GRAS 12AK 1-Channel Power Module with gain and filters

Connection: Traditional 200 V
Channel(s): 1

The GRAS 12AK is a single-channel power module with a 7-pin LEMO 1B connector for power and polarization of an externally polarized microphone set. It features instantaneous and latched overload indication, adjustable gain settings, A-weighting, and Lin and HP filters. These features make the 12AK the ideal choice for a wide range of applications such as monitoring, laboratory use, and sound level meter measurements.


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 preamplifier 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 GRAS 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.

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.


All GRAS products are made of high-quality materials that will ensure life-long stability and robustness. The 12AK 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 GRAS 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
2 to 200 k
Frequency response (±1.0 dB) @ Gain 50 dB
2 to 100 k
Output channel(s)
Output impedance
Direct coupling input to output
Inherent noise, LIN (20 Hz to 20 kHz), grounded input
Inherent noise, A-weighted, (20 Hz to 20 kHz), grounded input
Inherent noise, A-weighted with dummy preamplifier (20 Hz to 20 kHz),
Inherent noise, LIN with dummy micophone (20 Hz to 20 kHz)
Gain settings, 10 dB steps
0 to + 50
Gain error
< 0.2
A-weighting filter according to
IEC 60651 Type 0
High-pass filter
3-pole Butterworth, -1 dB @ 20 Hz
Linear mode
SysCheck level @ 1 kHz
Traditional power supply (LEMO)
Input channel(s), traditional power supply
Preamplifier supply
28 / 120
Polarization voltage
0 / 200
Overload indication
PC controlable
External filter option
Power amplifier overload detection
Power supply, battery
10 x LR6 (AA)
Power supply, external
12 to 18
Power consumption
180 to 210
Battery life, 28 V preamp. supply
Battery life, 120 V preamp. supply
Battery low indication
250 (slow)
Temperature range, operation
°C / °F
-10 to +50 / 14 to 122
g / oz
770 / 27.16

GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.

Ordering info


GRAS EL0001 10 x LR6 (AA) alkaline cells
GRAS AB0002 DC mains/line adapter, Europe
GRAS AB0003 DC mains/line adapter, USA


GRAS AK0040 19˝ Rack mounting System

GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.