The Darkglass Harmonic Booster is a clean bass preamp pedal in the Finnish maker's Enhancer Series, built to enhance attack and presence while sculpting the mids for what Darkglass calls "a very percussive and aggressive character"1. It is a revival of the first Darkglass design, and its circuit is derived from the first few gain and filter stages of what would later become the core of the company's overdrive technology1. Where a Darkglass overdrive adds grit, the Harmonic Booster stays clean: it is about shaping and strengthening the tone you already have, not distorting it.
Premier Guitar reviewed it in those terms, calling it a pedal that is "all about the clean" and describing the effect as "simply giving additional life, clarity, and openness to a tone I was already content with"2.
What it does for your sound
Darkglass positions the Harmonic Booster as a clean preamplifier that enhances attack and presence4. In practice that means it sits in your chain as a tone-shaping and level stage: the EQ sculpts the mids for a percussive, aggressive character, and the boost section can lift or cut the whole signal by up to 20 dB13. Premier Guitar's reviewer found it "conjures a more present, thicker, tone without coloration" and praised the "solid build" and "great EQ"2.
A very bright white LED in the center of the enclosure indicates on/off status2.
The controls
Six knobs sit on the enclosure: a boost control, a Character control and a three-band EQ with a semi-parametric midrange52. Here is what each one does, from the maker's manual:
| Control | What it does |
|---|---|
| Boost | Flat, with -20dB to +20dB cut or boost of the overall level3 |
| Character | Blends in the amount of the tone-shaping circuitry; set counter-clockwise for a flatter frequency response3 |
| Bass | ±20dB at 80 Hz3 |
| Mid Frequency | Selects the mid frequency the mid gain acts on, from 250Hz to 2.5kHz3 |
| Mid gain | ±20dB at the frequency selected by the Mid Frequency knob3 |
| Treble | ±20dB at 5 kHz3 |
The semi-parametric mid is the heart of the EQ. Pick a center frequency anywhere from 250 Hz to 2.5 kHz, then cut or boost it by up to 20 dB32. That range covers the low-mid body of a bass through the upper-mid attack, which is where the pedal's percussive character lives.
The Character knob is the other control worth understanding. It is a blend, not a switch: counter-clockwise gives a flatter frequency response, and turning it up feeds in more of the pedal's tone-shaping circuitry3. Set against flat EQ, it is the fastest way to hear what the Harmonic Booster's preamp voicing adds.
Power and connections
The pedal runs on a regulated 9V DC adapter with a center-negative plug, drawing 30mA3. There is no battery option; the maker's page specifies adapter power only4.
Darkglass warns that unregulated power supplies or higher voltages may result in suboptimal noise performance and can damage the unit, voiding the warranty. Stick to a regulated 9V DC center-negative supply3.
Connections are simple: a ¼" mono input jack for your instrument or the output of your pedalboard, and a ¼" output jack to your amplifier or another effects pedal1. Input impedance is 470kΩ and output impedance is 1kΩ3.
To activate the warranty, Darkglass asks you to register the product on mypedal.darkglass.com using the serial number on the back of the pedal3.
Where it came from
The Harmonic Booster was Darkglass Electronics' first effects pedal, a clean bass preamp5. The current pedal is a revival of that first Darkglass design4, and its circuit lineage runs through the company's later overdrive work: the Harmonic Booster is derived from the first few gain and filter stages of what would become the core of Darkglass overdrive technology1.
In November 2019 Darkglass took another pass at the design and unveiled the Harmonic Booster 2.0, which MusicRadar described as a "clean harmonic-excitation preamp" reengineered to give bassists more headroom, less noise and a comprehensive EQ section compared to the original5. MusicRadar's Jonathan Horsley wrote that "for bassists looking to seize full control of their midrange, they could do worse than check out the Harmonic Booster 2.0"5.
Availability
The maker's product page lists the Harmonic Booster as sold out as of October 20261. The page also lists a UK price of £198.00 GBP1; Premier Guitar gave a $199 street price in its November 2021 review2.
Darkglass notes that specifications are subject to change without notice in the interest of continuous improvement3.
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Questions
Does the Darkglass Harmonic Booster take a battery?
No. The pedal runs on a regulated 9V DC adapter with a center-negative plug only, and the manual does not list a battery option. Darkglass warns that unregulated power supplies or higher voltages can cause noise problems, damage the unit and void the warranty.
What does the Character knob do on the Harmonic Booster?
Character blends in the amount of the pedal's tone-shaping circuitry. Set it counter-clockwise for a flatter frequency response, or turn it up to bring in more of the percussive, aggressive mid shaping that Darkglass built the preamp around.
Is the Darkglass Harmonic Booster discontinued?
The maker's product page lists the Harmonic Booster as sold out as of October 2026, so new units are not currently available from Darkglass. The design lives on in the Harmonic Booster 2.0, a reengineered version announced in November 2019 with more headroom, less noise and a comprehensive EQ section.
Can the Harmonic Booster be used as a clean boost?
Yes. The Boost knob offers up to 20 dB of cut or boost, and with the EQ set flat and the Character knob counter-clockwise the pedal passes a flatter frequency response, so it works as a clean boost for a bass rig.
Sources (5)
- Harmonic Booster, Darkglass
- Darkglass Electronics Harmonic Booster Review, Premier Guitar, 2020-01-24
- Harmonic Booster Manual, Darkglass
- Harmonic Booster, Darkglass
- Darkglass Electronics unveils the new and improved Harmonic Booster 2.0, MusicRadar, 2019-11-01
