Neumann & Co. Gefell CMV 551

The legendary microphone company Georg Neumann and Co. was founded by Neumann and Erich Rickmann in 1928, in Berlin, Germany and the business produced high quality cutting lathes as well as their first microphone, the CMV3 bottle microphone., which consisted of a large body containing the high impedance tube amplifier circuit and transformer. In 1932 the CMV3 was updated to use interchangeable lollipop style heads with different patterns.

Production continued in Berlin through to 1943, when the Neumann factory was damaged by allied bombing and the company relocated to the small town of Gefell. After World War II, Gefell was in the area of eastern Germany controlled by Russia, and later the Soviet Union, who eventually took over and nationalised the factory. Georg Neumann resumed manufacturing in the Western part of Berlin with a new company called Georg Neumann GmbH, which is the company we know today as Neumann. These events led to the farcical and confusing situation of having two separate companies selling microphones with the Neumann name. For clarification we will refer to the East German company "Neumann & Co. Gefell." After the reunification of Germany, the former East Germany company became Mikrotech Gefell.

The CMV 551 was the first new microphone to be designed and built at the Neumann & Co. Gefell. factory in East Germany after WW2. This new model used an EC92 triode tube which allowed the body of the microphone to be much smaller and lighter than the large and imposing CMV3.

The 551 was quickly replaced by the CMV 563 which was a very similar design with a slightly revised circuit to improve signal to noise performance. The 551 uses the grid and cathode of the tube to provide the polarisation voltage for the capsule, whereas the 563 takes the polarisation from the high volt supply, via a suitable voltage divider and filter capacitor. However, the CMV 551 was powered by the N551 power supply which used a higher voltage than would be required by the later CMV 563. Consequently, the power suppled for these two models were not compatible with one another.

Both CMV 551 and CMV 563 use the same family of interchangeable screw-on capsules, including the M7, M8, M9, and M55K. These allow the user to change the pattern of the microphone by swapping the head assembly. A "Bajonett-Gewinde (G/B)" adapter allows compatibility with the earlier bayonet-mount capsules that were used on the CMV3.

Our example is pictured with an M8S and M55K capsules and has been modified internally to 563 specification.

From the CMV 563 manual - when used with M55 capsule.

The CMV 563 condenser microphone is a truly universal microphone. It is particularly well-suited for speech and music recordings of the highest transmission quality, i.e., for studio use. The microphone's robust mechanical construction ensures high operational reliability. Depending on the application, the M 55K microphone capsule can be replaced with the M 7S or M 8S capsules. Furthermore, the older M7 or M8 capsule types can be used by screwing on the G/B adapter.

The ability to use microphone capsules with different characteristics allows the microphone to be adapted to the most favorable acoustic conditions.

The microphone is connected via the shielded C 57 microphone cable. The cable length between the microphone and the power supply can be up to 100 m. The N 61 power supply unit is provided.

• Frequency range: 30 - 20,000 Hz
• Transmission factor: approx. 1.6 mV / μbar
• Distortion at 200 µbar 1000 Hz: approx. 1%
• Gain at 80 pF equivalent capacitance: -0.5/+1 dB
• Balanced output: < 200 Ω
• Operating voltage: 120V
• Anode current: approx. 0.9 mA
• External voltage: approx. 15 μV
• Charging voltage: 80V
• Heater voltage: 5.8V
• Heater current: approx. 142 mA
• Tube (low noise): EC92
• Size and weight: 420 x 120mm; 0.4 kg

A post about the CMV 551 at Micpedia

A history of the Neumann company at ElektroAkustika

A manual for the CMV 563, dated 1966.