KORG TR-S

The Korg TR-S, sold as the Nu:Tekt TR-S Power Tube Reactor, is a build-it-yourself effects pedal kit that uses Korg's Nutube, a miniature vacuum tube, to recreate the sag and compression feel of a tube power amp. Korg describes it as an effects unit that "features a Nutube, to deliver the responsiveness, the feel, of a vacuum tube guitar amp"¹. Where most pedals in the overdrive family push gain at the front of an amp, the TR-S is aimed at the behavior of the power stage: the way a valve amp's sound compresses momentarily when you dig in.

The TR-S is an effects unit that features a Nutube, Korg's compact vacuum tube component, to deliver the responsiveness and feel of a vacuum tube guitar amp¹. Korg says the Nutube recreates sag, the compression feeling that is a behavior of vacuum tube power amps, letting players achieve compression effects similar to a tube powered amp¹.

What it does: tube power-amp sag from a Nutube

Sag is the compression feeling that comes from a vacuum tube power amp working hard: the sound ducks briefly in response to a loud transient and then recovers. The TR-S is built to put that behavior on a pedalboard. Korg says the unit uses the Nutube "to recreate sag (the compression feeling), a behavior of vacuum tube power amps"¹, and Guitar World's review describes how the circuit design "can mimic the sag of a vacuum valve power amp where the sound compresses momentarily in response to transients"³.

The practical use case, as Curwen put it in Guitar World, is for players without a cranked valve amp³:

Guitar.com's launch coverage made the same point from the player's side, reporting that the pedal "will give guitarists the 'feel of a tube amp even when recording or playing through a transistor amp'"⁴. Gearnews described the result as "an amp-like sag and power amp-like compression"⁵.

How the Nutube drives the compression

The core of the circuit is the Nutube 6P1, Korg's miniature dual-triode vacuum tube². Korg states that the TR-S "features a patent-pending circuit design that drives the compression for the vacuum tube itself, only possible with the Nutube"¹. In other words, the tube is not decoration or a clipping stage bolted onto a conventional circuit: the compression effect comes from the tube's own behavior. RockBoard's listing echoes the maker's claim, noting the patent-pending technology "makes use of the Nutube" for "compression effects, similar to a tube powered amp"⁶.

The circuit type is analog⁶, and the pedal is sold as an "EFFECT PEDAL KIT" rather than a finished unit².

Controls

Four external knobs shape the effect, with two trim pots inside for fine tuning⁷³.

The Mix knob is the key to using the TR-S subtly: at the Direct end the pedal passes your clean signal, and toward Tube the sag and drive character takes over⁷.

Building it: no soldering required

The TR-S is a DIY kit, but the assembly is deliberately light. Korg positions self-assembly as part of the appeal of the Nu:Tekt series¹, and no soldering is required: all the tools needed come in the kit, along with a circuit diagram⁵⁴. Guitar World's review found the build amounts to very little work:

The enclosure is a gray-colored unit⁵. In the box you get the pedal's parts, an owner's manual and a Tool&Pick².

Power

The TR-S runs on a 9V alkaline battery or a 9V DC adapter, neither supplied³². Current draw is 85mA³², which is modest for a tube-based pedal but worth knowing if you run a tight pedalboard power supply. Battery life is approximately 5 hours with alkaline cells², so the adapter is the practical choice for regular use.

TR-S versus the Nu:Tekt HD-S

The TR-S and the HD-S Harmonic Distortion were announced together in January 2023 as the two newest members of Korg's Nu:Tekt kit range⁵⁴⁷. Both are solderless Nutube kits in the same format, but they target different parts of the signal:

• TR-S Power Tube Reactor: power amp-style sag and compression, with Volume, Power Sag, Tube Gain and Mix controls³⁴
• HD-S Harmonic Distortion: a distortion pedal, drawing 45mA against the TR-S's 85mA³

The TR-S is the one to look at if what you want is the feel of a tube power stage rather than more gain³⁴¹.

Where it sits in the Nu:Tekt line

The TR-S is part of Korg's Nu:Tekt line of effect pedal kits, and it carries the Nutube into a compression effect: Korg describes it as an effects unit that features a Nutube to deliver the responsiveness, the feel, of a vacuum tube guitar amp¹. Where a typical compressor levels your signal with circuitry alone, the TR-S uses the Nutube to recreate sag, the compression feeling that is a behavior of vacuum tube power amps¹.

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