The Neumann M149 Large Diaphragm Condenser Microphone
The M149 Tube built from 1995 to current, is a variable dual diaphragm microphone. The K49 capsule well known from the legendary U47 and M49 microphones is followed by a tube functioning as an impedance converter. In contrast to earlier concepts, utilizing a transformer, the tube is complemented with a transformerless output circuit design. The M149 Tube can feed long microphone cables without any coloration.
Two slide switches are located below the large, acoustically very open head grille. The selection switch at the front allows for one of nine directional patterns. The slide switch at the rear operates a seven-step high pass filter. It allows a very fine adjustment of the cut-off frequency.
There are nine polar patterns to choose from, making this microphone an ideal choice for a wide range of recording situations. As its ancestors, the M149 Tube is a superb vocalist microphone, not only because of the capsule, but also due to its modern circuitry, characterized by extremely low noise level.
The polar pattern switch selects one of nine directional patterns: omnidirectional, wide-angle-cardioid, cardioid, hypercardioid, figure-8, and one additional intermediate pattern between each major position.
The circuit of the M149 microphone has been developed to exceed traditional designs. We have selected a modern tube (triode) and combined its exceptional transmission characteristics with the advantages of our proven transformerless output circuit. The aim was to provide a more controlled environment for the audio signal on its path from the capsule to the output section.
The final stage is an integrated amplifier, especially designed for such applications. It features very low distortion (THD < 0.002 % at ± 10 V), very low self-noise, and high output current capability.
As a result, the tube circuit is completely decoupled from the microphone output and its characteristic response curve will be unaffected by very high signal levels or varying load conditions. The lower output impedance and higher output current capability allow cable lengths up to 300 m (1000 feet) without any degradation of the audio signal.
The tube amplifier changes the high impedance of the capsule and adds 10 dB of gain to the audio signal, providing optimum operating specifications. The wide dynamic range is impressive, as peak output can be ±10 V, at 20 mA.
The ideal operating point of the tube is maintained throughout its entire life expectancy. Plate current and filament voltage are constantly regulated. A sensor circuit monitors and compensates for any voltage drop across the microphone cable. The tube is heated up slowly through inverse current limiting to guarantee long life. Optimum operating conditions are reached within a very short time.
A seven-position slide switch is located on the back of the microphone. It selects a high-pass filter, advancing in half-octave steps between 20 Hz and 160 Hz (-3dB). This filter is useful to suppress rumble from air-conditioning and in windy situations.
In addition, the filter provides an effective tool to control the audio signal when the microphone is used at close distance and therefore proximity effect alters the program material. ~ Info courtesy of neumannusa.com