The MXR MB301 Bass Synth is a bass synthesizer pedal that puts a range of monophonic synth tones in a standard-sized MXR enclosure. MXR says it "serves up intergalactic grooves and vintage analogue-style vibes with a range of monophonic synthesizer tones that call back to hits from Stevie Wonder, Michael Jackson, Parliament Funkadelic, and more"1. It was developed with session bassist, content creator and educator Ian Martin Allison2.
The controls
The face of the pedal carries six knobs and two buttons along the top. The core functions are straightforward2:
| Control | What it does |
|---|---|
| Cutoff | Sets the filter cutoff frequency1 |
| Resonance | Boosts that frequency1 |
| Mix | Blends the processed and dry signals21 |
| Mod | Adds movement, which MusicRadar describes as "shimmering liquid tones, from subtle, musical motion to bold, mind-bending pulses"1 |
There is more depth under the surface. Each of the six pots has two further functions, accessed by turning the knob while pressing one or other of the buttons along the top, which gives eighteen different parameters hidden in the rotary controls2.
The footswitch button handles presets: hold it down and cycle through them, or hook up a tap switch and use that to switch them1. There are eight preset slots, pre-loaded with factory presets2. MusicRadar notes the factory sounds draw on material including Michael Jackson's Thriller, Herbie Hancock's Chameleon, Peter Gabriel's Sledgehammer and Nine Inch Nails' Head Like A Hole1.
You do not have to live with the presets. Bass Magazine's reviewer used the pedal in "live" mode, without the presets, dialing sounds in from the knobs3.
Power, connections and stereo
The MB301 needs 9V DC, center negative, and draws 330mA2. Bass Magazine confirms the polarity, noting "any other 9-volt, 330mA center-negative power supply" will run it3. That 330mA draw is well above a typical single pedal, so it is worth checking what your supply's individual outputs deliver before adding it to a board.
Connectivity is an instrument input and output, an input for an external footswitch or expression pedal, and the power jack2. An expression pedal can sweep each effect, which opens up real-time filter and parameter moves while you play3.
Stereo recording is built in. As Bass Magazine puts it, "Recording the MB301 in stereo is as easy as flicking the CTR side switch to AUDIO and using ordinary two-conductor cable" at the OUT and CTR jacks3. No special leads are needed.
Bypass is listed as switchable, dependent on the output mode2, so the bypass behavior follows how you have the output configured rather than being fixed.
What reviewers said
Guitar World's reviewer found the enclosure up to the usual standard: "The pedal sits in a standard-sized, typically sturdy and well-finished MXR enclosure"2. On the sounds, the verdict was broad:
"It's difficult to think of a synth bass sound that couldn't be achieved with the new MXR Bass Synth."
The same review notes that the presets reach back to familiar territory: you'll find sounds inspired by Michael Jackson's Thriller, Herbie Hancock's Chameleon, Peter Gabriel's Sledgehammer and Nine Inch Nails' Head Like A Hole1. Switching between them is straightforward: hold down the footswitch button and cycle through presets, or hook up a tap switch and use that to change them1.
If you are building out a bass board around it, MXR's bass line also includes the M82 Bass Envelope Filter, the M288 Bass Octave Deluxe and the M85 Bass Distortion, and the pedal sits within the wider field of synth pedals and bass pedals.
Videos
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Questions
Does the MXR MB301 Bass Synth work with an expression pedal?
Yes. The pedal has an input for an external footswitch or expression pedal, and Bass Magazine's reviewer found that using an expression pedal to sweep each effect is part of how the pedal works. That makes it possible to move a filter or other parameter in real time while playing, rather than relying only on the knob positions.
Can the MB301 be used in stereo?
Yes. Bass Magazine's review explains that recording the MB301 in stereo is as easy as flicking the CTR side switch to AUDIO and using ordinary two-conductor cable at the OUT and CTR jacks. No special cables are needed, just standard two-conductor (tip-sleeve) leads.
What power supply does the MB301 need?
The MB301 runs on 9V DC, center negative, and draws 330mA. That current draw is higher than many pedals, so a supply rated for it matters, and a battery or a shared daisy chain with lower-current outputs is not the way to run it. Bass Magazine notes any other 9-volt, 330mA center-negative supply works.
Is the MB301 true bypass?
Guitar World lists the bypass as switchable, dependent on the output mode. In practice that means the bypass behavior changes with how you have the output set, rather than being fixed as true bypass or buffered bypass.
Can I use the MB301 without the presets?
Yes. Bass Magazine's reviewer describes using the pedal in live mode, without the presets, dialing in sounds directly from the controls. The eight preset slots are there when you want them, but they are not required for everyday use.
Who helped design the MXR Bass Synth?
MXR developed the Bass Synth with Ian Martin Allison, a session bassist, content creator and educator. Guitar World's review credits him as the collaborator on the design, which is intended to put a range of synth bass sounds in a single pedal.
Sources (3)
- “Thunderous sub-octave, expressive envelope, and lush modulation effects with killer tracking and sustain”: MXR unveils the MB301 Bass Synth, MusicRadar, 2025-07-02
- MXR MB301 Bass Synth Pedal review, Guitar World, 2025-08-01
- Review: MXR MB301 Bass Synth, Bass Magazine, 2025-10-14
Ian Allison
