The Glory Hole - dark spot at centre of Neumann-Gefell capsules.

Hi!

Does anyone recall seeing a thread with pictures showing a Neumann or Gefell centre terminated capsule with dark spots spreading out from the centre, where some component (copper?) in the solder had alloyed with the gold membrane.

I remember finding this during a search relating to CMV563, UM57 or UM70, but failed to bookmark it. Actually, it might have been over at PSW, but I can't see it there either.

I'll keep looking!

Cheers

Stewart

It was over at PSW. Affects RFT, Gefell.... (East German), and Russian mics like the Lomos. I think it was a Lomo that was the example at PSW IIRC.

Someone at gearslutz was calling that the "tone hole;" apparently you get a more vintagey sound if you sing towards it.

Right! Thanks Roddy. Probably why it didn't come up when i searched again. I'll look for lomo.

Really I'm wondering at what point this goes from being cosmetically undesirable to becoming a cause for reskin (beyond 'suck-it-and-see'!). Presumably the alloy created will still hold charge, but the weight of the diaphragm may increase, oxidation may occur, and the surface may become more hygroscopic etc.

kato said:

Someone at gearslutz was calling that the "tone hole;" apparently you get a more vintagey sound if you sing towards it.

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Right...  ???

OK, found the lomo thread.

http://recforums.prosoundweb.com/index.php/m/218162/3507/

In that thread a galvanic effect is mentioned, which I hadn't considered but makes sense (My background training was chemistry, so I should have thought of that!). I've definitely seen a picture of an M7 style with a similar effect.

kato said:

Someone at gearslutz was calling that the "tone hole;" apparently you get a more vintagey sound if you sing towards it.

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I can repeat this effect with my "glory hole '69" mod if you like.

rodabod said:

I can repeat this effect with my "glory hole '69" mod if you like.

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Oh dear god. Don't google that mod....

zebra50 said:

rodabod said:

I can repeat this effect with my "glory hole '69" mod if you like.

Click to expand...

Oh dear god. Don't google that mod....

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Bwahahahaha!!!

You guys are a crack-up.

Back on topic, and the reason that I mentioned this is that I have an M71 and UM70 capsules. I'm blind-testing these with a (modified) CMV563 and a M691 head amp.

One of the capsules is noisy and problematic.

The other has the dark spots and sounds great.

I don't for a moment subscribe to the 'glory hole' theory (loving the name - that's going to stick) and I'm sure the problematic one has other issues which I need to sort out.

I'll investigate further, although taking these apart is a PITA.

zebra50 said:

Back on topic,

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Sorry bout that...
I was always under the tutelage that diaphragms, unless audibly crapping out, should be left as is.
A blind A/B could be a good starting point to see if the 'glory-hole' is sucking sonics or not...

Here's a Neumann capsule suffering from Glory Hole affliction:

http://recforums.prosoundweb.com/index.php/m/159339/0/

I couldn't resist opening up the M71 for a photo. And so here's a snap of my glory hole...



This capsule sounds OK to me. If I hadn't noticed the discolouration I would not have thought twice about this one. Is the discolouration really due to copper crystals? I could get some scanning electron microscopy done on this to confirm that theory, but it's performed at high vacuum and would probably wreck the PVC membrane.

If it sounded crap I wouldn't hesitate to get it reskinned and get the analysis done. Is the knowledge worth more to me than a working PVC capsule? What a dilemma!

The Glory hole?

Beyond suck-it-and-see?



You guys need to stop now.

;D ;D

Don't fuck... ah...mess with a working capsule. If it sounds good and doesn't crap out, I wouldn't worry about the discoloration.

You might wanna have a look at the noisy capsule, though. The capsule in my UM92 was totally fucked. The glue had come off and the diaphragms warped badly. It still worked and even sounded okay, but the output was low. As I had bought the mic used, I thought it was just a noisy tube. The seller said it was checked recently, and, as you say, the heads are a pain to open. So I kept swapping tubes instead of having a look at the capsule. When I finally did, I couldn't believe my eyes. The capsule looked so bad, I was surprised it worked at all. I also bought a non-working MG head from a colleague that showed the same symptom. Warping diaphragms seem to be a common problem, at least for M7 capsules of a certain period. I have a much, much older UM57 whose capsule is fine. Anyway, I had my warping M7s reskinned by Siegfried Thiersch, and now the UM92 sounds very nice and is low noise. Excellent service.

Thanks Rossi,

In this case the other one looks fine - just dirty & showing the usual humidity sensitivity - dust and salty spit on the diaphragm conducting, I'm pretty sure. I've cleaned it tonight and will give it a test over the next few days to see how it goes. Otherwise off it goes for a new diaphragm.

I'd read these were tricky capsules to disassemble, but it wasn't bad once I'd figured them out. More on that soon, in another thread.

You guys need to stop now.

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I know!