FET circuits - topologies, user experience, etc

[Delta Sigma]

What are people's experiences with different FET circuits? Looking for opinions; not concerned if you use vague non-technical terms like colour; words are hard sometimes.

I'm looking at simple circuits like U87/KM84, 414EB P48, "Schoeps", etc and the many-semi U47FET.

I was comparing the U87/KM84 circuits to see which would be better for a simple "here's my capsule" type circuit and realized they're the same circuit. Seems like only a 3.3p drain to capsule cap, bypass cap value, and transformer size/ratio are different.

The 414EB P48 is pretty simple too. Not sure I get the output stage (is the FET constant current for the BJT?).

My other rabbit hole I'm looking at, is the idea of a cathode or source follower mice, specifically for loud sources like drums. But that's for another day!

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Useless background fluff words:

I'm pretty clueless when it comes to semiconductor circuits. A little strange, since I did learn it in an electronics diploma program. Things tend to fade after 20 years though.

I got into mic building out of an interest to learn. I started with tube circuits mostly because of bias from vintage lore. I've built some fantastic tube circuits and love them. Built a 47FET out of leftover components and I really don't care for the result. I used a capsule I'm not a huge fan of, and a toroidal transformer. Is it the capsule, the transformer, or the circuit I'm not big on?

All my winter projects fell apart this year, so I figure it's time to research/plan the direction for 2025/26 winter projects.

 

[untamedfrontier]

Have you played around with the ORS87 at all? That's a pretty simple version of the 87 circuit and can be tuned to preferences, although probably not the "here's my capsule" transparency that you are looking for.

 

[Delta Sigma]

I haven't tried the ORS87.

I guess I should rephrase the question, to what the difference is between some major FET design choices like constant current biasing and BJT output stage before a transformer? I see that the ORS87 project is a good platform for experimenting with some component changes - I haven't read the whole thread though; just some skimming.

U87/KM84 - plain old voltage divider resistor bias
414EB P48 - constant current bias of FET, plus a BJT stage before the transformer
U47FET - constant voltage bias of constant current current for FET, plus a BJT stage before the transformer

I get the feeling that people like the KM84/U87 simplicity for sources like vocals, and constant current biased FETs for more accurate sounding mics, but that's from piecing together various comments and making assumptions.

Also, why the BJT output stage before the transformer on 414/47FET? Simply for the filter on the 414?