G.R.A.S. 12AA 2-Channel Power Module with gain, filters and SysCheck generator

Connection: Traditional 200 V
Channel(s): 2

Typical applications and use

  • Building-acoustics measurements
  • Acoustic-transfer measurements
  • Sound-intensity measurements


It has the following signal-conditioning settings:

  • Linear-response
  • A-weighting
  • High-pass filtering

Whichever one is selected is applied to both channels.

The G.R.A.S. 12AA can be powered either by internal standard batteries or an external DC supply (12 V-18 V), e.g. a mains/line adapter. It is built into a sturdy anodized aluminium cabinet. The polarization voltage for the microphone fitted to the preamplifier can be set to 0 V for prepolarized microphones, or 200 V for externally polarized microphones. The voltage supply for the preamplifier can be set to 120 V  for maximum dynamic range, or 28 V for minimum power consumption. The  G.R.A.S. 12AA will run for up to 10 hours on fresh standard alkaline batteries. A Battery meter indicates the condition of the batteries.

The inputs are two 7-pin LEMO sockets (A and B) on the front panel which are wired up for G.R.A.S. microphone preamplifiers, e.g. 26AB, 26AC, 26AJ and 26AK, but are also compatible with other available makes of similar microphone preamplifiers.

The outputs are two standard BNC connectors (A and B) on the rear panel. Both channels have an overload indicator. The gain in each channel can be set individually from – 20 dB to + 40 dB in steps of 20 dB.

The standard A-weighting filter in each channel complies with IEC Standard 60651: Sound level meters Type 0. The high-pass filter in each channel is a 3-pole Butterworth filter with a – 1 dB cut-off at a frequency of 20 Hz. These filters are for reducing unwanted low-frequency signals, e.g. caused by wind-induced noise on the microphone.

For intensity measurements, which require extremely good phase matching, the preamplifier signals can be coupled directly to the outputs of the 12AAby selecting direct output. This makes the output of each preamplifier available free of any signal conditioning.

A built-in precision 1 kHz oscillator enables a complete check of each measuring channel when used with G.R.A.S. preamplifiers 26AH, 26AJ or 26AL, which include SysCheck. The oscillator can be activated directly via a push-button on the front panel or remotely via a mini-jack connector on the rear panel. The output level of the oscillator can be individually adjusted in each channel using a small screw driver on potentiometers accessible via holes in the front panel.

The cabinet of the 12AA is 1/12 of a standard 19-inch rack; up to 12 of these Power Modules can be mounted in a standard 19-inch rack using the AK0040 Rack-mounting System.


All G.R.A.S. products are made of high-quality materials that will ensure life-long stability and robustness. The 12AA is delivered with a 2-year warranty. The warranty does not cover products that are damaged due to negligent use.

Service and Repairs

All repairs are made at G.R.A.S. International Support Center located in Denmark. Our Support Center is equipped with the newest test equipment and staffed with dedicated and highly skilled engineers. Upon request, we make cost estimates based on fixed repair categories. If a product covered by warranty is sent for service, it is repaired free of charge, unless the damage is the result of negligent use or other violations of the warranty.

Frequency range (±1 dB) Hz 3.5 to 200 k
Frequency range (±3 dB) Hz 2 to 250 k
Output channel(s) 2
Output impedance Ω 30
Direct coupling input to output Yes
Inherent noise, LIN (20 Hz to 20 kHz), grounded input µVrms <1.6
Inherent noise, A-weighted, (20 Hz to 20 kHz), grounded input µVrms <1
Inherent noise, A-weighted with dummy preamplifier (20 Hz to 20 kHz), µVrms <3.2
Inherent noise, LIN with dummy micophone (20 Hz to 20 kHz) µVrms <5.7
Gain settings, 20 dB steps dB -20 to +40
Gain error dB < 0.2
A-weighting filter according to IEC 60651 Type 0
High-pass filter 3-pole Butterworth, -1 dB @ 20 Hz
Linear mode Yes
SysCheck level @ 1 kHz Vrms 1
Type Traditional power supply (LEMO)
Input channel(s), traditional power supply 2
Channel separation (20 Hz to 20 kHz) dB >65
Preamplifier supply V 28 / 120
Polarization voltage V 0 / 200
Overload indication Yes
Power supply, battery 10 x LR6 (AA)
Power supply, external Vdc 12 to 18
Power consumption mA 160 to 190
Battery life, 28 V preamp. supply h 10
Battery life, 120 V preamp. supply h 8
Battery low indication Yes
Fuse mA 315
Weight g / oz 810 / 28,572
G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.


G.R.A.S. EL0001 10 x LR6 (AA) alkaline cells
G.R.A.S. AB0002 DC mains/line adapter, Europe
G.R.A.S. AB0003 DC mains/line adapter, USA


G.R.A.S. AK0040

19-inch Rack-mounting System

G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.