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CMV 5 overview

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CMV5 frontside

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CMV 5 backside with heating resistor

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TELEFUNKEN VF 14 inside the CMV 5B

VF 14

Stereo microphone with 2x M7 capsule -not so well known!

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The M49 debuted in 1949 . The microphone was designed on contract for the IRT, the governmental regulating arm of the German broadcast system. The salient feature of the M49 was that it was the first condenser microphone capable of remote pattern control, achieved through electronic means. By varying the rear-diaphragm voltage against the backplate reference, a full range of patterns, from omni to cardioid to figure-8, was accomplished. A Dr. Grosskopf held the patent on this method of pattern selection.

The 49 had several other interesting features, including one of the first attempts to limit the effect of grille resonance on the response. Because the grille is slanted and presents a continuously varying profile to the capsule, there are fewer standing waves generated. It is also an interesting microphone because it was one of the first to incorporate a special ultra-miniature triode tube specifically designed for microphones. This was the MSC2, which was later refined and further miniaturized before seeing mass production as the AC701. The M49 used the same capsules as  the 47.M7 and K47.

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M7 capsule

The M7 capsule first showed up in 1933 and was skinned with a 10µm PVC. The material back then had to be – and still is today at MTG as well as STM – casted on water. ( The thickness of the material fluctuates between 10 and 12µm. After the war Neumann Berlin obtained their M7 capsules from Gefell, later on only the membranes . In 1955 Neumann Berlin hired a chemist responsible for the production of membrane films . In 1956 the first M7 capsules with PET polyestermembrane showed up. Those new capsules had a much better longterm stability as well as (because of the thinner membrane of about now only 6µm) the remarkable side effect of better low frequency response. In more than 50 % of all M49 microphones that were fitted with a M7, you can still find the M7 PET capsule, not only (like often times falsely assumed) the M7 PVC capsule. Since 1958/59 the M7 was abandoned and replaced by the K47 capsule. The failure rate in the production process of the M7 capsule was simply too high since you only had about 10 minutes to correctly position and finetune the membrane until the glue started to stiffen . The cogset of the K47 made it easier to finetune the membrane (it now got screwed on instread of glued Because of that the failure rate of the capsules got reduced drastically and so about 80 or even 90 % of the capsules could now be used after production. Back then the PET 6µm membrane film was obtained by the companies that also produced the capacitors.DSC00793

M 7 PVC; M 7 PET; K 47 old version ; K 47 new version

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a description of all in the U 47 microphone used transformers:

1. The oldest transformer used in the U 47 P (same amplifier, but with a Z2 adapter for the M7 capsule)

2. First transformer in the U 47, used in microphones up to a serial number of around 700, mounted in the frame vertically manufactured by Neumann & Co. Gefell, 32 x 40 mm
Type GN 107

3. Second transformer in the U 47, serial number between about 700 and 1300, mounted vertically with the frame manufactured by Neumann GmbH Berlin, 30 x 35 mm
Type BV-08 (it’s hardly possible to distinguish from the outside if there is a GN 107 or a BV-08 on the inside)

4. Third transformer in the U 47, used in microphones with a serial number between estimated 1300 and 5700, embedded lying in the mounting plate
manufactured by Neumann GmbH Berlin, 30 x 35 mm
Type BV-08

5. Fourth transformer by HAUFE, used for repair services, identical to BV-08, but with a “4 hole”-mounting

Soundwise there are no differences between transformers 2 – 5,
but transformer 1 has about 1 db less output at around 50 hz, as well as 1db less output at 20 khz (compared to the other mentioned transformers).

These statements are a little vague though, since every now and then microphone and transformer combinations show up, that differ from that classification. I suppose it could be, that during the beginning of the fabrication in Berlin still sometimes transformers were ordered at Gefell. Also often times the transformers got changed during maintenance and repair. This is similar to the exchange of capsules. Sometimes old U 47 microphones with a k47 capsule show up, even though at the time of production of some of those microphones the k47 didn’t even exist yet. That means that they were exchanged some time during service.
On about 95 % of all U 47 microphones the serial number was also engraved or swaged on the inside of the microphone.  When comparing the serial numbers  inside of the microphone with the one printed on the outside, you may notice that those sometimes differ from each other. I suppose that sometimes owners of multiple U 47s simply may have mixed up the housings of the microphones during e.g. tube swaps or maintenance work. Also some U 47s without serial number on the foot exist. Usually this are microphones from an early production stage, or from when Neumann had to change the foot when the connection thread got broken somehow.

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Transformers from U47`s

1. from U 47 P
2. GN 107 in metal case  from TELEFUNKEN / NEUMANN U 47 very old version ~ -> # 500
3. BV 08 in metal case from NEUMANN / TELEFUNKEN U 47 old version ~ # 500 -> # 1300
4. BV 08 normal series after # 1300 ( repair vrsion by HAUFE )
5. BV 08 new version made by HAUFE