match.
that sounds very thorough and labour intensive.
__________________
regards Andrew T.
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Old 21st December 2008, 07:59 PM   #25
steenoe is offline steenoe  Denmark
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Patrick, superb idea. Finely crafted little thingie

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Old 21st December 2008, 08:50 PM   #26
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Location: Tempe, AZ
Quote:
Originally posted by EUVL
I was never suggesting you to take 500.

But someone has to volunteer to start a GB, and we probably need 20 people each taking 25 to make it work.

I had 20 prototype made as a favour from a friend, but it was a lot of setup work that the friend who did it is not willing to do it again unless he gets his hours compensated, which is of course fair.


Patrick

count me in for 25
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Old 21st December 2008, 11:14 PM   #27
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EVUL:

I have some LSK389 SOIC-> 2SK389 7zip converter boards I'd be willing to let you try for free. Send me an e-mail.
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Old 22nd December 2008, 02:56 AM   #28
EUVL is offline EUVL  Europe
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> that sounds very thorough and labour intensive.

So is your method, for a two point match.

> Patrick, superb idea. Finely crafted little thingie

Don't you want some ???

> I have some LSK389 SOIC-> 2SK389 7zip converter boards I'd be willing to let you try for free.

I also made some a while ago, and I also have SOT23 converter boards for the likes of LSK170 or BF862, but they do not solve the P-JFET problem. The heatsink does, to a large extent. You just need to match 2SJ74s. And for normal 3% match, it is not as bad as what Tim & I were discussing. That was extreme matching that I only do when I am building my reference systems.


Patrick
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Old 22nd December 2008, 03:04 AM   #29
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if you have some extreme matched N-P complementary pairs that you need to let go....
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Old 22nd December 2008, 03:14 AM   #30
EUVL is offline EUVL  Europe
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> if you have some extreme matched N-P complementary pairs that you need to let go....

They do not exist because the P and N devices have quite different transconductances (something like 25mS vs 33mS). But you can find good P & N match for Idss only. From a batch of 200 of each type, I got something like 12 pairs last time (complementary pairs).

Even if I were prepared to let them go, I doubt if you are prepared to pay the price.



Patrick


PS In theory this transcoductance difference does not allow for perfect harmonic distortion cancellation. But if you use 2 identical pairs in balanced mode, then things improves drastically. See also my old article on JFET buffers.

http://www.diyaudio.com/forums/showt...92#post1592492
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