Premier Guitar features affiliate links to help support our content. We may earn a commission on any affiliated purchases.

Darkglass Microtubes B7K Ultra Review

A sturdy box for bassists that delivers wide-ranging drive and an impressive EQ section.

Clip 1 - Nash P bass with tone dial set at 60 percent. B7K settings: Master at 2 o'clock, blend maxed, level at 1 o'clock, drive 9 o'clock, low at 12 o'clock, lo mids (@ 500Hz) 1 o'clock, hi mids (@ 3kHz) 2 o'clock, treble at 1 o'clock. High boost setting on attack switch. Grunt set flat.
Clip 2 - Ritter R8 5-string with both pickups balanced and EQ set flat. B7K settings: Master at 2 o'clock, blend maxed, level 1 o'clock, drive 2 o'clock, low at 1 o'clock, lo mids (@ 1 kHz) 1 o'clock, hi mids (@ 3kHz) 2 o'clock, treble at 2 o'clock. High boost setting on attack switch. Bass boost setting on grunt.
Caption here

It’s no secret that pedal builders are notorious tinkerers, be it perpetually developing new sonic machines or improving on previous designs. The creative minds at Finland’s Darkglass Electronics follow this philosophy, and it’s exemplified in their latest creation, called the Microtubes B7K Ultra. This smart-looking stompbox is an enhancement of the company’s revered Microtubes B7K. In short, the next-generation B7K packs in expanded EQ flexibility, a separate distortion footswitch, and a master volume control.

Microtubes Under the Microscope
Darkglass products have consistently clean aesthetics, and the Ultra’s silver-and-black dressing with prominent blue LEDs is no different. The B7K Ultra is also rock solid. All the switches and knobs felt strong and functioned smoothly, and the stout chassis felt like it could easily take on the rigors of the road. Removing the base plate requires a Torx screwdriver, but once inside, I found a clean and well-organized interior.

The B7K Ultra contains all of the tonal essentials of its predecessor, along with a few extra tone-shaping goodies. A 4-band EQ highlights the preamp section with similar voicings for the bass (+/-12 dB @100 Hz) and treble (+/- 12 dB @5 kHz). However, the lo-mid and hi-mid controls are connected to frequency center switches that provide expanded midrange manipulation. Low mids can be boosted or cut at 250 Hz, 500 Hz, or 1 kHz, while the center frequencies for the high mids can be set at 750 Hz, 1.5 kHz, or 3 kHz.

Additional features of the B7K Ultra include the master control for balancing the overall signal, separate footswitches for engaging the pedal and operating the distortion, a balanced direct out, and a ground lift. Owners of the original B7K will note that the parallel output was not carried over to the Ultra model, but the added features more than make up for it.

Cranking the drive to 4 o’clock and boosting the attack and grunt switches delivered a beefy, percussive gnash that would likely satisfy the most fervent Meshuggah fans.

The Sound and the Fury
Shortly after receiving the pedal, I took it straight to a rehearsal for an upcoming rock show covering music from Sabbath to Slayer. My basses of choice were a Nash P-style and a Ritter R8 5-string. For my rig, I brought along a Bergantino B|Amp and a pair of Bergantino HD112s.

Players have lauded Darkglass’s saturation circuit for its sounds that range from subtle bite to gut-punching distortion. The conventional level, drive, and blend controls offer different overdriven concoctions, but what sets the BK7 Ultra apart from the pack are the attack and grunt switches. These 3-way switches set the amount of saturation for the bass (grunt) and treble (attack) frequencies with the choice of boost, cut, or flat.

Though it took a little bit of time to adjust the levels of the bass signal and saturation section, experimenting with the dials elicited many pleasing tones. When I set the attack switch in boost mode and positioned the drive around 9 o’clock, the B7K Ultra created a mellow, clang-y grind—ideal for copping Geezer Butler lines. Cranking the drive to 4 o’clock and boosting the attack and grunt switches delivered a beefy, percussive gnash that would likely satisfy the most fervent Meshuggah fans. With enough tweaking, the B7K Ultra is capable of wide and satisfying dimensions of drive.


Clean to crass tones. Excellent EQ section. Rugged design.

Switch layout a bit unintuitive. Adjusting drive and levels take some time. Does not come cheap.


Ease of Use:




Darkglass Microtubes B7K Ultra

The EQ was impressively clean. I dialed in thick lows that weren’t muddy and highs that didn’t bite but still presented crisp clarity in the top end. And the midrange frequencies were tailored to the most responsive tonal areas of bass instruments. Whether it was boosting the high mids at 3 kHz for a pleasant edge to the Nash or a low-mid bump at 500 Hz to plump up the notes of the Ritter’s 5th string, the Ultra had loads of room for cutting or boosting the desired frequencies.

A few nights later, I applied the B7K Ultra in a more unconventional scenario—a 6-piece jazz band performing for a ballroom-dance club. Wielding a Ned Steinberger EUB, I connected the bass to the pedal and sent the signal from its DI to the small sound system used by the ensemble. With a slight cut in the high mids at 750 kHz and a tiny touch of drive with the grunt boosted, I achieved a convincing upright tone. While it didn’t precisely replicate a full-bodied upright, the B7K Ultra helped deliver the appropriate timbre to play waltzes and foxtrots for three hours. Ouch.

If I had any quibble at all, it would be the order of the frequency switches. For example: Setting the low-mid switch in the up position sets the frequency at 500 Hz, moving it to the middle sets it at 1 kHz, and then 250 Hz in the down position. One might get used to these settings over time, but I found myself instinctively switching up for higher frequencies and down for lower frequencies. The same was the case with the high-mid switch. And with the functions of the attack and grunt switches also arranged somewhat inconsistently, it made on-the-fly adjustments a bit frustrating.

The Verdict
Darkglass’ Microtubes B7K Ultra is an excellent upgrade to its predecessor. The added features allow players to immerse themselves in deeper tone-shaping and season their overdriven preferences just right. Most all of the issues that plague other distortion pedals—such as low-end loss or separated sound—are answered on the Ultra in the form of a switch or control. Its price tag won’t likely resonate with budget-conscious players, but the Ultra’s additional flexibility and practical tones will be worth the investment to many others. Whether you’re a distortion disciple looking for new flavors or in need of a portable, super-clean preamp, the Microtubes B7K Ultra has you covered.

Watch the Review Demo: