Benchmark MPA1 Stereo Preamp, from Benchmark

Benchmark MPA1 Microphone Preamplifier

The MPA1 is a 2-channel microphone preamplifier designed and manufactured by Benchmark Media Systems, Inc. The MPA1 is meticulously designed to Benchmark standards of transparency, ultra-low distortion, and ultra-low noise performance - making the MPA1 a perfect choice for stereo pairs, ribbon mics, and any other application where purity is the goal.

Pristine Input Stage

The input stage of the MPA1 is designed with high-voltage headroom (+29 dBu) and single-stage gain control to maximize signal-to-noise ratio. The MPA1 maintains superb noise performance across the entire gain range (74 dB) by utilizing precision-matched, low-noise, transistor quad-arrays. A servo-controlled circuit minimizes DC-offset and maximizes headroom.

Complete Low Frequency Response

The MPA1 exhibits exceptional low-frequency performance with a clever dual-capacitor AC-coupling design. This dual-capacitor design defeats the limitations of single-capacitor AC-coupling designs, achieving an exceptionally low corner-frequency with excellent subsonic phase-accuracy.

Innovative Stepped-Resistor Gain Control

The gain control of the MPA1 is completely unique. The gain is controlled via a 38-position, switched resistor ladder, set up in a continuously rotating orientation via relay control. This gain control circuit offers 2 dB per step, 0-74 dB of gain without attenuation, and inter-channel gain precision of +/- 0.03 dB. A make-before break scheme creates a silent switching circuit.

Elegant Phantom Power Protection

The transistor stage is protected from phantom power surges with an ultra-fast, multi-stage protection circuit. This circuit utilizes the high-speed capabilities of low-capacitance Schotky diodes and the high-current capabilities of TVS diodes to absorb the phantom power surges caused by shorts and plugging/unplugging microphones with +48V on. This circuit is pre-biased so that it is isolated from the circuit in normal operation and activated when a surge occurs.