True rotating speaker sound and SansAmp overdrive in one compact pedal
By Jon Chappell
Senior Editor, Harmony Central
Guitarists have availed themselves of the whooshy electronic sounds of phase shifters, flangers, and choruses for decades. But until recently, a convincing emulation of rotary-speaker devices—as exemplified by the famed Leslie and Fender Vibratone—has remained a bit out of reach. Tech 21, maker of the classic SansAmp as well as a host of full-line effects, has done what it does best in its new Roto Choir: Create a simple-to-use, single-stomp effect that perfectly captures the rotary speaker sound in all its complex, swirling, 3-D glory. And because rotary speaker effects of yore were almost always tube-driven, Tech 21 also incorporates its own SansAmp technology—unmatched for realistic tube-style distortion and the classic ideal of overdriven guitar sound. Let’s give the Roto Choir effects pedal a “spin”!
A bit of history
The original, physically rotating speaker cabinet, as exemplified by the Leslie, consisted of two speakers: a woofer for low frequencies (placed at the bottom of the cab) and a horn for high frequencies (at the top). Each speaker faced into a rotor—a reflective baffle with sloped sides—that revolved 360 degrees, independently, at user-controlled speeds. Standing in the vicinity of a Leslie allowed you to hear sound in changing physical phase relationships, based on the changing distances, rate of movement, and the unique interaction of the rotor-modulated speaker output. The Roto Choir pedal captures the essence of these mechanical operations and complements the “moving” part of the sound with an arsenal of analog tone-shaping controls. Working the Tech 21 Roto Choir is simple and intuitive, despite the complex circular calculations at play.
Controls in the round
The Tech 21 Roto Choir pedal features six knobs arranged comfortably on two rows. The four top-row knobs (Level, High, Low, and Drive) comprise the bank of all-analog tone-shaping controls (along with the Speaker Sim, described below) and operate as you would expect: Level controls the overall output of the signal; High and Low are for EQ; and Drive dials in tube-like grit and overdrive. Since the guitarists who created classic Leslie sounds almost never used it (or other rotating speaker effects) without a fair amount of overdrive, it’s only natural that the Tech 21 Roto Choir includes a Drive control.
Beyond their intuitive operations, though, there is some sophisticated subtlety. For example, instead of being simple passive filters, as your guitar tone knobs are, the High and Low controls are active, providing boost as well as cut for their respective frequency bands. You can use the High and Low to color any aspect of the signal—accenting or attenuating the edge in the Drive (gain-based distortion), bringing the top horn into sharper focus, or balancing the low and high rotors to each other.
The Roto Choir’s Drive control works in an interesting way too. For the first half of its travel, it boosts volume as well as preamp strength. Once past the 12:00 position, the character of the distortion changes in greater proportion to any added gain. This means that you have creative options in the interplay between the Level and Drive controls, and you’re not just limited to loudness and dirt on two unrelated knobs. Nice.
On the bottom row are two knobs devoted to the specific aspects of the rotating speaker effect, and the Tech 21 Roto Choir also implements them in clever ways. The Position control emulates the relative distance of a microphone to the high-frequency horn. Turn down the knob, and the mic is placed further away, creating a more even blend between the high and low speakers. Turn the knob up, the mic is pushed closer, and you hear the high-frequency horn much more prominently. Turning the Position knob all the way up creates a deep-cut tremolo sound, where the bottom of the cycle has almost no amplitude. This is exactly what happens when you stick your ear right up to the upper slots of a real Leslie! The Top Speed knob varies the rotation rate of the upper rotor in either Fast or Slow mode (selected by a footswitch). Since this is really the most significant sound variable in the Leslie and Vibratone effect, the Roto Choir effects pedal enables us to exercise precise control over it. The lower speaker—being less critical-—has well-chosen, pre-determined speeds. (Many Leslie owners typically disconnect the lower rotor anyway.)
Just because we covered the knobs doesn’t mean the Roto Choir is out of tricks. A biamp switch (on/bypass) changes the Roto Choir from single-speaker rotating mode (as in the Leslie 125 and Fender Vibratone) to a dual-speaker (recalling the Leslie 122 model), where both the top and bottom rotors rotate—at different speeds and in opposite directions. A Speaker Sim circuit, when engaged, allows the unit to be optimally patched into a recording rig or full-range speaker system—aided by the Tech 21 Roto Choir’s board-friendly Low-Z output impedance of 1 kOhm. Additionally, the unit features buffered bypass (preferred by this reviewer to “true bypass”) and a mono/stereo out. It can be powered by a single 9V battery or any DC power supply (with negative tip polarity and a 50mA output).
In the ring with the Roto Choir
It takes some time with the unit to understand how the different parameters interact, but that speaks to the Tech 21 Roto Choir’s versatility and sonic depth. Even when you grasp how the parameters dynamically influence one another, you can still discover new and exciting textures for your musical visions. I got instant vintage sounds—from classic to psychedelic—with the controls in their upper ranges, but managed to create subtly moving and thickening effects that were new, unfamiliar, and wholly original. Best of all, the rotary speaker sound, in the Roto Choir’s rendition of it, is as different from a chorus as it is from a flanger and phaser. It’s a new effect, with new uses, and the exploration is ongoing.
What I especially like about the Roto Choir pedal is that it feels like a guitar effect. Its controls are housed in a compact, guitar-stomp format, yet it includes the essentials, both tonal and spatial. Best of all is the integration among the tone, distortion, and the rotary-specific effects. Whether it’s an underwater psychedelic tremolo or a slow-moving undulation, there’s just not a bad setting on the Roto Choir. That’s a good sign that the pedal is well-designed and well-voiced. The fact that it has one of the best-ever distortion technologies on board, the SansAmp, seals the deal. The Tech 21 Roto Choir presents the complete signal-chain solution for the rotary speaker experience in a well-designed, compact pedal that’s equally at home in the studio or onstage.
For ultrarealistic rotary-speaker emulation, coupled with the classic SansAmp tone, check out the new Roto Choir from Tech 21.