what you are looking for is a "battery box" :
http://www.minidisc.org/homemade_mics.html
http://webpages.charter.net/tidmarsh/binmic/
And yes a bass rolloff is a good idea to prevent overloading the input stage of the mini disc.This cap not only acts as a DC blocking cap so the nine volts from the battery does not shoot straight into your MD but also sets the bass cut frequence F3.
For years i have been using one with all radio shack parts :
metal film resistor pack for the two 10K
small printed circuit project board
1uf X 2 in parallel per channel metal film caps,the big blue ones .
2X4X1 project box-black plastic
1/8 " stereo mini phone jacks X2 (1 input/1 output)
9V battery clip and connector.The clip is bolted down to the board and holds the battery in tight.
I even use the rat shack mics even though many report bad things.I never had a problem.
and if your MD is a sony you better think about adding an inline pot as a volume control for best results.
The preamp is nothing special and is as easy as either an jfet or transistor used as a single stage amplifier.Simple and effective without the hassle of soldering in a multipin IC.But it is rare i need this extra preamp stage.The mics have a jfet amp built in.That is why you need the bias box (battery box) to begin with-to power the amp/impedance matching jfet stage and a microphone puts out voltage according to the sound pressure hitting it.Soft sounds i preamp.Music no.