Jfet match clarification

[Mbas974]

Hi, I have matched some J201 using this article :
http://www.geofex.com/article_folders/f ... tmatch.htm

it is really simple and fast (so I suggest it... )


The lower Vgs I measured was 0,22 the higher was 0,74

Question 1 : What is the range for J201 in order to say that these are GOOD / POOR / SO-SO ?
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Then I pickup the two extremes FET ( 0,22 and 0,74 )

putting 1K on source I've start biasing.
TRX 0,22 was biased with 15K resistor on drain
while 0,74 was biased with 8K2 resistor on drain

In my thought I was thinking that the 0,74 should be better then 0,22 but standing to the experiment the 0,22 can assure more gain...

Question 2 : Is there someone that can better clarify the theory behind this ?

Many thanks in advance

[The G]

1. It depends on the circuit. Where are you using them? In the usual Dr. Boogie stage (common source voltage amplifier) the input clips the signal when it's larger than ±Vp, i.e. ±0.22V or ±0.74V. You have to tradeoff between input voltage range and gain.
2. The gain depends on gm (the JFET's transconductance or Forward Transfer Admittance as it is found in datasheets), Rd and Rs (see this page for some formulas). Meaning the gain goes higher with higher gm, higher Rd and lower Rs. Just remember the input level limitation.