3–6 Dual Microphone Supply Type 5935 Brüel&Kjær
User Guide
Chapter 3 — Operation
Setting the Gain
If you need to send a signal into the Type 5935 other than from a preamplifier, for
instance for testing and alignment, adaptor WJ 0185 can be fitted. This adaptor
converts an unbalanced BNC to a 7-pin preamplifier plug. The supply voltages from
the Type 5935 are not available in this mode.
Always screw the locking ring on the input plug home to avoid mechanical vibra-
tions introducing noise from a loose connection. The electrical noise generated is
very short duration high intensity spikes that can cause overloads to following
circuits.
3.6 Setting the Gain
Once the power, inputs and outputs are correctly connected to the unit it is desira-
ble to set the system up for optimum performance. The idea behind the set-up
procedure is to provide the maximum dynamic range with the minimum noise floor.
The actual settings of the stepped gain switch and the screwdriver sensitivity ad-
just depend heavily upon the instruments used in the application.
Example:
Suppose that the output of the Type 5935 is attached to a piece of equipment which
has a reference level of 1V peak to peak, and the microphone/preamplifier combina-
tion gives an output of 50mVPa
-1
as stated on the calibration chart.
The microphone is attached to a Type 4231 calibrator which gives an output of
+94dB re 20µPa at 1kHz – i.e.1Pa. The output of the preamplifier is therefore
50 mV.
To amplify this 50mV to 1V, a gain of 20 is required. This is a 26dB increase. Set
the gain knob to 30 dB and adjust the sensitivity control with a small screwdriver
to give 1V at the input of the equipment; the preamplifier output has now in-
Fig.3.4 Preamplifier connections (external view)
921882e
Ground
Polarization
Voltage
Supply
Ground
Signal Input
Heater
+24V DC
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