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MXR M81 Bass Preamp

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MXR M81 Bass Preamp

Guitar Effects Pedal

Brand New


Regular Price: $169.99

Special Price: $129.99

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Product Description for the MXR M81 Bass Preamp

The Bass Preamp combines a pristine bass preamp with a studio-quality Direct Out so you can adjust your sound to any live or recording scenario.

The MXR Bass Preamp combines a pristine bass preamp with a studio-quality Direct Out in a Phase 90-sized box, providing clear tone without hogging precious pedalboard space. Use it to add a new voice to an old passive bass, sweeten up any amp, or put some special sauce on a particular song. Dial it in just the way you want it and send it straight to the house-pre or post-EQ-with the built-in Direct Out.

The Bass Preamp features separate Input and Output level controls and a 3-band EQ section with sweepable midrange-from 250hz to 1khz-for extensive tonal flexibility. It's all delivered super clean with high headroom thanks to our own Constant Headroom Technology™ , and you can use the PRE/POST EQ switch to set whether or not your Direct Out signal is affected by the Bass Preamp's EQ section. And of course, the Bass Preamp features a GROUND LIFT switch in case you encounter ground loop hum.

The Bass Preamp 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.



  • 3-Band EQ with
  • sweepable midrange
  • Studio-quality Direct Out
  • Constant Headroom Technology for clean, crystal clear tone


The MXR Bass Preamp is powered by one 9-volt battery (remove bottom plate to install), a 9-voltAC adapter such as the Dunlop ECB003/ECB003E, a DC Brick power supply, or phantom power


  • Run a cable from your bass to the Bass Preamp’s INPUT jack and another cable from the Bass Preamp’s 1/4” OUTPUT jack to your amplifier.
  • The Bass Preamp’s default setting is DIRECT OUT ‘ON’ Mode. To use the Direct Out function, run a balanced line (XLR cable) from the Bass Preamp’s DIRECT OUT jack to your mixing board or PA.
  • Set all controls to their 12 o’clock position.
  • Turn the pedal on by depressing the footswitch.
  • Rotate OUTPUT control clockwise to increase overall volume or counterclockwise to decrease it.
  • Rotate INPUT knob clock wise to increase Pre-EQ gain or counter clockwise to decrease it.
  • Rotate BASS knob clockwise to boost low end frequencies orcounter clockwise to cut them.
  • Use MID FREQ control to select midrange frequency to be affected by MID control.
  • Rotate MID control clockwise to boost midrange or counterclockwise to cut it.
  • Rotate TREBLE control clockwise to boost high end frequencies or counter clockwise to cut them.
  • With the DIRECT OUT ‘ON’, push in the PRE/POST switch to allow your Direct Out signal to be affected by INPUT, EQ and OUTPUT controls. When PRE/ POST switch is ‘out,’ your Direct Out signal will be unaffected by these controls
  • Push GROUND LIFT button in to remove possible ground loop hum when using the Direct Out.

Direct Out And Bypass

The Bass Preamp’s default setting is Direct Out ‘ON’ and BUFFER 1/4” OUT bypass ‘ON.’With Direct Out ‘ON,’ True bypass is not possible because the input signal must stay connected to the input buffer in order to send a bypass signal to the Direct Out With Direct Out ‘ON,’ the Bass Preamp also offers 1/4” Out Hardwire bypass and is selected by removing the pedal’s bottom plate and by setting switch SW4 to the down (‘OFF’) position.

Preamp Only (True Bypass)

The Bass Preamp can be used with the DIRECT OUT ‘OFF’ in order to utilize 1/4” Out true bypass switching. To activate true bypass switching, set SW4 and SW5 to their “down” (‘OFF’) positions. This setting disables the DIRECT OUT signal.

Where should you put the Bass

Preamp in your effects chain? If you’re only using the Bass Preamp for its 1/4” Output, put it at the beginning of your chain of effects.

When using the DIRECT OUT,

you have two options:

To send your clean signal to the PA or mixing console, put the Bass Preamp at the front of your chain. If you want your DIRECT OUT signal colored by all of your other effects, put the Bass Preamp at the end of your effects chain.

Phantom Power

The Bass Preamp can be powered through its DIRECT OUT from equipment that provides phantom power. To utilize the phantom power option, place the Bass Preamp’s GROUND LIFT button to the out position.


  • Input Impedance : 2.2 MΩ
  • 1/4” Output Impedance : 300 Ω, 40 Hz           
  • Balanced Output Impedance : 120 Ω, 40 Hz
  • Maximum 1/4” Output Level : +13 dBV
  • Maximum Balanced Output Level : -2 dBV
  • Noise Floor* : -98 dBV
  • THD : 0.03%, 1 kHz
  • EQ Controls Bass  : ±16 dB, 40 Hz ,Mid : ±17 dB, 250 Hz to 1 kHz ,Treble : ±18 dB, 4 kHz
  • Input Control : Pre EQ, ±10 dB
  • Output Control : Post EQ, +20 dB
  • Bypass* : True ,Hardwire ,Buffer
  • Current Draw :  8.5 mA
  • Phantom Power Current Draw : 5 mA
  • Power Supply : 9 volts DC
Brand MXR
Weight 1.1000
Dimensions (WxHxD) No


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