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Gamechanger Audio Plasma Rack

Gamechanger Audio Plasma Rack

With more control and functionality than the Plasma pedal that preceded it, is this box the new king of controllable carnage?

Gamechanger Audio's Plasma pedal, reviewed in SOS February 2019 ( is a unique, love-or-hate-it fuzz-like distortion, which adds lots of harmonics courtesy of a very high-voltage xenon discharge tube. It's a peculiarly aggressive, crunchy, fizzy, spluttery distortion that I love: an addictively disruptive effect, with potential applications in various genres. However, pedals aren't the most convenient format for me, so when I learned of the new 1U rackmount Plasma Rack, which includes a host of studio-friendly features, I had to check it out.

The Plasma Rack's I/O options mean it should appeal to musicians, sound designers and mix engineers. Unbalanced TS instrument and balanced combo XLR line inputs (the latter with a switchable 20dB pad) are joined by balanced (XLR) and unbalanced (TS jack) line outs. Between these, on the rear, are three TS-jack pairs for unbalanced insert loops, each at a different point in the signal path. A button sets these (globally) to operate at instrument or line level, so studio outboard or guitar pedals can be used. There are also MIDI In, Out and Thru ports, and a TRS jack expression pedal input. Power arrives through an IEC inlet with on-off switch, and there's also a standby mode, switched from the front panel.

A wealth of connectivity caters for instruments and line sources, stompbox and studio insert effects, as well as MIDI control/sync.A wealth of connectivity caters for instruments and line sources, stompbox and studio insert effects, as well as MIDI control/sync.

Starting Out

The front panel can seem bewildering at first, not because of poor design (it's very well thought out), but because the controls interact with each other. So dive-right-in, ignore-the-manual types willl need to break their habit: read the user guide, check out the signal-flow block diagram, and you'll soon develop the mental map needed to dial in some deliciously dirty distortion.

The discharge tube, running at a whipping 5500 Volts, isn't the only effect. There's also a cool tremolo/ring mod, some op-amp distortion, a three-band EQ and an interesting gate. But these are best left until you've acquainted yourself with the main event. To do that, I suggest starting with the Blend knob fully clockwise (100 percent wet). You'll hardly ever want it there for your final sound, but it's the quickest way to figure things out.

With a healthy signal, you'll see electrical discharges in the tube and hear the result. With too low a signal you won't. A good starting point, with a signal flowing through, is to set the Voltage control fully anti-clockwise (minimum) and tweak the input Gain so you always see a weak discharge. This gives you plenty of useful range in the Voltage control, which you can then use to dial in the core of your distortion sound. At lower Voltage settings, the tube doesn't just add harmonics but also acts as a gate, because the tube discharges only when it receives sufficiently strong signals. On its own, that can sound terrible! But mixed with some dry signal, it can sound great on the right material. A button next to the Blend knob engages a 'clean gate', which operates on the dry signal but tracks the gating behaviour of the tube, which can be another interesting effect.

The higher the Voltage setting, the less dynamic/gate-like the effect, and the more it tends towards bright, fizzy fuzz. So you'll find that getting a result you like requires you to juggle the Gain, Voltage and Blend controls to taste. Depending on the source, you might also want to try the Sustain button — this engages a simple compressor to increase the sustain of the sound fed to the tube — or the Over-Saturate button, which feeds more power to the tube, stimulating the production of yet more overtones. As I say, this is all very interactive, and you'll want to tweak the output Volume, which affects the global level after the Blend, often.

Essential Extras?

'Really bright' isn't always what you want, of course, and to address that there's a three-band EQ, with a single boost/cut knob per band. The CL.EQ button that sits between these knobs and the master Volume switches the EQ from operating only on the wet signal to processing the post-Blend wet-dry mix. It's a versatile, broad-brush tool, and just what's needed to sculpt the sound to suit a mix. If you need to do more, you can also add in other filtering externally, using one of the effects loops or after the Plasma Rack in your signal chain.

On the far left is the Tremolo section, which applies to the post-Blend sound. Quite what prompted Gamechanger to add this I don't know — it wouldn't have occurred to me when designing a distortion box — but I'm glad they did! A Tremolo on-off switch is joined by two knobs, Rate and Depth. Rate's purpose is self-explanatory, but Depth is less obvious. Turned clockwise from 12 o'clock, it sets the depth of a standard tremolo, and can take you well into ring-mod territory, adding siren-like sweeps to the sound, if you wish. It's one of the parameters I could see myself wanting to control in real time. Turning it anti-clockwise also sets the depth but out of phase, so that the Tremolo alternates between the dry and wet signals. This is best auditioned with Blend set to 50:50 in the first instance. Another button, Dynamic, makes the depth respond to the input signal level. It interacts with the Depth control, which can be set so tremolo only occurs on louder or lower-level signals. Very cool!

If Dr Frankenstein invented a distortion device, it would probably look something like this! The main distortion comes courtesy of a  high-voltage (5500 Volts), xenon-filled discharge tube, in which you can see your audio signal being processed.If Dr Frankenstein invented a distortion device, it would probably look something like this! The main distortion comes courtesy of a high-voltage (5500 Volts), xenon-filled discharge tube, in which you can see your audio signal being processed.

I've talked about dry and wet signal paths, but the 'dry' one can be treated separately to op-amp distortion, courtesy of a button combination (press and hold the Sustain and Clean Gate buttons until the Over-Saturate button blinks). With Blend set 100 percent dry and the CL.EQ engaged, it's conventional but nice and useful amp-like distortion. There can be some phase cancellation as you mix this with the wet signal, but it's easy to find a usable sound. Other unmarked button combinations give access to functions such as setting the state of different controls at power-on, and a factory reset. It's all very thoughtful.

The front-panel settings are controllable, and up to eight presets recallable, over MIDI, and the manual lists the MIDI CC and Program Change messages used. Another button sets all the front-panel controls transmit MIDI data via the Out port — data which can be recorded in your DAW, or perhaps used to sync a second Plasma Rack for stereo operation.

The Plasma Rack is capable of delivering an insanely bright, edgy distortion. A viciously fizzy, buzzy, popping, spluttering breakup that sounds like nothing else I've heard.

Popping The Fizz

But what of the sound? The distortion cannot offer 'warmth' or 'saturation'. Rather, it puts me in mind of the Hitchhiker's Guide's Pan Galactic Gargle Blaster: "like having your brains smashed out by a slice of lemon wrapped around a large gold brick". It's an insanely bright, edgy sound. A viciously fizzy, buzzy, popping, spluttering break-up like nothing else I've heard. But one that's also very usable, because Gamechanger have put a lot of effort into making it controllable. The EQ, in particular, is helpful in this respect, allowing you to sculpt the generous overtones into something that will work in real projects. The gate and tremolo extend your options too, and will appeal to synth-heads as much as guitarists.

The Plasma Rack excels on electric guitar. You can easily achieve the bright but ballsy sort of fuzz sound you might expect of Jack White, and you can use the tremolo for some very interesting effects with ringing chords. When mixing a track with two distorted guitar parts, I found that opposition panning the parts and treating one quickly to some really aggressive, but EQ'd Plasma distortion injected width and attitude, while keeping the overall sound pleasingly thick and full. I tried to replicate the sound with plug-ins, and gave up after several minutes' tweaking! The op-amp distortion is a useful flavour, too. Feed that into a power-stage/cab modeller and you have a nice, playable amp.

It loves electric bass (hardly a surprise; bass and fuzz are old acquaintances). On electronic drums you can create carnage, and on other percussive and staccato sounds you get a squelchy break-up, somewhat reminiscent of bit-crushing. Synth and guitar arpeggios can be transformed utterly but in a musically appealing way, and for vocal distortion it's a full-on, wild-card effect, but great in the right context.

In short, the Plasma Rack sounds unique and looks the part. We're not talking stompbox prices, but there's a whole load more going on here. And while a sound mangler like this won't be to everyone's taste, and won't be used on every song, it has definitely put a smile on my face!


There are countless distortions out there, but nothing on the market that sounds or looks anything like this!


  • Wonderfully vicious, aggressive distortion that's also controllable.
  • Line/instrument inputs and effects loops make it easy to use in different applicatons.
  • Versatile: the tremolo, gate, EQ and op‑amp distortion extend its usefulness.


  • Reading the manual is not optional!


The high-voltage electrical-discharge distortion is the unqiue-sounding headline effect here, but there are several more strings to the Plasma Rack's bow that extend its appeal considerably.


€1238 including VAT.