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[chconnor]

[update note: Just re-read the forum rules... this is a "cross post" in the sense that I had a thread going on another forum about this mic and posted similar questions, but now that I know what the issue is, I brought it here to seek more expert advice... I hope this doesn't violate the letter or spirit of the cross-posting rule; if so, please delete. It's not my intention to scattershot audio boards with this.]

Hi there - I've read all the threads warning me, wisely, no doubt, not to attempt cleaning the diaphragms on my mic (CAD E-350) myself. I believe I understand how crazy it is to try.

I'm considering barging ahead, anyway. I just bought the mic very cheap (because of its issues), and I'm willing to risk its demise. It's cutting out when breathed on in a way that sounds exactly like the descriptions I've read about dirty skins. I've eliminated battery issues (it has two), etc etc.

The center connection shows some corrosion around the screw terminal. What I'm wondering about is the risk of distilled water finding it's way into the threads of that center screw. I'm also wondering if I need to worry so much about that corrosion: since it's not at a part of the membrane that moves, and since (AFAIK) it is electrically connected to the skin anyway (i.e. this is not contamination causing an electrical bridging that isn't already there), maybe I should just leave that part alone (and dry) and focus on cleaning the main part of the skin and the non-metallized ring on the edge. (I'm assuming that unscrewing that center screw is a terrible idea.)

Any advice is welcome, though again, I know most experts are loathe to give advice on this subject, and I understand why, and don't necessarily expect an answer. :-)

I'd also love any recommendations of a north american tech who does this work, and/or any rough ballparks on how much this kind of cleaning would cost me to have done.

Pics at:

http://lacinato.com/cm/images/stories/capsuleclean/CAD-E350-capsule-front.jpg
http://lacinato.com/cm/images/stories/capsuleclean/CAD-E350-capsule-back.jpg
http://lacinato.com/cm/images/stories/capsuleclean/CAD-E350-capsule-back2.jpg

Thanks!
-Casey

[Kai]

Here's how I did it on a mic that's price wouldn't have justified to be cleaned by an expert.
It's a center tapped type LDC.
It failed in normal use as instrumental mic, so I had nothing to lose.
Inspection showed a lot of residue (spit) on the diaphrag, much more then in your pictures, where I can see just some dust.

I used:
- double distilled water.
- isopropyl alcohol 100%, chemically pure.
- a very soft fine artists brush (expensive, natural rotmarder (redmarten?) hair, with natural tips).
- A binokular working microscope (set. to 10x magnification).

- First I washed the brush with alcohol 50% + distilled water 50% several times.
- I wetted the brush with little distilled water 90% + alcohol 10% (put it into the fluid and shook out the most).
- I carefully wiped the diaphrag from the edge to the center by holding the brush angled flat to the surface, using only the tip of the hairs, to minimize pressure.
After drying I could see a little white residue close to the center tap, that didn't hurt.

Since then (some years ago), the mic works without problems.

I would not recommend this for an expensive or older mic, as the probability to break the diaphrag unrepairable in some way is quite high.

The problem starts with the selection of the correct solvent and how to apply it.
Brushing like I did will very likely remove the gold coating from older mics, something I've seen when I tried the same on a broken capsule with perforated diaphrag I used for testing.

Regards
Kai

[chconnor]

Thanks Kai. that's helpful.

My plan at this point is to use a dry (or lightly steam-moistened, as in the Josephson post going around: http://www.josephson.com/clean.txt) to carefully pull off dust particles without rubbing them in to the skin. Assuming i can get most of them off that way, then I'll try wrapping a q-tip with fluffy cotton (again, per Josephson), lightly moistening it, and try to coax the residue off without brushing or rubbing any more than necessary.

I have 99% isopropyl if I need it. I might use the brush wet for the un-metallized band at the edge. (I have a very soft, but synthetic brush.) I have a hand lens for magnification, and bright lights.

Given what i've read, I'm gaining some confidence that water won't seep under the outer edge of the ring holding the skin.  Also it sounds like it probably won't go down the center tap screw, so I might try to clean there with the brush, too.

Of course, things may not go as I plan, in which case I will improvise. :-)

-c

[Kai]

...down the center tap screw, so I might try to clean there with the brush, too.

Don't overdo the cleaning, it's only important to clean the goldless outside ring of the diaphrag.
This is why I wiped from out- to inside, a little remains on the inner part doesn't hurt.

Regards
Kai

[chconnor]

Don't overdo the cleaning, it's only important to clean the goldless outside ring of the diaphrag.
This is why I wiped from out- to inside, a little remains on the inner part doesn't hurt.

Ok, will do, thanks. The importance of the goldless ring is that that's where the capacitance bridging happens, right? And it's safer to clean because there's no gold on it, i assume...

In terms of my mic being over-sensitive to moisture, the corrosion around the center screw tap is probably irrelevant, yeah?

I wanted to get some of those dried-residue areas cleaned up; e.g. the smear on the front skin from the center out to the edge (goes up from the center)... i was suspecting that these might be contributing to the cutting out, and that if I only cleaned the edge ring it would be a temporary fix only.... ?

Thanks,
-Casey

[klaus]

Before contemplating even an experimental diaphragm cleaning, you need to remove the center screws that affix the lead-out wire eyelets to the two diaphragms to inspect how much of the conductive gold is gone in that vicinity.

If the eyelet or its washer underneath do not touch and conduct over at least 80% of the gold sputtering at the mounting surface, no cleaning will revive this capsule.

[chconnor]

Thanks Klaus, I will do that.

-Casey

[chconnor]

I unscrewed the screw off the back diaphragm... looking pretty bad under there. The screw itself offered no resistance... as if it was already started to be unscrewed. Here's a pic (of the back -- screw on the front is tight, I didn't remove it yet...): http://lacinato.com/cm/images/stories/capsuleclean/CAD-E350-capsule-back-noscrew.jpg

Since there's risk of water/alcohol getting in the hole, and I have no brilliant way to prevent that, I assume this is where the experiment ends.

The capsule was working fine except the cutting-out-with-moisture issue... so does this situation mean that the capsule can not be recovered by a professional? Or just that cleaning this at home is twice as crazy as it already was?

If the capsule is a loss (meaning: it'll cost hundreds of dollars to repair), then I'll go for it, but if it's salvageable for like <$200, I'll put off my experiment and get some estimates from techs...

Thanks again,
-c

[radiovinhet]

There's oxidation under the screw?

[chconnor]

Sure is... (see the picture linked in the last post). Well, I don't know what it is, exactly, but it's there.

My very uneducated guess is that someone was using the mic without a screen or otherwise recklessly and spit or water or other humidity was landing on the capsule, gathering around the center taps, and causing the problems seen there. The fact that the back diaphragm screw was totally loose was interesting to me, too... like maybe the buildup somehow worked the screw loose, or maybe the previous owner took it out to have a look...

Anyway, given Klaus' last post, I decided I was more out of my depth than I could handle, and sent the mic off to a tech for professional attention, and will report back later. Hopefully they can work some magic.

One thing I learned: if you're removing the center tap screw, have that diaphragm facing down, so the washer isn't left behind on the surface of the skin, needing to be picked up somehow. :-)

-c

[chconnor]

Just a report back on what finally happened... I sent it to the tech, he sent it back a week or so later. It works fine now.

Here are the "after" pics:

http://lacinato.com/cm/images/stories/capsuleclean/CAD-E350-capsule-after-front.jpg
http://lacinato.com/cm/images/stories/capsuleclean/CAD-E350-capsule-after-back.jpg

I'd be interested in anyone's opinion on the job he did. I mean, the mic works fine now, so he did a great job, and he was a pleasure to deal with, but just curious if anyone has any thoughts on the work. What did make me a little nervous was the green plastic-like fibers you see that apparently got stuck under the perimeter screws. Not hurting anything by being there, i'm sure, but i pulled them off. Just seemed a little rushed, maybe? And do such fibers seem like a safe thing to clean a diaphragm with?

He obviously didn't touch most of the diaphragm: all the dust and smears are still there, and seems to have just cleaned around the perimeter, which I assume is because the idea is to break the transient conductivity between the skin surface and the edge of the capsule, and since there is no gold there it's safer to work. You can see that a tiny bit of gold came off in the bottom right of the back skin (not a big deal, i know).

The center tap screw corrosion is still there, though I don't know what he might have done in the hole itself.

I'm hoping this is just the mark of a wise professional who applied the lightest touch necessary to get the job done, and not the mark of a rush job. Sound right?

He mentioned that I was very lucky in one aspect: he recommended that I not touch the mic any more before sending it to him, and, taking him perhaps too literally, I sent it without re-screwing the screw into the center tap on the back skin. Little did I know that there is a washer underneath the skin that keeps it off the back plate. By some miracle (probably all the corrosion/residue built up in there) that washer didn't fall out of place... he said that if that were to happen the capsule would likely be a loss. So, ironically, the corrosion might have saved the day. :-)

-c

[klaus]

I would ask you tech to remove the fiber strands. The reason: once moisture or humidity hits the capsule, some of the strands may bridge and conduct between the capacitor blades, and may cause discharge noise.

As to the spacer underneath the membrane: no big deal. If it were to be dislodged, it can be repositioned without harming the capsule.

[chconnor]

Thanks Klaus - I did remove the fibers, they came off easily.

And interesting to know the spacer isn't as crucial a mistake as he thought.

-c

[mike zietsman]

I would ask you tech to remove the fiber strands. The reason: once moisture or humidity hits the capsule, some of the strands may bridge and conduct between the capacitor blades, and may cause discharge noise.

I remember finding an old u87 for a very good price that was dropping out when breathed near.

Before I took it to my tech to clean I decided to open it up to see if it was anything obvious. I removed a single fine fibre (with my fingernails believe it or not) and it hasn't dropped out since (even during a direct breath test). It was a very lucky find though as the fibre was pushed up against the outer ring and touching the actual diaphragm - thus making a direct bridge.

It's as close as I have ever come to cleaning a capsule succesfully...