Korg OD-S NuTube Overdrive

September 15, 2020Sebastian

The Korg OD-S Nutube Overdrive pedal is a fascinating pedal which, unlike most overdrives, ships as a kit. As if this wasn’t neat enough, it showcases Korg’s NuTube technology and is highly moddable.

Vacuum tubes are heralded as the ultimate guitar tone solution for how beautiful they sound, but they’re full of disadvantages. They’re large, they’re unreliable, and they’re very energy intensive. Furthermore, according to Korg’s website, the equipment used to produce their tubes is aging badly and can’t consistently produce reliable tubes.

This is where the NuTube comes in. It’s the result of a collaboration between the legendary music technologists at Korg and Noritake Itron, a Japanese manufacturer of fluorescent displays. NuTubes are produced in a similar fashion as VFDs, and behave similarly to a typical preamp tube, but require much less power, voltage and space. It’s therefore an ideal solution for getting that authentic vacuum tube mojo in a stompbox.

The OD-S was one of my favorite pedals at NAMM 2020 (see my writeup here), so I’m thrilled that Korg USA sent me one to review and keep. Thanks, Korg!

Assembly: almost too easy

If you’ve ever assembled a piece of Ikea furniture, you can assemble the OD-S. In fact, if you have a socket wrench left over from an Ikea build, you can use it for fastening the jacks to the enclosure.

The process of building the OD-S is incredibly simple. It amounts to little more than attaching the bypass switch and NuTube daughterboard to the PCB, putting it into the enclosure, and attaching the knobs and hardware. It requires no electronics knowledge at all. The build took me about twenty minutes and I did it at my kitchen table with my kid. 

Personally, I didn’t find the OD-S’s “build it yourself” angle particularly compelling. I’ve built a few DIY pedals, and for me, the challenge is a big part of fun. I had to source components, populate a PCB, solder dozens of connections, and solve lots of problems. It’s hard, but the results are incredibly rewarding. By contrast, the OD-S touts “no soldering required” on the box. Ease of assembly is part of the deal.

That said, an easy DIY kit is such an attractive proposition for many people. I had never soldered until about three years ago, and the prospect of performing even a simple tweak to my guitar wiring was extremely stressful, let alone a pedal build. Furthermore, even if you’re a die-hard pedal DIYer, there are still opportunities to mod and tweak your OD-S. Unlike a lot of modern pedals, it comes with a schematic and every component is through-hole mounted. This means advanced DIYers have a wealth of options to hotrod their OD-Ses. Furthermore, the op-amp is in a socket, so you can replace it with any compatible dual op-amp. Mine came with a TL072, but I switched in a JRC4558 for a slightly different sound.

Controls

The Korg OD-S has the typical overdrive controls (Level, Tone, Gain), plus some additional ones (a Tube Gain knob on top of the pedal plus a “Wide” switch and bias trimmer inside the housing). The Gain knob controls the level of distortion, and the Tube Gain control (according to the manual) changes the harmonic characteristics of the NuTube by tweaking its anode resistance value.

The Wide switch, simply put, is a bass cut. With Wide on, the pedal sounds fat and can serve as your base drive sound; with Wide off, the bass is cut (think Tube Screamer), thereby making it ideal for pushing another drive section. The bias pot lets you set the NuTube’s bias to whatever sounds best to you. Typically, you’ll want to set it to whatever makes the pedal loudest.

Sound

The Korg OD-S Nutube Overdrive has a lot of the sonic qualities I’d expect from a small, quality tube amp – think the Blues Junior or AC15. When I think about the sound I like in a small amp like that, the following things come to mind:

  • The ability to precisely dial in the level of dirt I want, depending on my mood.
  • Responsiveness and dynamics. When I can effectively control the level of distortion by playing harder or softer, I feel extremely “connected” to my sound.
  • A sonically balanced sound – not too much bass or treble.
  • A little extra “bite” in the mid frequencies.

The Korg OD-S NuTube Overdrive has all of these things. I love how every sound in it, whether it’s a slight warmth around the edges, a cranked Plexi-style roar, or anything in between, sounds amazing. The fact that the pedal provides “Gain” and “Tube Gain” knobs means you have an almost surgical level of control over your distortion. Wherever the OD-S’s dials are set, my guitar sounds like my guitar.

Furthermore, the OD-S stacks incredibly well with other drive pedals. I’ve had particular success with my Mosky Silver Horse, a Klon-style overdrive that pushes the OD-S from crunchy into growly. I’m also enjoying my Boss DS-1, on a low drive and medium output, into the OD-S, although in that scenario I like to mellow the overall sound by reducing the DS-1’s Tone knob..

I made a short demo/review video to accompany this article.

Cons

My list of complaints about the Korg OD-S NuTube Overdrive is extremely short.

  • The NuTube is slightly microphonic; when I stomp the OD-S to turn it on, the vibrations cause the NuTube to make a quiet high-pitched noise for a few seconds. It’s a minor issue, but this does make me reconsider using it in a live setting.
  • The “Gain” knob has to be at at least noon before you’ll even hear anything. The OD-S has great range, but it would be even better if it was usable at more gain settings.
  • For as much control as you have over the drive level, the single Tone knob gives you comparatively little control over the EQ. I’d love if the OD-S had separate high/low tone knobs.
  • The OD-S doesn’t have tons of input headroom, which is a little disappointing considering that I’m using it preamp-style. In practice, this means if you have super hot pickups or you run too hot of a boost into it, your sound gets kind of compressed.

This small list notwithstanding, the OD-S sounds wonderful in a broad range of applications. I am convinced that if you pick one up, you’ll find a lot of reasons to be happy with it.

The Shape of Drives to Come

For me, the most exciting thing about the Korg OD-S NuTube Overdrive is what it means for the future. It proves the NuTube can enable incredible tube-style pedals; the OD-S is just one expression of that capability.

Korg owns legendary ampbuilders Vox, who have had NuTube-based amps in their lineup for a few years. Their initial NuTube efforts cover the familiar classic Vox sounds, and their upcoming Valvenergy line of pedals covers an even wider range of drive styles. They’re Japan-only at the moment, but I’m really keen to check them out when they come out in the US.

Conclusion

I am super happy with the Korg OD-S NuTube Overdrive. The fact that the NuTube enables a pedal to express all the best qualities of a tube amp in such a small package is an absolute gamechanger. It’s been my go-to low-to-mid-gain drive pedal since I got it, and I can’t express enough how grateful I am that Korg let me keep this review unit.

You can buy your own on Amazon or wherever else you buy pedals.

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