Benchmark PRE420 Mic-Pre/Mixer  

Product #485681

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This product has been discontinued but may be available as a Open Box item.

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For the studio, the symphony hall, and the quest for superior recordings.

The 4-channel Benbchmark PRE420 Mic-Pre/Mixer gives you a remarkable microphone preamplifier with an integrated stereo mix bus and stereo/mono solo bus in a sleek 1RU chassis. The PRE420 is designed for maximum transparency, wide bandwidth, low-noise, low-distortion, and superior RF immunity. It is well suited for the most demanding pro audio applications in studios and live venues.

What makes one mic pre superior to others?
Even high-end preamplifiers can mask subtle details because of intermodulation distortion, a symptom of RF interference and nonlinear performance at ultrasonic frequencies. This non-linearity causes intermodulation distortion (IMD) components that fold down to audible frequencies.

Unlike harmonic distortion (THD), IMD produces distortion tones that are very unnatural and nonmusical. 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 equips the PRE420 with the exclusive CMF1 RF-filter
The CMF1 has been extensively tested and proven in Benchmark's MPS mic-pre series by experienced studio and remote recording engineers in heavy RF fields - such as venues in close proximity to broadcast antennas. This RF-immunity is coupled with ultra-low distortion performance at high frequencies beyond the reach of most mic pres, giving your audio remarkable realism. With amazingly low THD+N of 0.00024% (see specs), we welcome you to compare the PRE420's performance specifications with any other mic pre available.

MirrorPan minimizes distortion & ensures constant-power precision panning
MirrorPan's innovative mirrored-circuitry, from which the name is derived, eliminates the nonlinear distortion caused by potentiometer wiper-current. The result is excellent channel separation 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 uncompromising sonic integrity of the PRE420.

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 (internally adjustable up to 70dB for special applications).

The next evolution of Benchmark's legendary MPS-420 microphone preamplifier.
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 PRE420 has a 500 kHz bandwidth - and wide bandwidth demands exceptional RF filtering and shielding. The multilayer printed circuit board uses a special construction technique that creates a 3-dimensional shield surrounding all signal traces.

Each microphone input features Benchmark's exclusive CMF1 common-mode RF input filter. This circuit removes common-mode RF interference without affecting the balanced microphone input signal. The CMF1 has always been a key component in Benchmark preamps, and has resulted in a proven track record for exceptional performance in difficult high-RF venues.

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
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 & uncompromising 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.

  • Ultra-low noise/distortion: (THD+N @ 22dB Gain 10Hz to 20kHz = 0.00027%)
  • RF-immune, wide bandwidth (500kHz)
  • Stereo mix bus & isolated stereo/mono solo bus
  • MirrorPan - Benchmark's proprietary zero-distortion, constant-power panning technology
  • 4 direct XLR outputs, 2 control room XLR outputs, & 2 stereo XLR outputs
  • HPA2 - Benchmark's signature high-current, 0-Ohm headphone amplifier with convenient, switchable mute control room output on headphone insertion.
  • Adjustable peak warning indicator & variable intensity signal level meter on each channel & mix bus
  • Independently switchable +48V phantom power, 40Hz switchable high-pass filter, & -20dB pad.

PRE420 Mic-Pre/Mixer Specifications:

  • Microphone Preamps
    Number of Preamps: 4
    Connectors: Gold-Pin Neutrik female XLR with direct ground feature
    Grounding: Direct bonding of pin 1 to chassis
    Input Impedance (with pad off): 8.1k Ohms
    Input Impedance (with pad on): 1.37k Ohms
    Gain Range (with pad off): 22 dB to 60 dB (to direct outputs)
    Gain Range (with pad on): 2 dB to 40 dB (to direct outputs)
    Maximum Input Level (with pad off): +7 dBu (+4.8 dBV, 1.7 Vrms)
    Maximum Input Level (pad on): +27 dBu (+24.8 dBV, 17.4 Vrms)
    Phantom Power: +48V with individual switches
    High-Pass (rumble filter): 40 Hz second-order 12-dB/octave
    RF Protection: CMF1 common-mode choke
    Preamp Bandwidth

    -0.02 dB at 10 Hz

    -0.17 dB at 200 kHz

    - 3 dB at 500 kHz

    EIN at 60 dB Gain

    (20 Hz to 20 kHz) to any output

    -128 dBu at 150 Ohms

    -131 dBu at 40 Ohms

    -133 dBu at 0 Ohms

    THD+N (1 kHz, BW=20 kHz) to any output at +27 dBu

    -112 dB, 0.00024% at 22 dB Gain

    -110 dB, 0.0003% at 35 dB Gain

    -108 dB, 0.00038% at 40 dB Gain

    -101 dB, 0.00085% at 55 dB Gain

    IMD (50Hz and 7 kHz) to any output at +24 dBu

    -104 dB, 0.0006% at 35 dB Gain

    -104 dB, 0.0006% at 40 dB Gain

    Direct Outputs
    Number of Outputs: 4
    Connectors: Gold-Pin Neutrik male XLR with direct ground feature
    Output Impedance

    60 Ohms Balanced

    30 Ohms Unbalanced (pin 3 floating )

    Maximum Output Level without clipping : +29.5 dBu
    Drive capability at rated THD+N: 300 Ohms
    Output Type: Transformerless Voltage and Impedance Balanced

    Control Room and Main Outputs
    Number of Outputs

    4 total

    2 control room

    2 main

    Connectors: Gold-Pin Neutrik male XLR with direct ground feature
    Output Impedance

    60 Ohms Balanced
    60 Ohms Balanced
    30 Ohms Unbalanced (pin 3 floating)

    Maximum Output Level without clipping: +29.5 dBu
    Monitor Gain Control L/R Balance

    ±0.01 dB at full clockwise rotation

    ±0.3 db at middle of rotation

    Drive capability at rated THD+N: 300 Ohms
    Output Type: -126dBu
    EIN @ 60dB Gain, 20Hz-20kHz, Inputs Common


    Voltage and Impedance Balanced

    MirrorPan Constant-Power Pan Circuit
    Number of pan controls: 4
    Pan Law: 3-dB (constant power to stereo out)
    Deviation from Constant Power: ±0.25 dB
    Channel Separation when Fully Panned: > 71 dB
    Balance at Center Detent: ±0.25 dB
    THD+N: Better than -112 dB, 0.00024%

    HPA2 Headphone Amplifier
    Number of Outputs: 1
    Connector: 1/4" TRS with switch contacts
    Output Impedance: 0.11 Ohms, 10 Hz to 200 kHz
    Maximum Output Level at 0.001% THD+N:

    +23.5 dBu into 600 Ohms (0.24 W)

    +19.5 dBu into 30 Ohms (1.78 W)

    Maximum Output Current: 250 mA
    Overload Protection (independent per channel)

    Current limited at 300 mA

    Thermal Shutdown


    > 500 kHz

    -0.014 dB at 10 Hz

    > -0.013 dB at 200 kHz


    -106 dB, 0.0005% into 30 Ohms at

    +18dBu (1.26 W)

    LED Status Indicators and Meters
    +48V Phantom Indicators: 4
    Solo Warning Indicator: 1
    Power Indicator: 1 Blue
    Meter Indicators: 6 Dual LED Meters
    Meter Locations:

    4 microphone inputs

    2 main outputs

    Meter Specifications

    Green LED: intensity modulated signal presence threshold = -8 dBu, full brightness at +24 dBu

    Red LED: threshold = +24 dBu adjustable includes peak-responding pulse stretch circuit for viewing fast transients

    AC Power Requirements
    Input Operating Voltage Range (VAC RMS)

    120 V setting: 105 V min, 140 V max

    220 V setting : 200 V min, 285 V max

    Frequency: 50-60 Hz

    27 Watts Idle

    27 Watts Typical Program

    35 Watts Maximum


    5x20 mm (2 required)

    0.5 A 250 V Slo-Blo Littelfuse

    HXP218.500 or Equivalent

    Form Factor: 19" Rack Mount, 1 RU High
    Depth behind front panel: 11.75" (298.5 mm)
    Overall depth including knobs and connectors without power cord: 12.625" (321 mm)
    Width excluding 19" rack ears: 17.5" (445 mm)
    Height excluding removable feet: 1.725" (43.8 mm)

    PRE420 only: 8.05 lb. (3.65 kg)
    PRE420 with power cord, extra fuses, and manual: 9 lb. (4.1 kg)
    Shipping weight: 11 lb. (5 kg)
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