B&O BM3 two trafo's inside, any idea ?

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andre tchmil

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Putting my BM3 back together ( after an excellent ribbon repair by Marik by the way), I noticed that the microphone has two trafo's.
One attached to the riboon assembly, and the other close to the switch.
Anyone have an idea what the use is for these two.
Maybe I can rip one out for a better performance :green:
 
Well, the BM3 has switchable impedance, so perhaps they decided to use a simple ribbon transformer and then another to provide the necessary three taps to provide different output impedances?
 
Are the BM3 and BM4 similar in config(I think they are)?

I thought the BM4 had a multitapped secondary, which depending on position, gives you different taps(some switch in a resistor), and one having an inductor.

I've got a datasheet somewhere around here =)

ju
 
Hey Andre,

Thanks for nice word about my work.
Don't change anything. The second transformer is an inductor to change LF response for close miking (bass cut for proximity effect), and is bypassed in one of positions. For reference here is the schemo:

BangandOlufsenBM3.jpg
[/img]
 
Ahh... Very interesting!

I think I have the same switch on my BM5 stereo ribbon but was not sure of what the switch actually did!

Is there any reason why they use an inductor for a bass-cut then? I just thought it seemed a little expensive to make.
 
[quote author="gyraf"]very-low impedances. Think loudspeaker crossovers...[/quote]

Ahh, of course! Thanks.
 

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