The Darkglass Microtubes B3K is a compact analog bass overdrive pedal from Darkglass, later updated as the V212. Its whole design idea is keeping your low end intact while adding saturation: a Blend knob mixes your clean input signal with the overdriven signal, so the fundamental stays solid underneath the grind3. Darkglass describes the pedal as "a perfect combination of brutality and clarity" that delivers "defined and powerful saturation in an intuitive format"4.
The circuit is built on hybrid JFET and CMOS gain stages, which No Treble credited with a natural dynamic response at launch1. Aion FX's technical analysis notes that a single overdriven CMOS stage is used for the clipping tone, in contrast to the cascaded inverters used by other similar circuits5. Darkglass says the pedal aims for the natural dynamics and organic compression of vintage tube amps and tape machines4.
A blendable bass overdrive with clean low end
The B3K's defining feature is its parallel blend. The clean signal stays at unity gain while the Level knob sets the volume of the overdriven signal, which the manual says allows fine control of the blend ratio47. That means you can push the Drive knob hard for saturation while your clean low end carries the bottom, a common approach for bassists who want grit without losing definition on the low strings.
Aion FX traced the circuit and released it as the Maelstrom Bass Drive project8. Darkglass itself describes the B3K as "the same pedal we designed nearly a decade ago"8. No Treble reported it was available by order through the Darkglass Electronics website1, and the B3K V2 is listed on the maker's store at £198.00 GBP4.
The controls
The control set is small and focused. Here is what each control does, per the Darkglass manual and product pages643:
| Control | What it does |
|---|---|
| Level | Sets the volume of the overdriven signal. |
| Drive | Sets the amount of saturation in the overdriven signal. |
| Blend | Mixes the clean input signal with the overdriven signal; the clean side stays at unity gain. |
| Grunt switch | A pre-gain switch that, when engaged, provides a massive low end boost to thicken your sound. |
| Attack switch (V1) | Adjusts high-frequency saturation content; No Treble described it as replicating the "Ultra Hi" option from many tube amps, giving a treble boost for clarity, presence and definition. |
| Tone knob (V2) | A variable low pass filter from 3kHz (counterclockwise) to 8kHz (clockwise), controlling the high frequency content of the sound. |
| Mid Boost button (V2) | Gives a subtle 6dB boost from 300 Hz to 1kHz to help you cut through a bit more. |
The Grunt switch works in tandem with the Drive knob: No Treble explained that it lets you choose between bass boost levels that essentially determine the level of low-end saturation1. The V1 was housed in a durable aluminum enclosure3, and the V2 carries the same 75 by 111 by 43 mm footprint4.
Power: 9V, center negative
The B3K runs on a regulated 9V DC adapter with a center-negative plug6. There is no battery option on the V1: RockBoard's spec page states power is supplied exclusively through an external direct current adapter3. No Treble's 2010 launch report said the pedal was powered by either a 9V battery or power supply1, so early units may have differed; the maker's own documentation specifies adapter power only.
Darkglass warns that unregulated power supplies or higher voltages may result in suboptimal noise performance, damage the unit, and void the warranty. Use a regulated 9V DC, center-negative supply64.
On current draw the maker's own documents disagree: the manual lists approximately 17mA7, while the product page states 20mA4. Either figure is modest, so the pedal is easy to accommodate on a typical isolated power supply.
Connections are simple: a quarter-inch mono jack input for your instrument or pedalboard output, and a quarter-inch output jack to your amplifier or another effects pedal4.
V1 versus V2
MusicRadar reported in October 2017 that the B3K and B7K had both reached version 22. The changes on the B3K V2, per Darkglass4:
- You get all the features of the original, with the ability to restore the mids for natural character.
- The Attack switch has been replaced by the Tone knob, giving much more control of the higher harmonic content (3 kHz to 8 kHz).
- A Mid Boost button adds a subtle 6dB boost from 300 Hz to 1kHz.
The B3K and the B7K
The Microtubes B7K V2 shares the B3K's core overdrive concept but adds a four-band EQ910:
| EQ band | B7K V2 |
|---|---|
| Low | plus or minus 12dB at 100Hz |
| Low Mids | plus or minus 12dB at 500Hz |
| Hi Mids | plus or minus 12dB at 1.5kHz |
| Treble | plus or minus 12dB at 5kHz |
Where the B3K shapes its top end with the Tone knob and thickens the bottom with Grunt, the B7K gives you cut and boost at four fixed frequencies. Players who want more tonal control at the pedal itself lean B7K; players who want the simpler, smaller box lean B3K910.
What reviewers said
Published and community opinions on the B3K ran mostly positive, with some dissent. Pedal of the Day's reviewer Max F. wrote in 201611:
"Because of its intuitive control set, musical gain structure, and blending abilities, the B3K is in a class of its own when it comes to bass distortion."12
On the Guitar FX Layouts vero-build thread for the circuit, builders who finished the project were enthusiastic. Paul_5 wrote "Finally finished mine today and it's a GREAT pedal," and another commenter reported "It sounds really great!"11. One player compared it directly against a familiar rival:
"The B3K really makes my Rick & Ampeg growl in a way the Bassdrive just can't."11
Not everyone was convinced, though. Highsmith, on the same thread, wrote "I don't think it's any better than the Boss ODB-3 or Fulltone Bassdrive..."11. The thread also contains useful technical detail for anyone building or repairing one: the clipping diodes around the 4049 CMOS chip are there to protect the CMOS input from over-voltages rather than to shape the clipping itself11, and one owner's unit was PCB version 3.111.
Videos
Darkglass Electronics
Darkglass Electronics
The Bass Channel
Questions
What is the difference between the B3K V1 and V2?
The V2 keeps everything from the original and adds the ability to restore the mids for a more natural character. The Attack switch is replaced by a Tone knob, a variable low pass filter from 3kHz to 8kHz, which Darkglass says gives much more control of the higher harmonic content. A Mid Boost button, a 6dB boost from 300 Hz to 1kHz, is also part of the V2 control set.
Does the Darkglass B3K take a battery?
No. Power comes exclusively through an external 9V DC adapter with a center-negative plug. Darkglass warns that unregulated supplies or higher voltages may cause noise or damage and can void the warranty, so use a regulated 9V supply.
Is the Darkglass B3K true bypass?
Yes. No Treble reported at the pedal's launch in 2010 that the Darkglass B3K features true bypass, so your clean signal passes through the pedal untouched when it is switched off.
What does the Grunt switch do on the B3K?
Grunt is a pre-gain switch for low-end emphasis. When engaged it provides a massive low end boost to thicken your sound, and it works in tandem with the Drive knob to determine the level of low-end saturation. No Treble described it as offering a choice of bass boost levels.
Is the B3K analog?
Yes. The B3K is an analog pedal built around hybrid JFET and CMOS gain stages. Aion FX notes that a single overdriven CMOS stage is used for the clipping tone, in contrast to the cascaded inverters used by other similar circuits.
What is the difference between the B3K and B7K?
Both are Microtubes bass overdrives with the same core Drive, Blend and Level concept, but the B7K V2 adds a four-band EQ: Low at plus or minus 12dB at 100Hz, Low Mids at 500Hz, Hi Mids at 1.5kHz, and Treble at 5kHz. The B3K keeps its tone shaping to the Grunt switch and, on the V2, the Tone knob and Mid Boost.
Sources (12)
- Gear Watch: Darkglass Electronics Microtubes B3K Overdrive Pedal, No Treble (www.notreble.com), 2010-11-05
- Darkglass's bass drive pedals get a boost as B3K and B7K are updated to version 2, MusicRadar, 2017-10-19
- Darkglass Electronics Microtubes B3K v1, Rockboard PedalPedia
- Microtubes B3K V2, Darkglass
- Maelstrom Bass Drive / Darkglass Microtubes B3K, Aion FX, 2021-11-12
- Microtubes B3K Manual, Darkglass
- Microtubes B3K Manual, Darkglass
- Microtubes B3K V2, Darkglass
- Microtubes B7K V2, Darkglass
- Microtubes B7K V2, Darkglass
- Guitar FX Layouts: Darkglass Microtubes B3K, Guitar FX Layouts (tagboardeffects.blogspot.com), 2017-05-28
- Guest Reviewer Fridays: Darkglass Electronics Microtubes B3K Bass Overdrive, Pedal of the Day (pedal-of-the-day.com), 2016-08-26
