Keeley produced the Dark Side (KDARK-U) as a multi-effect workstation pedal, combining three core effect categories — fuzz, delay, and modulation — into a single unit. It was designed to offer a wide range of textural and atmospheric sounds within one enclosure.

The fuzz circuit was based on a 1977 op-amp style topology, developed in relation to Keeley's Psi Fuzz but implemented differently, with tuning intended to retain guitar character across both single-coil and humbucker pickup types while delivering sustain. The delay section offered 12 syncopated rhythmic delay settings derived from multi-head tape delay machines, with subtle filtering to approximate the warmth of spinning drum tape machines; the repeat count was controllable via an expression pedal, and the circuit was capable of feedback oscillation. The modulation section provided four distinct effects — Flanger, Rotary Speaker Cabinet, U-Vibe, and Phaser — selectable and blendable in pairs: Flanger with Rotary, and U-Vibe with Phaser. An expression pedal port (TRS) was included on the unit.

Owners seeking alignment, calibration, or integration assistance with external expression pedals should consult a qualified guitar technician familiar with multi-effect signal chain setups.