The MXR M87 Bass Compressor is a compressor pedal for bass, made by MXR, a brand of Dunlop Manufacturing. MXR describes it as a studio-style compressor for bass, with CHT Constant Headroom Technology for clear, clean performance1. It launched with a street price of $189.99 in the US2.
What sets the M87 apart from simpler compressor pedals is control. Instead of one or two knobs, it gives you the same parameters you would find on a studio compressor: Attack, Release, Ratio, Input and Output, plus an LED meter that shows how hard the compressor is working in real time13.
The controls and the LED meter
The M87's front panel has five knobs and a meter. Each control maps directly to a studio compressor function3:
| Control | What it does |
|---|---|
| INPUT | Controls the gain level of the input signal |
| RATIO | Sets the degree of compression, from mild 4 (4:1) to extreme 20 (20:1) |
| ATTACK | Controls the reaction time of compression |
| RELEASE | Controls how quickly the compressor lets go |
| OUTPUT | Controls overall effect volume |
| METER | LED display showing gain reduction level and compressor response time |
The Ratio knob offers four settings: 4:1, 8:1, 12:1 and 20:1. The 8 setting selects an 8:1 compression ratio, 12 selects 12:1, and 20 selects 20:11. Attack time ranges from 20 µs to 800 µs and release time from 50 ms to 1.1 s1.
The LED meter is the feature players notice first. It shows gain reduction level and compressor response time, so you can see exactly how much the pedal is compressing at any moment and how it reacts to your playing1. Dunlop's own history of its compressor line highlights this: "With knobs for Attack, Release, Ratio, Input, and Output, plus a bright LED meter to monitor gain reduction, these are s[tudio-style controls]"3.
Because the ratio goes up to 20:1 with fast attack and release available, the M87 can also serve as a limiter. Premier Guitar notes that "most adjustable compressors can also serve as a limiter by changing the ratio to 20:1 or higher and dialing-in fast atta[ck and release]"4.
Power and specifications
The M87 runs on 9 volts DC and draws 14 mA with the LEDs off1. Power comes from one 9-volt battery, installed by removing the bottom plate, or from a 9-volt AC adapter such as the Dunlop ECB003/ECB003E, or a DC Brick power supply1.
The manual lists two current draw figures, 14 mA and 19 mA, both with LEDs off.
The maker's full specifications1:
| Specification | Value |
|---|---|
| Max input level | +14 dBV |
| Max output level | +8.5 dBV |
| Gain | 31 dB |
| Compression ratio | 4:1, 8:1, 12:1, 20:1 |
| Attack time | 20 µs to 800 µs |
| Release time | 50 ms to 1.1 s |
| Frequency response | ±1 dB, 20 Hz to 20 kHz |
| Noise floor | -90 dBV A-Weighted, all controls at mid position |
| THD | > 0.5% at 20 dB gain reduction, 1.1 s release setting, 50 Hz to 20 kHz |
| Input impedance | 1 MΩ |
| Output impedance | 600 Ω |
The frequency response of ±1 dB from 20 Hz to 20 kHz means the pedal passes the full bass range without emphasis or cut, which matters for an instrument whose fundamentals sit below 100 Hz1.
Where it came from
The M87 launched as part of MXR's bass pedal lineup, with a street price of $189.992. It sits in a long line of MXR compressors, a family that includes the Dyna Comp, the Super Comp, the Custom Comp and the Dyna Comp Deluxe3.
The M87 predates the M76 Studio Compressor, a guitar-focused pedal that MusicRadar describes as following the M87, which "has been around for a little while now"5. A Blackout Series version, the M87B, carries the same Bass Compressor design with the same meter display and release time range in a black finish6.
What reviewers said
Premier Guitar reviewed the M87 and found it quiet and transparent: "It added no noticeable noise to the signal and left my bass lines intact"4. The reviewer also noted its "compact size makes it a handy tool for real-estate-conscious bassists"4. One practical criticism: the enclosure is an aluminum box with softer metal that screws can cross-thread into, which the reviewer experienced when a screw "tried to cross-thread into the softer aluminum box"4.
Vintage Guitar reviewed the M87 in December 2012 alongside the MXR M234 Analog Chorus, praising the compressor's transparency and control.
How it differs from other MXR compressors
The M87's control set puts it at the full-featured end of MXR's compressor range. Its RATIO knob selects between three fixed compression ratios: the 8 setting selects 8:1, 12 selects 12:1, and 20 selects 20:1, and its attack time is adjustable from 20 µs to 800 µs21. For players who want a studio-style control set in a guitar-oriented pedal, the M76 Studio Compressor is the closest relative5.
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Questions
Can the MXR M87 run on a battery?
Yes. The M87 is powered by one 9-volt battery, installed by removing the bottom plate. It can also run from a 9-volt AC adapter such as the Dunlop ECB003/ECB003E, or a DC Brick power supply. Current draw is 14 mA with the LEDs off.
Is the MXR M87 true bypass?
Yes. The maker lists the bypass type as True Hardwire, so the signal passes through without processing when the pedal is off.
Can the MXR M87 be used as a limiter?
Yes. Premier Guitar notes that most adjustable compressors can serve as a limiter by setting the ratio to 20:1 or higher and dialing in fast attack and release. The M87's Ratio knob goes up to 20:1, with attack from 20 microseconds to 800 microseconds and release from 50 ms to 1.1 s.
Does the MXR M87 work on guitar?
The pedal is designed for bass, with an input jack intended for a bass and a frequency response of plus or minus 1 dB from 20 Hz to 20 kHz. The maker describes it as a classic studio compressor in a Phase 90-sized pedal, and its controls are not instrument-specific, but the manual addresses it to bass players.
What is the difference between the M87 and the Dyna Comp Bass?
The M87 is a full-size, five-knob studio-style compressor with Attack, Release, Ratio, Input and Output controls and an LED gain-reduction meter. The Dyna Comp Bass (M282), released in 2019, is a mini-pedal bass version of the classic 1970s Dyna Comp circuit, which is a simpler two-control design.
Sources (6)
- M87.pdf, Jim Dunlop, 2019
- Dunlop Announces MXR M87 Bass Compressor Pedal, No Treble, 2011-02-06
- A Dyna Comp-rehensive History, Dunlop (lifestyle.jimdunlop.com), 2018-10-25
- MXR M87 Bass Compressor Pedal Review, Premier Guitar, 2011-09-20
- MXR M76 Studio Compressor review, MusicRadar, 2016-09-14
- M87B.pdf, Jim Dunlop (jimdunlop.com), 2023
