Matching Jfets

Sunsun22 · 20th January 2010, 02:36 AM

I am matching Jfets (J74/K170) with a curve tracer.

When matching same channel Jfets for preamp, should I choose closest Idss or closest gradiant pairs?

What about matching N-P channel Jfets?

Thanks

h_a · 20th January 2010, 07:14 AM

I could imagine that in a differential pair closest gradient could be better, but without checking it with a distortion analyzer we will never know.

Don't expect too much from matching, the very most people are happy with IDSS-sorted jfets.

N to P matching is usefull to lower offset, but with respect to distortion cancellation I never had the time to test it, but I'm still thinking of it.

Have fun, Hannes

Sunsun22 · 20th January 2010, 01:58 PM

Thank you, that's what I think too. Matching uses up a lot of time but the result is still ????

AndrewT · 20th January 2010, 02:08 PM

closest gradient over the SAME current range.
That requires the gradient to be measured at fixed matching currents.
How do you do that at a fixed and repeatable Tj?

The above condition virtually demands selecting the same Idss to yield the same gradient at a lesser operating current.

20th January 2010, 02:36 AM	#1
Sunsun22 diyAudio Member Join Date: Jul 2004 Location: Hong Kong	Matching Jfets I am matching Jfets (J74/K170) with a curve tracer. When matching same channel Jfets for preamp, should I choose closest Idss or closest gradiant pairs? What about matching N-P channel Jfets? Thanks

20th January 2010, 02:08 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	closest gradient over the SAME current range. That requires the gradient to be measured at fixed matching currents. How do you do that at a fixed and repeatable Tj? The above condition virtually demands selecting the same Idss to yield the same gradient at a lesser operating current. __________________ regards Andrew T.

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20th January 2010, 07:14 AM	#2
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	I could imagine that in a differential pair closest gradient could be better, but without checking it with a distortion analyzer we will never know. Don't expect too much from matching, the very most people are happy with IDSS-sorted jfets. N to P matching is usefull to lower offset, but with respect to distortion cancellation I never had the time to test it, but I'm still thinking of it. Have fun, Hannes

20th January 2010, 01:58 PM	#3
Sunsun22 diyAudio Member Join Date: Jul 2004 Location: Hong Kong	Thank you, that's what I think too. Matching uses up a lot of time but the result is still ????

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