Microphone Preamplifiers | Low-Noise IEPE and Voltage-Mode Signal Conditioning

PLACID preamplifiers provide the signal conditioning stage between a condenser measurement microphone capsule and the data acquisition system or sound level meter. The preamplifier serves two essential functions: it provides the polarisation voltage required by an externally-polarised condenser capsule, and it converts the high-impedance capsule output to a low-impedance signal capable of driving cables without significant signal degradation from cable capacitance.

The preamplifier contributes directly to the measurement system's self-noise floor, its frequency response flatness, and its dynamic range. A preamplifier with insufficient dynamic range will clip on high-SPL transients even when the microphone capsule itself is within its specified range. A preamplifier with excessive self-noise raises the measurement system noise floor above that of the capsule. PLACID preamplifiers are specified to complement the performance of the associated capsule class rather than being a limiting factor in the measurement chain.

Output Types

• IEPE (ICP) output — constant current power supply from the DAQ system; signal superimposed on DC bias; most common for modern multi-channel DAQ
• Voltage-mode output — requires external power supply; used with legacy DAQ systems and some sound level meter inputs
• Balanced low-noise output — for long-cable-run applications and interference-sensitive environments

Key Performance Parameters

• Self-noise: typically below 3 dB(A) equivalent input noise at 1 kHz for Class 1 preamplifiers
• Bandwidth: 3 Hz to 100 kHz (-3 dB) for standard models
• Maximum output level: ±10 V peak before clipping, compatible with standard DAQ input ranges
• Input impedance: >1 GΩ to avoid loading the high-impedance capsule output
• TEDS variants available for automatic preamplifier identification in multi-channel systems

Compatibility

PLACID preamplifiers are designed for use with PLACID 1/2-inch and 1/4-inch condenser measurement microphone capsules. They are also compatible with most other IEC 61094 compliant capsules using the standard 7-pin microdot or 10-32 UNF thread connection. IEPE output preamplifiers are compatible with any IEPE-compatible data acquisition system, sound level meter input, or signal conditioner that provides 2 to 20 mA current supply at 18 to 30 V compliance voltage.

Calibration and Ordering

PLACID preamplifiers are calibrated as part of a matched set with a specific capsule. The combined system sensitivity is stated on the calibration certificate and represents the sensitivity of the complete sensing chain from acoustic pressure to electrical output voltage. When a preamplifier is replaced in an existing measurement chain, the combined sensitivity must be re-verified. ISO/IEC 17025 accredited calibration of the new capsule-preamplifier combination is available, and is recommended for compliance and accredited testing programmes to maintain measurement traceability continuity.