JFETs from Linear Systems

LSJ74B purchased from authorized German Distributor

Hallo



first of all, this is my first Post on DIY Audio, im not so familiar with postings so im sorry for the form an errors, anyway......


I orderd 20 original Linear Systems LSJ74B from a German, authorized Distributor an masured them for matching. I like to build Stuart Yaniger's Equal Opportunity phono preamp described @ Linear Audio Vol.7.
I was surprised about the Results. The FETs I-Dss of all Parts differ just about 0.8 mA in a range from 10,95 to 11,70 mA. So it looks that they are already mached or am i just wrong or a lucky guy ?? I read here in the forum that for matched pairs the I-Dss should not differ for more than 1mA. I measuerd with -12V@D an the Voltage over 100 Ohms 0,1% @ G+S to GND, also described here: JFET matching information – diyAudio Store . The results are in the Picture below. Maybe Linear Systems optimised the production process for tighter tolerances ?


greetings Matze
 

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> So it looks that they are already mached or am i just wrong or a lucky guy ??

Those were not purchased from the diyAudio store, but 20 randomly selected units should have a random distribution between 6-12. Only your supplier can answer that for you, but it looks like they were pre-graded as the odds of getting 20 within 1mA are very slim. I think someone did some grading, somewhere along the path to you.

> Maybe Linear Systems optimised the production process for tighter tolerances ?

Their production process results in a wide Idss distribution.

> I read here in the forum that for matched pairs the I-Dss should not differ for more than 1mA.

It depends on your application, but 1mA is the gold standard as used in Toshiba 2SK389 and Linear Systems LSK389 duals. You can read more here on our JFET Matching Information page.