MXR M81 Bass Preamp Review
Can it make your bass sound better?

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If you’re looking to sculpt the tone of your bass without coloring the sound of your performance the M81 delivers in spades. This is one of the cleanest bass preamps on the market. Distortion enthusiasts should move along, this preamp is crystal clear. Perfectly portable and built for life on the road, we found this little bass preamp a joy to use.


  • Sweepable mids are wonderful
  • Fantastic tone shaping capabilities
  • Can run off phantom power


  • Fans of distortion should look elsewhere

The first thing we noticed when unboxing the MXR M81 was the incredibly compact size, this thing is built for portability and is the same size as a Phase 90. The construction feels as high quality as you would expect from an MXR product, we were very impressed.

Where this pedal truly shines is its ability to add a full and hearty tone to any bass with an incredibly clean signal. If you’re looking to extend the dynamic range of your instrument then the detailed EQ settings may be just what you need.

The sweeping mid-frequency dial is arguably the biggest selling point of this pedal. You can adjust your sound, dial it right down to where you want and boost the gain with incredible precision.


The M81 offers separate input and output with dedicated control knobs, an XLR based Direct Out, 3 bands, EQ control covering bass, mid & treble, sweepable middle frequencies from 1kHz to 250kHz allow for detailed tone sculpting without coloring the sound of the instrument.

One incredibly useful feature is that the m81 can operate in either Direct Out active and 1/4″ out buffered bypass, but if you want to solely use the 1/4″ out MXR have offered the option to disable Direct Out and buffered bypass in order to operate in true 1/4″ bypass mode.

No need to worry about power with this pedal, the ability to run off phantom power from your PA system means you’ll never be caught short with dead batteries.


MXR M81 Bass Preamp

MXR doesn’t disappoint with the control layout of this little box. Simple and intuitive, but comprehensive enough to offer the fine-tuned detail that professional use demands.

We have dedicated input and output dials, a 3 dial bass, mid & treble EQ, a ground lift switch, a pre/post switch and the mid freq dial that allows the user to control that delicious sweepable frequency that this preamp is so loved for.

Two internal switches allow the switching of Direct Out/buffered bypass and true bypass modes.

Sound quality

If you like the way your bass already sounds and you want to bring out more of those qualities then the MXR M81 is very likely the perfect preamp for you. Sound quality is exceptionally clear and the ability to sculpt tone to fit exactly what you want is incredibly useful.

This preamp would likely be useful for anyone who wants to add more dynamic range to their bass without coloring the sound. If you’re looking for distortion or other effects then you won’t find what you want here.