U87 degraded sponge on capsule mount.

[Electrobumps]

My U87 is cutting in and out, typical dirty capsule issue. Opening up the mic there is a sponge on the capsule mount. It is degraded and depositing debris all over the capsule.

What does this sponge do (apart from getting the capsule dirty). Obviously this has to go but can I forget it. the 87i does not seem to have this and I see quite a few vintage 87's with no sponge and some with sponge. I imagine the ones with the sponge will at some point suffer the issue I have.

 

[k brown]

Only there to reduce reflections from the plastic dome below the capsule. At some point Neumann dropped it. Others can give more info on safely removing any loose/remaining debris.

Of greater concern is, it looks like the diaphragm has wrinkles.

 

[Electrobumps]

Only there to reduce reflections from the plastic dome below the capsule. At some point Neumann dropped it. Others can give more info on safely removing any loose/remaining debris.

Of greater concern is, it looks like the diaphragm has wrinkles.

I actually cleaned the mic several years ago. It was probably the sponge starting to degrade that caused the issue back then. I noticed the wrinkles on the capsule which freaked me out. However the mic had never sounded off to me.

It is the back side of the capsule and I'm pretty sure this is from production. I figured they put the badly skinned side of the capsule on the rear by choice. I don't see how this could have happened over time, but happy to be corrected on this. I'll post a close up tomorrow of the skin in decent light.

i'm happy with its performance and it sounds like an 87 to me. I have to admit I have no detailed knowledge of how the two skins interact and I only use it on cardiod for vocals.

 

[k brown]

Well, on cardioid setting, the rear diaphragm is inactive.

 

[soliloqueen]

Only there to reduce reflections from the plastic dome below the capsule. At some point Neumann dropped it. Others can give more info on safely removing any loose/remaining debris.

Of greater concern is, it looks like the diaphragm has wrinkles.

they chose to move the capsule upwards instead iirc, might want to look into getting an extender

 

[Electrobumps]

Well, on cardioid setting, the rear diaphragm is inactive.

isn't the negative signal of the rear used for cancelling?

 

[k brown]

No, the two capsule halves are both cardioid; in cardioid setting the rear one is simply off.

If they're both on, and the rear is positively polarized, you have omni; if both on and the rear is negatively polarized, you have figure 8.

Sometimes, if the front diaphragm gets damaged, but the rear one is OK, and the user only wants cardioid, the front and back will be swapped by a tech.

 

[soliloqueen]

No, the two capsule halves are both cardioid; in cardioid setting the rear one is simply off.

If they're both on, and the rear is positively polarized, you have omni; if both on and the rear is negatively polarized, you have figure 8.

Sometimes, if the front diaphragm gets damaged, but the rear one is OK, and the user only wants cardioid, the front and back will be swapped by a tech.

you are right about it being inactivated in cardioid, but the rest is how a k67 works, not a k87. the u87 doesn't have a dc-dc converter, so it actually achieves figure 8 by positively polarizing the rear backplate at 48v to invert the signal. that's why the k87 has isolated backplates.

can we see the front? if the front has the issue, then the front has the issue...

 

[TLRT]

I repaired many of these, usually tantal cap problems, and the broadcasters sometimes smoked cigarette near the mic, not always possible to clean it. Usually I just clean them or order a new capsule, change the tantals and they are ready to go,very reliable mics.

 

[k brown]

Is this a U87, or U87A?

 

[Electrobumps]

It's a U87 with a battery compartment. Originally used for voiceovers. the front of the capsule looks great as pictured and pretty clean from spit and grime. It's just foam dust.

I'm just curious if people think this is bad production or is the result of an incident. Can one side be repaired or is it a new capsule?

 

[soliloqueen]

I'm just curious if people think this is bad production or is the result of an incident. Can one side be repaired or is it a new capsule?

drefahl can measure side A and redo side B until it matches, IIRC.

 

[GeorgeToledo]

I think the wrinkles are more likely from a drop or hit, as opposed to naturally happening on their own.

 

[soliloqueen]

I think the wrinkles are more likely from a drop or hit, as opposed to naturally happening on their own.

Definitely. Just saw something really similar when a customs agent dropped one of my capsules.

 

[Electrobumps]

I purchased complete with a few dings. So it for sure has had one or two heavy falls in the past. I would have hoped when purchased I would have tested all patterns......I don't remember now.

The mic has only just come out of storage after a trip across the Atlantic. Hopefully when my overpriced lab grade distilled water arrives I will be able to test figure 8 and omni.

 

[xeawr]

I repaired many of these, usually tantal cap problems, and the broadcasters sometimes smoked cigarette near the mic, not always possible to clean it. Usually I just clean them or order a new capsule, change the tantals and they are ready to go,very reliable mics.

what went wrong with the tantals?

 

[TLRT]

what went wrong with the tantals?

They fail and go into short-circuit.(mic stop working in that case,no sound) Easy to check with a DMM.

 

[Khron]

They fail and go into short-circuit.(mic stop working in that case,no sound) Easy to check with a DMM.

"Comforting" to know that can happen even in strongly current-limited situations

 

[TLRT]

"Comforting" to know that can happen even in strongly current-limited situations

They are min 40-50years old,what can we expect? At least they won't smoke or blow up as there is no high current on them. I still like the old 87's because they are easy to service and reliable mics with good sound.

 

[Khron]

... As if i didn't distrust tantalums enough already...

"... But the tooooone..."