Bang & Olufsen BM6 - Low Output Issue

[smilan]

Hi, I have a Bang & Olufsen BM6 microphone with very low output.
I disassembled the mic and connected the output of the transformer to a XLR cable with no change, so it's not the filter /phase switch that are faulty here.
The DC resistance of the OT transformer is 168 Ohms.
The ribbon itself seems to be installed right (attached picture of the motor).
So the only thing that might wrong is the strength of the magnets.
When I put a screwdriver on the magnet the magnetic strength seems to be pretty weak, I could remove the screwdriver by using a very little power.
Unfortunately I don't have a gauss meter so I can't tell the exact power of the magnetic field.
Does someone here have serviced those mics and remember how strong are the magnets on those mics?
Any other things that might be worth to test?

 

[dmp]

The magnets do get weak on these. But it doesn't happen suddenly.

 

[smilan]

I just got a couple of those mics (second hand), one is working well while the other is faulty.

 

[Whoops]

You could try to re-magnetize the magnets, there's some tools for that.

There's 2 members here that probably have experience with those mics, Mark from Sammar microphones (Marik nickname here) and Stewart from Xaudia (Xaudia nickname here) , you should contact them as they have experience in repairing a lot of ribbon mics are are both great people

 

[emrr]

Isn’t measuring transformer resistance withs ribbon connected a no-no? Perhaps it was disconnected.

 

[dmp]

Stewart from xaudio helped me with a b&o years ago with weak magnets. Replaced with neodymium of the same size. If you do it yourself, make sure the orientation of the magnetic field is correct. The replacements will give much higher output but will change the sound compared with your working one

 

[smilan]

Isn’t measuring transformer resistance withs ribbon connected a no-no? Perhaps it was disconnected.

In this case I had nothing to loose, the mic wasn't functioning so I took the chance.
I'm pretty sure that the ribbon is connected since there is sound coming from the mic, it's just very very low.

 

[Whoops]

In this case I had nothing to loose, the mic wasn't functioning so I took the chance.
I'm pretty sure that the ribbon is connected since there is sound coming from the mic, it's just very very low.

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