G.R.A.S. 12AK 1-Channel Power Module with gain, filters and SysCheck generator

Connection: Traditional 200 V
Channel(s): 1

Typical applications and use

  • General-purpose measurements
  • Precision measurements
  • Acoustic monitoring
  • Microphone calibration


It has the following signal-conditioning settings:

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

The 12AK 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 preamplfier can be set to 120 V — for maximum dynamic range, or 28 V — for minimum power consumption.

The 12AK will run for approximately 11 hours on fresh standard alkaline batteries. A Low Batt LED indicates the condition of the batteries.

The input 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 similar microphone preamplifiers.

The output is a standard BNC connector also on the front panel.

There are two overload indicators; one instantaneous, and one latched which can be reset. The gain can be set from 0 dB to + 50 dB in steps of 10 dB.

The standard A-weighting filter complies with IEC Standard 60651: Sound level meters Type 0. The high-pass filter 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 can be coupled directly to the output of the 12AK by selecting direct output. This makes the output of the preamplifier available free of any signal conditioning.

A built-in precision 1 kHz oscillator 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 push-button on the rear panel or remotely via a minijack connector also placed on the rear panel. The output level of the oscillator can be adjusted using a small screw driver on a potentiometer accessible via a hole in the front panel.

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

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
Output channel(s) 1
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 1
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 180 to 210
Battery life, 28 V preamp. supply h 11
Battery life, 120 V preamp. supply h 9
Battery low indication Yes
Fuse mA 250 (slow)
Weight g / oz 770 / 27.16


G.R.A.S. AK0040 19˝ Rack mounting System