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[Oleh Malyy]

I would appreciate advices how to clean up this M7 capsule

and

[klaus]

Your question implies that you are inexperienced in cleaning capsules. The chance that you will ruin the capsule if you were to try it is close to 100%.

What you should therefore NOT do: use a brush to remove the hard debris or use water (let alone alcohol) on the diaphragms. While PVC (my assumption that this older Gefell M7 capsule you are showing does not have Polyester membranes) is not hygroscopic, it is very hard to remove any type of cleaning moisture from the cracks that weather-checking in the gold deposits form.

A long way to tell you that removing contamination from this neglected capsule is not a job for a lay person, internet advice to the contrary be damned.
(I could go into the pitfalls of the interwebs as the almighty remedy for all that ails us, but maybe another time.)

[Oleh Malyy]

you are right - I have not such experiences.

And, yes, this is an M7 capsule from a Neumann/Gefell UM57 microphone

[klaus]

One more thought about the delicate cleaning of sophisticated condenser mic capsules:

Servicing capsules is not a growth market that would attract new apprentices to the field, because there is more profit in either re-skinning or replacing a capsule, regardless of whether that would be appropriate in all cases. Therefore, the few people who have experience with restoring capsule surfaces probably not grow much.  Hence the understandable desire of microphone owners to try to do it yourself. Hence the increasing number of capsules I see now whose surfaces have been damaged after amateurish cleaning attempts.

[soapfoot]

Klaus, do you utilize ultrasonic cleaning technology when cleaning capsules?

[Tim Campbell]

I agree with Klaus. In the last few years a large number of the capsules sent to me for re-membraning show obvious signs of amateurish attempts at cleaning. Most show a large loss of gold from the surfaces or worse, actual perforations.

Jim, the cleaning of each membrane is different based on it's condition. The least amount of cleaning necessary is always best.

Klaus, the time required to clean a capsule is much less than that necessary for re-membraning so the profit margin should be the same.

[Oleh Malyy]

Please PM me (or email direct: olehmalyy(att)gmail(dot)com) your offer (price, terms etc.) for cleaning this capsule.
Who can do that and have such experiences.

[Kai]

Therefore, the few people who have experience with restoring capsule surfaces probably not grow much.

Just by curiousity, not that I want to try that by myself:
what are the basic techniques for cleaning?

I don't ask you to tell us your business secrets, just the basics.

Regards
Kai

[klaus]

Chemically, ultrasonically, mechanically. Not always all three, and not always in that order.
Examples of deviation: ultrasonic on very thin metal membranes is detrimental to the membrane's pre-tension. Likewise, ultrasonic cleaning can dislodge fine particles between the backplate and its membrane. Likewise, mechanical removal before other methods on a capsule as shown here would severely scratch the gold deposit.

I also choose my chemicals carefull-after having destroyed a few of my customers' capsules and having to replace them with precious vintage ones from my stash- but that is really the only method to get better in this esoteric field: you can make some assumptions from the materials you are dealing with, but in the end, a few catastrophic mishaps along the way are the only way forward!

There was a thread in my old forum about this subject, as well as an extensive "sticky" in my "Sticky" forum. Read more there.

[gkippola]

I have a few AKG CK1 caps that I don't want to pay a bunch to have cleaned----is Trichloroethane a suitable solvent for removing polar stuff from these diaphragms, assuming one has good work environment for doing so?

[Tim Campbell]

Do you mean methyl chloroform or vinyl trichloride?
I wouldn't allow either of them anywhere close to a membrane. The metal is deposited on the PET film by evaporation, there is no other method used for binding it.
Even using isopropyl alcohol with any undue pressure will completely remove the gold. Remember what it is you're trying to remove - mostly spit,sweat, nicotine and dust-
all fairly soluble in water. Any other chemicals should be used in a very diluted form.

[kats]

What other issue can cause one side of a capsule to have no output assuming the rest of the mic electronics are as they should be?

I have a k47 with this problem, the capsule had been reversed years ago - probably for this reason. I ordered a new K47 from Neumann resigned to the fact that the original will probably need a less than desirable re-skin. With at in mind, I figured there's only one way to learn how to clean a capsule and "went for it". I think I did a decent job, and it seems like I never caused any damage. The front side sounds exactly as it did before (lacking in bass) and the back side still doesn't output signal.

Besides dirt getting in between the membrane and backplate (which surface cleaning will not help) what else could cause a capsule to "just stop"?

[Tim Campbell]

Tony, like all other electronics, if you hear hum most likely a broken or open connection . If you hear silence probably a shorted connection.

[klaus]

Why not start with the most obvious measurement of any capacitor, including one that is used as a microphone capsule?
Measure the capacitance between backplate and the front diaphragm. Then measure between rear diaphragm and backplate. There should not be a greater difference between the two measurements than ca. 10pf.

[Tim Campbell]

Although capacitance can tell you a lot, most people don't have capacitance meters that can read accurately within the 40-90 pf range. I've had customers give me capacitance readings from capsules that turned out to be more than 20pf wrong because they measured with a standard multimeter.