The MXR M281 Thump Bass Preamp is a bass preamp pedal in an MXR mini housing. According to the manual from Jim Dunlop, it combines the tone of the Echoplex Preamp with a three-band EQ and a midrange frequency adjustment, so a bass player can boost a solo, lift their signal in a live mix, or add edge to the sound of a passive bass1. The Echoplex circuit it draws on has its own history: Premier Guitar's reviewer described the MXR Echoplex Preamp as a "sturdy, elegant, and stupidly simple stompbox"2.
Controls
The pedal has five knobs plus a footswitch, all documented in the manual1:
| Control | What it does |
|---|---|
| OUTPUT | Sets output level of effect |
| TREBLE | Boosts or cuts high end frequencies at 4 kHz |
| BASS | Boosts or cuts bass frequencies at 40 Hz |
| FREQUENCY | Sets midrange frequency from 250 Hz to 1 kHz |
| FOOTSWITCH | Toggles effect on/bypass, blue LED indicates on |
The mid control itself is part of that three-band EQ, and the FREQUENCY knob is what separates the Thump from a fixed-mid design: you choose where in the 250 Hz to 1 kHz range the mid boost or cut lands1.
Specifications
| Specification | Value |
|---|---|
| Mid control | ±16 dBV, 1 kHz |
| Bass control | +15/-7 dBV, 40 Hz |
| Treble control | ±10 dBV, 4 kHz |
| Frequency sweep | 250 Hz to 1 kHz |
| Noise floor | -95 dBV, A-weighted, all controls at mid position |
| Input impedance | 1 MΩ |
| Output impedance | 100 Ω |
| Bypass | True Hardwire |
All values are from the maker's manual1.
Power
The Thump runs on 9 volts DC and draws 9 mA. The manual is direct on the subject of batteries: "This pedal cannot be powered by a battery." The maker specifies the Dunlop ECB003 9-volt adapter as the power source1.
The M281 cannot run on a battery, so it needs the Dunlop ECB003 9-volt adapter or an equivalent 9V DC supply on your pedalboard power unit1.
Connections are simple: a cable from your instrument to the pedal's INPUT jack, and another from the OUTPUT jack to your amplifier1.
Where it came from
The Thump was announced at NAMM 2020, when Dunlop and MXR unveiled it for bass players alongside the Cry Baby Q Zone Fixed Wah for guitarists3. Its circuit basis is the Echoplex Preamp, the same tone-sweetening preamp MXR sells as its own pedal, here paired with the EQ section that turns it into a full bass preamp1.
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Questions
Can the MXR Thump Bass Preamp run on a battery?
No. According to the manual from Jim Dunlop, the pedal cannot be powered by a battery. It runs on 9 volts DC and is powered by the Dunlop ECB003 9-volt adapter, drawing 9 mA. Plan for a dedicated power supply output or a supply with enough headroom rather than a battery or a daisy chain.
What frequencies does the Frequency knob cover?
The FREQUENCY knob sets the center point of the midrange control from 250 Hz to 1 kHz, according to the manual. That lets you place the mid boost or cut where it does the most for your bass, rather than being stuck with a single fixed mid frequency.
Does the Thump Bass Preamp have a bass knob?
Yes. The BASS knob boosts or cuts bass frequencies at 40 Hz, with a range of +15 to -7 dBV according to the manual. It sits alongside TREBLE and FREQUENCY knobs as part of the pedal's three-band EQ with midrange frequency adjustment.
What power adapter does the MXR Thump use?
The manual states the Thump Bass Preamp is powered by the Dunlop ECB003 9-volt adapter. The pedal runs on 9 volts DC, draws 9 mA, and cannot be powered by a battery.
What is the input impedance of the MXR Thump Bass Preamp?
The manual lists the input impedance at 1 MΩ, with an output impedance of 100 Ω. That high input impedance is typical of a preamp designed to sit first in the chain and accept a passive bass signal without loading it down.
Sources (3)
- M281.pdf, Jim Dunlop, 2020
- Quick Hit: MXR Echoplex Preamp Mini Review, Premier Guitar, 2014-06-09
- NAMM 2020: New from Dunlop/MXR: Cry Baby Q Zone Fixed Wah & MXR Thump Bass Preamp, gearnews.com, 2020-01-16
