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MXR M81 Bass Preamp

MXR M81 Bass Preamp DI

MXR M81 Bass PreAmp: Versatile Tone Shaping for Any Scenario

The MXR M81 Bass PreAmp combines a pristine bass preamp with a studio-quality Direct Out, providing you with the ability to adjust your sound for any live or recording scenario. Encased in a compact Phase 90-sized box, this pedal delivers clear tone without hogging precious pedalboard space. Whether you want to add a new voice to an old passive bass, sweeten up any amp, or enhance a particular song, the M81 Bass PreAmp has you covered.

Comprehensive Control and Flexibility

The Bass PreAmp features separate Input and Output level controls along with a 3-band EQ section with sweepable midrange, ranging from 250Hz to 1kHz, for extensive tonal flexibility. The high headroom and super clean signal are achieved through MXR's Constant Headroom Technology™, ensuring your sound remains pristine. Additionally, the PRE/POST EQ switch allows you to set whether your Direct Out signal is affected by the Bass PreAmp's EQ section.

Key Features

  • Input and Output Controls: Separate level controls for precise adjustment.
  • 3-Band EQ with Sweepable Midrange: Bass, Mid (250Hz to 1kHz), Treble for extensive tonal shaping.
  • Constant Headroom Technology™: Provides super clean sound with high headroom.
  • PRE/POST EQ Switch: Selects whether the Direct Out signal is affected by the EQ section.
  • Ground Lift Switch: Eliminates ground loop hum.

Compact and Powerful Design

Despite its compact size, the MXR M81 Bass PreAmp offers powerful features and flexibility. It is factory preset to operate in ¼" out buffered bypass and Direct Out active. For players who only want to use the ¼" out, there are two internal switches that disable the Direct Out and ¼" out buffered bypass for true ¼" out bypass mode.

Power Options

This pedal can be powered by a 9-volt battery, a Dunlop ECB003 9-volt adapter, or the DC Brick™, Iso-Brick™, and Mini Iso-Brick™ power supplies (not included).


  • Input Impedance: 2.2 MΩ
  • 1/4” Output Impedance: 300 Ω at 40 Hz
  • Balanced Output Impedance: 120 Ω at 40 Hz
  • Maximum 1/4” Output Level: +13 dBV
  • Maximum Balanced Output Level: -2 dBV
  • Noise Floor: -98 dBV (A-weighted, all controls at mid position)
  • THD: 0.03% at 1 kHz
  • EQ Controls:
    • Bass: ±16 dB at 40 Hz
    • Mid: ±17 dB, sweepable from 250 Hz to 1 kHz
    • Treble: ±18 dB at 4 kHz
  • Input Control: Pre EQ, ±10 dB
  • Output Control: Post EQ, +20 dB
  • Bypass: True Hardwire, Buffer (internally selectable)
  • Current Draw: 8.5 mA
  • Phantom Power Current Draw: 5 mA
  • Power Supply: 9 volts DC
  • Dimensions: 0.75 x 16.00 x 49.00 inches

The MXR M81 Bass PreAmp is a versatile and powerful tool for any bassist looking to enhance their tone. With its extensive control options and compact design, it’s perfect for both live performances and studio sessions.

This pedal ships fully insured with signature required.