I know from conversation with friends deep into audio, Interfet manufactures some of the best, as in most linear and low noise, devices on the market today.
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While the paper is intended for AF, many of the considerations apply to audio as well.
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There is a new method (to me) of matching JFETS. I have no idea how much better or worse it is then the methods I currently use.
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Given the way webpages come and go, I'd dropped a copy in the files section as "audio-electronics-jfet-new-frontier1-2.pdf".