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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
Follow Ups:
First of all they are low sensitivity mics. I remember reading a review in STUDIO SOUND when they first appeared and this was the overriding complaint. NEVER NEVER NEVER get a ribbon microphone close to a phantom powered microphone input EVEN IF IT'S TURNED OFF!!!!!!!!! Any amount of leakage (which is common on phantom lines) DC will find it's way to the ribbon and might possibly sever it (yes, cut it) because DC will cause an excessive excursion movement of the ribbon. NEVER EVER check the contimuity of a ribbon mic with a VOM meter!!!!!! Equip your equipment with inputs just for ribbon microphone use with no phantom power attached to them. SCR light dimmers dump a lot of trash to ground. Excise them from your whole house if you record using these mics in your house. I think you will have to find a low noise mic preamp just ot use with these mics. You could also investigate Jensen transformers. They make a ribbon mic interface transformer. But let Steve Sank do the work! They are good mics which Royer patterned his mics after. Ray Hughes
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
Residual phantom power DC will not blow your ribbon. Neither will your ribbon be blown if you hot plug the mic into an input with phantom on. Since a ribbon requires an impedance matching transformer to step-up the voltage, the ribbon itself is transformer isolated from the phantom power. Transformers cannot pass DC, especially DC that appears as a static potential.Of course, there are times when phantom power can blow the ribbon. But this can only happen when there is a condition that would allow that to happen. Shorting either the + or - from the mic to ground would instantly allow current to flow through the secondary of the ribbon's transformer in the presence of phantom power. This instant on current would create a transient across the primary that certainly would cause the ribbon to scream in horror just before it went pop.
Miswired cables and cables in poor condition can contribute to his happening, and running mic inputs through a patchbay can allow it to happen also. When inserting a plug into a jack in a patch bay, there is a moment at which the tip and sleeve are shorted. Instant pop if a ribbon is patched to that channel and phantom power is present.
So, as a rule of thumb, never have phantom on when using a ribbon. But, don't soil yourself if you find that you patched it to a channel that has phantom on. If your input cabling isn't compromised, there will be no damage to your mic.
Hi, "T-J":Much thanks for the suggestions!
I always make certain that any phantom power is OFF before I operate a mic pre and also never plug in any condenser, let alone a ribbon microphone when the power to the mic pre is switched on. I power up carefully and power off before I remove the cabling from the input.
Thanks again!
Richard Links
Berkeley, CA
Hi, "gr":I really appreciate your words of caution!
I knew about the danger of accidental phantom powering, but you are the very first individual to warn me of simply plugging them into a given mic pre which has the phantom power SWITCHED OFF!
Again, thanks!So, I own this cool old Ampex MX-10 ALL TUBE mixer, which I restored many years ago, replacing the coupling caps, installing Jensen Type 115 trannies in place of the Beyers, which I also removed. I also replaced all of the original potentiometers with Alps units, including a very close-trimmed ALPS dual pot for the master control.
The tubes all test well on my five checkers, so that much has been accomplished. What I have not yet checked on is whether or not the previous owner, who installed a second set of line inputs, also managed to convert the former "pin 3 = hot" convention to that of standard XLR pinout, which as you know, happens to be "pin 2 = hot". If this was NOT yet done, it may in fact account for the great amount of noise I experienced the other evening when I used the microphones with the Ampex mixer to test record a chamber ensemble. The microphones were perhaps no more than 6 feet from the ensemble.
Incidentally, as I may have previously reported to this forum, once I had the microphones set up in this hall, there were NO problems with interference at all.
That much was GOOD NEWS to me!
Now to cure the other noise issue!
I have been informed that to use these B&O BM-4's even with Stephen's "BX" ribbon modification, will require a mic pre with as much as 65 dB of gain. Wasn't the Ampex MX-10 of that specification?
Surely, in the days of B&O's BM-4, most recording engineers would probably have used one of these old tube Ampex mixers, which makes me think more in terms of continuing the use of that MX-10 with these nice microphones.
They did sound pretty amazing, albeit with a noise floor problem, which was probably in part, due to the "unbalanced" XLR situation.
I need to investigate further!
Any further comments on your part are most appreciated!
Thanks!
Richard Links
The pin 3 hot issue would not cause an unbalance. The only thing it does is inverts the input.All passive ribbons need a huge amount of gain, and most typical preamps only provide about 55 dB of it. I've got some preamps that can do up to 80 dB of gain and a setting of 60 or above reveals the noise floor of the preamp. I tend to reserve my ribbon use for loud sources like guitar cabs and horns miked at a couple of feet. This allows me to use less gain, and the signal masks the noise that is there.
Hi, Again, "T-J"As I suspected! I really had visions of recording chamber music with a pair of these ribbon microphones but never ever suspected that I would have encountered this much of a noise problem.
I still think that correcting the pinout on inputs / outputs of my MX-10 mixer would not hurt at all.
Well, perhaps I need to return to using my Milab VIP-50's or otherwise, continue recording with the MBHO 603's, which I like very much.
The allure of the B&O pair was certaining an option, though!
Rich Links
...if there is not a bleeder resistor acoss this cap then any residual Dc charge in the capacitor might damage a ribbon mic plugged into a plug even with the 48 volts turned off. Also the two 6.8 K phamtom power resistors need to be highly matched to prevent any DC leakage. Don't use carbon film or carbon comp because soldering them will change their value. This 48 volts needs to be from a good linear supply not a switching power supply.
The EF86/6267 made a decent mic preamp but I haven't used one since the late 60s. I don't think you can buy a better transformer than a Jensen. Ray Hughes
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
Hi, Ray:The decision to replace the original Beyer mic trannies with the Jensens in the Ampex MX-10 was based on the recommendation of another recording person I knew years ago and this guy happened to be a stellar talent in his own right.
I used the Ampex MX-10 for a while to record mostly orchestral material and at that time, I used both non-phantom-powered microphones, specifically a pair of Nakamichi CM-700's, or otherwise was hooking up my Milab VIP-50 multi-pattern large diaphragm condensers with an outboarded phantom box made by AKG.
The signal was sent to a ReVox A-77 open reel machine and later on, a DAT recorder.
The results were excellent, but as time went on, I required much more flexibility, including pan pot functionality and more.
I would never sell that Ampex mixer, however, since I did put quite a lot of my own time into the unit trying to improve it.
I also kept the Beyer trannies that were once in it for other projects, which never quite materialized over the years!
Thanks
Richard Links
Berkeley, CA
I believe have a much higher turns ratio. Jensen doesn't wind anything much past 1:10 as a bandwidth measure. The Beyer units were tiny so they won't take much level like a line level.
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
Hi, Ray:So, are you suggesting that the original Beyer transformers might possibly offer me MORE gain than the Jensen 115's I installed years ago?
If this is true, all I need to do here is commit two mic inputs to the use of the orignal Beyer transformers and use that pair of inputs for the use of these restored B&O microphones.
I have to tell you that the Jensen transformers on the input stages brought about a much smoother and in my opinion, much more "musical" sound than the original Beyers. My friends who did location recording were the ones who originally made the suggestion of swapping out these Beyers for the Jensens, but that was over twenty years ago, so I did it (and kept the Beyers just in case).
Let me know your thoughts on this. It does make me wonder.
There is no problem for me removing the Jensens and substituting the orignals on the two other channels, since I normally only record two channels with this mixer.
Thanks
Richard Links
Yes, I think the Beyer's have more gain. They also might have some ringing artifacts or tizzy frizzies! You could probably damp them out with a cap and resistor in series across the secondary. You just have to experiment. Ray
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
Thanks, Ray:I'll that in mind!
Rich Links
...the ribbons were cut by plugging them into a phantom powered mixer of unknown origin equipped for Neumann +48 power. The mics were loaned out and when they returned the ribbons were cut. The user said he couldn't use them because they were "dead". I'm just relaying what has happened to me in the past. Somehow, plugging them into the XLR plug caused this. Good luck! I've also experience interferrence using ribbon mics on Sony pro betacam video cameras in mic inputs equipped for their shotgun mics; a popping noise that sounds like a teletype writer at low levels. Ray
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
Try the low impedance setting. Ideally you want the device impedance very low and the mixer input impedance very high for minimal loading of the device output. One problem with tube pre's is they have lower impedances than SS and can be difficult loads to drive. It's surprising that the Mackie was a problem. You may have to use another gain stage, one with a very high input impedance and impeccable noise specs would be a must.
Wall mounted dimmers should be outlawed, you'll never get a clean signal where they're present.
Hi, Bill:Thanks for responding!
Actually, I tried selecting the low impedance position on the B&O microphones and the output was even lower than it was in the mid position. As I said, in the high position, the signal just disappeared for some odd reason. I sent Stephen Sank a note about this, but since his move from New Mexico to Arizona, he has not yet responded.
Here are my thoughts on this issue:
For one thing, the B&O microphones I own were almost contemporary with the Ampex MX-10. They should work well with that mixer. I do get a fairly decent level when connecting with the mixer, but all of the controls were nearly at their fullest rotation when this was accomplished, which was a surprise to me.
Since this is my first experience in attempting to use a restored pair of these classic ribbon microphones (even though I own some original RCA Varacoustics and a single 77-D, all of which still operate)I was expecting better levels from the B&O's once they came back from Stephen Sank. There is probably NOTHING wrong with what Stephen has done--he is an expert on this stuff.
Basically, I am concerned about the noise level at full rotation and more importantly, the susceptibility of the microphones to interference from house dimmer circuits and the low level hum that I have noticed thus far. Aside from the three connections on both ends of the cable, there is an extra side ground lug on the Neutrik plug connecting to the mixer side. I may want to insert a short jumper from pin 1 on the Neutrik (shield of the cable) to this little point on the side to see if anything improves.
Otherwise, they may be candidates for display because of their unique good looks!
Thanks again!
Richard Links
Berkeley,CA
The thing with the dimmers is that they mess up the AC everyway possible and throw off RFI that no amount of shielding or grounding will eliminate. Flourescents are almost as bad.
Hi, Bill:Just a little follow up on the B&O microphone "issue".
Last night, I brought the restored BM-4 ribbon microphones out to do a live location recording of a great chamber music ensemble over in Burlingame, CA. This was only test situation and I already had my trusty Milab microphones in-place with my Aphex 1100 going straight into my Masterlink.
I set them up, connected them to my restored Ampex MX-10 all-tube mixer and my Tascam DA-30-III DAT, and got them to work without any interference whatsoever. You were correct that the wall dimmer in my dining room, where I had run them up to test them, was the source of the previous encounter with RF, etc, fortunately.
Unfortunately, though they sounded MAGNIFICENT, there was such a high level of noise and such a lack of level that even though my test recording sounds decent, there is still the remaining issue of background noise. The Ampex MX-10 had to be cranked up full rotation (individual mic gain and master gain) to get decent level and then I had to crank up the DAT machine levels to give me even more gain. I had the B&O's operating in the M impedance position, since in "L" the output was too low and "H" did not work at all, not that I expected much.
Stephen Sank sent me a nice note indicating that I may need to stack up two mic pre's to get enough gain, or possibly insert an outboarded transformer to boost level and match them better.
I was not expecting this, however, particularly since the Ampex mixer is contemporary with the microphones and works just dandy with all other microphones, as long as you outboard phantom power to THOSE microphones. Anyway, I am working on resolving the issue of inadequate level now.
Thanks for your input!
Richard Links
Berkeley, CA
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