The MXR Thump Bass Preamp is a bass preamp pedal from MXR, a miniature-format pedal that MXR positions as a tone sweetener suited to solo boost or always-on use12. It carries a list price of USD 129.993, and warranty information is available on the product page32.
MXR describes the result as "a tone-sweetening, signal-boosting, and altogether groove-enhancing machine"2. The idea came from the MXR design team and the company's in-house bass players, who found the Echoplex Preamp's conditioning worked well for bass and built a tone-shaping interface on top of it2. The manual sums up the uses: "Whether you need to punch up a solo, boost your signal in a live mix, or sculpt more edge into the sound of a passive bass"4.
MXR lists the Thump Bass Preamp as a legacy product, no longer in production2. It was announced at NAMM 2020 with a recommended retail price of USD 129.993.
A bass preamp built on Echoplex circuitry
The Thump's foundation is the Echoplex Preamp, the circuit taken from the preamp section of the Echoplex tape delay unit. Premier Guitar's reviewer described that pedal as delivering its sound "in a sturdy, elegant, and stupidly simple stompbox that even a pedal hater could love"5. MXR says the Echoplex Preamp circuit conditions the signal with a carefully balanced EQ profile, and that the design team and in-house bass players found that character worked for bass before adding the tone controls2.
On top of that base circuit, the Thump adds a three-band EQ with midrange frequency adjustment2. The whole thing fits into an MXR mini housing, the same compact box size as the rest of the MXR mini line24.
Guitar World's Amit Sharma called it "miniature in size, but the opposite in tone, it's the kind of sweetener that serves perfectly for a solo-boost or 'always-on' application"1. Gearnews wrote that it "should be a useful tool for players looking to add more boost and that extra 'oomph' to their bass signal"3.
Controls and EQ
The pedal carries five controls: an Output level knob, then Bass, Treble, Mid, and a Frequency knob that sets where the Mid control operates24.
| Control | What it does | Range (manual) |
|---|---|---|
| OUTPUT | Sets the output level of the effect | 4 |
| BASS | Cuts or boosts bass frequencies at 40 Hz | +15/-7 dBV, 40 Hz4 |
| TREBLE | Cuts or boosts high end at 4 kHz | ±10 dBV, 4 kHz4 |
| MID | Cuts or boosts the midrange as set by the Frequency knob | ±16 dBV, 1 kHz4 |
| FREQUENCY | Sets the midrange frequency from 250 Hz to 1 kHz | 250 Hz to 1 kHz4 |
The midrange sweep is the flexible part: the Frequency knob moves the Mid control's center point anywhere from 250 Hz to 1 kHz, so a player can push upper-mid growl around 1 kHz or thicken the low mids at 250 Hz3.
Gearnews' NAMM 2020 report gave the treble and bass frequencies as 8 kHz and 4 Hz3. That disagrees with the maker's own product page and manual, which both give 4 kHz and 40 Hz24. The maker's figures are the ones to trust here.
Other measured specifications from the manual, taken with all controls at their mid position: a noise floor of -95 dBV, A-weighted, with specifications measured at 1 kHz4.
Power and connections
Setup is straightforward: run a cable from your instrument to the M281's INPUT jack, then another cable from the OUTPUT jack to your amplifier4.
Power comes from the Dunlop ECB003 9-volt adapter, at 9 Volts DC with a current draw of 9 mA4. The pedal is also compatible with Dunlop's DC Brick, Iso-Brick, and Mini Iso-Brick power supplies, which are not included2.
The Thump cannot be powered by a battery4. Plan on a 9V adapter or a powered pedalboard.
Videos
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Questions
Is the MXR Thump Bass Preamp still in production?
No. MXR lists the Thump Bass Preamp as a legacy product that is no longer in production. It was announced at NAMM in January 2020 with a recommended retail price of USD 129.99, and it now appears only on the maker's legacy pages.
What frequencies do the Bass and Treble knobs control?
The Bass knob cuts or boosts at 40 Hz, and the Treble knob cuts or boosts at 4 kHz. The manual gives the treble range as plus or minus 10 dBV and the bass range as +15/-7 dBV. One news report gave different figures of 8 kHz and 4 Hz, which disagree with the maker's own numbers.
What is the midrange frequency range on the MXR Thump?
The Frequency knob sets the midrange center from 250 Hz to 1 kHz, and the Mid knob then cuts or boosts at that point. The manual lists the mid control range as plus or minus 16 dBV, measured at 1 kHz.
What power supply does the MXR Thump Bass Preamp use?
It runs on the Dunlop ECB003 9-volt adapter, at 9 Volts DC with a current draw of 9 mA. It cannot be powered by a battery. It is also compatible with Dunlop's DC Brick, Iso-Brick, and Mini Iso-Brick power supplies, none of which are included.
Sources (5)
- NAMM 2020: Jim Dunlop announces 4 new pedals, including the Green Day Dookie Drive V3, Guitar World, 2020-01-17
- MXR® THUMP™ BASS PREAMP, Dunlop (jimdunlop.com)
- NAMM 2020: New from Dunlop/MXR: Cry Baby Q Zone Fixed Wah & MXR Thump Bass Preamp, gearnews.com, 2020-01-16
- M281.pdf, Jim Dunlop, 2020
- Quick Hit: MXR Echoplex Preamp Mini Review, Premier Guitar, 2014-06-09
