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Summary of Contents for GRAS 12AA
- Page 1 Instruction Manual 12AA 2-Channel Power Module with gain, filters and SysCheck generator...
- Page 2 Power Module Type 12AA Revision 20 05 2019...
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Page 3: Table Of Contents
G.R.A.S. Sound & Vibration CONTENTS Introduction and Description ........4 Polarization Voltage . -
Page 4: Introduction And Description
The G.R.A.S. Power Module Type 12AA (Fig. 1.1) is a dual-channel power supply for preampli- fiers used with condenser microphones. It is for general use in acoustic measurements as well as for intensity measurements; both in the laboratory and in the field. It provides: • a polarization voltage for two condenser microphones • a voltage supply for powering up to two microphone preamplifiers. • a choice of signal conditioning. A block diagram of its main components is shown in Fig. 1.2. Polarization Voltage The polarization voltage can be set to either 0 V or 200 V via an internal switch (see section 3.2). Use: • 0 V for prepolarized microphones, and • 200 V for externally-polarized microphones (default setting) 1.2 Preamplifier Voltage Supplies The preamplifier voltage supply can be set to either 28 V DC or 120 V DC via an internal switch (see section 3.2). Use: • 28 V for minimum power consumption (default setting), and • 120 V for maximum dynamic range Fig. 1.1 Power Module Type 12AA Power Module Type 12AA - Page 4... - Page 5 G.R.A.S. Sound & Vibration Power Module Type 12AA - Page 5...
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Page 6: Signal Conditioning
4 0 dB 1.3.3 Direct-mode Coupling Finally, the microphone signal from each preamplifier can be coupled directly with its BNC output socket via independent internal switches (see section 3.2), thus by-passing all signal conditioning. For intensity measurements, where extremely good phase matching is required, use Direct mode in both channels. Also, to fully use the dynamic range possible with 120 V pre- amplifier supply, use Direct mode, see also Section 4.2. SysCheck (System Check) The Type 12AA has a built-in 1000 Hz SysCheck generator for verifying the stability of the com- plete measuring system including the microphone. The signal level from the generator can be pre-adjusted before it is applied to the measurement set-up. A system check can be activated locally via a push button on the front panel, or remotely via a Mini Jack socket on the rear panel. SysCheck (or similar technique) can be used with preamplifiers supporting this feature, e.g. the G.R.A.S. preamplifiers Type 26AJ and Type26AL. Power Supplies The Type 12AA can run on internal batteries with a battery life of approximately 10 hours using G.R.A.S. preamplifiers, or from an external power supply of 12 - 18 V DC, e.g. the mains/line adapter included with the Type 12AA. Input/Output The Type 12AA has two 7-pin LEMO input connectors (A and B) for microphone preamplifiers such as the G.R.A.S. Preamplifiers Types 26AM, 26AC and 26AK. Fig. 2.2 shows the wiring dia- gram of these input connectors which are also compatible with a range of microphone preampli- fiers from other suppliers such as Norsonic, L&D and Brüel & Kjær. The corresponding outputs for the two 7-pin LEMO input connectors are available via standard BNC sockets (A and B) for direct use with analyzers, voltmeters, oscilloscopes etc. Power Module Type 12AA - Page 6... -
Page 7: External Features
Preamplifier Input Channels (In. A / In. B). 7-pin LEMO input connector for microphone preamplifier. Wiring diagram shown in Fig. 2.2 • Gain switches and Overload LEDs (In. A / In. B). Adjust the gain of each channel (attenuator/amplifier) individually to suit requirements and without overloading the input circuits (Overload LED lights up). Gain settings are from – 20 dB to + 40 dB in 20 dB steps. Disabled if Direct mode is selected (see section 3.2). When set to +40 dB, the Overload LED lights up with open input. This is normal. Power, On/Off toggle switch Battery-level indicator SysCheck adjustment Ch. A SysCheck adjustment Ch. B SysCheck push button Overload LED Ch. A Preamplifier input Ch. A Gain Ch. A, rotary switch (-20, 0, +20 and +40 dB) Overload LED Ch. B Preamplifier input Ch. B Gain Ch. B, rotary switch (-20, 0, +20 and +40 dB) Fig. 2.1 Front panel of the Power Module Type 12AA Power Module Type 12AA - Page 7... -
Page 8: Rear Panel
Remote SysCheck Start. • Mini Jack input for remote SysCheck start. Apply a + DC voltage of 4 - 9 V (e.g. from the RS232 output of a computer) to activate the SysCheck generator; centre pin +terminal. • Ouput channels (Out A / Out B). BNC socket for the output signal either via signal conditioning or directly from the micro- phone preamplifier. • Locking screw Unscrew to remove baseplate and gain access to internal setting switches. Fuse 315 mA (<1.5 Ω), 250 V Input for external power supply 12 - 18 V DC Remote SysCheck start Output Ch. A Output Ch. B Locking screw for baseplate Fig. 2.3 Rear panel of the Power Module Type 12AA Power Module Type 12AA - Page 8... -
Page 9: Internal Features
G.R.A.S. Sound & Vibration Internal Features Note: switch the Type 12AA off and disconnect it from any external power supply before remov- ing the baseplate for any reason. Afterwards replace the baseplate. The battery pack and user-servicable switches are contained within the cabinet of the Type 12AA. To gain access to these, first remove the knurled locking screw (see Fig. 2.3) and slide the baseplate off. Fig. 3.1 Showing the battery pack of the Power Module Type 12AA Battery Pack Take out the battery tray (Fig. 3.1) and replace all the batteries (10 x LR6 (AA) standard alkaline cells), making sure that the polarity is as indicated on the battery tray. User-servicable Switches The (internal) user-servicable slide switches are shown in Fig. 3.2. • Filter selection (applicable to both channels, disabled if Direct mode is selected): 3-posi- tion signal-conditioning switch; Lin. routes the signal through the amplifier alone H.P. routes the signal through the amplifier and the 20 Hz high-pass filter (e.g. to supress infra-sound) routes the signal through the amplifier and the A-weighting network •... - Page 10 • A-weighting Ch. B Polarization voltage Note: • Direct mode • 0 V Switch off the Power Module before chang- • Amplifier mode • 200 V ing any preamplifier power settings Fig. 3.2 Showing the internal switches of the Power Module Type 12AA Power Module Type 12AA - Page 10...
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Page 11: Operation
Preamplifier supply voltage can be switched from 28 V or 120 V. Use 28 V for minimising power consumption, it is also sufficient for most applications but limits the dynamic range of the micro- phone preamplifiers used with the Type 12AA. Use 120 V to utilise the full dynamic range of the microphone preamplifier. In this case the dynamic range will be determined by the Type 12AA which should be switched to its Direct mode (section 3.2) or its Gain switched to –20 dB to avoid overload. Filter Settings and Direct Mode There are three internal slide switches (section 3.2), two for selecting Dir. (Direct) or Ampl. (Amplifier) mode for the two channels and one for selecting which Amplifier mode, viz. (a) Lin. (linear), (b) A-w (A-weighting) or (c) H.P. (high-pass) filtering. In the Direct mode, all amplification and filtering circuits are by-passed for that channel; the signal goes directly from LEMO input to BNC output. Direct mode is preferable when using the Type 12AA in intensity measurements, which require extremely accurate phase response in both channels. In this mode, the corresponding Gain switch on the front panel has no effect and its overload LED registers nothing. In the Amplifier mode the input signals are amplified internally and passed through a selected filter. Use Lin. if no filtering is required. Use A-w if A weighting is required by the measurement standard. Use H.P. if low frequencies (below 20 Hz) are to be suppressed. SysCheck (System Check) SysCheck (or similar technique) can be used with preamplifiers supporting this feature, e.g. the G.R.A.S. preamplifiers Type 26AJ and Type 26AL. Use SysCheck to verify the stability of a complete measurement set-up. If the signal registered by the measuring equipment as a result of activating a SysCheck remains unchanged, then system stability (including the microphone) can be assumed. Power Module Type 12AA - Page 11... -
Page 12: Service And Repair
G.R.A.S. Sound & Vibration Service and Repair Repairs should be carried out only by qualified personal. The Power Module Type 12AA should not be dismantled with power on because of high-voltage circuits. Power Module Type 12AA - Page 12... -
Page 13: Specifications
Inherent noise: (20 Hz - 20 kHz with input grounded) A-weighted: < 1 µV Lin: < 1.6 µV (20 Hz - 20 kHz with G.R.A.S. preamplifier and 20 pF dummy microphone) A-weighted: < 3,2 µV Lin: < 5.7 µV (values valid for +20 dB and +40 dB gain re. input) A-weighting filters: Compliant with IEC 60651 Type 0 High-pass filter: 3-pole Butterworth, – 1dB at 20 Hz Output impedance: 30 Ω Power supply: 10 x LR6 (AA) standard alkaline cells, or DC mains/line adapter supply: 12 V - 18 V Power consumption: With one G.R.A.S preamplifier using:- 120 V: 190 mA 28 V: 160 mA Fuse: 315 mA (low impedance <1.5 Ω), 250 V Power Module Type 12AA - Page 13... - Page 14 19-inch Rack-mounting System Manufactured to conform with: CE marking directive: 93/68/EEC WEEE directive: 2002/96/EC RoHS directive: 2002/95/EC G.R.A.S. Sound & Vibration continually strives to improve the quality of our products for our customers; therefore, the specifications and accessories are subject to change. Power Module Type 12AA - Page 14...
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