| (mp3, 1.2 mb) These samples (Cream's "Badge", Blind Faith's "Well All Right", & Mountain's "Nantucket Sleighride") were selected to demonstrate the classic grinding, drone-like chorale sound of a guitar played through a Leslie during Rock's heyday. These were mixed to mono for the channel which best showcased the sound. I have no idea which models they were playing through but I do know that they weren't using Leslie simulators. |
The Leslie Doppler effect produces vibrato (cyclic frequency variation) and tremolo (cyclic amplitude variations). The mix varies through the frequency spectrum, when projected through the horn and rotor, which rotate in opposite directions. Another distinctive characteristic of the Leslie sound is the change in speeds between the slow chorale and the fast tremolo ("ramp up/down"): Just like a car, it takes time to go from 0 to 60 mph (or brake). The lighter horn and the heavier bass rotor ramp up and down at different rates.
The main downside to using a Leslie speaker is that they're big, heavy, and have peculiar sound projection characteristics. The big & heavy part is easy enough to see, since they look like furniture and no sane person likes to hump heavy furniture. However, the sound projection is unlike any other speaker: The spinning parts hurl sound around the room, and the environment (reflectivity of walls & speaker placement) plays a big role in the sound that reaches the eardrums. Because of this, for the wattage, they're not as loud as a stationary speaker that's aimed at your eardrums. The rotating parts also make a palpable "swooshing" sound from the air being pushed around. It's all part of the in-person sensory experience-- a mono or stereo recording doesn't capture the full essence of the experience, and the wind noise and belt whine aren't something that's purposefully replicated in any rotary speaker simulator I've encountered (not that it needs to be). Furthermore, a recording of the Leslie sound always represents a particular microphone(s) placement. Even with stationary speakers, microphone placement has a dramatic affect on the resultant sound. Close-miking a Leslie emphasizes the throbbing tremolo component over the vibrato; at a greater distance, that difference is averaged out.
If you're looking to get the complex sound of a rotating speaker with a direct mono/stereo output and without the size, weight and maintenance requirements of the real thing, a stompbox simulation looks like a really attractive proposition. Another point in their favor is that you can't crank up a real Leslie at 4 AM and play through headphones (well, you can, but sleeping people probably will hate you...).
THE STOMPBOX SOLUTION A bunch of stompbox pedals have come out since the '60s that produce modulation effects electronically, no doubt inspired by the Leslie speaker. I've read that the Phase Shifter was the first; the Univibe (Hendrix/Band of Gypsies/Machine Gun, Robin Trower) was another early attempt. (The Flanger was inspired by a recording studio trick, so it doesn't really qualify.) Modulation effects can sound similar to a Leslie, and that may be good enough for many folks. I think that the Chorus pedal is probably the closest of the non-Leslie simulators in capturing the slow Leslie chorale sound. Combinations of these pedals may approximate the fast speed mode, and you can manually simulate the ramp up/down speeds. At any rate, times have changed, technology has lept forward, and Flangers, Phaser Shifters and Vibes have established their own distinct sound identities: Presently, they aren't considered rotating speaker simulators since there's a newer category of effects specifically for that.
Once you start searching for a rotary speaker simulator, you may find that there's a limited selection available (compared to Overdrive pedals). It's a specialized topic, mainly of interest to keyboard players, so there aren't as many Internet reviews or discussions, and some of the most recommended choices aren't available anymore. Many folks mention the Dynacord CLS222 as the best ever made, but it hasn't been available since the early nineties. The sound samples I've heard do sound very good. They show up occasionally on eBay, but they're expensive. The highly-rated Hughes & Kettner's Rotosphere is a more recently discontinued product that's easier to find (but still, isn't cheap).
I've bought several through the years: Hughes & Kettner's Rotosphere Mark II, Digitech's EX-7 Expression Factory pedal, Line 6's ToneCore Rotosound, Danelectro's Rocky Road and DLS's RotoSIM. The rotary speaker FX is also available in various multi-effects processors like Line 6's PodXT and Roland's VG-99, as well as in some amps. There are others that I chose not to buy, like Boss's RT-20 Rotary Speaker Simulator (tried briefly in store but didn't like), Option 5's Destination Rotation (wasn't impressed by sound sample) and Voce's Spin II (no info)-- funds are limited, so I researched Internet opinions and sound samples to help steer me to my choices.
FWIW, There's a saying about opinions... bottom line is that they should always be taken with a grain of salt (including mine-- I'm certainly no expert). I know it sounds snotty, but I've spent some bucks based on opinions, and later wondered if the opinion-givers knew what a real rotating speaker sounded like. Shocking, huh? I reckon that when you're happy with a purchase, there's a real strong urge to tell the world good things about it.
Clearly, hearing a sample is better, but unfortunately I've never heard an Internet sound sample or Youtube video for any of them that screamed "BUY ME!!!"... and in hindsight, that might have been a clue. An in-store or at-home trial would be ideal, but rotary simulators are an esoteric piece of hardware that have a hard time competing with the plethora of overdrive pedals for retail shelf space. Fortunately, they're available via mail order from places with satisfaction guarantees, but return postage costs can be expensive.
I think that the easiest Leslie sound to replicate is the fast mode, as heard in Stevie Ray Vaughan's "Cold Shot" (probably the most recognized of modern usage). It's a Vibratone running at fast speed, so there isn't that much subtlety involved. Soundgarden's "Black Hole Sun" has another example of a rotary speaker in fast mode. To my ears, any of the stompbox simulators is probably as good as any another for getting that sound. The Leslie mode that I like most is the slow chorale, especially when it has a distorted, "grinding" and organ-like quality. This is the sound that's heard on the old Blind Faith tunes. The other distinguishing feature I like are the ramp up/down sounds; This is the brief transitory mode between the fast and slow speeds that sounds great when it's actively managed. Organists are masters of this. The simulators include an overdrive function, which I usually turn down or off if possible; I prefer getting overdrive through other means.
PHYSICS SIMULATION VS. HARDWARE MODELING I've come to believe that that there's a difference between a "rotary speaker simulator" and a "Leslie modeler". Although products don't refer to the distinction, I believe that some manufacturers focus on electronically simulating the physics of a rotating speaker (doppler effect, ramp speed, etc.), but don't focus on modeling the tonal coloration of the actual hardware. Unearthing the Mysteries of the Leslie Cabinet provides an excellent in-depth analysis of the hardware, and the way that it creates that distinctive sound. The sound through a horn driver and drum rotor isn't hi-fi and it has a distinctive resonance that may not sound great when simulated and amplified to a high volume through a guitar amp speaker. A pedal that focuses on "transparency"-- preserving the guitar's natural tonality -- probably isn't going to sound like a real Leslie speaker unless the guitar signal is preprocessed through an equalizer. However, a rotary physics simulator may be a more practical tool for adapting to a variety of playing situations. The tonality modeling approach appears to be more set-in-stone & less flexible as a single modeled sound. It doesn't scale up to volume change as well as the separate components of a real Leslie cabinet. (That's just my WAG for why pedals that capture the Leslie tone don't do as well at higher volume levels.)
For one reason or another, I'm not completely satisfied with any of the stompbox simulators I've bought. Sound-wise, it's a very subjective call and that's reflected in the imprecise vocabulary that's commonly used to describe the sonic qualities of guitar gear. Basically, I knew the sound I was looking for, but it didn't have to be perfect. The convenience factor counts for a lot, so I was willing to make allowances for the fact that a Leslie simulation through a stationary speaker is going to lack some aspects of the in-person experience of the real deal.
HUGHES & KETTNER ROTOSPHERE MARK II (stock photo)
sample (300kb, mp3)This is the first rotary speaker simulator I bought, and should have been the last, considering the cost. Though recently discontinued, this has received many favorable reviews on the Internet. Generally speaking, it's praised for having a "warm" sound, for realistic modeling of the ramp speeds of the treble and bass drivers and for having a tube preamp to accurately model the tube preamp "growl" of the genuine article. I consider this to be a "physics simulator": Even though the tube preamp is a nod to replicating authentic "Leslie growl", the guitar's signal isn't filtered to accurately model the tonal output through a horn and rotor. The enclosure is a sturdy metal box, fairly huge by stompbox standards (approx. 8" x 8"), with a cool blue light shining through an opening to show the tube. Three footswitches allow you to switch the effect in/out (true bypass), stop the rotors from spinning ("breaker") , and toggle the speed (ramp up/down). The knobs allow adjustment of gain, output level, and balance between the high and low frequency rotors. Trimpots are accessible from the top to adjust the running speeds of the rotors. LEDs show whether the unit is on/off, the breaker engaged, and speeds of the rotors. The unit has stereo inputs and outputs, with a switch to match input impedance to guitar or keyboard. Remote stomp switches can be connected to control in/out and the speed. Finally, the unit is powered by a non-standard wall-wart, through a 1/8" plug-- and with very specific instructions to use only their power supply. I like the sound of the Rotosphere. It's very clear, crisp, and uh... "shimmery". It sounds great when run in stereo, and the ramp up/down models the different speeds that the horn and rotor spin at. I'm less enamored of the tube preamp simply because it (or the analog circuitry) introduces a lot of hiss. Mainly though, I don't think it adds much to the sound that couldn't be done by other means (overdrive pedal or the amp), making for a much smaller package. Consequently, this makes the pedal bigger, with special power requirements. While it's certainly more practical than a real Leslie, it doesn't nail the Leslie sound 100%, and I felt that there should be something out there with as good or better sound in a smaller package, with more standardized power requirements. [Note, 08/02/08: This just came back from loan, so I've had a chance to reassess some aspects of it. The hiss can be minimized to an acceptable level by fiddling with the Drive and Output knobs. It actually sounds better than I recalled it sounding, and responds well to an overdriven input signal.] |
 DIGITECH
EX-7 EXPRESSION FACTORY (stock photo) sample
(300kb, mp3)This is a multi-function pedal that switches between a bunch of guitar toys like wah-wahs, a weird "Space Station Synth Swell", a pitch-changing whammy, a Univibe, a Flanger, and a Leslie emulation. It also has overdrive/distortion stompbox emulations that can be paired with each of those modes and activated by clicking on the stomp switch under the heel end of the pedal. The main selector is a digital encoder rotary switch (which has implications for any random-access modding you might hope to do). You don't get very many parameters to tweak: The three primary controls (drive, minimum speed & volume) are multi-functional, and depend on what mode the pedal is in; the overdrive/distortion controls are paired underneath in a concentric-pot arrangement. If you want to do more than trial & error tweak your way through the various modes, you definitely want to keep the manual nearby. External footswitches can be plugged in to go up/down in the mode selection, or switch between the distortion on/off modes. This unit requires it's own special 9-volt AC (not DC) adapter and doesn't operate on batteries. I consider this to be a "Leslie modeler". It has a great growling grind when in slow speed, and gets very close to the "Badge" sound. Yes, it colors the guitar's sound very heavily and you're stuck with the way it sounds-- a consequence of this pedal's "Swiss Army knife" approach with a limited common set of knobs, and perhaps limitations of the technology. Using the pedal (instead of a switch) to change the ramp speed feels a little weird, but it does work as it should sound, with a delayed ramp up/down. Unfortunately, I found that the modeling of the Leslie sound didn't work well with my Cube 60 amps at high volume levels-- there's a sharp frequency peak that resonates with the speakers, and sounds really awful, almost like feedback. It was slightly better through my Twin Reverb. Nevertheless, it's a pretty amazing gizmo, considering that it's packed with so many cool effects in a wah wah pedal-sized package. I think the main disappointment (other than the Leslie's resonance) is that it can only be one thing at a time-- and changing modes is not something you'd likely do on a dark stage. You'd need an up/down selector switchbox, and there's no indicator to let you know which mode is selected. The knobs are awfully tiny and difficult to decipher at a glance too. |
 LINE
6 TONECORE ROTO-MACHINE
sample (270kb, mp3)
This is an economical, single-function pedal from Line 6's modular "ToneCore" stompbox series. It's a very compact & heavy (for its size) pedal that requires minimal space on a pedalboard. The modularity comes from the heavy cradle that the electronic "guts" can be swapped in and out of. In theory, you could buy one cradle and a batch of modules. I don't know how useful that would be in practice: Who wants to hassle with swapping the guts just to save a few bucks? I thought that it would be a no-brainer for Line 6 to produce a multi-module cradle for their modules so you could mix & sequence effects in a patchcord-free, single power source pedalboard, but so far they haven't. The pedal has a number of control options. There are pots to set the fast and slow speed, rotor balance, and drive. In addition, there are 3-position slide switches to select the ramp up/down time (slow/medium/fast) and the tone (to model 3 Leslie models: the 145, the L16 (vibratone) & the 122. The footswitch is totally unlike other stompbox footswitches: A light tap initiates speed change and a heavier stomp switches the effect in/out. It's a little weird feeling and doesn't inspire great confidence in the switches' durability; It's definitely not as straight-forward as two separate switches on a pedal's face, but this keeps the pedal at a compact size. This isn't a true-bypass pedal so it requires power even when it's bypassed. It powers up with the effect on and in the fast speed mode. If there's power supply noise in the signal, you'll hear it when the pedal is in bypass. You can even hear the modulation chuffing when in bypass. There's a slight but noticeable boost when the effect is engaged. Many folks don't like this pedal since it colors the guitar sound very heavily and can sound awfully muddy at high volume levels. Tonally, it attempts to capture the Leslie sound of "Badge" more than some costly and highly-regarded pedals (although it's a little over-the-top). This was a natural approach for Line 6, since they specialize in digital modeling of actual hardware. They've modeled the quirky frequency response and resonance of 3 Leslie models, whereas other pedal manufacturers seem to focus on simulating the physics of the rotating speaker principle, rather than a specific model. Between the 3 models selection and rotor balance, you can probably find something that you like. It's not a complete simulation of the rotating speaker physics though; the ramp up/down doesn't model the difference rates of the horn and rotor spin up/down, as it does in the H&K Rotosphere. Only a die-hard rotating speaker geek would notice and care about that though. This would be a good selection for a pedal board except... The pedal lacks true bypass and the bypassed mode isn't always clean-- I've heard power supply hum and a faint phantom pumping from the effect circuitry when the thing was supposed to be bypassed. I think the biggest downside of this pedal is in its powering. Although you can use a battery, I suspect that this pedal, like most digital pedals, is a power-hog. Unfortunately, the ToneCore series is well-known for being "difficult" when sharing power in simple daisy-chained power supplies. It works best with its own separate Line 6 wall-wart, or with an expensive power supply with isolated outputs. Visual Sound even singles out the ToneCore series as incompatible with their Spot One switching power supply. |
 DANELECTRO ROCKY ROAD sample (560kb, mp3) This is a super-economical single-function pedal (discontinued) that's even more compact than Line 6's Rotosound! It doesn't attempt to simulate any of the dual rotor Leslie models; it's strictly a Vibratone simulator. It's received some fairly high praise for being an authentic simulation of the Vibratone's sound. The effect is fairly subtle, pleasing, and it doesn't color the guitar's tone very much, which may be preferable to some. Out of the box, the pedal's got an aggressive boost, even with the drive turned down; there's a Google-able mod that shows you where to jumper one of the circuit boards to fix that. Unfortunately, the circuit is rather hissy, with a noticeably poor signal-to-noise ratio. My main disappointment is the ramp speed, which takes waaaaay tooooo looooong. Maybe it intentionally models a unit with a slipping belt? Unfortunately, there's not a built-in way to change that. That's a near deal-killing deficiency for me. Besides that, this is one case where the compact size of the pedal is actually a significant negative-- the knobs and switch are too small, and the too-far recessed stomp switches make you doubt whether your switch stomping has been successful (especially with the slow ramp up/down, since it's subtle and there's no LED to indicate speed). As others have said, this is clearly designed for barefooted guitarists who are skilled at pressing buttons with their big toe. This makes it pretty unusable in a performance setting unless you leave it on all the time (or are a barefooted guitarist with a well-trained big toe). I suppose you could glue marbles on the switches? |
 DLS ROTOSIM sample (300kb, mp3)(stock
photo) There are a few online discussions about the "best leslie simulator"; besides the Dynacord, the DLS RotoSIM and H&K Rotosphere are often mentioned. There are several things that distinguish this product from the pack and make it look mighty promising: For one, it's got the highest count of knobs on the outside, and more user-tweakable trimpots on the inside. Their design philosophy seems to recognize that everyone has their own idea of what a Leslie should sound like... so make the box as configurable as possible. Clearly, they were listening to some of the complaints about H&K's Rotosphere; it's in a smaller package, with less hiss, and has very unfussy 9-volt power requirements. I really wanted to like this pedal and had high hopes for it, since it might mean the end of my search (yay!). Unfortunately (sigh)... for my tastes, this pedal's biggest disappointment is that it's too "transparent". Before I bought (and returned) mine, I didn't know what forum posters meant when they claimed it was more "sterile" than the H&K. I think they meant that the pedal doesn't have much effect/tonal color; it makes your guitar sound like your guitar, and not like a real Leslie box. At chorale speeds with a clean guitar sound, the effect can be very subtle. Even though Output B is more heavily flavored and there's a trimpot to blend the effect/straight signal, the factory adjustment is only 1/16th of a turn away from fully clockwise: I wanted to turn up the effect ratio at least 50% more, but alas, there is no more! This reflects what I generally felt about this pedal's many knobs and adjustments: The pedal operates within a mild sonic range of transparency, so many of the knobs seem to have only a subtle and minor effect. For example, the "Overdrive Gain" knob does produce a noticeable change, but the knob's full travel is like turning up the gain of an overdrive pedal from 7:00 to 8:00. It's like that for the Tweeter & Bass Rotor level knobs, and the Tweeter Response trimpot. Yeah, you can hear the difference, but I found myself wondering whether it was worth the bother. This was the pedal that gave me the idea that there was a fundimental difference between the simulator vesus modeler approach. This one's called "RotoSIM" for a good reason. One of the main things I look for in these pedals is the ability to get that "grinding" sound. Some don't do it on their own (even using the built-in Overdrive/Growl/Gain control) so they have to be fed a distorted signal. This usually makes the rotary effect stand out more, and can over-emphasize the high frequency swishing to the point where it sounds wrong and patently artificial, like a phase shifter. With this pedal, I noticed something else, weird but familiar-- At medium speed, an artifact of the modulation sounded similar to the vowel-ish modulation tone I get from my BBE "Soul Vibe", a Univibe clone. I don't consider that to be a good thing, since the Univibe isn't a particularly accurate simulation of a rotating speaker (It's great for that unique Univibe sound though). As I looked at the circuitboard and saw two things that look like opto-couplers (the heart of the Univibe sound), I had to wonder...??? In fairness though, I don't have a clue how this thing works. A lot of people really like this pedal, so I'm probably in the minority in my tepid assessment of it. I think it's because most people aren't comparing it to the tonality of the "Badge" Leslie, and simply like the way it sounds and transparently responds through their setup. It's a neat sound, but I consider it a simulation of the rotating speaker physics rather than an accurate modeling of a specific, real Leslie speaker, so it therefore doesn't have "That Sound". I'd been hoping that the combination of current state-of-the-art electronics and spending enough bucks would finally give me the best of both worlds: a true "Leslie in a stompbox", with adjustments to take it from transparent to heavily colored. Nope, not The One. |
 MOTION SOUND SRV-212 (stock photo)Off and on, I'd considered getting a real Leslie work-alike. Motion Sound's product line includes unamplified Vibratone-style speakers (without horn) designed for guitarists, as well as independent horn and rotor units with built-in amplifiers, designed for the keyboardist. These are considerably smaller, lighter and more road-worthy than traditional Leslies, with their wooden furniture look. I recently played through their 100 watt SRV-212 model at a store. I was very tempted... despite that at low volume, I could hear a slight belt squeal when changing speeds, and the single-coil pickups on the store's Strat clearly picked up and amplified the motor's electromagnetic field when I was in close proximity. If the salesdude had checked back, I might have thrown reason & practicality out the window and bought the sucker. In retrospect, I'm glad I didn't. Despite the compact size, there were the questions of "Where would I put the sucker?", "Do I really need another amp-like thing?", "What amp will I run it from?", "Does the impedance work with my amps?", "How would it fit in with my stereo amp setup?", and "How do you bypass the thing?". Mainly though, the single rotor Vibratone design didn't sound special enough to me to warrant dealing with those issues-- it's an easier sound to electronically simulate than the horn/rotor model, and some stompboxes came pretty close. It wasn't really a fair test drive though, since I wasn't using my guitar & amp, and couldn't really crank up as much as I would have liked. At any rate, I never heard that particular tonality that I'd been searching for. Maybe hearing their PRO-145 with its independently rotating horn & rotor would have pushed me over the edge and motivated me to find the salesdude? Given the price, I'm kind of glad that they didn't have one on the floor. |
 MOTION SOUND PRO-3X sample (340kb, mp3)(stock photo)After all my not-quite-there experiences with stompbox pedals and not being sold on the SRV-212, I was awfully frustrated. Frustration can drive you to making rash or desperate decisions. It drove me to taking a final look at Motion Sound's lineup, as well as Hammond-Suzuki's Leslie products, before resigning myself to the possibility that there might be no satisfaction in store for me. Although I would have preferred to throw restraint out the door, I established $1K as my arbitrary limit (but preferably less), which ruled out any full rotating speaker systems. That left the Vibratone work-alike (which I'd already tried) and a peculiar hybrid, Motion Sound's PRO-3X.
The PRO-3X is a small (20" x 16.5" x 6.5", 40-watt) amp with a true rotary horn section and an output for the electronically simulated lower rotor. The crossover between the two is 800 Hz, and the lower rotor simulation is fed to an external amplifier. I felt that this held a lot of promise, since the most "Leslie-like" portion of the sound happens in the upper frequencies through the horn. The bass frequencies exhibit less frequency modulation (because the wavelengths are longer) but plenty of amplitude modulation (the "throb", or tremolo effect). When mulling over my decision/gamble to buy, I reasoned that the quality of the simulated lower end wasn't as important as the quality of the higher end-- and you can't get more authentic than having a real rotating horn: The PRO-3X's horn is reputedly voiced like a Leslie model 147. Furthermore, this worked with my 2-amp setup in a non-stereo, A/B switchable configuration. The PRO-3X isn't nearly as portable as a pedal, but it's a lot smaller and lighter than a cabinet with 12" speakers. Unfortunately, it's impossible to make a rotary speaker that you can mute and play through headphones (unless you get the model that's acoustically sealed), but you can play this one at very low volume and send the internally mic'd horn & rotor sim mix out to a headphone monitor (which doesn't sound nearly as good as playing through it "straight"). The controls plate has a lot of knobs for all the essential stuff: Gain, Volume, FET Amp Mode, Horn Mid & Treble EQ, Simulator Low and High EQ, and a Mix Output Blend for sending a mixed signal of the mic'd horn and low rotor simulator. The circuit board has trimpots for fine tuning operational parameters like ramp up/down and fast/slow speeds of the horn and simulated rotor. The previous version (PRO-3T, discontinued) had a tube preamp; this version features an FET (transistor) preamp that simulates a tube amp's class A/AB/B bias setting. Basically, this affects how signal clipping occurs when the gain is turned up and therefore affects how the "growl" sounds. If you don't connect the PRO-3X's simulated rotor to an external amplifier, the horn sounds horrible! It's like playing your guitar through a narrow-band megaphone. However, that's part of the magic: Once you introduce a mere hint of the simulated rotor, the separate outputs magically blend in your ears to produce "The Sound". I suspect that this blending occurs because bass is relatively omnidirectional compared to the horn. Even when separated by several feet, they still sound like a single, blended unit. As I said, it's like magic. The other magic is that within moments of plugging it in, I was getting all the true Leslie sounds that I'd been looking for, that I couldn't coax from a stompbox simulator. The grinding "Nantucket Sleighride" sound was there, as well as "Badge" and "Presence of the Lord". Cleaned up, the shimmering chime of the Beatles and Badfinger were there as well. Unfortunately, this solution is a compromise-- For a live performance solution, it's not as simple and convenient as a stompbox. The 40-watt horn can be awfully loud and piercing and should be complimented by a +100-watt amp for the bass/rotor simulator section; that's probably enough juice for a small venue. For larger venues, a combination of the mic'd horn and simulator amp out can be fed to a PA system. For home use, that's not an issue: The unit is very usable at bedroom volumes and doesn't need to be cranked up to get a good tone. The fact that the distinctive tonality is produced by an actual horn and bass simulator instead of being a modeled and played through a 12" speaker probably helps with the scaleability issue-- it can easily be made to sound good loud or soft, and isn't eaten up by bass or weird resonant peaks at when running at high volumes.
 |
CONCLUSION Oddly enough, I'm not obsessively fussy about the sound of my guitars' pickups and the wood that their bodies are made of, or whether I'm playing through my tube amp or my solid state amp. I can always manage to dial in an acceptable sound. When it came to nailing that Leslie sound, I've been very fussy. I had that Leslie sound burned into my brain decades ago, and apparently it was impressive enough for me to recognize when I hadn't and when I had achieved it. I've never felt that way about my long-lost '71 Deluxe Reverb!
If your brain isn't similarly imprinted (or cursed), any one of the electronic simulators, or perhaps any modulation effect will probably sound pretty cool, with the benefit of being a practical solution for your pedal board.
That's not to say that you can't get the Leslie tonality with a stompbox; with equalization, many things are possible. From my experience though, it's just not available through plug 'n' play.
If you can accept that, it's a matter of priorities and preferences. Stompbox simulators vary wildly in price, from the relatively cheap Danelectro Rocky Road (discontinued- approximately $40 on eBay) to the somewhat pricey DLS RotoSIM ($300). The H&K Rotosphere currently fetches anywhere from $300 to $500 on eBay, and the rare Dynacord CLS-222 can fetch in the neighborhood of $700. The Digitech EX-7 typically retails for around $200 (but it's a multi-function pedal). The Line 6 Rotomachine typically goes for about $120; much less if you buy just the core module.
If you want a simulator for a pedalboard, the footprint and power requirements are probably important issues as well. The Line 6 Rotomachine and Danelectro Rocky Road have the smallest footprints, and the H&K Rotosphere has the largest. The DLS RotoSIM and Digitech EX-7 fall in between. The Danelectro Rocky Road and DLS RotoSIM have the easiest power requirements (unfussy 9-volt DC); the others require special power supplies (H&K Rotosphere & Digitech EX-7) or need clean, isolated 9-volt DC (Line 6 Rotomachine). It's not an easy decision with an obvious choice... and this isn't even a complete list of available choices.
For those with my affliction, my recommendation is to get the real deal first to take care of the jonesin'; then get a quality electronic simulator for gigging convenience and for an audience that can't tell the difference...
--07/19/08, 08/02/08