Korg HD-S

The Korg HD-S is a distortion pedal kit from Korg, part of the company's Nu:Tekt series of self-assembly products. Instead of one clipping stage, it combines three different distortion circuits to create what Korg calls harmonic modulation, and you can use those circuits singly or together to move from traditional fuzz to sounds Korg describes as "out of this world"¹.

Because the three circuits can be freely combined, Korg positions the HD-S as usable well beyond guitar. The company says it works with bass guitars, synthesizers and other instruments, not just guitar². It was announced in January 2023 alongside the Nu:Tekt TR-S Power Tube Reactor, another kit pedal³.

Three distortion circuits combined for harmonic modulation

The core idea of the HD-S is that distortion comes from three separate circuits rather than one, and that blending them produces harmonic modulation Korg says goes beyond traditional distortion. The three circuits are dialed in with three Harmonic trimmers, and they can be used singly or combined⁵.

In Guitar World's review, Trevor Curwen described the range this opens up: the circuits can 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 scale"⁵. Gearnews reported that the balance between the circuits can be adjusted from smooth to aggressive via hidden controls under a front panel³.

The HD-S is based around Korg's Nutube, which the company says operates exactly as a triode vacuum valve⁵. Its three distortion circuits can be used singly or combined, producing 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 scale⁵.

The controls: four knobs and three trimmers

On the top panel the HD-S has four control knobs, plus a bypass footswitch. The published sources disagree on the fourth knob's name: Guitar World's review lists Volume, Tone, Gate and Chain⁵, while Guitar.com's launch report lists Volume, Tone, Gate and Gain⁶. The other three names match across both.

Inside the top cover of the housing sit three trimmer knobs, labeled Harmonic 1, 2 and 3, one for each distortion circuit¹⁵. Korg says using these trimmers to adjust the balance between the three circuits is how you create the pedal's wide range of sounds¹. Guitar World described them as screwdriver-adjusted and designed to be set and forget⁷.

How the three trimmers behave was a point Josh Scott of JHS Pedals made in 2023: rather than giving three independent voices, they shape one overall character⁷.

The four main knobs handle the everyday tone shaping. Korg's documentation lists Volume, Tone, Gate and Chain controls on the panel, alongside a Harmonic section with three positions and a bypass footswitch⁵. Beyond those, three trimmer knobs sit inside the top cover of the housing, and Korg says that by using them to adjust the balance between the three different distortion circuits you can create a wide range of sounds¹. The manual warns that they should be turned carefully: forcing them beyond their designed range may damage them¹.

Scott still called the HD-S the most cool and unique distortion device he had seen in decades⁷.

Power and connections

The HD-S runs on a 9V alkaline dry cell battery (6LF22/6LR61) or a DC 9V AC adapter through its DC.9V terminal, and neither is included in the kit⁴. Current draw is 45mA⁴, and battery life is approximately 10 hours with alkaline batteries⁴. Connection is simple: one monaural phone jack input and one monaural phone jack output⁴.

A Nu:Tekt kit designed by Fumio Mieda

The HD-S was developed by Fumio Mieda, the original designer of many well-known Korg pedals and synths, including the Uni-Vibe¹. Guitar World calls him the Japanese pedal designer behind the Shin-ei Uni-Vibe⁷. Mieda has said the HD-S came about because most distortion effects rehash the sounds of the past, and that Korg developed a new distortion type based on harmonic synthesis covering both classic sounds and new sonic territory².

As a Nu:Tekt product, the HD-S is a kit you build yourself. Korg presents the build as one of the appealing features of the series, a chance to assemble the product¹. No soldering is required, and all the tools needed come in the kit³. The box includes the owner's manual and a combined Tool&Pick⁴.

The HD-S is an effect pedal kit, measuring 122 x 96 x 55mm (W x D x H) and weighing 340g excluding batteries⁴. A related kit, the Korg Nu:Tekt HD-S Harmonic Distortion, appears under that fuller name in some coverage.

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