Korg Nu:Tekt HD-S

The Korg Nu:Tekt HD-S Harmonic Distortion is a distortion pedal from Korg, first announced in January 2023 and sold as a self-assembly kit. It is built around Korg's Nutube, a mini vacuum tube device that the company says operates exactly as a triode vacuum valve, and it carries three separate distortion circuits that can be used on their own or blended together¹².

The pedal was developed by Fumio Mieda, the original designer of the Uni-Vibe and many other Korg pedals and synths. Mieda describes the HD-S's distortion as an all-new, "never-before heard" kind based on harmonic synthesis, an approach he took because most distortion effects rehash the sounds of the past¹².

Three distortion circuits and a Nutube

The heart of the HD-S is its three distortion circuits, dialed in with three trim pots labeled Harmonic 1, 2 and 3. Guitar World's reviewer, Trevor Curwen, found they can be used singly or combined to create everything from traditional cranked stack-style distortion sounds, through a range of fuzz shadings, to highly resonant, raucous distortion at the more extreme end of the scale¹.

The balance between the three circuits can be adjusted from smooth to aggressive via hidden controls under the front panel³. Josh Scott of JHS Pedals, who featured the pedal in a May 2023 video, was impressed by the range of sounds it produces, from classic fuzz to Univox Superfuzz and beyond².

The circuits sit alongside Korg's Nutube, jointly developed by Korg and Noritake Ise as a next-generation vacuum tube⁴. The Nutube can run on battery power, which is what allows the OD-S overdrive in the same range to work from a 9V battery⁵. In the related Nu:Tekt HS-2 Harmonic Distortion, the Nutube is visible through a glass opening on the bottom left of the pedal⁶. Curwen's review of the Nutube-based pedals found that "Nutube technology gives authentic valve-like response"¹.

The HD-S sits in a Nu:Tekt range that began with the OD-S overdrive kit in 2020, a solderless build with a promised 45-minute assembly time⁷⁸. The HD-S was announced alongside the TR-S Power Tube Reactor, a tube amp emulator kit that uses the Nutube to emulate the feel of a tube amp⁹.

The controls

The HD-S carries four main knobs plus the three Harmonic trim pots and a bypass footswitch¹.

The Gate knob addresses what Curwen found at the pedal's extremes: "It can get a bit wild, but an adjustable noise gate can bracket out the noise and keep things in shape"¹.

The three Harmonic trim pots are the hidden controls under the front panel. They adjust the balance between each distortion circuit, letting you weight the blend toward the smoother circuits or the more aggressive ones¹³. This is a different arrangement from the companion TR-S Power Tube Reactor, whose three trim pots handle Tone, Sustain and Threshold instead¹⁹.

The kit

Korg positions the Nu:Tekt series as products the buyer can assemble themselves, and the earlier OD-S kit was described as ideal for teaching kids how to build a simple circuit, though more advanced DIY hobbyists might find it less challenging¹⁰. With the HD-S, the "build" is closer to final assembly than electronics work: the circuit itself is complete, and the player finishes the enclosure¹.

What reviewers said

Josh Scott's verdict, reported by Guitar World in May 2023, was blunt:

Guitar World's own review found the pedal can get wild at extreme settings but that the gate keeps it usable, and credited the Nutube with an authentic valve-like response¹. At the time of Scott's video, the pedal was newly on shelves at what Guitar World called an obtainable price of around $200 to $250⁹; the listed price in the 2026 review was $299¹.

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