Re: LF noise measurements
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At the risk of revealing my ignorance (as if that's a real risk), a lifetime ago I built some moving coil phono cartridge amps using paralleled JFETS.
From https://www.edn.com/your-friend-the-jfet/
"Another trick you can use is to parallel many JFETs to give lower noise. You add the outputs of each JFET. That way the noise adds as an RMS value, since it is random, but the signal adds arithmetically. So if you have two JFETs you get twice the signal but only 1.4 times the noise. Four JFETs means four times the signal but double the noise, so 4 JFETs can cut your noise in half. There is a diminishing return to all this, and you will burn an incredible about of current in all those JFETs, but if you really need low noise, this is a great way to get it."
[You might read the entire article, the explanation of some of the FJET issues aren't well understood by seasoned EEs.]
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I used 8 per stereo channel. ?[And yes there are much better ways today then in 1977.]
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A point to keep in mind is JFETS suck as discreet devices, even units from the same production run will have extremely different characteristics and need to have the Idss matched, failure to match Idss will result in unequal current and unequal "random noise."
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One possible matcher
https://tagboardeffects.blogspot.com/2012/07/greatly-improved-jfet-matcher.html
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Another is the DCA75. Sort of pricy, a friend designs custom high end exotic audio amplifiers and swears it is the way to go.
I used it to sort 30 J310 (yes I know, not exactly a low noise device.)
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The J310s are from Onsemi and their Idss varied by over 10:1. I found 2 that matched reasonably close.
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I thought this worthwhile to bring up and decided this thread was as good as any.
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