Differential mic head amp

[mhelin]

Bob Cordell mentions the use of dual JFET as (first) differential stage in condenser mic amplifier in LSK489 application note:
http://www.cordellaudio.com/JFETs/LSK489appnote.pdf

Worth experiments?  Are the any other reasons to use such arrangement as lower distortion? I guess practical circuit would look much like the dynamic mic pre on the same app note with 1G input resistor(s) and the capsule voltage feed, and the opamp replaced with transformer. LSK489 availability is problem though, wonder if LSK389 might do (25pf Ciss is quite a lot though)?

 

[JohnRoberts]

Wayne started a thread about that app note back in 2014, on his forum. http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=12&t=640&hilit=lsk489 

I've always liked Cordell's work, even a "work for hire" app note to pimp one part.

Brad Wood (aka BCARSO) was working with a 0.8nV/rt Hz JFET  before he passed. https://www.nxp.com/docs/en/data-sheet/BF862.pdf  IIRC he was making a head amp for MC carts with it. 

Somewhat higher capacitance but no free lunch in low noise world.

JR