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Line 6 Helix Rack

Amp & Effects Modelling Processor
By Bob Thomas

Line 6 Helix Rack

Eighteen years after the launch of their ground-breaking POD, Line 6’s new flagship amp-modeller looks brimful of promise.

Can you believe it’s 18 years since Line 6 launched their revolutionary POD processor? The company have continued to develop modelling-based hardware and software and now offer an extensive product range. Their latest offering, the Helix, is their most ambitious to date, and is the culmination of a multi-year development programme. It’s a dual-processor DSP effects and amp modeller, available in floorboard or rackmount formats. It offers, at the time of writing, models of 41 guitar and seven bass amps, 30 cabs, 16 mics, 19 modulation effects, 15 distortion pedals, 14 delays, 12 reverbs, 10 wahs, five compressors, four EQs, four pitch-shifters, three volume/pans, three filters, a single synth and a solitary looper. All 185 models (‘blocks’) can, with certain limitations in the case of the amp, cab and looper, be deployed in multiple instances across four eight-block stereo signal paths, which may be combined, cascaded or run in parallel. Add in the extensive analogue and digital I/O, and the ability to load up to 128 user or third-party 1024/2048-point cabinet impulse responses (IRs), and you should see that the Helix isn’t short on functionality!

The Tour

The Helix Rack sent for review comes in the form of a black, 3U enclosure that’s built like a tank. Its front panel is dominated by a large colour LCD screen that displays graphics and text relating to the selected preset, and any active setup or edit functions. An optional Control floorboard connects to the Rack via a Cat5 cable, and shares the build quality of its parent. This has a small, monochromatic, text-only display that shows the active preset. It features editable LCD scribble strips above each of its 12 capacitive, touch-sensitive footswitches, the contents reflecting which of its three modes (edit, preset and stompbox) is operational.

The Rack’s function controls are arranged in three groups around the screen. All eight encoders incorporate a switch, which confirms a selection or accesses a lower-level menu. The Preset encoder in the left-hand control group scrolls through the currently loaded preset list (the selected preset loads instantly) or can be switched to display the eight possible preset lists, known as Setlists. The right-hand encoder, which incorporates a two-axis joystick, is required to move to the list of Setlists, at which point either it or the Preset encoder can be used to select and confirm a Setlist and any preset within. Each of the Setlists can contain up to 128 presets in 32 banks of four; the Control board, which can display two consecutive banks simultaneously, offers a more convenient method of Setlist navigation.

The two upper switches on the left bring up the Save and Settings menus respectively. Of the lower pair, the Home switch returns the display to the current preset and its Amplifier neighbour instantly recalls the amp and cab block in the edit section of the display.

Once a block is selected, its parameters are displayed above the six edit encoders beneath the display. If a block has more than six editable parameters, they’re displayed on additional pages, the number of which depends on the complexity of the model. For example, separate amp and cab blocks take two pages apiece, but a combo block fills three pages. When the Control is switched into edit mode, the top row of six scribble strips show the information in the same way; their footswitches select the parameter to be edited and the edit functions of the lower footswitches are shown in their displays.

The right-hand encoder/joystick/switch is used to place processing blocks in situ and select them for editing; to activate, split, route and navigate inside, around and between the Helix’s four signal paths; and to select the paths’ inputs and outputs. Of the two upper switches, Bypass disables the selected block, and Action is used to ‘pick up’ a block and ‘put it down’ in a new position. The lower two are used to move between the display’s block parameter-edit pages.

On the far right lies a large volume knob, that can be set to control the analogue and digital output levels either globally or for individual outputs). It’s joined by a headphone socket and level control and the red-illuminated Tap Tempo/Tuner button.

The analogue and digital I/O are numerous, and allow for plenty of routing options.The analogue and digital I/O are numerous, and allow for plenty of routing options.

Inputs & Ouputs

The Rack’s rear panel reflects the flexibility of its signal-processing paths with an array of input and output sockets, both analogue and digital. The guitar input jack, on the front, offers a range of impedances and a switchable pad, and on the rear is a 10kΩ aux in, intended for active guitars and basses. Next to that sits a balanced XLR mic input with software-switchable 48V phantom power. The analogue outputs, which are individually switchable between instrument and line level, comprise four send and four return jacks (accessible individually or paired in loops), and a pair of left(mono)/right outputs on both balanced XLR and unbalanced quarter-inch TS jacks. A guitar thru jack carries a parallel, buffered signal from the front-panel input jack.

The Rack can act as an eight-in/eight-out 24-bit/96kHz audio interface via its USB socket, which can also carry MIDI information and act as a send and return for re-amping purposes. For digital I/O, you can select either S/PDIF (RCA phono) or AES3 (XLR), and a BNC word-clock synchronisation input is also fitted. A Cat5 connector allows for two-way communication between the Helix and a Line 6 Variax guitar, and a second Cat5 connector powers and communicates with the Control. This is followed by MIDI in, out and thru sockets, and a pair of quarter-inch jacks, the upper of which acts as a conventional single- or dual-amplifier reverb on-off or channel-change switch. The lower jack is designed to drive an external expression-pedal input or supply a Control Voltage to any synth that can accept one. Finally, there are jacks for the optional footswitch and three expression pedals.

The Control has the same four expression-pedal and footswitch jacks, but its USB connector is “reserved for future use”. Its DC input is similarly reserved but, should your Control be on the end of an extremely long Cat5 cable and short of power, you can plug in a Line 6 DC-3G power supply (not supplied).

The optional Control floorboard connects to the Rack unit via an Ethernet cable, from which it also draws its power.The optional Control floorboard connects to the Rack unit via an Ethernet cable, from which it also draws its power.

The floor-mounted version of the Helix, which wasn’t sent for review, combines the functionality of the Rack and Control. It provides almost exactly the same features and facilities, but it’s not fitted with Control, word-clock or guitar thru connectors and, since it has an integral expression pedal, connects to only two external expression pedals.

Path Building

DSP load permitting, you could potentially have, in each of the 128 presets within the eight playlists, four separate paths, each with a different stereo or mono I/O and each containing eight blocks. Line 6’s user interface developers deserve a lot of credit, because setting that lot up is a relatively simple, speedy front-panel task; the only hard work lies in planning the signal flow you wish to achieve!

By way of example, consider the screenshot overleaf, which shows a preset made up of three pathways. The top path begins with the front-panel guitar input, which is followed by a volume pedal (usually assigned to EXP1), and then a wah, with reduced brightness to indicate that it’s bypassed. A distortion block comes next, then a combo amp, after which the signal path splits to feed the parallel second pathway that contains a delay. The highlighted border around the delay icon indicates that this block is selected for editing; you’ll see its name and the first of its four parameter pages at the bottom.

On the original path, the split point is followed by a modulation block, after which the two paths recombine, enter a looper (bypassed) and are then routed to the output. The arrow output icon indicates that this signal path feeds the stereo jack, XLR, digital and USB 1/2 outputs.

Note that, since the combo amp is mono, the signal path to the inputs of the modulation and delay blocks defaults to mono. You can’t tell from the screen graphics whether or not the modulation, delay and looper blocks are in stereo, though, even if they are. A mono looper instance would switch the other two blocks to mono, which makes sense and saves DSP.

The separate third pathway is fed by the mic input, runs through the Studio Tube Preamp model (the only mic pre currently available), into a dynamics block, then to an EQ and then a filter, before the path is routed to one of the external send/return loops. The main signal then passes to a modulation block and a reverb, the output of which feeds one of the remaining free USB pairs, so the reverb and modulation blocks are probably running in stereo.

Building your own signal path is simply a matter of using the joystick button to navigate to an empty slot and enter the processing block ‘type’ selection menu, deciding on whether or not the block is to be stereo or mono, and selecting the model you fancy. You then carry on in the same vein, adding, removing and editing blocks and pathways until you achieve the sound you want. (There’s a very detailed description of the process in the manual.)

The screen discussed in the main text, showing blocks in different pathways.The screen discussed in the main text, showing blocks in different pathways.

With the exception of original Line 6 models, the individual processing blocks are modelled on existing, often iconic products. Thankfully, the menu names are translated in the manual so I can tell you, for example, that a Soup Pro is the Helix model of a Supro S6616.

In analysing the modelled products, their circuit stages have been measured and matched back to the originals to ensure the models act and interact like the real thing, and there are plenty of tweakable parameters. On a combo guitar amp, for example, there are drive, bass, mid, treble, presence and channel and master volumes, as you’d expect, but also power-supply sag, hum and ripple, output-tube bias (Class AB to Class A) and Bias X, which determines how the voicing and compression of the output tubes change when pushed hard. You can also change the mic being used, its distance from the speaker (proximity effect), low-cut and high-cut filters and early reflections settings. All models enjoy a similar level of customisation; in some cases there are over 18 editable parameters.

The Control unit allows you to edit a Rack preset and the parameters of its individual blocks with your feet, via its capacitive touch-sensitive footswitches. The touch-sensitivity is useful when setting up a preset but, unless you play in bare feet, it’s useless on stage; the footswitches’ physical switching functions are used to access edit mode, select parameters and (along with an expression pedal if attached) to edit values. This sounds more complicated than it is, and once you’ve got the idea you’ll find yourself tap-dancing away, changing values on the fly. Again, the manual has all the details, including how to change the colour of the switches’ illuminated rings.

The final chapter in this necessarily limited run-down of the Helix’s features is its extensive ability to control external devices. MIDI controllers and commands can be assigned to footswitches (except Mode and Tap) and expression pedals. In addition, the Helix can send up to six separate MIDI commands instantly when a pre-programmed preset is recalled.

In Use

The Helix is a fine example of the current performance level that hardware and software engineering can achieve. I’m still scratching the surface of the Helix’s potential, but I haven’t yet found a block or a preset that’s failed to impress. The effects are excellent, the models for the amps, speakers and cabs I own or know well sound and feel pretty accurate, and the overall performance is of a very high order.

Without too much work on the US Deluxe Vib model, I was able to get as close as I’d ever need in a studio to the sound of my 1968 Fender Deluxe Reverb, recorded with a Sennheiser MD421 sitting an inch away from the grille. In a live situation, I’d happily use a Helix Rack and Control to feed that virtual Deluxe Reverb to the PA from the XLR outputs, while running a post-effects, pre-amp send to my actual Deluxe Reverb, to take advantage of Helix’s effects processing and give me physical interaction with a real amp.

In terms of playing dynamics, the Helix’s amp/speaker models react very much like the real thing in their response to changes in volume control levels, and pick and finger attacks. I found I needed to edit in detail all the models I explored, to get them to respond and sound the way that I wanted them to — but I have to do that in the real world, and editing the Helix is much easier than changing components in a tube amp!

Playing through the Helix isn’t the same as playing through a real amp in a real room, if only because the Helix itself cannot reproduce the guitar/player interaction that you or I experience in any given room. It would be interesting to make a 2048-point IR of my Deluxe Reverb in my studio to see if that made things feel a little more real... but since I can feed the Helix-modelled version to my recorder whilst playing through the real thing, I’m not sure I need to!


Compared with Line 6’s previous flagship product in this area (the Pod HD Pro X), the Helix Rack is a significant upgrade, in terms of performance and price. This has led to it being compared with the Kemper Profiling Amplifier (KPA), Fractal Audio’s Axe FX II XL+, and even Atomic Amplifiers’ lower-cost Amplifire. Although all these units generally aim to achieve the same thing, the routes they take to get there define their differences and similarities. The KPA is an outlier in that, rather than analysing and replicating the internal workings of specific amps, Kemper’s approach is, broadly, to use its algorithms to create and store a profile of the sound of particular amps, at particular settings, through particular speakers, close-miked with particular mics. This enables the KPA to reproduce the sound of a profiled amp accurately. The result is less flexible than with the modelling approach, but that’s compensated for by the hundreds of amp profiles available, many of which are of rare or highly desirable amps — a KPA can store up to 650 profiles in Performance mode and 1000 in Browse mode, though multiple profiles of a single amp may be needed to cover different sounds.

The Axe FX II XL+ takes a similar approach to both the Helix Rack and the Amplifire, but the granular detail Fractal Audio have put in place to enable the deep editing of their amp models in the most subtle of ways is mind-blowing. Tweak-head that I am, I could spend many happy hours deep inside that processor’s menus. Performance-wise, the algorithms produce extremely impressive results and the factory load of 188 amplifiers and 159 cabinets, again incorporating many sought-after models, is more than enough. Mind you, all this comes at a price; the Axe FX II XL+ is by far the most expensive of the four competitors.

Finally there’s the Amplifire. The approach is very similar to that of the Helix, and the Amplifire’s editing facilities and sonic performance are broadly comparable, but its price (it costs around a third the price of a Helix Rack and Control) reflects the differences between the Amplifire’s cosmetic quality, limited (though adequate) user interface, internal routing flexibility, inputs, outputs and control capability, when compared to the Line 6 devices.

To me, despite the fact that each of the four units has its own particular advantages and disadvantages, the Line 6 Helix Rack offers the most complete overall package. It’s probably the most practical, too, if only for its control capabilities and its I/O complement. When push comes to shove, you’ll have to audition a Helix for yourself — but it certainly works for me!

Nice Rack!

Line 6’s Helix Rack indicates to me that we’ve reached the point at which high-performance modelled effects and amplifiers are a more-than viable alternative to the real thing. Even if the Helix models didn’t produce such close facsimiles of the hardware they’re based on, they’d be more than capable of producing great-sounding, responsive amps with their own qualities and attractions. I remain very impressed by the performance of both the Helix Rack and the Control floorboard, and the ease of operation of the user interface.

For me, the Line 6 Helix Rack is pretty much ideal as it stands, and the way in which each succeeding software version has fixed bugs and introduced enhancements inspires confidence for the future.


  • Highly responsive, realistic playing feel.
  • Sounds great, and is easily and supremely tweakable via a superb user interface.
  • Lots of cabs, mics and effects to play with.
  • Very flexible signal path routing.
  • Accepts third-party cabinet impulse IRs.
  • Eight in/out 24-bit/96kHz audio interface.
  • Extensive MIDI control capability.
  • I could go on and on with this list!


  • None.


The Helix and Helix Rack effects, amp and cab modellers are the culmination of a multi-year software and hardware development programme, and it shows: they’re capable of a very high level of performance. Most impressive!


Helix Rack £1156; Helix Control floorboard £330. Prices include VAT.

Yamaha UK +44 (0)844 811 1116

Helix (stompbox format) $1499.99; Helix Rack $1399.99; Helix Control floorboard $399.99.

Published June 2016