How can I measure a ribbon microphone ?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

andre tchmil

Well-known member
Joined
Jun 4, 2004
Messages
1,654
Location
land of chicon
I have two identical Ribbon microphones here; One of them gives me a much lower output although the ribbbons on both seem to be ok.
Is there a safe way to measure them ?
 
If you disconnect the transformer from the ribbon assembly (only one side) then you can measure the resistance of the ribbon motor.

Just place an accurate digital ohm-meter on each clamp or terminal and compare the resistances. Should be in the range of 0.25 - 2.0 Ohms. It depends on the mic. Some people say this can be dangerous, but it should usually be ok. It is only really dangerous if you test through the transformer because the current gets stepped up.

At this point (with the transformer disconnected, you can also make a (very rough) check of the transformers by checking the resistance on the primaries and the secondaries.

I would have a good look at each ribbon. Make sure that they are not slack (loose), that they are straight, that they are flat (not bent), that they still have good corrugations and finally, that they don't touch the magnets or pole-pieces.

Does the more quiet one have less bass?
 
[quote author="andre tchmil"]
Yes , one of them has less bass
[/quote]

Is the one with less bass the quieter one? It could be the ribbon then....

Are they exactly the same model of microphone?

BTW, I am still waiting for a cable in the post so that I can test my B&O stereo ribbon microphone - it could have two broken ribbons! (I hope not!)
 
[quote author="andre tchmil"]
I have a stereo type also, if you need the pinout.[/quote]

Ohhh! Great!

I might have to PM you about the pin-out when I get the cable and connectors. :razz:
 
[quote author="rodabod"]If you disconnect the transformer from the ribbon assembly (only one side) then you can measure the resistance of the ribbon motor.

Just place an accurate digital ohm-meter on each clamp or terminal and compare the resistances. Should be in the range of 0.25 - 2.0 Ohms. It depends on the mic. Some people say this can be dangerous, but it should usually be ok. It is only really dangerous if you test through the transformer because the current gets stepped up.
[/quote]

Why would you want to do that?

It would not tell you anything except there is an electrical contact, but if it gives at least some signal you already know that.

The DMMs in that range are exceptionally nonlinear and won't tell you if there is some clamps corrosion. But on the other hand, some excessive noise would tell you that immediately.

I remember, there were a few suggestions here from Jacob and PRR as for how to measure ribbon resistance accurately, make a search. I do it on GenRad 1650A bridge.

Andre,

The problem is most likely in the ribbon itself. The duralum these mics were ribboned, unlike aluminum tends to harden with time and lose its compliance. It can look OK, but the first symptom of this problem is LF and output loss.

I'd check the ribbon resonance, the first thing.
Alnico magnets lose their field with time, and should be also checked.
If you have some spare time, you could also try swap transformers between mics, to see if something has changed, although I highly doubt they would be a problem.

As far as I know, nobody anymore re-ribbons B&O with original corrugation. Actually, it would not be possible with use of aluminum foil as a ribbon.

If you cannot find anybody to re-ribbon them, send the mics my way, and I will do it for you. PM me if you are interested.
 
[quote author="Marik"]
Why would you want to do that?

It would not tell you anything except there is an electrical contact, but if it gives at least some signal you already know that.
[/quote]

Fair point, it is not exactly scientific, but if you are comparing two identical microphones and find a difference in resistance reading, then his would point the problem to the motor assembly and away from the transformer.

Also, another wee check on some tightly-fitted ribbons is checking continuity between the ribbon and the pole-pieces / magnets. This can highlight if a slack ribbon is touching the sides. I had this problem recently with a Beyer M260. It looked fine, but the ribbon was occasionally touching the magnets.
 
hey ...
ribbon clamp corrosion .. good suspect here ..
i have an RCA 74b from ebay .. stated "not working"
when i got it .. i cleaned the xlr .. it worked .. but .. stil somethng was wrong ..
i pulled it apart and simply used my finger to press on the clamp .. (kinda hard) and BAM! pretty ribbon mic !

this method is kind of non-intellectual .. but it gets results ..
the best solution ,if that is the case , is re-ribbon or if the finger thing does 95% of what you need then .. your done... :grin:
so ... try giving it the finger (in another way hehe) LOL

ALSO: if the ribbon touchs the magnet/pole structure even the tiniest bit you can have problems too...
hope this helps.

later
ts
 

Latest posts

Back
Top