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Old 14th January 2008, 06:23 PM   #1531
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by gl
Nelson,

I would like to ask a question regarding "how good is good enough" in matching discrete JFETs used in diff pairs. In particular I'm looking at creating DIY 2SK389's with matched 2SK170's.

On pg. 10-11 in your article on DIY op-amps there is excellent information on how to match different device types. But there isn't any advice on how on how close the match should be.

I guess the best way to put the question would be to ask you how loose would you tolerate the match if you were building something for your own system that you wanted to have sound really first rate?

Regards,
Graeme

whatever way of matching you choose - Ids or Ugs , difference of 2~3% is perfectly OK ;

just be careful to achieve few other important conditions in matching process ...... same temp , duration under test etc ......

sorry - I'm not Nelson


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Old 14th January 2008, 08:28 PM   #1532
EUVL is offline EUVL  Europe
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> sorry - I'm not Nelson

You say it yourself !!! No one asked you.......



I thought of answering also, but then I want to hear what Nelson says. So I shut myself up.


Patrick
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Old 14th January 2008, 09:22 PM   #1533
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Quote:
Originally posted by gl
I guess the best way to put the question would be to ask you how loose would you tolerate the match if you were building something for your own system that you wanted to have sound really first rate?
This depends on the application, but generally you want to get
it as close as possible. I don't have an in-house standard as
we continue to use monolithically matched parts.

I have noticed that with JFETs run in opposition, either as diff
pairs or with a Drain-Source connection for output (example -
follower biased by a CSS) that there is a bias "sweet spot"
where the 2nd harmonic distortion of the two devices best cancels.

For tightly matched parts, this occurs at the same voltage and
current. For slightly mismatched parts it does not, but it's still
nearby, and if you have a distortion analyzer and the means to
adjust this, you can find the spot.
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Old 14th January 2008, 09:26 PM   #1534
gl is offline gl  United States
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Thank you.
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Old 14th January 2008, 09:46 PM   #1535
Variac is offline Variac  United States
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These comments from Nelson point out that our clones may be very similar to First Watt devices but don't necessarily perform to exactly the same standard! (pretty close thought I'll bet!)
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Old 14th January 2008, 10:57 PM   #1536
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Variac
These comments from Nelson point out that our clones may be very similar to First Watt devices but don't necessarily perform to exactly the same standard! (pretty close thought I'll bet!)

naah............
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Old 15th January 2008, 08:50 AM   #1537
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Quote:
Originally posted by Zen Mod



naah............


To do things list for Z V9 is:

to match the J fets (vgs)
to match the Fets (vgs)
to match the power resistors for the jfet source
to precisely fine tuning the CCS to the same currents between channels
to precisely set the Aleph CCS resistor to my sweet taste ( around the 50 % )

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Old 15th January 2008, 12:34 PM   #1538
steenoe is offline steenoe  Denmark
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Quote:
Originally posted by stefanobilliani




To do things list for Z V9 is:

to match the J fets (vgs)
to match the Fets (vgs)
to match the power resistors for the jfet source
to precisely fine tuning the CCS to the same currents between channels
to precisely set the Aleph CCS resistor to my sweet taste ( around the 50 % )

Nifty little checklist
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Old 21st January 2008, 08:43 PM   #1539
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The F5 is heading toward the gate. An article is being prepped
to appear first in AudioXpress, and then on the net. Here's
a teaser - distortion into 8 ohms.
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Old 21st January 2008, 09:24 PM   #1540
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Woah! Nice figures.
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