Boss RT-2 Rotary Ensemble

Nineteen years after their first stereo rotary speaker effect, Boss deliver an even more convincing emulation in a compact pedal format.

While approximating the effect of a rotary speaker might be simple enough, creating a genuinely convincing emulation is something of Holy Grail quest, because it turns out that modelling the real thing is both incredibly complicated and DSP intensive. The classic Leslie speaker features a woofer that’s aimed into a rotating drum, incorporating an angled reflector, and this acts much like the rotating mirror in a lighthouse. Meanwhile, the tweeter feeds into a revolving horn assembly, comprising one real horn and a dummy one that acts as a counterweight. These two elements rotate separately, at different speeds and in opposing directions. All this is driven by motors and pulleys, making the vintage hardware extremely heavy as well as bulky. (Carrying a pedal emulation up a fire escape to gig is a far more appealing prospect than lugging around the real thing!)

There are many different effects caused by this mechanical rotation and the reflections within the cabinet: stereo movement, amplitude modulation, a little doppler frequency modulation and tonality modulation all affect the sound. As if that weren’t challenge enough for the pedal design team, they must also replicate the effect caused by the inertia of the mechanical parts: when switching from slow to fast speeds and vice versa, the woofer and tweeter sections change speed at different rates, and this speed ramping effect is one of the key characteristics of the Leslie sound. And yet another important element to recreate is the coloration of the amplifier that drives the speakers, especially when it’s deliberately being driven into distortion.

Despite this complexity, a number of manufacturers have risen to the challenge, with some success. You can now buy capable rotary‑speaker effect pedals from various companies, including Neo Instruments, Strymon, Fender, Electro‑Harmonix and, of course, Boss...

Changing speed when the ramp speed is set to slow recreates the dynamic magic of the real thing, and can really add to a performance.

RT‑2 Overview

The Boss RT‑2 Rotary Ensemble offers a choice of three voicings, and PSU or battery operation. It’s not Boss’ first rotary speaker pedal — I reviewed the larger RT‑20 way back in SOS August 2006 — but the RT‑2 exploits today’s greater DSP capability to more closely model authentic vintage Leslie speakers. And though the RT‑2 is perfectly valid for use with keyboards and other sources, it also includes tweaked variations that might appeal more to guitar players. Furthermore, Boss have managed to make all this fit into their popular compact pedal format, with options for mono or stereo in and out, and a TRS speed jack that supports separate slow/fast switching using an external footswitch. There’s also a Brake function, which can be activated by a second footswitch. Alternatively, an optional expression pedal can be used to control one of the assignable parameters: Speed, Level, Drive, or Balance.

Rear‑panel switches help to pack more features into the compact pedal format.As well as modelling the classic Leslie‑type rotary speaker, with its separate rotating drum and horn, the RT‑2 emulates the preamp’s overdrive tonality — it’s this that’s responsible for that classic growl when the amp is driven hard. A small toggle switch selects between the three modes of operation. The first mode models a vintage rotary speaker and its preamp tones. The second adds a natural spatial ambience, while the third mode offers enhanced modulation and more drive range. Modes two and three also seem to me to sound less ‘bloomy’ at the bass end, which can often make these options a little more guitar‑friendly. An LED indicator lights when the effect is on, and shows red if the speed is set to fast and green when set to slow.

Control‑wise, the RT‑2 uses a pair of dual‑concentric knobs for adjusting rotor speed, preamp drive, slow/fast speed settings, Level and Drive, although Drive may also be used in conjunction with a rear‑panel switch to adjust the horn/bass rotor mix. A further switch on the rear panel enables the user to choose slow or fast ramping rates. Changing modes is done using a power‑on sequence, with the Drive knob selecting the required mode. The pedal footswitch defaults to bypass, and the transition between slow and fast rotor speeds (complete with the essential speed ramping characteristics) is triggered by pressing and holding down this switch. While I do understand that compromises are often needed if you’re to pack everything into a compact format, I found it too easy to bypass the pedal accidentally when trying to change speeds in this mode; I much prefer using an external switch, ideally something hard to miss like a keyboard sustain pedal.

There are three modes, one aiming to replicate the classic Leslie effects accurately, and others that seem to be optimised for guitar use.The pedal’s second mode reverses the default action, so that a short press changes speed and a long press activates bypass — this feels like a more reliable mode of control to me. The third mode brings in the fast setting only while you hold down the pedal. Mode four is similar, but the default speed is fast and slows only when the pedal is held down.

A ‘virtual rotor’ display, similar to that used on the RT‑20, follows the motion of the horn and bass rotor, using a rotating pattern of red and blue LEDs. It’s simple but works well: other than bypass and speed change, what more do you really need when playing live? Once you’ve chosen a switch mode, voicing mode and rotor balance to suit your style, you can leave the pedal set like that. In the studio however, where you have time to experiment, you have the option to try all three modes and to make drum/horn balance adjustments.

In Use

I tried the RT‑2 both with regular guitar and with my EHX B9 organ pedal, and it produced very believable results with both. The fast speed gives you that Pink Floyd ‘Echoes’ or Cream ‘Badge’ sort of vibe, while the slow speed provides a more organic alternative to a chorus or phaser. Changing speed when the ramp speed is set to slow recreates the dynamic magic of the real thing, and can really add to a performance. Adding a little drive delivers a realistic sense of churning grit, and if you find the sound a bit bass‑heavy, a slight tweak to the rotor/drum balance soon addresses that. Modes two and three, being voiced to suit guitar, have a slightly more focused sound, with less very low‑frequency content, while the first, set up more like a traditional Leslie, is probably the best option for keyboards. The sound becomes very spatial when this pedal is used in stereo, and that can sound wonderful — but, importantly, it still delivers the goods when used in a mono rig. All in all, this is a very welcome addition to the Boss pedal range.

Information

£233 including VAT.

www.boss.info

$239

www.boss.info

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