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[aamicrophones]

Hi Klaus, how has the Thiersch-manufactured PVC capsule overcome the tendency of the softening agent or modifier which creates application failure in pressure sensitive films where the plasticisers are found to migrate into the adhesive system causing the film to delaminate from the substrate surface and cause the "crinkling effect"?

My sense is the U47 with its large wirewound filament dropping resistor that ran very hot was a contributer to the early aging of the M7 capsule and the stress fractures in the PVC film were the result of the temperature changes between the microphone being on then cooling down when it was turned off.

Are the PVC formulations better now and the newer tube microphone generate less heat because they don't have the large filament dropping resistor that generated more heat than even the VF14 tube.

Cheers, Dave

[Klaus Heyne]

Dave, I am not privy to Thiersch's PVC formulations. That's his proprietary domain.

It is true- PVC does dry up with time; yet, I am not aware that there are PVC formulations that have the mechanical properties of the traditional formula, but avoid the deterioration over time.

The devil is in the detail with PVC: one manufacturer of PVC capsules no longer has access to the original, post-WWII powder. When that was replaced, with a current formula, the capsules no longer sounded the same.

[aamicrophones]

Hi Klaus, I hypothesize  that the PVC was more likely to "age" quicker in the U47 which ran quite hot as there would be a greater difference in the temperature between when it had been running for a few hours and then turned off after the session.   It is my novice understanding of PVC film that these temperature difference age it more quickly.


Cheers, Dave

[Jim Williams]

Andy Simpson wrote on Sat, 21 March 2009 03:52

Barry Hufker wrote on Fri, 20 March 2009 19:59 There are examples by DPA, Sennheiser and Sanken.  Schoeps also makes a claim about ultrasonics, but the most dramatic example is linked here, the Sanken CO-100K: http://www.sanken-mic.com/en/product/product.cfm/3.1000400 Hi Barry, This is a great example of the trade-off. Looking at the frequency response (15dB up at 50kHz) and the quoted distortion spec (<1% @125dB SPL), I would expect really really high levels of distortion in the ultrasonic range where sensitivity peaks. In this case, the worst thing that can happen is that there actually is ultrasonic acoustic energy, because it will simply 'fold down' to the audible range in the form of intermodulation distortion. Andy

Then you can add to the stew the effects of hf DC converter oscillators that are observed under a scope. Many popular mics show large amounts of HF oscillator leakage into the audio path, looking much like record bias on magnetic tape. I know of no research into the possible negative effects of this type of intermodulation to the audio path but since so many makers use this topology, it would be a great AES paper if AES was interested in analog electronics enough to publish it.

[J.J. Blair]

aamicrophones wrote on Sat, 21 March 2009 15:40

Hi Klaus, I hypothesize  that the PVC was more likely to "age" quicker in the U47 which ran quite hot as there would be a greater difference in the temperature between when it had been running for a few hours and then turned off after the session.   It is my novice understanding of PVC film that these temperature difference age it more quickly. Cheers, Dave

You should see the M7s that were in my M49s, then.  Just as crappy as any I've seen in a U47.

[David@The-Tone-Room]

Klaus;

I wonder, in addition to listing your favorite M7 replacement capsules, if you could provide some information as to actually finding and purchasing one of those capsules.  (For example, how would I go about identifying and purchasing a Microtech Gefell M7 from 4 or 5 years ago? Or, how would I find and identify a Berlin M7?)

If it's not appropriate to provide vendor details in the forum itself, could you perhaps by email?

Many thanks!

David K

[Klaus Heyne]

Microtech Gefell PVC M7 are easily recognized by two unique features.

One, the center screw has a 1.0mm thread, rather than the 1.2 mm thread which was and is standard on all Neumann capsule lead-out screws. Though you cannot see the thread when the screw is fastened, its smaller head size gives it away. (someone else can supply some nice JPGs to illustrate!)

Second, Gefell used, and still uses, Neumann's M7's pre-World War II ridge configuration:

Looking at the rim of the capsule, you will recognize several concentric ridges and troughs that are visible under the stretched diaphragm, towards the edge of the capsule, where the diaphragm is glued to the backplate. Neumann used three ridges, Gefell two.

However, after the war, Neumann used many different configurations as to width of ridges and troughs, which allow for M7 period classification, yet there were always three ridges, until the introduction of the K47, which had only one.

When discussing visual identifiers, please keep in mind that Gefell's backplate configuration for its current-day Gefell M7 with Mylar

[J.J. Blair]

Klaus, I just wanted to chime in and say that I got a chance to test one of the Thiersch made M7s the weekend.  The blue line is the PVC?  

It was fantastic!  I don't know how to compare it to a Berlin M7 in proper condition, but  I have a Gefell M7 that is less than ten years old, and a recently reskinned (by Gefell) Berlin M7, and I referred it to both.  The high end was gorgeous and I preferred the over all timbre.  I also compared it to a cream K47 that I have here, and the mid range was smoother.  The K47 was piercing, in comparison.  I might even replace the K47 with the M7, after further testing, I liked it so much.  I need to do some tests on an upright bass first to see what the low end is like.  

If you're telling me that there's another 5% better they can still go with these, I'm terribly excited to hear what that will sound like.  I would totally recommend anybody consider using these as a replacement in their U47.

I'll try the M49 tests later!

[delcosmos]

This is really good news JJ. I hope it passes the upright bass test too. I have a beautiful U47 that really needs a new capsule. I don't want a re-skin.

Thanks for the report.

delcosmos.

[Klaus Heyne]

J.J. Blair wrote on Mon, 13 April 2009 11:59

...I don't know how to compare it to a Berlin M7 in proper condition, but I have a Gefell M7 that is less than ten years old, and a recently reskinned (by Gefell) Berlin M7, and I referred it to both.

Agreed, compared to the recent Gefell PVC output, the Thiersch M7-PVC wins, and wins in a manner fairy obvious to even a casual listener.

But that comparison (as sad as what it says about Microtech Gefell's current M7-PVC quality) is not relevant for anyone who wishes to replace an original capsule in his precious U47/U48 or M49. That standard (and my expectations) is higher: The capsule  has to deliver magic.

You may be right we are still a few (but vital!) percentages short of that magic with Thiersch's new PVC capsules.

[MDM,]

hmm....

think I'll get thiersch to re-skin, the re-skin he did in mylar years ago on a capsule I have.

JJ

do you find that the top-end is a bit 'gummy' ?

[J.J. Blair]

Max, no.  Clear as a bell.  

[synthetic]

Klaus Heyne wrote on Mon, 13 April 2009 15:14

...compared to the recent Gefell PVC output, the Thiersch M7-PVC wins, and wins in a manner fairly obvious to even a casual listener. But that comparison (as sad as what it says about Microtech Gefell's current M7-PVC quality) is not relevant for anyone who wishes to replace an original capsule in his precious U47/U48 or M49. That standard (and my expectations) is higher: The capsule  has to deliver magic. You may be right we are still a few (but vital!) percentages short of that magic with Thiersch's new PVC capsules.

Are new production Gefells to be avoided? A few years ago that was one of your top picks.


Jeff Laity

[Klaus Heyne]

If with "Production Gefells" you mean MG microphones with PVC M7 capsules (there are only two models in the company's current line-up, if I calculate correctly), it is hard to imagine how a mic can sound frequency balanced, emotionally attractive and musical if its capsule is so harsh and constricted in the mids as these capsules now are.

It has been widely reported by those in the know that MG finally ran out of the original PVC material they were using for decades a few years ago (in addition to the retirement of the original diaphragm specialist.)

I can tell you this with confidence: MG's PVC capsules made until about 5-10 years ago were outstanding, and fully compatible with the quality expected of an original Neumann Berlin M7 from the 1950s. Quite a few of them had the 'magic'.

On the other hand, MG's polyester (Mylar) M7 are among the best one can find these days.

[synthetic]

I was looking at a UMT 70S. Their website doesn't specify if the capsule is PVC or Mylar, "The pressure gradient transducer is a dual capacitor design using a single brass back plate and two large diameter gold plated plastic membranes."