Darkglass Microtubes B7K V2

The Darkglass Microtubes B7K V2 is a bass preamp and overdrive pedal from Darkglass, the Finnish company behind the Microtubes line. Darkglass describes it as delivering "tone crushing overdrive and super transparent modern sound," and says it "doesn´t compromise the original sound of the instrument, but it enhances its presence in the mix"¹. The core of the design is a clean blend: your untouched bass signal stays at unity gain while a separate overdriven signal, set by the Drive and Level knobs, is mixed in with the Blend knob². On top of the drive section sits a four-band EQ, and the pedal ends with a balanced direct output, so it works as a preamp, an overdrive and a DI in one box¹.

Guitar World's reviewer called the B7K "the other modern classic of the bass preamp world," saying it "shaped a whole new generation of rock and metal bass sounds, and is bursting with tone-shaping options"³.

What it does to your sound

The signal path is built around parallel clean and dirty paths. The Drive knob "sets the amount of saturation in the overdriven signal," and the Level knob sets the volume of that overdriven signal¹⁵. The Blend knob then mixes the clean input signal with the overdriven signal, with the clean side remaining at unity gain, which allows fine control of the blend ratio². For a player, that means you can push the drive hard for grind and aggression while keeping the low fundamental of the bass intact underneath it.

Bass Musician Magazine's Ty Campbell, reviewing the original B7K preamp, found exactly that when using it for overdrive: "I was really comfortable with the fat setting as it did seem to not loose the low end"⁶.

After the blend, a four-band EQ shapes the result before it leaves the pedal.

The controls

The V2 carries the original B7K's EQ bands plus switchable center frequencies on both mid bands, which is the main change from the first version⁵.

The Attack switch is new on the V2. Darkglass describes it as an addition that "helps to keep the treble portion of the signal under control, specially useful when playing with new strings and/or cabinets with tweeters"¹. On the B7K Ultra, the Attack switch works differently: it is a three-way control setting the amount of saturation for the treble frequencies, with a choice of boost, cut, or flat⁷.

Power and connections

The B7K V2 runs on a regulated 9V DC adapter with a center-negative plug, drawing 26 mA¹. There is no battery option in the maker's specifications. Darkglass warns that "unregulated power supplies and/or higher voltages may result in suboptimal noise performance and even damage your unit, voiding the warranty"¹.

Connections are straightforward:

• Input: a ¼" mono jack for your instrument or the output of your pedalboard¹
• Output: a ¼" jack to your amplifier or another effects pedal¹
• Parallel Output: a passthrough of your input signal, useful for parallel processing¹
• Direct Output: a balanced version of the ¼" output, for a desk or interface¹

The parallel output opens up routing options the Ultra model does not have: Premier Guitar's reviewer noted that "the parallel output was not carried over to the Ultra model, but the added features more than make up for it"⁷. Bass Musician Magazine's review of the original B7K also noted a ground lift on the direct output⁶.

History and versions

The Microtubes story starts with the B3K: Aion FX's circuit documentation records that "the updated Microtubes B3K became Darkglass's first product"⁸. The B3K was a compact CMOS-based bass overdrive in a durable aluminum enclosure, designed to retain fundamental low frequency response under heavy gain⁹. The B7K grew out of that line as a preamp version with the four-band EQ and direct output⁶.

MusicRadar reported in October 2017 that both the B3K and B7K "hit version 2," with the B7K V2 priced at £319 in the UK at launch¹⁰. The V2's change over the original is focused: all the original features, plus the switchable mid frequencies (Low Mids from 1 kHz to 500 Hz, Hi Mids from 3 kHz to 1.5 kHz) and the Attack switch⁵¹.

B7K V2 vs the B7K Ultra

The B7K Ultra is the expanded sibling. Premier Guitar described it as "an enhancement of the company's revered Microtubes B7K"⁷. Where the V2 gives you two mid frequencies per band, the Ultra's mid controls are three-way switchable: Low Mids at 250 Hz, 500 Hz or 1 kHz, and Hi Mids at 750 Hz, 1.5 kHz or 3 kHz⁷. It adds a master volume for balancing the overall signal, separate footswitches for engaging the pedal and operating the distortion, a balanced direct out with ground lift, and an internal stereo headphone amplifier driving a minimum load of 16 ohms from a 3.5 mm jack⁷¹¹. The Ultra is also bigger and hungrier: 125 mm wide, 96 mm long, 57 mm high, 430 g, with a current draw of about 120 mA at 9V DC center negative¹²¹³.

Premier Guitar's verdict on the Ultra: "Darkglass' Microtubes B7K Ultra is an excellent upgrade to its predecessor," with added flexibility and practical tones worth the investment to many players⁷.

The Squid limited edition

In August 2020, Darkglass announced a limited edition of the B7K Ultra V2 with Aux In, called "The Squid," with custom artwork by Ignacio Bazan Lazcano¹⁴¹⁵. No Treble described it as "the company's all-time best-seller with an auxiliary input and in a special enclosure"¹⁶. It runs the same Microtubes dynamic saturation circuit as the B3K V2 and B7K V2, adding a four-band EQ and a dedicated footswitch to engage the overdrive section independently¹⁴. Its feature set includes:

• A single user-loadable cabinet simulation impulse response¹⁷
• A Micro-USB B port to connect to a PC or Mac and load a different Virtual Cabinet through the Darkglass Suite¹⁷
• A 3.5 mm headphone output with cabinet simulation¹⁷
• A 3.5 mm stereo aux input for practicing with backing tracks¹⁷
• Balanced XLR and quarter-inch output sockets¹⁵

Guitar.com reported The Squid releasing "this week" as of 12 August 2020, with independent bypass and distortion footswitches that let the onboard EQ be engaged separately¹⁵.

What reviewers said

Published reviews of the B7K family have been consistent in praising its flexibility. Guitar World's reviewer called the B7K v2 "the other modern classic of the bass preamp world," noting it "shaped a whole new generation of rock and metal bass sounds, and is bursting with tone-shaping options," at $399³. Bass Musician Magazine's Ty Campbell wrote that "some one of the most versatile direct boxes come from Darkglass electronics, and the Microtubes B7K Analog Bass Preamp is no exception," and found the EQ section let him control lows, lo mids, hi mids and treble effectively⁶. For the Ultra, Premier Guitar found the upgrade worthwhile despite the loss of the parallel output⁷.

Related Darkglass pedals

If you are comparing circuits across the range, related models include the Microtubes B3K and B3K V2 overdrives, the B7K Ultra, the B7K Ultra with Aux In, and The Squid edition of the B7K Ultra V2. All sit in the wider bass pedals and preamp pedals categories.

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