G.R.A.S. 12AG 8-Channel Power Module with gain, filters and SysCheck generator

Connection: Traditional 200 V
Channel(s): 8

Typical applications and use

  • General-purpose measurements
  • Precision measurements
  • Sound-power measurements
  • Multi-channel measurements  


Each channel has the following signal conditioning settings:

  • linear-response
  • A-weighting
  • high-pass filtering

The 12AG can be powered either from a mains/line supply or from an external DC supply (12 V - 18 V), e.g. a car battery. It is built into a sturdy anodized aluminium cabinet.

The supply and polarization voltages are set by two pairs of switches, one common to channels 1 - 4 and one common to channels 5 - 8. The polarization voltage in each group can be set to 0 V — for prepolarized microphones, or 200 V — for externally polarized microphones

And the voltage supply for the preamplifiers can be set to 120 V — for maximum dynamic range, or 28 V — for minimum power consumption; may be important when using an external DC power supply.

The input to each channel is a 7-pin LEMO socket on the front panel which is wired up for G.R.A.S. microphone preamplifiers, e.g. 26AB, 26AC, 26AJ and 26AK, but is also compatible with other available makes of microphone preamplifiers.

The output of each channel is via a standard BNC connector also on the front panel as well as via one of the 4-channel VXI outputs on the rear panel.

Each channel has two overload indicators; one instantaneous, and one latched which can be reset by a common push button. The gain in each channel can be set from 0 dB to + 50 dB in steps of 10 dB.

The standard A-weighting filter in each channel complies with IEC Standard 60651: Sound levelmeters 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. This filter is for reducing unwanted low-frequency signals, e.g. caused by wind-induced noise on the microphone.

The preamplifier signal in each channel can be coupled directly to the output of the 12AG by selecting direct output. This makes the output of the preamplifier available free of any signal conditioning.

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

The cabinet of the 12AG is 1/2" of a standard 19-inch rack; meaning that 2 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 12AG 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 response (±1.0 dB) @ Gain ≤40 dB Hz 2 to 200 k
Frequency response (±1.0 dB) @ Gain 50 dB Hz 2 to 100 k
Frequency response (±0.2 dB) Hz 20 to 20 k
Output channel(s) 8
Output impedance Ω 30
Direct coupling input to output Yes
Inherent noise, LIN (20 Hz to 20 kHz), grounded input µVrms <4
Inherent noise, A-weighted, (20 Hz to 20 kHz), grounded input µVrms <2.8
Inherent noise, A-weighted with dummy preamplifier (20 Hz to 20 kHz), µVrms <4
Inherent noise, LIN with dummy micophone (20 Hz to 20 kHz) µVrms <5.6
Gain settings, 10 dB steps dB 0 to + 50
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 8
Channel separation (20 Hz to 20 kHz) dB >65
Preamplifier supply V 28 / 120
Polarization voltage V 0 / 200
Overload indication Yes
Power supply, external (±10 %) Vac 110 to 240
Power supply, external Vdc 12 to 18
Power consumption mA 100
Fuse mA 1250 (slow)
Weight g / oz 2500.00 / 88.18
Weight with batteries g / oz 2.5 k / 88.185
G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.
G.R.A.S. AK0040 19˝ Rack mounting System
G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.