Darkglass Microtubes X Ultra

The Darkglass Microtubes X Ultra is a bass preamp pedal that splits your signal in two and treats each half differently: the low end is compressed so the bass frequencies stay tight and solid, while the top end is distorted through CMOS circuitry¹². Darkglass describes it as a powerful preamp pedal covering the whole bass distortion spectrum, from articulate high gain to punchy mild overdrive and raw, gnarly fuzz³. At its core are two channels, clean and multiband distortion, plus a variable low-frequency compressor⁴.

It is the latest in the Microtubes series, built on the Microtubes X7 with more features, and it is made in Finland by Darkglass²⁵. Darkglass's own store lists it as sold out, with a regular price of £380.00 GBP; MusicRadar's review lists it at £395³².

Compressed lows, CMOS-distorted highs

The X Ultra's approach to bass distortion is multiband. When distortion is engaged, the signal is split into two variable filters, low-pass and high-pass⁴. The bottom end of the signal is compressed to maintain the bass frequencies, while the top end is distorted via CMOS distortion circuitry⁸. MusicRadar notes this is what Darkglass's CMOS gain circuit is designed for: aggressive distortion on the low-end signal without losing the foundation².

The clean channel, on the other hand, is touted to give you pristine cleans⁴. Two footswitches let you engage or bypass the EQ section and the distortion independently, so you can run the pedal as a clean preamp and EQ, or add the distortion on top².

The controls

The control layout has four large knobs for Low Comp, Low Level, High Level and High Drive, with a 4-band EQ, master volume and two shelving frequencies around them².

The compressor can also be enabled for the clean signal in the Darkglass Suite software, at which point the same control sets the compression amount⁷.

Power and connections

The X Ultra runs on a regulated 9V DC adapter with a center-negative plug only, drawing approximately 200mA⁷. Unregulated power supplies or higher voltages may result in suboptimal noise performance and can damage the unit, voiding the warranty⁷.

Connections are a 1/4 inch input jack (500kΩ input impedance) and a 1/4 inch output jack (1kΩ output impedance), plus a balanced XLR DI output with Ground Lift and Cab Sim selectors for going straight to a desk or interface²⁷.

History: from the Microtubes X to the X7 and X Ultra

The Microtubes X and X7 debuted in October 2018 as multiband bass drive pedals, with adjustable low-pass and high-pass filters and controls for level, drive, mix and mids; the highs are distorted using CMOS circuitry⁵. The X became part of Darkglass's Core series⁹.

The X Ultra is the latest in the Microtubes series, built on the X7 and giving it more features². RockBoard's PedalPedia describes it as greatly expanding on the versatility of the X7 with four major additions while maintaining the same compact footprint⁶. Like the others in the Microtubes series, its high-pass side is distorted with CMOS circuitry¹⁰. The Microtubes X distortion later became one of the three engines inside the Microtubes Infinity, alongside the B3K and Vintage¹¹.

What reviewers said

MusicRadar's review called the X Ultra an exceptional unit packed with features, with a wide range of tones, though noted it is not cheap².

Guitar World's review found lots of functional versatility with a wide tone range, and listed the pedal as made in Finland⁸. In Guitar World's guide to overdrive pedals for bass, Mike Brooks wrote:

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