B&O

[erik_DK]

B&O - Bang og Olufsen is a very well known Danish company, making mainly home audio and TV products. Back in the 1950ies and -60ies they made some very good ribbon microphones.

 

[erik_DK]

B&O BM-microphones.

BM is short for Bånd Mikrofon, the Danish words for ribbon microphone

There never was a BM1, but there was a dynamic bakelite microphone before the BM2 and there was also the cheaper model "Belcanto". None of these are interesting for modern use, except maybe for lo-fi effects.

The MD8 omnidirectional dynamic mic can be quite useful.

They are all in these scans except for the bakelite mic and the BM2 (BM2 has same pin-out as BM3):

 

[erik_DK]

B&O mic amp.

The BM2 - BM6 were intended for use with the best B&O reel to reel tape recorders:

BM2, 3 and 4 for model 509U and 512K (both tube designs with mu-metal encapsulated mic transformers)

BM 5 and 6 for Beocord 1800, 2000 and 2400 (germanium and later on silicon transistors). They featured a semi-modular design with a dedicated, transformerbalanced mic amp board. You have the possibility of switching between 50 ohms (for BM 2, 3 and 4) and 200 ohms (for BM 5 and 6) input impedance.

BTW: Since the first versions of this board used germanium transistors, it is wired with positive ground. As far as I can see, they just put in silicon transistors in the later series with almost no changes in the circuit.