Using B&O BM-4 ribbon microphones

Posted by Marantzguy (P) on February 23, 2006 at 17:53:24

Hello:

I hope that someone can assist me. I just had Stephen Sank re-ribbon three old B&O ribbon microphones for me. He has moved from Albuquerque, NM to Arizona, so he is a bit out-of-touch these days.

In any event, I have the microphones back from Stephen and the other evening tried using them. First, let me say that I have the original connectors for two out of three of these microphones.

The original pin-out is non-standard from the standpoint of our "pin 2 = hot" convention. I removed the original cable, substituted Canare star-quad and at the microphone end, solderedup the connector, as normal. At the other end, the termination was adjusted to have "pin 2 = hot".

I plugged them in (WITH PHANTOM POWER SWITCHED OFF!) and used first my Mackie 1402 mixer. It took nearly a full rotation of the input level pots to get a decent level and that was really pushing things.

I noticed the presence of quite a bit of low-level hum and in my dining room, the mics were VERY sensitive to interference from the wall mounted dimmer switch. I turned the switch off and a lot of the buzzing disappeared. But there was still some hum present.

The microphones are very sensitive to each other's magnetic fields, apparently, something that I noticed previously with some 1940's RCA Varacoustics I own.

Last night, I operated the mics with my Aphex 1100 hybrid tube 2-channel mic preamp. The mics sounded great, but again, they required a nearly full rotation of the gain controls to get any decent levels.

Next, thinking that there might be an impedance mismatch present, I connected them to my trusty old restored Ampex MX-10 tube mixer. I got slightly more level but the same low-level hum was there and of course, the same sort of interference from the lighting in the place.

The microphones have a little 3-position screw switch for adjusting their impedance. The adjustment goes from low to medium to high.

I used the MEDIUM setting, since when I switched them to the HIGH setting, I lost the signal completely. I really do not know why this was, but it was true on all three of these microphones.

I would greatly appreciate hearing from anyone who is familiar with the B&O BM-3 or BM-4 microphones and could tell me what I may need to do to eliminate the interference and/or boost signals to a better level.

Is it necessary for me to use some sort of transformers between the microphones and any given mixer?

Thanks in advance!

Richard Links
Berkeley, CA

This post is made possible by the generous support of people like you and our sponsors:

Topic - Using B&O BM-4 ribbon microphones - Marantzguy 17:53:24 02/23/06 (17)

CAUTION!!!! - grhughes 07:10:34 03/01/06 (12)

Re: CAUTION!!!!, BOGUS WARNING - Top Jimmy 12:36:46 03/02/06 (1)

Re: CAUTION!!!!, BOGUS WARNING - Marantzguy 13:28:14 03/02/06 (0)

Re: CAUTION!!!! - Marantzguy 13:39:05 03/01/06 (9)

Re: not unbalanced - Top Jimmy 13:13:42 03/02/06 (1)

Re: not unbalanced - Marantzguy 13:30:59 03/02/06 (0)

Some units have a decoupling electrolytic cap on the +48 volts - grhughes 14:51:51 03/01/06 (6)

Re: Some units have a decoupling electrolytic cap on the +48 volts - Marantzguy 16:04:14 03/01/06 (5)

The Beyer Transformers... - grhughes 07:42:10 03/02/06 (4)

Re: The Beyer Transformers... - Marantzguy 13:36:40 03/02/06 (3)

Re: The Beyer Transformers... - grhughes 14:23:14 03/02/06 (2)

Re: The Beyer Transformers... - Marantzguy 16:13:14 03/02/06 (1)

2 RCA BK11A mics in a studio I worked at were ruined... - grhughes 17:51:56 03/02/06 (0)

Re: Using B&O BM-4 ribbon microphones - Bill Fitzmaurice 18:57:06 02/23/06 (2)

Re: Using B&O BM-4 ribbon microphones - Marantzguy 10:12:55 02/24/06 (1)

Re: Using B&O BM-4 ribbon microphones - Bill Fitzmaurice 12:09:18 02/24/06 (0)

Re: Using B&O BM-4 ribbon microphones - Marantzguy 11:10:56 02/27/06 (0)

You can not post to an archived thread.