The Darkglass Electronics Microtubes B7K is an analog bass preamp, overdrive and booster in a stompbox format1. RockBoard's PedalPedia describes it as delivering "tone crushing overdrive and super transparent modern sound," a pedal that does not compromise the original sound of the instrument but enhances its presence in the mix1. In practice that means one box covers three jobs: a blendable overdrive circuit for grit, a four-band EQ for shaping, and a balanced DI output for feeding a PA or interface directly.
The B7K family grew into one of the most acclaimed Darkglass pedals in the bass community2, and Guitar World's reviewer called it "the other modern classic of the bass preamp world," crediting it with shaping "a whole new generation of rock and metal bass sounds"3. Both the B7K V2 and the B7K Ultra are listed as sold out on Darkglass's product pages as of late October 202624.
What it does for a bass player
The B7K sits in the bass signal chain as a preamp pedal: it takes your bass, adds an EQ section and an overdrive stage you can blend with the clean signal, and hands you a direct output for the desk. Bass Musician Magazine's reviewer Ty Campbell described the EQ portion as letting you "control the amount of lows, lo meds, hi meds, and treble," and found the pedal worked well as an overdrive, particularly with the fat setting, because it "did seem to not lose the low end"5.
The parallel output and direct output mean you can drive an amp and a PA at once, with the ground lift on the direct output available if a ground loop hum appears between the pedal and the desk5.
The controls
The original B7K's front panel, from Darkglass's manual6:
| Control | What it does |
|---|---|
| Level | Sets the volume of the overdriven signal |
| Blend | Mixes the clean input signal with the overdriven signal |
| Low | +/-12dB @ 100Hz |
| Low Mids | +/-12dB @ 1kHz |
| Hi Mids | +/-12dB @ 3 kHz |
| Hi Mids switch | Changes the Hi Mids center frequency from 3kHz to 1.5kHz |
The Blend knob is the heart of the design: because the clean signal stays in the mix, you can push the overdriven side hard without the low end disappearing, which is what Campbell found in his review6. The Hi Mids switch gives two usable presence points, 3kHz for cut-through brightness and 1.5kHz for a rounder, more vocal midrange6.
B7K, B7K V2 and B7K Ultra
The B7K V2 carries all the features of the original B7K with a revised EQ layout. Its Low Mids band moves to +/-12dB @ 500Hz and its Hi Mids band to +/-12dB @ 1.5kHz, with the same switch that shifts the Hi Mids center frequency between 3kHz and 1.5kHz27. Compared with the original's 1kHz Low Mids and 3kHz Hi Mids6, the V2's bands sit lower, which pushes its shaping power toward the frequencies where a bass guitar's body lives.
The B7K Ultra is a bigger step. Premier Guitar's reviewer described it as "an enhancement of the company's revered Microtubes B7K" that "packs in expanded EQ flexibility, a separate distortion footswitch, and a master volume control"8. Bass Musician Magazine's Kilian Duarte noted the Ultra came out of customer input, adding a master volume, mid selector switches and a dedicated overdrive footswitch to the original9.
The Ultra's EQ, from Darkglass's manual10:
| Band | Range and frequencies |
|---|---|
| Bass | +/-12dB @ 100Hz |
| Lo Mids | +/-12dB switchable 250Hz, 500Hz and 1kHz |
| Hi Mids | +/-12dB switchable 750Hz, 1.5KHz and 3kHz |
| Treble | +/-12dB @ 5kHz |
Both mid bands become three-position frequency switches, so the Ultra covers 250Hz through 3kHz in switchable steps rather than the original's two fixed mid points10. Premier Guitar's reviewer confirmed the low mids "can be boosted or cut at 250 Hz, 500 Hz, or 1 kHz" and the high mids at "750 Hz, 1.5 kHz, or 3 kHz"8. The Ultra also adds a Grunt switch, which selects between three bass boost levels before the clipping stage to set how much low-frequency content gets saturated4, a master volume for the overall unit level, and an internal stereo headphone amplifier with a 3.5mm Aux In for practicing with a backing track4. Its balanced XLR direct output connects to a microphone preamp or PA system11.
There was also a limited edition, the B7K Ultra V2 "The Squid," a preamp with cab sim, overdrive and distortion finished with custom artwork1213. Guitar World reported that on this version a three-way toggle offers additional control for each mid-range section12.
What reviewers said
Guitar World's Connor Flys, reviewing a different bass overdrive but pausing to place the B7K in context, called it3:
"the other modern classic of the bass preamp world - the B7K shaped a whole new generation of rock and metal bass sounds"3
Videos
Darkglass Electronics
Darkglass Electronics
SpectreSoundStudios
Questions
Does the Darkglass Microtubes B7K run on a battery?
No battery operation is part of its design. The B7K is powered by a typical 9-volt adapter of the kind used for pedals, so it needs a spot on a power supply rather than a battery compartment.
What does the ground lift on the B7K do?
The B7K has a ground lift switch for the direct output. It breaks the ground connection on the balanced DI line, which is the usual fix when a ground loop between the pedal and the PA or mixing desk produces a hum.
What is the difference between the B7K and the B7K Ultra?
The Ultra keeps the B7K's character but adds expanded EQ flexibility, a separate distortion footswitch and a master volume control. Its mid bands become frequency-switchable, and it adds an internal stereo headphone amplifier with a 3.5mm Aux In for silent practice.
Does the Microtubes B7K have a DI output?
Yes. Alongside the quarter-inch input and output and a parallel output, the B7K has a direct output: a balanced connection for feeding a microphone preamp, PA system or recording interface, with a ground lift switch on that output.
What frequencies does the Hi Mids knob on the B7K Ultra control?
The Ultra's Hi Mids knob gives plus or minus 12dB of boost or cut, and a switch selects the center frequency: 750Hz, 1.5kHz or 3kHz. The original B7K's Hi Mids band is fixed at 3kHz, with a switch that drops it to 1.5kHz.
Is the Darkglass B7K still in production?
The current versions are listed as sold out on Darkglass's own product pages. Both the Microtubes B7K V2 and the B7K Ultra with Aux In show sold-out status as of late October 2026, so finding one means looking at remaining retailer stock or the used market.
Sources (13)
- Microtubes B7K V2 by Darkglass Electronics, RockBoard (PedalPedia), 2026
- Microtubes B7K V2, Darkglass
- Earthquaker Devices Scrolls Bass Odyssey review, Guitar World, 2026-10-21
- Microtubes B7K Ultra with Aux In, Darkglass
- Darkglass Electronics Microtubes B7K Analog Bass Preamp Review, Bass Musician Magazine, 2016-07-01
- Microtubes B7K Manual, Darkglass
- Microtubes B7K V2, Darkglass
- Darkglass Microtubes B7K Ultra Review, Premier Guitar, 2016-05-19
- Darkglass B7K Ultra Review by Kilian Duarte, Bass Musician Magazine, 2016-03-01
- Microtubes B7K Ultra Manual, Darkglass
- Microtubes B7K Ultra with Aux In, Darkglass
- Darkglass Electronics unveils limited-edition The Squid drive pedal with custom artwork, Guitar World, 2020-08-14
- B7K Ultra V2 'The Squid' Limited Edition by Darkglass Electronics, RockBoard PedalPedia, 2026
