The Maelstrom Bass Drive is based on the Darkglass® Microtubes® B3K, a CMOS-based drive circuit, with some additional tweaks adapted from the Vintage Microtubes.
The B3K started life as the Microtubes 2K, which was originally posted to the DIYStompboxes forum by Douglas Castro in 2008. After finishing university, he moved from Chile to Finland in 2010 and started Darkglass Electronics as a commercial entity.
During this time, he continued to work on the design, and the updated Microtubes B3K became Darkglass’s first product. While the original 2K was not described as a bass drive, the B3K and all subsequent Darkglass products have been designed for bass players and primarily marketed as such.
As the name implies, the original Microtubes 2K was inspired by the EHX Hot Tubes from 1979 as well as some other CMOS-based designs in the DIY community. However, by the time it had evolved into the B3K, it really bore no resemblance to any other circuits. A single overdriven CMOS stage is used for the clipping tone, contrasting with the cascaded inverters used by other similar circuits.
The Vintage Microtubes followed in early 2013. It’s essentially the same circuit as the B3K, but it removes the two toggle switches and adds a new control called “Era”, which is a midrange tone control.
The Maelstrom is a direct adaptation of the Microtubes B3K, with the Era control ported over from the Vintage Microtubes (renamed to “Tone” on the kit enclosure). With the Era control turned down, it’s identical to the standard B3K. The PCB build doc also includes part substitutions to build it to full Vintage Microtubes specs if you’d like.