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Benchmark PRE420 - Microphone Preamplifier / Mixer - Discontinued


The PRE420 has been discontinued.

A remarkable four-channel microphone preamplifier with an integrated stereo mix bus and stereo/mono solo bus in a sleek, 1RU chassis. The PRE420is designed for maximum transparency, wide bandwidth, low-noise, low-distortion, and superior RF immunity. It is well suited for the most demanding applications in studios and live venues.

What Makes a Microphone Pre-Amplifier Transparent?

Even high-end preamplifiers can mask subtle details because of intermodulation distortion, a symptom of RF interference and non-linear performance at ultra-sonic frequencies. This non-linearity causes inter-modulation distortion (IMD) components that fold down to audible frequencies.

Unlike harmonic distortion (THD), IMD produces distortion tones that are very un-natural and non-musical. IMD also masks and alters the subtle details of delicate high-frequency transients such as those produced by bells. Benchmark MPS series preamps have always had outstanding high-frequency performance as well as freedom from IMD. The PRE420 takes the Benchmark design one step further, and achieves the lowest IMD that we have ever measured in any microphone preamplifier - the innovative circuitry provides ultra-low distortion over a 500kHz bandwidth while maintaining RF-immunity in the most demanding environments.

Benchmark's Exclusive MirrorPan™ Circuit

MirrorPan™ uses an innovative current mirrored to eliminate the non-linear distortion caused by potentiometer wiper-current. Additional advantages include low impedance, low noise, excellent channel separation at full pan, constant-power panning, and remarkably accurate imaging. The center-detent position is factory calibrated for precise center-placement.

Elegant & Completely Unique Feature Set

An elegant and completely unique feature set compliments the uncompromised sonic integrity of thePRE420.

A solo section allows monitoring of any channel or combination of channels (with switchable stereo/mono) via control room XLR outputs and the integrated HPA2™ - Benchmark's signature high-current, 0-Ohm headphone amplifier. The PRE420's main mix bus XLR outputs are monitored via a dual, variable intensity signal level meter and peak-warning indicator*.

Each of the four channels has an independent direct XLR output, a variable intensity signal level meter and peak-warning indicator*, and MirrorPan™ control. Each channel features a precisely matched 41-position first-stage gain control factory preset to a maximum gain of 60dB.

The Next Generation of Benchmark's Legendary MPS-420

The PRE420 is the next evolution of Benchmark's legendary MPS-420 microphone preamplifier. We have improved the performance while adding meters, a mix bus, a solo bus,and an internal power supply. The added features do not compromise the performance of the classic Benchmark design. In all respects, the PRE420 meets or exceeds the performance of the MPS series preamps.

RF-Immune, Wide-Bandwidth Design

The entire signal path of the PRE420 has a generously wide bandwidth: 500 kHz. This creates a significant demand for exceptional RF filtering and shielding – a demand Benchmark fulfills.

All signal paths in the PRE420 are aggressively protected from RF. For example, the multi-layer printed circuit board uses a special construction technique that creates a 3-dimensional shield surrounding all signal traces. Benchmark's innovative shielding and filtering techniques have given Benchmark mic-preamps a proven track record for exceptional performance in difficult, RF-intensive locations.

This RF-immunity is coupled with ultra-low distortion performance at high-frequencies, beyond that of most mic-preamps, giving your audio remarkable realism. With an amazingly low THD+N of 0.00024% (see specs), we encourage you to compare the PRE420's performance specifications and sonic performance with any other mic-preamp.

Microphone Inputs

Each of the PRE420's four microphone inputs includes switches for +48V Phantom power, a 20dB pad, and a 40Hz high-pass filter.

The PRE420 achieves outstanding performance over a wide range of input levels. Gain is controlled by matched 41-detent pots and is adjustable over a range of 22dB to 60dB (without pad), or 2dB to 40dB (with pad enabled). The mix bus can provide an additional gain of up to 6 dB.

High-Current XLR Analog Outputs

The PRE420 has a total of 8 XLR-type analog outputs: four direct outputs, two control room outputs, and two stereo outputs. All outputs feature low-distortion, high-current drivers that easily handle long cables and other less-than-ideal loads.

Astonishingly Low-Noise Stereo Mix Bus

The PRE420 features an astonishingly low-noise stereo mix bus driven by Benchmark's proprietary MirrorPan™ circuitry to achieve precise, distortion-free, constant-power panning. The mix bus allows pristine direct-to-stereo recording from up to 4 microphones. The balanced stereo outputs are equipped with meters and a master level control.

Convenient Flexibility, Un-Compromised Performance

The convenient flexibility of these unique features in no way compromises the pristine audio path. The PRE420's RF-immune, wide-bandwidth circuitry faithfully delivers stunningly high resolution to all direct, stereo, control room, and headphone outputs.

Rugged Yet Elegant Chassis

A rugged 1 RU enclosure includes an internal power supply that supports all international voltages and has generous margins for over-voltage and under-voltage conditions. It features a core-banded toroidal transformer in a shielded enclosure.


  • Stereo mix bus & isolated stereo/mono solo bus
  • MirrorPan™ - low-noise constant-power pan controls
  • 4 direct XLR outputs
  • 2 control room XLR outputs
  • 2 stereo mix XLR outputs
  • HPA2 - high-current, 0-Ohm headphone power amplifier
  • Adjustable peak warning indicators
  • Variable intensity signal level meter on each channel
  • Variable intensity signal level meter on mix bus
  • Independently switchable +48 V phantom power
  • 40 Hz switchable high-pass filters
  • 20 dB pads


  • THD+N @ 22dB Gain 10Hz-20kHz = 0.00024%
  • EIN at 60 dB Gain = -128 dBu at 150 Ohms, -131 dBu at 40 Ohms, -133 dBu at 0 Ohms
  • Bandwidth = -3 dB at 500 kHz


Detailed specifications and performance plots are available in the downloadable manual.

PRE 420 Manual

Add Benchmark Cables to Complete You New System

Benchmark offers a no-nonsense selection of very high-quality cables.  Benchmark cables are designed for durability and transparency, and most are manufactured in the USA. Our optical cables are manufactured in Canada.


This Benchmark product was designed, assembled, and tested in the USA using USA and imported components. Most major components are made in USA.

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This Benchmark product was designed, assembled, and tested in the USA using USA and imported components. Most major components are made in USA.

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