Nor1447 Preamplifier-BNC adaptor and microphone equivalent

The line input adaptor Nor1447 provides a BNC line connection to a ½” preamplifier such as Nor1201. The main application is for connecting an electrical signal to a microphone preamplifier. But it may also be used to connect a transducer like an accelerometer to the high impedance input of a microphone preamplifier or as a “dummy microphone”. A built in screened capacitor in series with the line signal prevents the polarisation voltage from damaging the line signal source (Except from the Nor1447/S). The attenuation of the signal is small due to the design with use of a screened capacitor that is connected to the preamplifiers guard ring. The most popular version is the Nor1447/2 that has a capacitance equal to a ½” microphone. Other versions with other capacitance are available. Please note that all versions are for connection to a 1/2″ preamplifier. Each unit is individual calibrated with calibration certificate for the capacitance (Except from Nor1447/S).

The following versions are available:

Nor1447/S – Direct connection without serial capacitor
Nor1447/L – Low input capacity version C=2pF or 6.8F
Nor1447/2 – Replaces a 1/2″ microphone load. C=18pF

Using the Nor1447 as Microphone Equivalent – “Dummy microphone”
A microphone equivalent is mainly used to determine the electrical self noise of a sound level meter. The microphone is replaced by the microphone equivalent. As the microphone equivalent has impedance similar to that of the microphone cartridge, but no sensitivity to the acoustic field, the level displayed on the sound level meter will be the electrical self noise of the sound level meter including the preamplifier.

The capacitor used in the Nor1447 is a high quality type to minimise the microphone effect of the capacitor.

All units (except from /S and /L) are delivered with a BNC shortage plug included. The 1447/x with a BNC shortage plug connected equals to a microphone equivalent.

The method is not usable for measurement of the thermodynamic noise of the microphone cartridge.