Darkglass B7K Ultra

The Darkglass Microtubes B7K Ultra is a bass preamp and overdrive pedal from Darkglass, the Finnish maker whose Microtubes line has been a fixture of the modern bass pedalboard. Darkglass describes it as delivering "defined and powerful saturation in an intuitive format"¹. It combines the company's Microtubes drive circuit with a four-band EQ and a balanced XLR direct output, so one box can serve as a dirt pedal, a tone-shaping preamp and a DI into the PA.

The Ultra grew out of the original B7K. Bass Musician Magazine's Kilian Duarte described the B7K as the company's "crown jewel" and reported that it "has been revised with some new, more user-friendly options based on customer input"². The overdrive circuitry itself stayed the same; what changed is wrapped around it.

The controls: four-band EQ and a separate drive footswitch

The Ultra's front panel splits into a drive section and an EQ section, and the two can be switched independently. Darkglass lists a "dedicated footswitch to engage the overdrive section independently"¹, and Premier Guitar's review describes "separate footswitches for engaging the pedal and operating the distortion"⁴. In practice that means the EQ and preamp can stay active while the drive comes and go under your foot.

The EQ is where the Ultra earns its name. Kilian Duarte's review specifies a "4-band sweepable EQ with High (12db at 5kHz), Bass (12db at 100 Hz), Low and Hi Mids"², and Premier Guitar lists the treble band at +/- 12 dB at 5 kHz⁴. On the later V2 hardware, Guitar.com reported "a four-band EQ with six selectable mid-band frequencies" with "a three-way toggle" for each mid-range section⁵⁶,⁶.

The Ultra with Aux In version also adds a Micro USB B port for connecting to a computer, which Darkglass says lets you load cabinet simulation impulse responses and control other settings¹.

Can it be used as a DI?

Yes, and that is a large part of the design. Darkglass specifies a "balanced XLR output for connecting the pedal to a microphone preamp, PA system etc."¹, and the Master knob doubles as the DI level control¹⁷. Kilian Duarte called the direct output "perfect for use as a straight DI"².

The original B7K went further on connections: Bass Musician Magazine's review of that pedal lists a 1/4-inch input and output, a parallel output, a direct output and a ground lift for the direct output⁸. Premier Guitar noted that "the parallel output was not carried over to the Ultra model"⁴, so players moving from the B7K lose that extra tap.

From B7K to Ultra: what changed and what stayed

The lineage runs B7K, then Ultra, then V2 updates. The core drive sound did not change: Duarte wrote that "the beating heart of the Darkglass overdrive circuitry stays the same in the B7K Ultra"². What the Ultra added was a Master volume, mid selector switches and the dedicated overdrive footswitch².

The original B7K itself was later updated to a V2. Darkglass's product page says that with the B7K V2 "you'll get all the features of the original B7K, along with the ability to better sculpture your tone," with switchable center frequencies for the low mids and hi mids⁹. The B7K V2 is a variant of the original B7K⁹.

The B7K was revised into the Ultra model based on customer input, as MusicRadar put it, with "some new, more user-friendly options"¹⁰². While the overdrive circuitry of the original B7K stays the same in the B7K Ultra, the Ultra adds a 4-band sweepable EQ with High (12db at 5kHz), Bass (12db at 100 Hz), Low and Hi Mids¹⁰².

What reviewers said

Premier Guitar's 2021 review was positive overall, calling the B7K Ultra "an excellent upgrade to its predecessor"⁴.

The review's pros were "clean to crass tones, excellent EQ section, rugged design," and its cons were that the "switch layout [is] a bit unintuitive," that "adjusting drive and levels take some time" and that it "does not come cheap"⁴. On the EQ itself, the reviewer reported dialing in "thick lows that weren't muddy and highs that didn't bite but still presented crisp clarity"⁴. The same reviewer found the order of the frequency-center switches frustrating for on-the-fly adjustments⁴.

Kilian Duarte's 2016 review for Bass Musician Magazine tested the pedal through a Brubaker JXB, a Fender Japanese PJ, an Ibanez Soundgear SR1806 and an NS CR5 Radius, and found "the clarity that was present regardless of the bass in question and regardless of the saturation of the drive," with the pedal "cutting cleanly and musically with the drive engaged"². Premier Guitar's reviewer used a Ned Steinberger EUB, sending the DI to a small sound system in a six-piece jazz band for ballroom dancing, and reported achieving a convincing upright tone⁴.

The B7K family's standing in the wider bass world is hard to overstate. Reviewing a different bass overdrive for Guitar World, Connor Flys called the B7K "the other modern classic of the bass preamp world" and wrote that "the B7K shaped a whole new generation of rock and metal bass sounds"¹¹.

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