In the last episode of Pedal Board, I compared three would-be "tape-echo" analog delay pedals to an actual tube-powered tape delay based on the Echoplex EP-2. This time I'll check out three electronic rotary speaker emulators and an actual rotating speaker system.

I'm not a keyboard player, much less a seasoned Hammond organist, so I didn't evaluate these units solely according to their fidelity to the classic B-3 through a Leslie 122 sound. It's important to sound like the real thing, and that should serve as a primary benchmark, but as a guitarist and mixing engineer I'm interested in how I can use these products in a variety of applications.

I tried them with electric guitar and with keyboard (yes, I used a Hammond patch), and in one instance I used them to record Prepared Zither. (Ha!) I configured them for mono and ran them directly into my guitar amp-an ADA tube preamp-and-amp combo pushing a Marshall 4 5 10 cabinet-as well as patched into its effects loop. I also configured the units for stereo and ran them into my digital mixer's channel inputs. I even used them as outboard processors in my mixer's effects loop while mixing some recordings. By the time I finished, I was experiencing vertigo!

Before I examine the virtues and vices these little spinners exhibit, here's a bit of background.

Original Spin Don Leslie invented the Leslie Rotating Speaker in the early 1950s, when he set out to emulate the sound of a large pipe organ reverberating in a church. His rotating speaker systems not only brought a cathedral-like sound to small churches, but also eventually had a dramatic impact on the sound of jazz, blues, R&B, rock, and other popular music.

Leslie speakers come in many models, with differing components, but they are all based on the same concept. They consist of two stationary transducers-a tweeter for high frequencies and a woofer for lows-that project sound into rotating mechanical devices. The tweeter fires into a twin-bell conical horn (or treble rotor) open at one end, with a diffuser located at the mouth of the horn. The woofer fires downward into a wooden drum (or bass rotor), with a scoop that pushes out the sound as it rotates. The rotors spin in opposite directions at either fast (tremolo) or slow (chorale) speed, and exhibit a characteristic effect when transitioning from one speed to another (see Fig. 1).

The signature Leslie sound is an extremely complex mixture of Doppler effects (including amplitude and pitch modulation), phase shifting, frequency masking, and ambient reverberation. Add to that the coloration of the preamplifiers and amplifiers-most often tube driven-and you can easily see why this is such a difficult effect to emulate.

As far as I know, the first electronic Leslie emulation device was the Jax RT-18, invented by Fumio Maeda for the Japanese company Shin-Ei in the mid-1960s. Shin-Ei's follow-up product, the Uni-Vibe, first achieved fame as one of Jimi Hendrix's signature sound modifiers. Compare "Little Wing," recorded using a Leslie, to "Angel" or "Dolly Dagger," recorded using a Uni-Vibe, to judge for yourself the success of the emulation. Though the Uni-Vibe was a phase shifter, it had settings marked chorus (instead of chorale) and vibrato (instead of tremolo). Go figure.

Numerous companies have since tried their hand at the daunting task of emulation, and about a dozen products-not including multi-effects processors-are currently available, all designed to produce the Leslie sound. Let's take a look at four of them.

Voce Spin II ($525) The sturdily built, bright-orange Spin II features four knobs, two LEDs, a small slider switch, and two heavy-duty footswitches, as well as an onboard power supply. Because these functions are fairly obvious, the Spin II doesn't include a manual. Unfortunately, one of the unit's most important features is not obvious at all. Its single 1/4-inch output jack, labeled simply "output," can actually output stereo via a TRS stereo insert cable. If someone hadn't pointed this out to me, I would have reviewed the Spin II as a mono unit.

The Spin II has no input gain pot, but you can switch input sensitivity between line and guitar (instrument) levels. The output level pot reaches unity gain in the first quarter turn, with lots of additional gain available beyond that. Of the two footswitches, one is for bypass and the other switches between fast and slow speeds. The Spin II has first-rate bypass circuitry and exhibits little or no tone sucking overall. Using three small pots, you can adjust modulation rates for the slow and fast settings, as well as the rate of acceleration and deceleration between them. The modulation LED blinks in time with the modulation speed.

The first thing I noticed about the Spin II is that it is somewhat noisy, even without any input signal present, and this noise was most noticeable when I placed the device between my guitar and my amplifier. It was a little quieter when I switched it to line level and placed it in either the mixer's or the amplifier's effects loop, but not significantly so. Also, the sound of the unit itself is pretty gritty, and though I tried adjusting various input and output levels, I couldn't get a very clean signal. The gritty effect is quite good on guitar and keyboards, but you're limited to one basic sound. A clean setting would be nice, as would the ability to adjust the amount of distortion using an input gain pot.

To my ears, the Spin II resembles a phase shifter more than a typical rotary speaker simulator, and at slower speeds it has a pronounced warble at the end of the modulation cycle. In fact, if you get the low speed setting just right, the Spin II does a passable Uni-Vibe. Speaking of slow speeds, if you turn the slow speed knob fully counterclockwise, the Spin II stops modulating completely, another feature that could be mentioned in a manual.

I did not find the differences between stereo and mono operation to be particularly dramatic. Stereo mode created more apparent motion between the speakers and opened up the sound a bit, but for my purposes the Spin II sounded best in mono mode, patched either directly into my amplifier or into its effects loop. However, I also used it in stereo mode to process some guitar tracks during a mix, and got some nice sounds in that application, too.

Hughes & Kettner Rotosphere ($499) The classy-looking Rotosphere is housed in a solidly constructed black plastic casing, with a large polished-aluminum faceplate. At the center of the faceplate is a glass panel, behind which glows a single 12AX7 tube. The tube imparts a very musical, soft distortion to any signal that passes through it, and you can drive it into heavy distortion, producing a big, fat, warm growl (think "Smoke on the Water"). Unfortunately, even though the Rotosphere's tube draws a lot of current, the unit lacks an onboard power supply, necessitating the use of a wall wart-ugh!

The Rotosphere has three knobs: Drive adjusts the input sensitivity, Output controls the master volume, and Balance adjusts the relative levels of the high and low rotors. You cannot adjust the mix of wet and dry signals, so it's fortunate that the device achieves a pretty good balance between the two. The Rotosphere also features footswitches and accompanying LEDs for Bypass and Slow-Fast, along with an ingenious Breaker function. Pushing the Breaker switch momentarily cuts the power to the rotor, causing the speakers to slow down; releasing the switch lets them accelerate again. This allows you to get basically the same effect as the Leslie's speed switch, while keeping both hands free.

The Rotosphere does not tone suck-period. When I put the unit into bypass mode and switched it in and out of my amplifier's effects loop, I heard absolutely no difference in the sound. You get a little hiss with the effect engaged, but given the noise levels you'd typically encounter in this sort of unit, the hiss is marginal. The sounds the Rotosphere does make range from very clean and sparkly to rough and nasty, and while not identical to the sound of a live Leslie, it closely approaches the sound of a recorded Leslie, particularly one recorded in mono.

Of the three electronic emulators, the Rotosphere was by far my favorite. Besides playing guitar and keyboards through it, I used it to record Michael Masley's Prepared Zither-wired with four pickups, the instrument has a greatly extended low end, along with lots of high harmonics. We ran the two treble-most pickups through the Rotosphere in discrete stereo, blended the outputs with the bass pickups at the mixer, and recorded direct to DAT. The Rotosphere generally fattened and warmed the sound, and greatly expanded the richness of the upper end-no mean feat, given the instrument's complexity and harmonic richness. The Rotosphere is a rockin' box.

DigiTech RPM-1 (original list $599, discontinued price $199.95) Like the Rotosphere, the single-rackspace RPM-1 has a 12AX7 tube in the preamp gain stage. Unlike the Rotosphere, the RPM-1 has a built-in power supply. It also employs a combination of Intelligent Pitch Shifting technology, delay, and volume modulation circuitry, resulting in a sound very different from the other emulators. The RPM-1 does not sound like a phase shifter, but it sounds less like a Leslie than either the Spin II or the Rotosphere.

When it comes to controls and routing options, the RPM-1 takes the prize. It has knobs for input level and drive level, along with knobs for four additional parameters, and it can operate in mono, stereo, or Tri-Output (stereo horns plus low rotor) modes. However, it lacks an output level control, which is too bad, because the output level drops when you engage the effect. You have to push the input level almost to clipping to reach unity gain, and boosting the drive adds more distortion than level.

The Horn Speed knob affects the horn speed at both fast and slow settings. The Rotor Acceleration knob allows you to adjust how quickly the low rotor speeds up, from very slowly to very fast, and when turned fully counterclockwise, it stops the rotor altogether. The Spread knob adjusts the positioning of the right and left "mics" in relation to the "cabinet," ranging from a 180-degree stereo spread to a more or less mono blend. Balance adjusts the relative levels between the horn and the rotor.

The Speed, Brake, and Bypass buttons-which light up when engaged-also appear on the footswitch, although the latter has no status indicators. Brake stops the rotors, freezing the "speakers" in place, while leaving the drive settings and the speaker cabinet emulation engaged. You can use an optional voltage control pedal to sweep the full range of speeds.

I found the RPM-1 somewhat noisy, particularly with the drive control cranked up. It performed best in stereo mode, connected directly to my mixer. The Tri-Output setting, with the horns panned hard right and left and the low rotor in the center, produced a combination of sounds I found difficult to work with. In fact, I preferred the sound of the RPM-1 configured in the mono mode, running through my amp's mono effects loop.

Overall, the RPM-1 has a very electronic sound-not necessarily a bad thing. If you aren't particularly concerned with absolute fidelity to the Leslie sound, the RPM-1 can provide a wide variety of interesting alternative modulation effects. I certainly found this to be the case.

The RPM-1 has been officially discontinued, but DigiTech still has plenty of units in stock. The company is currently selling them at a reduced price on its Web site.

Motion Sound Pro-3T ($799.95) and Low Pro ($899.95) The Motion Sound Pro-3T is a tube-powered hybrid that combines an actual rotating horn assembly with an electronic low-rotor emulator. Those who desire a physically rotating horn-the primary characteristic of the Leslie sound-without the burden of moving a heavy cabinet will find this device an ideal compromise. For those who refuse to compromise, there's the Motion Sound Low Pro-when combined with the Pro-3T, it sounds authentic enough to give any Leslie's rotors pause.

The Pro-3T measures 20.5 by 7 by 17 inches and weighs 25.5 pounds. It looks like the top section of a small Leslie cabinet, with sound vents on all four sides. It routes input signals to a 12AX7 tube preamp section, then to an active 800 Hz crossover-the same crossover point the Leslie uses. The Pro-3T sends frequencies above 800 Hz to a 40W FET power amp, which powers the horn driver. It sends low frequencies to the two electronic low-rotor emulator outputs (or the Low Pro) for either mono or stereo operation.

The device offers knobs for pre- and postgain, Contour (a high-frequency cutoff filter for simulating the curve of a Leslie 147), and Separation (which changes function depending on whether you're operating the emulator in mono or stereo). Two LEDs indicate power-on and fast-speed settings. The Pro-3T ships with the fast and slow speeds preset to sound most like a Leslie 147, but you can adjust them internally if you're willing to remove lots of screws.

The Pro-3T sounds fantastic! The horn sounds like the real thing because essentially it is the real thing, and the low-rotor emulator produces a frighteningly authentic sound, in both mono and stereo. When I switched between the emulator and the Low Pro, I heard a fairly minimal difference. Wow! Thanks in large part to its tube preamp, the Pro-3T produces a very wide range of sounds, from crystal clear to ultragrungy, with lots of interesting variations along the way.

The Low Pro measures 20 by 22 by 16.75 inches, weighs 58 pounds, and supplies the bottom half of the system. It contains a 12-inch woofer, mounted facedown above a rotating drum, and is powered by a 120W FET amplifier. The Low Pro connects to the Pro-3T via a 5-pin DIN connector, which links control functions as well as routing audio. It has knobs for volume and bass boost (at 100 Hz) and offers four tiny recessed pots for adjusting slow and fast speeds as well as acceleration and deceleration times.

Simply put, nothing available on the market today sounds more like a Leslie 147 than the combination of the Pro-3T and the Low Pro. Their sound is simply stunning.

Full Circle I used to say there's nothing like the sound of a rotating speaker system, and I was right. No matter how good the electronic emulation-and there are some good ones here-all it really takes to settle the authenticity question is to fire up the real thing in the same room. You can't capture all of a rotating speaker system's complexities electronically. On the other hand, every attempt to do so results in a product with its own idiosyncratic personality-and ironically, the "failings" of particular products often turn out to be their most endearing and useful qualities.

Barry Cleveland is an associate editor for Electronic Musician magazine. He also operates a project studio, plays guitar with the improvisational quintet Cloud Chamber (www.mphase .com/cloud.htm), and is currently writing a book on the legendary Joe Meek.

Voce/Tonewheel LLC tel. (201) 599-0100; fax (201) 599-0404; e-mail info@voceinc.com; Web www.voceinc.com

Hughes & Kettner tel. (800) 452-6771 or (847) 439-6771; fax (847) 439-6781; e-mail info@hughes-and-kettner.com; Web www.hughes-and-kettner.com

DigiTech tel. (801) 566-8800; fax (801) 566-7005; e-mail customer@digitech.com; Web www.digitech.com

Motion Sound tel (801) 265-0917; fax (801) 265-0978; e-mail Sales@Motion-Sound.com; Web www.motion-sound.com

www.mitatechs.com/leslierumors.html Leslie speakers and Hammond organs: rumors, myths, facts, and lore.

www.theatreorgans.com/hammond/faq/mystery/mystery.html Unearthing the mysteries of the Leslie cabinet.

http://theatreorgans.com/hammond/faq Lots of information regarding Leslie speakers and Hammond organs.

www.akademisk-antikvariat.dk/lmv/hammond.htm Captain Foldback's Hammond and Leslie site, featuring downloadable schematics, links, and other useful information.