G.R.A.S. 12AU 1-Channel Universal Power Module with signal conditioning and power amplifier

Connection: Traditional 200 V / CCP
Channel(s): 1

Typical applications and use

Electroacoustic tests of:

  • Telephones
  • Hearing aids
  • Loudspeakers
  • Portable devices, for example tablets, GPS, etc.


It is designed for automated production line testing of key loudspeaker parameters, such as frequency response, rub and buzz, THD, and impedance. The 12AU’s design makes it ideally suited for test of portable devices with built-in loudspeaker such as mobile phones, hearing aids, tablets, and GPS devices.

The inherent noise is very low, and by design it avoids system-generated noise, for example from ground loops. In a measurement setup, it controls the paths of (a) the signal sent out to the loudspeaker and (b) the resulting acoustic signal picked up by a condenser microphone fitted to the preamplifier.

It is remotely controlled via its USB interface and is delivered with a control program for Microsoft Windows ®.


  • Single channel conditioning amplifier suited for both CCP and 200 V LEMO preamplifiers
  • Very low inherent noise
  • The speaker input and the analogue outputs are floating with respect to common ground to avoid system-generated noise
  • Speaker amplifier with measurement of loudspeaker impedance without disturbing the speaker
  • Fulfils EMC requirements according to EU regulations
  • Full remote control via USB interface
  • Gain settings:
    – Microphone conditioner: 0 to 50 dB in 10 dB steps
    – Speaker amplifier: –20 dB to +10 dB in 10 dB steps
    – Current output: 0 dB and +20 dB
  • Filters:
    – Microphone amplifier: 1 Hz or 20 Hz
    – Speaker amplifier: DC or AC coupling (10 Hz)
  • Comprehensive status and overload indication
  • Rack mountable in 19” rack.

Measurement Control with 12AU

In a complex measurement setup, it is often difficult to avoid system generated noise. Also, it can be tedious to correctly set up all the parameters of the measurement chain with respect to sensitivity, gain, filtering and overload handling.

With the 12AU, you can control the loudspeaker amplifier and microphone conditioner simultaneously.

The 12AU is remote-controlled via its USB interface and a control program for Windows. You can operate the 12AU using a graphical user interface or by entering commands. Multiple 12AUs can be controlled from the same PC.

These features make the 12AU ideal for automated production line testing.

Technical Specifications

All outputs except the speaker amplifier output have fixed 100 kHz (3 dB) low pass filters to minimize the need for anti-aliasing filtering in the following analyzing equipment. There is no phase shift between microphone input and output due to prepolarized or externally polarized microphones. It is designed without relays.


All G.R.A.S. products are made of high-quality materials that will ensure life-long stability and robustness. The 12AU 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 (±3 dB) Hz 1 to 100 k
Output channel(s) 1
Output impedance Ω 100
Inherent noise, LIN (20 Hz to 20 kHz), grounded input µVrms <1.5 (>= 20 dB Gain)
Inherent noise, LIN with dummy micophone (20 Hz to 20 kHz) µVrms < 5
Gain settings, 10 dB steps dB 0 to + 50
Gain error dB < 0.2
High-pass filter 3-pole Butterworth, -1 dB @ 20 Hz
Linear mode Yes
Type Constant Current Power (CCP) and Traditional power supply (LEMO)
Input channel, CCP 1
Input channel(s), traditional power supply 1
Preamplifier supply V ±15
CCP preamplifier supply @ +28 V mA 4
Polarization voltage V 0 / 200
Overload indication Yes
PC controlable Yes
Monitor output connector BNC
Monitor output impedance Ω 100
Power amplifier input impedance Ω 10 k
Power amplifer output connector 2-pin LEMO
Power amplifier output current monitor connector BNC
Power amplifier output current Ap 1.4
Power amplifier gain settings, 10 dB steps dB -20 to 10
Power amplifier frequency range Hz DC to 30 k
Power amplifier phase shift response (±1 deg) Hz DC to 20 k
Power amplifier output voltage Vp ±13.5
Power amplifier overload detection Yes
Power supply, external (±10 %) Vac 110 to 240
Fuse mA 500
Weight g / oz 2500.00 / 88.18
G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.

All dimensions in mm.