Electrostatic Actuator Amplifier GRAS 14AA

Typical Applications and Use

• Microphone measurements
• Driving microphone sound sources
• Electrostatic-actuator calibrations
• IEC 61094-6 Compliance

Design

The input to the 14AA is via a standard BNC socket on the front panel and any input signal up to 3 V peak-to-peak can be applied. This is then amplified by 40 dB to produce an AC output signal of up to 300 V peak-to-peak maximum. This AC output signal is also made available superimposed on + 200 V DC and + 800 V DC. This amounts to three parallel signal outputs available via sockets on the front panel marked as follows:

• AC Output (BNC socket)
• AC Output + 200 V DC (BNC socket)
• AC Output + 800 V DC (banana socket)

Driving microphone sound sources

• With the AC Output superimposed on + 200 V DC and used as a modulated polarization voltage on a standard measurement microphone such as the GRAS 40BP, the microphone becomes a precision sound-source for generating high-frequency acoustic signals. Alternatively, the AC Output alone can be similarly used with a prepolarized microphone such as the GRAS 40AD.

Electrostatic actuator calibrations

• With the AC Output superimposed on + 800 V DC, it can be used as a modulated polarization voltage for electrostatic actuators, e.g. the GRAS RA0014 or RA0015, for measuring the pressure frequency response of condenser microphones.
• Care should be taken when calibrating below 200 Hz because of the influence of pressure equalization in the rear volume of the microphone.