JFET matching

[Nelson Pass]

Since people are going ahead on purchasing the Lovoltech
power JFETs, I thought I would share some of my matching
data.

It's quite simple, as seen from the circuit. A measurement of
the Vgs under identical conditions is adequate for most
applications. The value is useful for creating differential pairs,
and in cascoded single-ended applications becomes valuable
when selecting a Source resistor to ground.

In the case of selecting a Source-to-ground resistor, the value
of the resistance can be used to set up the optimal load line
for the lowest distortion.

[Nelson Pass]

Here's a distribution of values of the population of a couple
of tubes:

[Nelson Pass]

Depending on all the other usual factors, optimizing the
Source resistance in a cascoded single-ended system can
improve the performance quite a bit. Your results will vary
somewhat, and so for a given circuit design, it is necessary
to test to find the optimal values, but here is an example
of a distortion curve in an arbitrary system where the cascode
has a grounded Gate. One curve shows the untrimmed value
of Source resistance, and the other has been adjusted slightly.

[Nelson Pass]

For this same circuit, here is a curve of optimal resistance
values for a range of Vgs values. Again, this is simply an
example of a single design, and these values should not be
applied in general. For a given design, there will likely be a curve
which resembles this in principle which will obtained by actual
testing.

[Nelson Pass]

Happy New Year.

[Zen Mod]

Originally posted by Nelson Pass
Happy New Year.

same to you and your folks



and many more-spent in good health and fun


hehe
same wishes to any DIYer around

[Alain Dupont]

Nelson, and all DIYer's

Happy New Year,

lot's of circuits and thanks so much for your
power JFETs matching advise.

Alain.

[jh6you]

How much I have learned thru Pass Labs forum . . .
Looking back myself . . .

Happy New Year !!!

[Looneytunes]

Thanks Nelson,
and Happy New Year to you and all.

[tmblack]

Mr. Pass,

How close do the Jfet's need to be matched as diff pair and as cascode?

Tom