Sennheiser MKH 110 power supply

I have a sennheiser MKH 110 microphone. According to some webpages i saw it's a measurement microphone capable of picking up sounds to 1 Hz

Unfortunately it uses an unusual configuration to get it's power. I found this schematic. http://frogrecordist.home.mindspring.com/images/Wiring-110.jpg
But it doesn't make much sense to me.

What i've got so far is that the mic has an unbalaced output. Pin 1 is signal, pin 2 is ground, pin 3 is +8V.

What i don't understand is what the 5V supply is on the schematics and what the 3V on pin 1 is for.

Right, you ground pin 2, apply DC power at pin 3.

The output is pin 2. If you can accept a low frequency roll-off, you add a series capacitor, as shown top-right. The formula gives the cap value for 1dB roll-off at a given frequency. Below that it reminds you that the "R" is really your amplifier input R plus the 90Ω of the mike; for most purposes you can ignore that.

So for -3dB at 17Hz, -1dB at 34Hz, amplifier input resistance of 1 Meg, use a 0.01uFd cap.

For -3dB at 1.7Hz, -1dB at 3.4Hz, amplifier input resistance of 10K, use a 10uFd cap.

If you object to caps and extra roll-offs, you can use the contraption bottom-right. The signal at pin 2 has a DC voltage, not precisely known, but about 3V. You want to subtract-out this DC voltage to get just the acoustic signal. The floating battery and potentiometer makes an adjustable DC source, in series with the signal. Fiddle the pot until the DC voltage on the wiper is zero V DC. You probably have to do this every morning, after the amp warms up; maybe every time you take a critical measurement. Kinda depends on your signal and your amplifer, whether the DC correction has to be exact or just close.

For anything like human-enjoyable music, I suggest you just use a cap, as shown top-right. 470uFd (+ side to pin 2) will be flat to 1Hz with 600Ω load, 4Hz into a dead-short.

Thank PRR, that makes things a lot more understandable.

I built this yesterday to test the mic with phantom and it works.

http://www.mendelt.nl/Sennheiser/mkh110p48.gif

But I was still not sure if i got everything right.

Here is some more info on the MKH 110:
http://avensonaudio.com/tech/mkh110/

It was provided to me by Rich Peet, a member of the Yahoo micbuilders group.