The paper has some details of a suitable amplifier too.
https://www.linkwitzlab.com/sys_test.htm#Mic
https://www.linkwitzlab.com/sys_test.htm#Mic
Better move seems to be to buy a decent capsule. I see JLI (and others) make some FETless capsules in the 5mm (ish) sort of diameter. Adding a FET to that is reasonably easy so long as the high impedance nodes are well screened.
What's lost in the "Linkwitz mod" fanfare is that a lot of people don't read Sigfried's paper - he's quite clear that this mod is primarily to reduce the sensitivity by bringing the source into play and allowing for a source follower rather than a common source amplifier (like pretty much all electrets that don't expose the source). I think people imagine that it's some sort of magic, and it does behave more linearly as a source follower, but for recording a rock concert it's hardly going to matter.
What's lost in the "Linkwitz mod" fanfare is that a lot of people don't read Sigfried's paper - he's quite clear that this mod is primarily to reduce the sensitivity by bringing the source into play and allowing for a source follower rather than a common source amplifier (like pretty much all electrets that don't expose the source). I think people imagine that it's some sort of magic, and it does behave more linearly as a source follower, but for recording a rock concert it's hardly going to matter.