Review: Darkglass Microtubes B3K CMOS Bass Overdrive

There are many ways to skin the distortion cat—if not, the Maestro Fuzz Tone would have been the basis for a multi-billion-dollar stompbox empire.
Image placeholder title

There are many ways to skin the distortion cat—if not, the Maestro Fuzz Tone would have been the basis for a multi-billion-dollar stompbox empire. Yet, in spite of the many cat-skinning concepts out there, most every distortion stompbox operates according to the same basic principle: overload or otherwise exploit the signal-mangling properties of some basic electronic components to compress and add harmonic content to an input signal. The super-hip Darkglass B3K achieves its distortion through use of a CMOS hex-inverter, a relatively rare method compared to the ubiquitous silicon-, germanium-, or LED-diode-based designs. Complementary metal-oxide-semiconductor (CMOS) chips are integral to digital microprocessors, but they aren’t inherently “digital” in our conventional sense of the word— there is no A/D conversion here. Other than their extraordinary utility in computing applications, a CMOS chip can be used as an analog operational amplifier, since it contains a series of MOSFETs, the transistor type renowned for its tube-like distortion character.

The B3K pairs its left-of-center distortion circuit with a few innovative features that help it achieve praise-worthy tone. Beyond the blend, level, and drive controls (all of which do what you might expect), the B3K offers a pair of 3- position switches that, while subtle, add just-right flavor to the pedal’s sonic stew. The attack switch alters the amount of treble introduced into the pedal’s clipping stage. The grunt switch governs three levels of bass boost in front of the clipping stage. Used in conjunction with the drive parameter, these two switches coax a gamut of sounds, from edgy and aggressive to smooth and mellow, out of an instrument.

The B3K’s construction is excellent. Like many boutique pedals these days, it doesn’t offer battery operation; thankfully, it’s compatible with a standard Boss-style tip-negative 9-volt power supply. The housing is rugged and the interior is filled with a slick-looking surface-mounted PCB. Interestingly, a momentary switch performs the on/off functions, although it operates like a normal latching switch thanks to some circuit trickery. It feels great, and without the mechanical click of a conventional switch, I expect it to last a long while.

With a name like “Microtubes,” it’s not hard to guess at the intent of the B3K’s overdrive personality. Of the many, many overdrive pedals that have come across my desk, the B3K is among the most tube-like I’ve bumped into. It’s never grating or harsh, with nasty intermodulation distortion and fizzy fluff. Rather, it’s dynamically sensitive, rich, and warm. Backing off drive and dialing in a 50:50 dry/distorted mix with blend offers up a subtle bit of hair, much like an all-tube amp at the edge of break-up. Pushing it harder, reducing the dry mix and engaging attack yields ever-more intense levels of mayhem, but it never goes full-on into maniac fuzz territory.

The B3K is a potent tool. If you just want to fatten and warm the sound of a shrill rig, it’s got you covered. It also has you covered if you’re playing an all-ages gig with giant subs and you want to teach the kids a lesson in visceral bass violence, especially because it retains low end so well. Those seeking a fresh and musical take on the omnipresent bass overdrive must include this in their hunt.



Microtubes B3K
Pros Versatile and musical overdrive with a few handy extra touches; skillfully designed and built
Cons No internal battery option
Bottom Line The Microtubes B3K is one of the most tubey stompboxes around, capable of tones from tame to insane.


Input ¼"
Output ¼"
Power 9V tip-negative Boss-style power adapter

Made in U.S.A.


Image placeholder title

TWA Little Dipper 2.0 (Review)

Whether it’s emulating the squelchy quack of classic Bootsy Collins, the tubby dub of Bill Laswell, or the intricate attack and frequency dynamics of an analog synthesizer, envelope filters are among the most useful—and radical— stompboxes available.