Positive Grid Reactor

Positive Grid’s newest guitar amp uses AI to sculpt your tone. We test its limits...

“I want AI to do my laundry and dishes so that I can do art and writing, not for AI to do my art and writing so that I can do my laundry and dishes.” So said author Joanna Maciejewska, and it’s a sentiment most musicians would agree with. But is the line between ‘laundry’ and ‘art’ so clear‑cut? Many musicians (myself included) are wary of generative AI that promises to create entire songs with minimal human intervention. But every month we see more and more AI tools designed to aid, rather than replace, creativity. Is it still a betrayal of humanity to ask AI to reduce hi‑hat bleed on your snare track, or colour‑code your backing vocals?

Similarly, and to inch slightly closer to the point, no guitarist wants AI to play their guitar for them. But what about your tone? Could you live with AI replacing your amp and pedalboard while you get on with the business of playing? Because that’s what Positive Grid’s new Reactor amp does. In addition to offering ordinary, human‑steered amp and effects modelling, the Reactor’s USP is that it can take a prompt — text, image or audio — and generate your tone from it. If you’re ready to delegate your tone to AI, read on...

The Reactor

The Reactor comes in two flavours — the 50W version supplied for review, and a 100W one — both of which are fitted with a 12‑inch speaker. They weigh around 11 and 14 kilos respectively, and look outwardly like ordinary modelling combos, with a familiar hardware control set. Deeper control (including the AI tone creation) is available from a dedicated app, but you can also use it as a fairly normal amp sans mobile device, which is where I’ll start. If you just want to find out what it’s like to WhatsApp your sentient guitar amp and ask it to make you sound like Steve Vai, skip ahead to the ‘Rise Of The Machines’ section.

Almost all the controls sit along the top panel, on the far left of which is the input jack. The first dial is a large Amp selector, with six options ranging from Clean to Extreme. To the right of it are two ‘AI’ (‘Amp Intelligence’, in Positive Grid‑speak) switches, which subtly adjust the amp model. The top one offers Push and Smooth modes, which primarily affect the frequency response; the lower switch is named Heat, and can increase or decrease the amount of saturation, independently of level. Next come five entirely self‑explanatory knobs (gain, bass, middle, treble, master), and then there’s an effects section. A rotary Level encoder is surrounded by buttons marked Drive, Comp, Gate, Mod, Delay and Revb, and each of these effects can be increased or decreased in level by pushing the relevant button and turning the knob, or bypassed with a long button press. Over on the right‑hand side there’s a volume knob and a power toggle switch, and finally, above the tone controls are two buttons and four LEDs that let you save and recall your own patches (whether made using the hardware controls or the app), or engage a rudimentary tuner.

The amp can largely be operated using the hardware controls, though for the AI tone generation you’ll need to use the mobile app.

There are two further controls round the back: a slide switch for selecting between three power ratings (1W, 25W or full power, ie. 50W or 100W depending on the model), and a Pair button for Bluetoothing your phone to the amp (both for control purposes and audio streaming). There’s a host of additional socketry on the rear too, allowing for MIDI control, connection to the optional Reactor Control footswitch, bypassing the modelling and going straight into the power amp, taking a line or headphone out, and hooking up your own pedals via an effects loop. Finally, a USB‑C port lets you use the Reactor as a 1‑in/2‑out audio interface.

Phone Home

The Reactor app runs on iOS and Android devices, and in common with Positive Grid’s Spark range, there’s no desktop control option. This I find slightly frustrating, because as slick as their mobile apps are, I much prefer using a proper computer for creative stuff; having to operate my phone tends to take me out of the zone somewhat. That said, it does work very well.

The Reactor features an external effects loop, which can be placed at any point in the modelled signal path.Functionality is split between three tabs, accessed at the bottom of the screen and named Tone, Creator Hub and ToneCloud. The Tone section is dominated by whichever of the 10 processing modules has focus. These modules are shown in a side‑scrolling list along the top of the UI, in the order the current patch places them in. Typical they’d be ordered something like Gate, Comp, Drive, Mod, Wah, EQ (seven‑band graphic), Amp, Delay, Reverb and Loop (that’s the external effects loop, not a looper). Happily, these can be rearranged in any order by tap‑holding a module’s icon and dragging it between any other two modules — and this includes the Loop module, so you can place your own wah in front of the Reactor’s amp model, or use your own chorus after the modelled overdrive. Modules can be brought in and out of play by swiping them up (off, greyed out) or down (on, coloured).

Tapping on a module opens its edit page, where you get access to parameters like Threshold and Decay (for Gate), Rate and Depth (for Mod), LFO shape and speed (Wah), and so on. Many of these modules offer a choice of processors, with GUIs inspired by real hardware. For example, Comp can be set to Sustain, Studio, Dyna or Opto; there are eight different Drive models (with names like Green Drive, Rat Dist and Muff Fuzz); the Mod menu includes two choruses, a flanger, a tremolo and a phaser; and there are four different flavours of Delay. The Amp module shows controls for Gain, Bass, Mid, Treble and Master, and these will reflect any changes to the same controls you make on the hardware. It’s all very intuitive; if you’ve ever used guitar rig modelling software before, you’ll be right at home.

At the bottom right of the app is the ToneCloud button, where you can access a huge library of complete rigs created by other Reactor users. The bottom middle button, though, is where the fun’s at, as this accesses the Reactor’s Creator Hub...

The optional Reactor Control footswitch.

Rise Of The Machines

Documentation was pretty thin on the ground when I first received the Reactor, although the AI‑powered guitar tone generation was well trailed, so the first thing I did was install the app and start generating.

The results were remarkably good — easily ‘professional cover band’ quality...

The Creator Hub lets you issue prompts to build your tone, and will usually offer a small selection of rigs based on your request.Like ChatGPT et al, you can prompt the Creator Hub using natural language. On prompting, the app will think for a minute or so, before sending a text reply (see screenshot) and presenting a handful of tone options, which you can immediately audition by tapping a Preview button. I tried asking it to reproduce various guitar tones that I know well — starting with the obvious and getting progressively more obscure — and in no time at all I was shredding in the style of Dimebag, Frusciante, Hendrix and more. Whatever ‘tone database’ it draws from is clearly very extensive indeed. The first option the app presented was almost always the closest match, but the others often provided a useful variant. And even when I tried to catch it out (an obscure Monster Magnet B‑side if you must know), it got the vibe right, if not the exact effects. Given a well‑known song, though, the results were remarkably good — easily ‘professional cover band’ quality — and arrived at much, much faster than if I’d tried to build the same sort of sound from scratch.

The Reactor can do more than just mimic famous guitar tones: it can also mimic specific pieces of equipment. And this is where I first encountered its limits. As I didn’t have access to a manual, I perhaps naively assumed that AI was governing the entire process, and that it was therefore capable of generating sounds outside of what you’d expect from a typical guitar rig. So when I asked it to “give me the sound of six Boss Metal Zones in series, all at maximum gain”, I was slightly disappointed to be told by the app that “Reactor only allows one Drive slot in the signal chain and doesn’t offer the Metal Zone specifically.” It did, however, give it a good go: all four options it presented me with were distorted and compressed in extremis, and while I’ve only ever been in a room with two Metal Zones, the results were not a million miles away from what I’d hoped for.

The Reactor app’s Tone page lets you view and edit any of the processing modules. The modules are listed along the top of the UI; tapping on one opens it for detailed tweaking.Having loaded the first preset it offered, I returned to the Tone section of the app, and saw that the Creator Hub AI had actually built my ‘six Metal Zones’ patch by sending parameters to the various modules (in this case it had decided that the Rat Dist drive pedal would deliver the best results, placed before a ‘tight aggressive modern’ amp model with the gain wound up). So if you’re wondering how it works, it seems that when you send a prompt, Positive Grid’s servers analyse it, determine which of the Reactor’s processing modules would achieve the closest results, decide on the settings for them, and then send all those parameters back to your phone and thence to the amp itself. It’s not quite the boundless AI tone generation I first thought it was, but it is bloody clever.

I wasn’t quite done conjuring tasteless guitar tones though, and I also wanted to test its gear repertoire a bit more, so as one final experiment I asked it to recreate the ‘Insane’ setting from an original Line 6 Pod. Reader, it excelled itself; from the fizzy distortion and ear‑splitting frequency profile to the overzealous noise gate, I was back in 1998 again and about to get kicked out of the guitar shop.

Sounds & Pictures

As an alternative to text prompts, you can also ask the app to interpret either audio or images, and build a tone from them.Sound and image prompting was more of a mixed bag. The Reactor app’s ability to divine the content of an image is impressive; it correctly identified (and built some very usable ‘glassy’ tones from) a photo of a Roland Jazz Chorus I found on the Internet, and when I uploaded a photo of Zakk Wylde I found on Wikipedia its response was uncanny: “You requested a Zakk Wylde ‘Berserker’ tone inspired by his Bullseye Les Paul and wall of Marshall stacks.” So far, so literal... but in the spirit of experimentation, I also uploaded a couple of selfies, one of which the app decided represented ‘Midwest emo’, the other resulting in a “melancholic, lo‑fi bedroom pop guitar preset inspired by a somber, weary portrait”. Thanks, I guess.

Feeding the AI images of Balrogs was also quite entertaining, and invariably yielded atmospheric and doomy metal tones, usually drenched in reverb and delay. I chalked those experiments up as a win.

As far as using audio goes, you can do this in two ways: either upload an audio file, or (more usefully) you can share your screen (and system audio) with the Reactor app. This makes it easy to play it a YouTube or Spotify snippet. Unfortunately, the results here were often wide of the mark, and the AI seemed to struggle to identify/mimic a guitar tone from a complete mix. Isolated guitar sounds worked better, but were still pretty hit and miss.

Intelligent Design?

So there is an element of novelty to the whole AI tone‑creation thing. But provided you stick to text prompts, and stay within the realm of ‘normal’ guitar tones, it works remarkably well, and builds very usable rigs very quickly. Moreover, those rigs are editable, so if the Reactor AI gets you part of but not all the way there, you can intervene — either by going into and editing the individual modules, or by refining your prompt. For example, it did a pretty good job at generating the ‘Under The Bridge’ intro tone, but added some chorus that wasn’t entirely faithful to the original, and the sound was lacking a little grit on the lower notes. A simple “No chorus please, and a bit more saturation and weight in the lower mids” remedied it entirely.

And, as well as being entirely intuitive to use, it sounds great too. Positive Grid’s amp modelling technology is well established and of excellent quality, and that’s very much on display here. The amp models sound organic and responsive, whether you’re asking for solid‑state cleanliness, edge‑of‑breakup blues or high‑gain mayhem.

That familiar combo format also guarantees the Reactor will work as expected in both live and recording situations: it’ll fill a rehearsal room like a combo should, you can point an SM57 at it and get entirely predictable results, and you can take a line‑level feed from it where that’s more convenient. I do understand why some modelling setups go the FRFR route, but using an extended‑bandwidth speaker (with a tweeter) to play a digitally band‑limited (via speaker emulation) signal strikes me as using a sledgehammer to crack a nut. The Reactor’s speaker sounds like a guitar speaker, and it sounds good. I don’t require more of a cabinet; your mileage may vary.

With the Reactor, you can simply use whatever descriptors you feel most comfortable with, and it’ll usually get you exactly what you want.

Laundry Service

To take things back to the beginning: does the Reactor only deal with laundry, or does it encroach on the art as well? Personally, I think it stays in its lane. While there is definitely something creative about assembling a hardware pedalboard, or selecting the right amp for a recording project, in the digital world those things often feel more like chores. Choosing effects emulations from a drop‑down menu certainly doesn’t get my creative juices flowing, and trying to figure out what ‘MkIV Scooped’ or ‘AC Chime’ mean in a list of virtual amps can be infuriating. With the Reactor, you can simply use whatever descriptors you feel most comfortable with — whether that’s ‘American ’90s metal tone’ or ‘Randall Warhead with an MXR Distortion+ in front’ — and it’ll usually get you exactly what you want.

Rather than trying to supplant you as the artist, in the case of the Reactor, the AI simply removes obstacles between the conception and the creation of your tone. Which is exactly as it should be.

Information

50W version £299, 100W version £379, Reactor Control pedal £129. Prices include VAT.

www.positivegrid.com

50W version $349, 100W version $449, Reactor Control pedal $149.

www.positivegrid.com

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