I've built this mic around two years ago. Nothing fancy to post a photo since it looks like every other mic in this thread (except Spence's diy bodied units!). It's a GT-2B body by Chunger.
I allways felt that it sounds weird on some sources. Sometimes it would be great, but on some vocalists and instruments it would suck big time! Especially since I built some other mics so I had others to compare with.
Few days ago I wanted to check what is going on with it. I tried swapping FET, going with 1000pf on C1, swapping capsule with spare one I had... I was checking freq. curve in a primitive way - putting headphone on the grille in front of capsule and doing sweep and playing pink noise. What I noticed in every situation is that I had a deep notch around 800-900 Hz. And it was a bit bumpy around 2.4k. There was nothing I could do to fix it. At least nothing in terms of component replacement.
I've put dummy capacitor instead of capsule and injected pink noise into the circuit to see if it has anything to do with bad capsules or mic acoustics - and it was flat this time! So there's actually nothing wrong with components...
After a day of experimenting and countles assemble-dissasemble cycles, I found out that the problem is with GT-2B body! It is resonant inside. When you assemble and screw the mic there's a large gap from grille/capsule into pcb section. If you stuff that gap with sponge foam it will fix this nasty 900Hz notch! It was an easy fix!
Try it!
You may seem that this mic sounds good already. But it's a one minute mod. Nothing to solder or desolder. Just some sponge foam on top of the pcb to fill area from pcb to the inner edge of the body. Try it and you can take it back if you don't like it.
Now I'm on a quest to find something better than this ugly sponge since I feel it will degrade in few years. I need something that will last longer.
just my observations...

Luka