I purchased a Gefell UM900 about 6 months ago and love it. I've been using it through a UA 610 for vocals and acoustic guitar mainly (it is also killer as a mono drum overhead with a bit of crunch from the 610!).
The microphone has -10 db / 0 db / +4 db options. What is going on in the design? I would assume there is some sort of small preamplifier in the mic itself? Is there improper ways to use it that could harm the microphone?
Well, this switch is an attenuator with a boost feature. When in +4 mode, only the cardioid pattern will be active at this higher sensitivity setting. There is no mic-preamp in the mic, it will just bring up the output.
hope this helps