G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 4
Fig. 1.1 Power Module Type 12HM
1.
Introduction and Description
The G.R.A.S. Power Module Type 12HM (Fig. 1.1) is a 10-channel power supply for the follow-
ing types of G.R.A.S. preamplifiers and microphones when making low-noise measurements:
•
1-inch Preamplifier Type 26HF with 1-inch Microphone Type 40EH
•
½-inch Preamplifier Type 26HH with ½-inch Microphone Type 40AH
With these, sound-power measurents of low-noise products, such as disk drives, can be made
under anechoic and/or semi-anechoic conditions according to IEC 3745:1977.
The Type 12HM provides:
•
polarization voltages (200 V) for 10 condenser microphones
•
voltage supplies (± 15 V) for powering 10 microphone preamplifiers
•
individual response setting, Pressure or Free field, for each channel
•
individual gain adjustment of ± 3 dB for each channel
1.1
Polarization Voltage
Polarization voltages of 200 V are supplied via the 7-pin LEMO EGA 307 1B sockets on the front
panel.
1.2
Preamplifier Voltage Supplies
Preamplifier voltage supplies of ±15 V are supplied via the 7-pin LEMO EGA 307 1B sockets on
the front panel.
1.3 Input/Output
Each channel of the Type 12HM has a 7-pin LEMO EGA 307 1B input socket for the G.R.A.S.
microphone preamplifiers mentioned above, viz. Types 26HF, and 26HH. Fig. 2.3 shows the
wiring diagram of this input socket.
The output of each channel is available via a standard BNC socket for direct use with analyzers,
voltmeters, oscilloscopes etc.
