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 1 
 on: Today at 10:38:43 am 
Started by karlengel - Last post by klaus
Condenser mics are not quite as fragile as you fear. But the obvious primary candidate for possible damage is the capsule with its micron-thin membranes.

And there, at least from my observation, it is fairly safe to assume damage to the performance if you can see wrinkles in the membrane (from the capsule whip-lashing against the inside of the protective basket, or, in the case of some pencil condensers, from the membrane making contact with the edge of the mic's capsule housing).

In the latter example, you will not be able to see the damage to the diaphragm platelet, but you may be able to see a dent in the housing, which would be indicative of a major hit having taken place.

If no diaphragm wrinkles, or deformation in the housing, can be detected, assume everything is ok.

The larger question (and answer) to whether more subtle damage occurred after a fall is indeed careful listening. And here, I would not rely on comparing current sound to past recordings, as exact mic positioning is always hard to recreate, but I would trust my ears which will tell me if the sound is grossly off from my expectation of stock performance.

What helps with even more subtle changes over time: compare your mic to a healthy specimen of the same model.

 2 
 on: Today at 10:22:26 am 
Started by mikezietsman - Last post by klaus
Thanks, Kai. Very thorough.

What I did not see covered in your method #2:
 
* how the new pin is secured in the plastic (glue?)
* how a smaller diameter replacement pin will make sufficient contact with the original (larger
   diameter) female counterpart in the mic's amp

 3 
 on: Today at 06:52:31 am 
Started by karlengel - Last post by karlengel
Condenser mics are fragile, but I often wonder how fragile?
If a mic has a fall, or is bumped hard, is damage going to be obvious? Or is there damage that could have happened that creates subtle changes, requiring careful listening to previous recordings, then new ones repeated under similar conditions by the same voice, to tell the difference?

 4 
 on: Today at 06:40:29 am 
Started by mikezietsman - Last post by Kai
I should have added that you cannot replace individual pins; at least, I have not been able to:

Transplanting a pin from another head, or fabricating home-made copies usually fails, because of the heat required to solder them to the remaining stump: the plastic in which the the original pin is encased, melts. Likewise, removing the stump and gluing a new pin is labor intensive and needs some experience.

But if anyone has found a better, simpler way to deal with a broken head pin, let us know!
The summary and essence of my lengthy post below:
Use water for cooling the plastic while working on it.

---

In detail:

 I had the problem of soldering parts that are stuck into plastic several times, so I developed a simple way of dealing with it.

There are two possible ways to work around the broken pins, both would use the same basic approach:

First you have to unmount (Klaus's instruction see below) and desolder everything from the bottom plate where the pins are stuck in (make a photo to later know which wire goes where).
Do not heat up the connections for more than a few seconds while doing so, or the plastic will melt and the pins will come loose.

Next place the plate into a platter filled with water and using tissue soaked with water to cover the top of the plastic except leaving a very tiny area around the pin you're going to work on.


Now you have two options, either completely replace the pin or soldering an extension just on top of what's still there.
Soldering on top is easier, but will not make a very strong mechanical connections so it will easily break. This might be sufficient if you do not remove the microphone's head on a regular basis.

If you are going to solder on top, clean up and scratch the remains until you see pure metal.
Then pre-tin this area using high quality solder, a relatively hot iron (380°C) and a short soldering time.
Do this until you are sure the solder has really connected to the brass metal, not just being glued to it.
You might need to repeat the cleaning if the first attempt was not successful.
Now you can solder the pre-tinned replacement pin on top.
Always keep the working area's close surroundings wet to avoid melting the plastic.
.
.
The second and more professional way is, to drill out the remains of the old pin with a tiny drill.
It might be possible that you can pull out the remains once you removed the collar that holds the pin in place using a 2mm drill or a grinder.

If not, you have to drill very straight and very centered through the original, starting with a new sharp tiny drill 1mm or smaller.
In a second step drill just big enough to fit the replacement pin.

Doing so will heat up everything, so cooling like mentioned above is absolutely necessary. This time it's easy: just do it completely under water.

The replacement pin needs to have a working diameter of exactly 1.5 mm, anything smaller will not make reliable contact. There are a lot of connectors out there using this sized pins.

When everything is done, cover the serial number with plastic tape, then wash the plate with a mix of distilled water and pure alcohol, (whiskey won't do ;D ) dry and remount.


---

Here is a copy of Klaus's instructions how to dismount the basic plate:

The three large slot screws that hold the head assembly in the grill need to come all the way out. Place the head upside down (contact pins at top)

What is absolutely essential for removal:
BOTH ATTENUATOR SWITCHES MUST BE IN THE 'OFF' POSITION. If even one is not, the assembly will not clear the basket!

After removal of the screws, the best way to clear the nipples of the roll-off switches past the viewing windows in the head grill without breaking them off is to:

1.without trying to pull the head assembly out, slightly tilt it forward inside the grill (capsule moves toward the front of the grill)

2. grab the head assembly by the pins and lift up at the front only, until the purple pattern selector switch plate has cleared the grill completely

3. move the head assembly as far to the front of the grill (pattern selector = front) as possible.
This will be just enough clearance for the rear nipples to clear the grill

4. keeping the head assembly slightly tilted vis a vis the grill, lift it up and out. (Try not to tilt the capsule assembly so much that it can scrape the rim of the grill.)

Reassembly is in reverse.

P.S.: Never loosen the smaller brass slot screws located toward the center on the bottom of the head assembly: These affix the various switches inside the head assembly and the assembly's cover.

 5 
 on: Yesterday at 06:37:04 pm 
Started by mikezietsman - Last post by klaus
Neumann only sells the complete head assembly which does not include any of the original U87's high-impedance head components.

 6 
 on: Yesterday at 03:03:27 pm 
Started by mikezietsman - Last post by mikezietsman
I see. Then you followed my train of thought with very little to go on haha.

I was thinking to attempt a pin replacement using a narrower pin and some epoxy. With experiments first being done on a much more broken plastic head which I have in my possession.

Do you know if Neumann sells a less complete version of that mounting assembly for a lower price?

 7 
 on: Yesterday at 12:24:21 pm 
Started by mikezietsman - Last post by klaus
I should have added that you cannot replace individual pins; at least, I have not been able to:

Transplanting a pin from another head, or fabricating home-made copies usually fails, because of the heat required to solder them to the remaining stump: the plastic in which the the original pin is encased, melts. Likewise, removing the stump and gluing a new pin is labor intensive and needs some experience.

But if anyone has found a better, simpler way to deal with a broken head pin, let us know!

 8 
 on: Yesterday at 09:18:03 am 
Started by mikezietsman - Last post by mikezietsman
Thanks Klaus, that is incredibly useful info. Once I get the mic in person I will mull over solutions. I would rather leave the mic "stock" but It is good to know that work- arounds are an option!

 9 
 on: March 23, 2019, 06:18:41 am 
Started by klaus - Last post by afterlifestudios
Perhaps my understanding is not correct, but the few concerns I have about this are:

1.  Would the null at 90 degrees from each of the front/back cardioid pairs be as deep as the null at 90 degrees of a figure eight where the capsules are truly “back to back” with precise spacing. This proposed arrangement has them somewhat vrtically “staggered” so I’m not sure a convincing figure 8 would be achieved.  If this is the case I would expect the pick up patterns to “overlap” more with the other front/back pair and cause phase issues.

2. I find it difficult to believe that there is “no audible effect due to shadowing” when stacking km84’s the way I’m imagining it...  But besides “shadowing”, it would also seem impossible that the metal cylinder housing tubes of the km84 bodies would not create reflections that would combine with the unreflected sound to creat some kind of comb filtering.  But I have not measured it (or tried it), so I cannot difinitively say.

Cool to think about, though...
John



 10 
 on: March 22, 2019, 08:52:20 pm 
Started by mikezietsman - Last post by klaus
You can reassign #1 and #2 pins:
#7 is ground and not really necessary (original K67 don't have it), and you could use pin #6 (low end cut, which in its stock configuration is rather useless because it cuts a tremendous amount of low end when engaged. It will take some rerouting of wires, but if you download a schematic (http://recordinghacks.com/microphones/Neumann/U-87) you should be fine.


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