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Author Topic: Gefell M94 capsules - original or not?  (Read 3196 times)

AusTex64

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Gefell M94 capsules - original or not?
« on: June 01, 2016, 03:07:09 pm »

Please see the attached pic. I am trying to determine if these capsules have replacement diaphragms, or are they original? From left to right, my guess is no - yes - no.

The one in the middle with the black ring sounds noticeably different than the one on the right with no ring. Much more bass, more subdued highs. The one on the right used to have the black plastic cover with holes (Gefell calls it the "resonator"), it was removed. I have two more just like it that all sound the same - plenty of mids and highs, not a lot of bass. Sounds great on acoustic guitar. Have not listened to the one on the left yet, just got it yesterday.

As always, thanks for your help!
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panman

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Re: Gefell M94 capsules - original or not?
« Reply #1 on: June 01, 2016, 06:14:15 pm »

I would say it is not possible to make conclusions about if the capsules were reskinned or original from that pic. Better quality pics would be required and even then it would be hard to say. If you find S.T. written on the bottom, then the capsule was reskinned by Siegfried Thiersch. If there were still the seals with letters on the holes on the bottoms, before you took out the capsules, then it most likely means original(now the seals are gone anyway). 
The capsule in the middle is solely used in PM 750. Better not put it on M582 or MV690/691/692, because it is meant to use 40V polarisation only and those mentioned have 60V and that can/will cause arcing, that destroys the membrane. The capsule is the same as the the others, but at least the one on the left has a 10M resistor(the one on the right should have it too) to get the voltage down to 40V. PM 750 has it built in the mic-amp and thus does not need the resistor inside the capsule. You can swap the bottom of the middle-capsule with the bottom of the left one to use it on other than PM 750.
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Esa Tervala

AusTex64

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Re: Gefell M94 capsules - original or not?
« Reply #2 on: June 02, 2016, 01:38:20 am »

I'm using these capsules with a custom tube buffer replacing the MV691 FET buffer. Kind of a poor man's KM54. So the polarization voltage is set for 40V, thus no 10M resistors on the capsules.

I thought the plastic rings would be an indication of possible reskins. That and the sloppy glue on the middle one. There are no ST initials on the bottom of the capsules. I just haven't seen enough of these to make a determination. The main thing that made me suspect a reskin was how different the one in the middle sounds than the one on the right. The middle one has a lot more bass.
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panman

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Re: Gefell M94 capsules - original or not?
« Reply #3 on: June 02, 2016, 06:24:31 am »

I thought the plastic rings would be an indication of possible reskins. That and the sloppy glue on the middle one. There are no ST initials on the bottom of the capsules. I just haven't seen enough of these to make a determination. The main thing that made me suspect a reskin was how different the one in the middle sounds than the one on the right. The middle one has a lot more bass.

Gefell was using those plastic rings sometimes or the reflectors you mentioned and sometimes not a bit depending on the time the capsules were made. The older M62 did not have a ring or reflector, at least i haven`t seen them on those. Thiersch reskins sometimes have a gold-sputtering (done only upon request), so that might be another indication. The sad thing is, that the M62 and M94 are soundwise all over the place today, because they are already old and the galvanized nickel used does not preserve as good as the rolled nickel of k54 and there are many bad ones among them too these days. Due to the difficulties Gefell had of getting good materials behind the iron curtain, the quality was not always stable and especially the contact spring inside the capsule tends to corrode causing failure. You really need luck to get a good N62/M94, but it is possible, if you get enough of them. They are not that expensive yet.
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Esa Tervala

AusTex64

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Re: Gefell M94 capsules - original or not?
« Reply #4 on: June 02, 2016, 08:49:30 am »

Thank you for your response. How would you define a good and bad M94 soundwise? That's what I'm really tryng to get a handle on. Is the middle one with more bass "right", and the others are not? Or vice versa? How does diaphragm degradation affect frequency response with these nickel capsules?
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panman

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Re: Gefell M94 capsules - original or not?
« Reply #5 on: June 02, 2016, 11:34:17 am »

How would you define a good and bad M94 soundwise? That's what I'm really tryng to get a handle on. Is the middle one with more bass "right", and the others are not? Or vice versa?
Reduced bass is usually a sign of a bad capsule, but also subdued highs, so there is probably something weird going on with the middle one. A good M62/M94 comes close to a kk54. Though very similar, M62/M94 has some minor differencies to k54, most meaningful beeing the back-plate holes, so it cannot sound the same. I have seen only a few getting very close to k54 AB:ing with two Km54:s. How to know if the k54 is good? It is difficult to be absolutely sure if no known to be good capsules are around.Testing a couple and if they sound the same, the capsules are supposed to be good. Testing with a known source tells you a lot.
How does diaphragm degradation affect frequency response with these nickel capsules?
That can vary a lot. Reduced bass or reduced anything like volume too. Sometimes there are no warning signs and it just stops working. With reduced tension the bass may increase and the highs get subdued like the capsule in the middle, but then it may not take long that the back-plate sucks in the membrane and final damage will happen. Wrinkles and discolorations are bad signs. 
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Esa Tervala

AusTex64

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Re: Gefell M94 capsules - original or not?
« Reply #6 on: June 02, 2016, 03:48:30 pm »

I also emailed Thiersch the picture, and they responded that while they could not be 100% sure, it appeared the middle one might have been reskinned by them.

I listened to the one on the left last night. It sounds like the three others I have, or at least very close. I now have four modified bodies and four capsules that sound pretty close, whcih is workable.

There appear to be no wrinkles or pinholes in these diaphragms when examined under a magnifying lens. They look pretty good, and decently clean too.

I think you are right about comparing to a KM54 to get a baseline for what I'm after. That should tell a lot. Gotta find the time to do that soon. And a willing KM54 owner!
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