Product Data 1/2” Microphone Preamplifier Nor1209 Applications • Sound level meters • General purpose • Laboratory and eld measurements Low noise High input impedance Wide dynamic range Wide frequency range Low output impedance System Check facility Large supply voltage range Detachable preamplier cable The microphone preamplifier Nor1209 has been designed for general use with most ½” condenser microphone of type WS2 or LS2 according to IEC 61094-4: Measurement microphones - Part 4: Specifications for working standard microphones. The microphones may be pre-polarized or use externally supplied polarization voltage up to 200 V. By the use of adaptors, the preamplifier may be used for other microphone sizes. The frequency response covers the range from below 1 Hz to above 200 kHz. The Nor1209 preamplifier may be mounted directly on a sound level meter like Nor140, or may be connected to the instrument by a suitable cable. The preamplifier is equipped with the system check facility. By supplying a test signal voltage on one of the terminals, the capacitance of the microphone as well as the complete signal chain from the microphone cartridge to the indication of by the sound level meter may be checked. The voltage gain of the preamplifier is very close to one or correspondingly 0 dB. As the input impedance is 10 GΩ, the attenuation due to loading of the source will mainly be determined by the low input capacitance.

Cables Long cables have a capacitance that may limit the slew-rate of the output signal. This will reduce the upper frequency response for signals with large voltage swings. Such limitation will be a non-linear process and may therefore also disturb the low-frequency content of the signal. The table shows the maximum frequency in kHz for linear operation as function of the cable length and level. For +120 V or ±60 V supply, connect the positive power supply to pin 6. For +28 V or ±15 V supply, connect the positive power supply to pin 5 as this will 3 Polarization voltage 7 Power supply - increase...