The MXR M81 Bass Preamp is the kind of pedal that earns its place on a board permanently. It lives in a Phase 90-sized enclosure, weighs almost nothing, and quietly handles your preamp, DI, and EQ duties all at once. In a pinch, you can survive a gig with just your bass, this pedal, and maybe a tuner.
The EQ section combined with the subtle saturation and the DI out makes this a genuine all-rounder for both gigging and recording bass players.
The panel reads across two rows. Top row, left to right: Output, Mid Freq, Input. Second row: Bass, Mid, Treble. The Input knob drives the signal into the circuit, which is where the saturation comes from when you push it. Output handles the level going to your amp or interface. The three-band EQ covers Bass, Mid, and Treble with the Mid Freq knob sweeping the midrange center point from 250 Hz to 1 kHz.
There’s also a PRE/POST pushbutton on the upper right side that determines whether the Direct Out carries the signal before or after the EQ section. That’s the key switch for live rigs: PRE sends a flat signal to front of house while your EQ shapes only the stage amp, or POST sends the full treated signal.
In the demo above I’ve set up sweeps for Mid Frequency, Bass, Mid, and Treble, so you can hear what each one does to the same riff.
The M81 runs on MXR’s Constant Headroom Technology, which keeps the clean tone tight and open even when Input is pushed. The Buttery Preamp preset shows the comfortable middle ground: Input at 7, bass and mid both at 6, treble at 5. It’s a controlled, studio-ready tone that works whether you’re sending to an amp or straight to an interface.
Push Input to 10 and you get the Gnarly Drive preset: bass up to 7, mid at 9, treble at 7. That’s where the saturation starts making its presence felt, adding grit and presence without turning into an overdrive pedal. The Gentle Mix preset dials mid back to 3 with Mid Freq up to 7.5, scooping the midrange for a rounder, more supportive low-end character.
The Mid Frequency sweep is the most useful tool in the EQ section. Scrubbing it from 250 Hz to 1 kHz audibly shifts where the bass sits in a mix, and paired with a Mid boost it becomes a parametric midrange shaper.
The Orange Bass Butler is the other bass preamp on this site worth comparing. It’s a fundamentally different proposition: a bi-amp preamp that runs a clean bass channel and a full guitar-style dirty channel in parallel, on 18V power, in a box roughly three Boss pedals wide. It comes with dual balanced XLR outputs with dedicated cab simulation, an expression pedal input, and serious headroom on tap.
The M81 is the opposite in almost every dimension. It fits in a gig bag pocket, runs on a 9V battery, and does the basics extremely well: clean preamp tone, flexible EQ with a sweepable mid, a DI out with the PRE/POST option, and just enough input-driven saturation to add presence. There’s no built-in cab sim, no compressor, and no parallel clean/dirty blend. If you need a complete fly rig in one box, the Bass Butler is it. If you want something compact and dependable that slots into any setup without complication, the M81 is the smarter call.
There’s also a side by side page for this one: JHS Colour Box V2 vs MXR M81 Bass Preamp, both pedals on the same loop so you can switch between them mid-phrase.
The M81 is for bass players who want a reliable preamp and DI without a complicated setup. It works just as well in a recording chain as it does on a live pedalboard, and the PRE/POST switch makes it genuinely useful in both contexts without any reconfiguring. The input gain saturation keeps things interesting beyond plain utility.
The honest caveat: if you need a compressor, a parallel drive blend, or cab simulation built in, the M81 doesn’t cover those. It’s a focused tool, not a Swiss Army knife. But for players who just want their bass to sound better at every stage of the signal chain, it does exactly that without getting in the way.
Wondering which Orange bass amp to buy? Here's how the Crush Bass 25 and 50, Little Bass Thing, Terror Bass, ...
A shootout of the best bass overdrive pedals. I love using guitar pedals on bass and experimenting with finding the ...
A shootout of the best bass distortion pedals. I love using guitar pedals on bass and experimenting with finding the ...
Your tone deserves this 
Impulse buy here Buy through these links and support Loopy Demos at no extra cost to you.
Get detailed specs on MXR's website
<div data-loopydemos="mxr-bass-preamp" data-title="MXR M81 Bass Preamp | Loopy Demos" data-width="400" data-height="585"></div>
<script src="https://loopydemos.com/embed.js" async></script>To embed this demo on your website, copy & paste the code above or customize your demo widget