Tube Microphone
With nine different directional characteristics, the M 149 Tube can be adapted to very different acoustic recording situations. Like its ancestors, it is particularly suitable for speech and song. This is not only due to its capsule, but also the particularly low replacement noise level of its modern circuit technology.
The M 149 tube is discussed from the side. Its front side is marked by the company nameplate and the directivity switch. Below the capsule, a dome ensures dispersion of sound from the upper half-space, so there is no disturbing interference with the direct sound components. To protect against structure-borne sound, the capsule is elastically mounted. The capsule is surrounded by the large microphone basket of the old M 49, which is now acoustically more open and behaves sound-neutral.
There are nine characteristics to choose from: Omnidirectional, wide cardioid, cardioid, hyper cardioid and figure eight, each with an intermediate position.
Unlike other tube microphones, the M 149 Tube combines a specially selected tube (triode) with state-of-the-art circuitry. The aim of the development was to use the special transmission characteristics of a tube and to bring the hereby amplified capsule signal controlled, unadulterated and feedback-free to the microphone output. Therefore, the usual in tube microphones output transformer is not used. Instead, to drive the different output loads, a particularly suitable for audio signals integrated amplifier with very low distortion (THD <0.002% at ± 10 V), very small noise voltage and high current capacity is used. Thus, the tube is completely decoupled from the microphone output and can be used with its typical characteristic up to very high levels for the input signal conditioning. Due to the high output current capacity, cable lengths up to a total of 300 m are permitted for the M 149 Tube, without having to compromise on signal quality. The tube amplifies the capsule voltage by approx. 10 dB in order to completely eliminate residual influences of the downstream electronics. Nevertheless, a very high dynamic range is handled, as a peak output power of ± 10V at 20 mA is available. The ideal operating point (anode current, heating voltage) of the tube is stabilised during the entire service life. In the microphone cable resulting voltage drops are detected and compensated by a sensor line. The heating of the tube takes place with regard to a long service life gently by a retrograde current limit.
On the back of the microphone is another slide switch. It operates a high-pass filter whose cut-off frequency (3 dB) can be selected in half-octave steps between 20 Hz and 160 Hz. In this way disturbances of air conditioners or impact sound can be faded out in a very targeted manner. In addition, e.g. the volume of a voice can be flexibly measured using the proximity effect.
The M 149 Tube is powered by an 8-core cable from its special N 149 power supply. At its output, the microphone signal is on a 3-pin XLR connector. The microphone is supplied in an aluminium case as a set together with the 8-pin microphone cable, the power supply N 149 and the elastic suspension EA 170.
- Acoustic operation Pressure gradient receiver
- Polar pattern: Omnidirectional, cardioid, wide cardioid, hyper cardioid, figure eight and one intermediate position each
- Transmission range: 20 Hz ... 20 kHz
- Field transmission factor at 1 kHz at 1 kOhm: 34/47/62 mV / Pa (Omnidirectional, / cardioid / figure eight)
- Nominal impedance: 50 ohms
- Nominal load impedance: 1000 ohms
- Replacement noise level CCIR468-3: 28/25/23 dB (omnidirectional / cardioid / figure eight)
- Replacement noise level DIN / IEC651: 16/13/11 dB-A
- Noise level CCIR 468-3: 66/69/71 dB
- Noise level DIN / IEC651: 78/81/83 dB
- Limit sound pressure level (tube characteristic) for K <0.5% 120 dB / for K <5% 136 dB
- Maximum output voltage 18 dBu
- Dynamic range of the amplifier DIN / IEC651 for K <0.5% (K <5%): 101 (121) dB
- Power Supply Power Supply N 149
- Weight 730 g
- Diameter 70 mm length 201 mm
- Including aluminium case, 8-pin microphone cable, power supply N 149 A, elastic suspension EA 170, dust bag
