Cleaning a LDC (K67-type) capsule... with pics

[SSLtech]

So I had a complaint of a U87 with "noise" issues.

If you want to clean a capsule, I accept no responsibility for any damage that may occur. Cleaning capsules is a "last resort" when all else fails. It should NEVER be undertaken as a "routine" procedure, and -if tried as a regular "routine" will be more likely to cause mroe harm than good.

OLD CAPSULES MAY LOSE GOLD. Don't do it unless your only other option is tossing the capsule in the garbage!

Now, if you still want to carry on...

Here's what you need to clean one:

The mic, three CLEAN plastic cups, some DISTILLED water, some high-purity (91%+) alcohol, and a VERY soft, VERY gentle sable-bristle brush.

Oh... and a CLEAR work surface! Steady hands, and some patience. This may take an hour or two...


Here's the capsule to be cleaned:

Pretty nasty, huh?

Here's another view without flash:

Here's the view of the other diaphragm... not much better there, either!

So... here's how I personally do it:
In the first of the threee cups, I mix about a 1:3 concentration of alcohol : distilled water. the other two cups are distilled water ONLY.

At first, try water on its own, to loosen the dirt. Use the sable brush, touching GENTLY... and ALWAYS watching the 'reflection' of the gold surface to see how much pressure you're applying. NEVER press too hard, NEVER have the metal "collar" of the brush any closer than 2/3rds of the length of the bristles from the capsule. (if the metal collar touches the diaphragm, it may as well be all over!)

If there's some greasy buildup which makes the water 'ball-up" and run off, without removing the dirt, try the alcohol solution. Either way, ALWAYS rinse the brush in ONE of the two pure-water cups, (to put the dirt in the cup) and use the OTHER pure-water cup to rinse the brush, prior to returning to the capsule. That way the dirt shouldn't be carried BACK to the capsule you just cleaned.

Here's the work in progress:

NEVER allow the brush to "dig" into the capsule. This takes patience... patience... patience!

Here's how the water should look... a little bit of "sheeting" without too much "balling-up".

Okay, in the end, try "steering" the clean water to the edge of the capsule, and lift it off. Alternate the brush between the capsule edge and a CLEAN... LINT-FREE cloth, like "Texwipe" or similar.

remember, with the type of casule which has a clear, unplated ring around the edge, the clear ring is MORE important in terms of cleanliness than the gold disc itself! -It's counter-intuitive, but VERY important that the ring is clean.

Okay... so here's what it should look like when the dirt is gone:

...and here's what the cups looked like when I'd finished with this particular capsule:

That's all I can think to write for now...

S'late...

Keith

 

[SSLtech]

A quick comparison:

Before:

After:

Keef

 

[pucho812]

looking good. wanna wash my car next. Seriously though

thats some fine capsule cleaning keef.(in my best chief Wiggum voice)

 

[gyraf]

Thanks.

Suggested to mic meta.

Jakob E.

 

[Gus]

I don't do it that way

 

[rodabod]

Nice work, Keef. I was expecting to see a lot of gold-loss.

[quote author="Gus"]I don't do it that way[/quote]

Well, it looks like Keith's method works fine by the look of things and assuming it sounds fine.

 

[Gus]

Keiths post works as long as the gold still has a good bond to the PET.
I have been told Gold does not form a strong bond with PET and the coating is somewhat open so moisture, spilt and smoke from years of use might migrate to the backside and lift the gold just like paint lifts from wood.
Add water and the gold floats off.
You can clean a coating like that you need to think like an art restorer/cleaner

Also look at the back side of some u87 capsules, often I have seen a pin hole.

You don't want to get water inside between the PET and backplate.
Does anyone know if this was done at the factory as a pressure vent?

 

[ruairioflaherty]

Hey Keith,

great job - you can't be half as old as I thought you were or you'd never have the steady hand required :green:

A few questions-

-did you listen to the mic beforehand? If so what sonic problems was the dirt causing?
-if you've listened post cleaning did you notice a big sonic improvement?
-aside from the weight on the capsule does dirt on the outside affect the capsule electrically?

cheers,
Ruairi

 

[Jonkan]

Whats your way then Gus?

cheers!
/J

 

[SSLtech]

Gus is ABSOLUTELY right, the gold is more firmly attached to the capsule in more recently-made capsules. I am assuming that this is an aging issue, and not a change in manufacturing techniques.

Mind you there may possibly be a difference in adhesion between vacuum-depsosited gold and sputtered gold... The physicists and practitioners will most likely know more about that than I do.

Either way, if the gold looks "old", you would probably do particularly well to pay heed to the disclaimer at the top of the page. :green:

Ruari, The mic was noisy most of the time, sensitive to temperature changes and door openings. (see, here in Florida, the Air-Conditioning runs 24 hours a day, so the mic is kept cool and dry. As soon as a door to the outside world opens, warmer, moist air currents enter the room, and condnse on cold things. The dust on the capsule was hydrophilic (retains water) and was forming and retaining a conductive moisture "bridge" across the insulating 'ring' around the gold disc.

The result was that if you even breathed anywhere near the mic, or opened a door two rooms away, the mic would start to "rustle, rumble, snap crackle and pop". I just did a second one in similar condition and went through the procedure with amorris, so he'd see what was involved, and how much care and patience was needed. They were both returned to service, and are now only the "normal" sensitivity to moisture (as most U87's and U67's are).

Sonically, the mic works and sounds about the same, believe it or not. This is why I tell people who think that regular capasule cleanings might be a good idea to "keep the mic sounding atits best" that they may be missing the point...

Keith

 

[Emperor-TK]

I just cleaned a U87 capsule for a friend, so I thought that I would add my notes for posterity:

This particular mic was about 15-20 years old, and the capsule basically looked like the floor of a truck-stop bathroom. Apparently, the assistant engineer from 15 years ago didn't know that he was supposed to use a pop filter for vocals. Knowing that I was going to rotate the capsule, I did the front skin with Keith's more aggressive technique first, and I lost about 2-3% of the gold in random spots. Since the mic was used for about 10 years in a smoking environment, I figured that I would do the back skin too (especially since it was going to be the new front skin). For this side, I used Gus' wet and blot technique and didn't loose any gold. Both sides came out equally clean. I can't say if it was the difference in technique or the difference in the amount of dirt that was responsible for the gold lifting.

One thing that I came up with on my own that might be useful too: Before I started the wet clean, I came up with a technique to remove the dust and foam from the skin. I took my artist brush and brushed the dust, them I "blotted" the bristles on a the sticky side of a piece of scotch tape, which took the dust off the brush. I was able to get all the dust off the capsule in a matter of minutes with this technique,

-Chris

 

[gyraf]

From the Horses's mouth:

Cleaning the membrane:
Every membrane is carefully brushed with a very soft brush with distilled
water.

The water with the dissolved dirt can then be removed with very
soft blotting-Paper.

This procedure has to be repeated several times until
the capsule is really clean.

Those capsules which cannot be cleaned by this method have to be exchanged.

Cleaning the membrane by means of solvents is not allowed
These solvents are too thinly liquid and fugitive.
For careful cleaning then no time remains and inhomogenitives
may remain on the membrane;

solvents could also transport dirt below the membrane fixing rinqs:
solvents can also cool down the membrane strongly and then humidity can
condense below the membrane which cannot be removed from there.

Besides that the use of solvents bears the risk that the mechanical tension
of the membrane is influenced.

From:

http://www.neumann.com/download.php?download=info0028.PDF

title: GN-Info 88043, 04/1988, English, "Disassembling and Cleaning of Neumann Condenser Microphones"


Jakob E.

 

[j.frad]

the pictures have saddly disappeared...

 

[RuudNL]

I won't encourage capsule cleaning.
It is a very delicate process that requires a lot of attention and experience.
I have seen many capsules that were ruined by 'do-it-yourself' cleaning.
If it is really necessary, then leave it to someone with experience in this field.
This may be a bit more expensive than DIY cleaning, but certainly cheaper than a new capsule!

Joke: someone who had just 'wiped off' the gold from his microphone  capsule, asked me if I had a spraycan to apply a new layer of gold on the membrane of his microphone!  ;D

 

[globalpurpose]

I just cleaned a U87 capsule for a friend, so I thought that I would add my notes for posterity:

This particular mic was about 15-20 years old, and the capsule basically looked like the floor of a truck-stop bathroom. Apparently, the assistant engineer from 15 years ago didn't know that he was supposed to use a pop filter for vocals. Knowing that I was going to rotate the capsule, I did the front skin with Keith's more aggressive technique first, and I lost about 2-3% of the gold in random spots. Since the mic was used for about 10 years in a smoking environment, I figured that I would do the back skin too (especially since it was going to be the new front skin). For this side, I used Gus' wet and blot technique and didn't loose any gold. Both sides came out equally clean. I can't say if it was the difference in technique or the difference in the amount of dirt that was responsible for the gold lifting.

One thing that I came up with on my own that might be useful too: Before I started the wet clean, I came up with a technique to remove the dust and foam from the skin. I took my artist brush and brushed the dust, them I "blotted" the bristles on a the sticky side of a piece of scotch tape, which took the dust off the brush. I was able to get all the dust off the capsule in a matter of minutes with this technique,

-Chris

Hello , what is the "Gus s Wet and Blot" cleaning technique You re talking about ?

 

[kraml]

the pictures have saddly disappeared...

Try this: NEUMANN

 

[terry setter]

Kraml's link works. Thanks, Kraml.

 

[MicMaven]

In addition to the caveats and warnings above, I strongly advise technicians to avoid coughing and dripping hot solder on the delicate gold sputtered membranes . . . and please do not ask me how I know . . . James - K8JHR -

 

[kraml]

Kraml's link works. Thanks, Kraml.

Welcome! It's nice to contribute a little!