Broken M7... what would you do?

[dale116dot7]

What would you do in this situation?

I've repaired a bunch of mics (Sony C37's and AKG C414's) for a studio owner. He has a U47, and we found it needed a new cable. So I built one. We fired up the mic, all the voltages were right, but no output. If you talked really close, the output would come up and it would work properly for a few seconds (and it sounded beautiful). Then the output would go away. Conclusion? Original PVC diaphragm dried out, and there are cracks in the gold (you can see them through a microscope - and a capacitance meter).

So I have re-diaphragmmed several mics - my own, some Chinese ones just to learn how to do it, C37's. But I do Mylar, not PVC. And this is a U47... like a U47! He is open to putting new diaphragms on, but I have some reservations. I don't doubt that I could put on new diaphragms - I looked carefully at how it's glued and it shouldn't be a problem... but it's a U47.

What would you guys do in this situation?

 

[Emperor-TK]

Would there be any irreversible damage from reskinning it, from glue or anything? If not, go for it. If it isn't up to snuf, he can always get one of the usual suspects to give it a go.

It's only a mic capsule, not a religious artifact. :wink:

-Chris

 

[wilebee]

give it a shot

 

[soundguy]

seriously, if you reskin the broken capsule, what are you gonna break it? I would maybe not charge the guy if you dont get it working and have him send it off then, but so long as he knows what he's getting into I dont see the harm in trying.

dave

 

[gyraf]

Dale,

Think of it this way: If you send the mic in for repair at Neumann Berlin, they simply change the capsule and scrap the old one. So I think a repair attempt is a fair action here. The M7 system should be much easier to get on-spec after reskinning than e.g. the CK12 type.

But you may want to try a simple capsule+connection cleaning first - just in case there's un-visible dirt causing the trouble.

And let the owner know, that there's a real chance that a new capsule will be needed anyway...

Jakob E.

 

[Rossi]

Neumann Berlin don't have any M7 capsules anymore, they would probably replace it with a K47. For M7 capsule repair or replacement you better contact Microtech Gefell (formerly Neumann/Eastern Germany). They still produce M7 capsules using the original equipment and materials. They're nice and helpful people. Or you could try Gunter Wagner: http://member.telpacific.com.au/gunter/U47-Images.htm

Given the value of good U47 it's probably wiser to have it repaired by a reknowned repair shop than experiment.

 

[Gus]

I believe Klaus posted a name years ago mybe in the neumann pinboard about a German company that still did PVC replacement Thirsh(sp) is what I seem to remember.

 

[Rossi]

For all I know Microtech Gefell do both PVC and mylar.

 

[BYacey]

I think once the diaphragm is damaged the mic is wortlhless. Tell your customer you can dispose of this hazardous waste and ship it to me. I'll make sure it gets "processed" in a suitable manner :wink: :wink:

 

[dale116dot7]

Apparently the shipping wouldn't be that much... are you in Cowtown?

I think I will leave the decision to the customer, but I will tell him what his options are tonight, so he can decide. The worst that can happen is that the diaphragm lifts when I put the glue on, which can make the capsule tough to clean, anything else is easily recoverable.

-Dale

 

[Gus]

found two possables

http://member.rivernet.com.au/gwagner/forsale/prices.htm


http://www.thiersch-mic.de/


I would check what Jakob posted


Maybe you could rub graphite in the cracks, kind of like how some people make electrostatic speakers? Or is the capsule getting a "short' from the edge of the gold to the backplate via water vapor trapped in the PVC?

 

[dale116dot7]

After doing a bunch of tests to make darned sure the capsule was pooched, I re-did one side. It sounds different - very similar to the FET47 we had as a comparison, but less sibilance. We're doing the other side tonight, then choosing the best sounding side for the front. The proximity effect is larger with the new diaphragm, and there's more bass response.

 

[gyraf]

Well done, Dale :thumb:

Keep us posted..!

Jakob E.

 

[jensenmann]

:shock:
You did it!
BIG RESPECT
:thumb:
Jens