Bruel & Kjaer DeltraTron supply for measuring mic / LEMO adaptor

Hello & Happy New Year!

A Bruel & Kjaer measuring mic popped up: a combination of a 4155 pre-polarized capsule and 2671 'DeltaTron' amplifier unit, like on the attached picture. Mid 90's, the calibr. chart is dated 1995.

The output is on a BNC-connector, so I'm assuming some two-conductor phantom-power for the amplifier.

Anybody familiar with the DeltaTron way of hooking up mics ? There seems to be a current & voltage mode,
and for the 2671 it's specified as:

Power Requirements: DeltaTron supply, 2 to 20mA. Nominal 4mA

Power Supply Adaptors
Supplies constant current from microphone sockets
ZG 00328  Brüel&Kjær 7-pin to BNC
WB1421  LEMO to BNC

I assume I could toy around with a DC-current source & isolate the AC-signal,
or just try a simple resistor to say +12V DC, and take the signal after a cap.

But no idea about reverse polarity protections inside etc (who knows it's meant for negative DC-voltages),
so I'd rather not just gamble & potentially destroy the thing.

So far I couldn't find the schematic for a front-end that further processes the signal; I guess that'd easily answer the question. 

Anybody knows some details for a straighforward way to interface it ?


Thanks!

Probably the nice'n'mighty ESP-site to the rescue again

I ran into this: "4mA Current Loop Microphone System" 
http://sound.whsites.net/project134.htm    might do the trick.

Still, if anyone has seen a schematic for the 2671, please tell.

Thanks