Review: PRO-3 Leslie Simulator

by Mark Longo

Following are facts and some subjective impressions about the Motion Sound PRO-3 Leslie Simulator, which I have owned and used for many months. I use the PRO-3 with my Hammond-Suzuki XB-2 in a live performance setting of mostly small to medium sized night clubs.


The PRO-3 is a Leslie simulator with a twist; rather than simulate the Leslie rotating speaker's audio characteristics purely electronically, it uses an actual rotating treble horn with a compression driver and a solid state amplifier for frequencies above 700Hz. Frequencies below 700Hz pass through a stereo bass rotor simulator and is made available at 1/4" output jacks for use with a user-supplied amplifier. Though not a rackmountable unit, the PRO-3 is a small, lightweight, and highly portable package.

While there's still room for improvement in the PRO-3 design, overall I believe that the PRO-3 does a far more convincing job of Leslie simulation than do conventional electronic simulators, and even has some advantages over real Leslies. This review criticizes the PRO-3 on some of the fine points, but in all I feel this unit is a great asset for live organ players.

Since the PRO-3 is effectively part Leslie, part Leslie simulator, it can be evaluated with respect to each. When compared to a real Leslie, the PRO-3 is far more portable, needs no maintenance, and when teamed with a good amp it's quite a bit louder than most Leslies. However the PRO-3 uses a bass rotor simulation so if you have finicky ears and listen in a quiet setting, you may miss a real bass rotor. Also, the PRO-3 does not quite have the warm tone associated with tube Leslies such as the 122 or 147, and it can't produce the classic tube Leslie overdrive sound.

Compared to an electornic Leslie simulator, the PRO-3 sounds larger, more animated and alive. In side-by-side comparisons, electronic simulators sound two dimensional and a bit flat. On the other hand, electronic simulators can be wired directly to a sound board (as can the PRO-3's bass rotor simulation, discussed below) while the PRO-3's treble rotor needs to be mic'd if you use PA reinforcement. It's arguable whether a mic'd PRO-3 would sound better than a good electronic simulation when heard through a PA only, though as a player I'd much prefer having a PRO-3 for my stage monitor over an electronic simulator. The PRO-3 has no MIDI control, as do some (though not all) of the electronic Leslie simulators.

Physical Description

The PRO-3's physical dimensions are 6.5"H x 20"W x 16.5"D and it weighs 26 Lbs. The front panel is vertically centered on the left third of the unit front. The control panel has volume and limiter knobs (described below) and also includes 1/4" jacks for the input, stereo/mono outputs, and footswitch. A small back panel has the power switch, a standard modular AC power receptacle, and access to the PRO-3's fuse. The PRO-3 is shipped with a power cord and footswitches (see below).

The rotor compartment has two screened vents (slots, not louvres) in the front and one on each of the sides and back. Motion Sound says that about 60% of the sound comes through the front vents and 40% through the rear and sides, simulating a 147 treble rotor compartment with the back off and turned around.

Two rails run along the bottom from front to back and are intended to straddle the handle of a keyboard amp. It's a small point, but I wish the rails along the bottom were removable (they are nailed and glued on). While convenient for straddling the handle of many keyboard amps, they do not fit all amps and are not suitable for stacking on the popular SKB rack cases or on some small footprint speaker cabinets. The rails could be removed forceably, but then could not be cleanly reattached at a later time.

The PRO-3 is manufactured in the Draper Utah in the USA.

Signal Routing

An organ (or guitar, etc.) is plugged into a standard 1/4" jack in the PRO-3's front panel. The input signal goes to a crossover circuit which routes signal above 700Hz to a military grade solid state 30 watt amplifier and into an Eminence compression driver firing upward into the throat of a counter balanced rotating horn. The input signal below 700Hz is routed to an electronic bass rotor simulator which supplies stereo or mono audio output at a pair of 1/4" jacks located in the PRO-3's front panel.

It is intended that the user connect the bass rotor simulation output to a conventional amplifier input, such as a typical keyboard amp or mixing board. In this way, your organ's highs are being amplified by the PRO-3 and output through its treble rotor while the PRO-3's bass rotor simulation is being amplified by your keyboard amp. The acoustical properties of a physically rotating treble horn are preserved, and since the human ear is less discriminating of lower frequencies, it's not very noticeable that the bass rotor is an electronic simulation and not the real thing.

Personally, I'd rather that the PRO-3 input and output jacks had been placed in the back rather than on the front panel for more convenient use with effects and mixer racks. Many people (myself included) use their PRO-3 with a rackmount EQ and/or effects units and a line mixer. A typical example of such a signal routing looks like this:

organ --> reverb/EQ --> PRO-3 --> mixer --> amp

Since the PRO-3's input and output jacks are in the front while rackmount boxes use the back, you need longer cords (I use 6 footers) to patch the PRO-3 into the signal path. This is inconvenient, messy, and a bit more prone to noise gathering than if the PRO-3 had rear-mounted jacks. Perhaps Motion Sound felt that when used with a front patching combo keyboard amp, front-mounted jacks would be easier. But many keyboard amps (the Barbetta comes to mind) are patched from the rear.


The PRO-3 front panel volume control is actually a 100K input attenuator in front of the PRO-3 pre-amp, which always runs at full gain. The PRO-3 uses a military grade 30 watts RMS solid state .3% distortion amp and it is astonishingly loud.

The front panel also contains a "Limiter" control, which controls a soft clipping ceiling type circuit that does nothing until the unit volume increases to the level the limiter circuit is set for. >From that point, the "limiter" clipping effect becomes more pronounced and distortion becomes more audible through the PRO-3's treble driver. This can be used to create distortion effects, but the distortion you hear is typical of solid state distortion (ie: not the warm tube Leslie distortion so many of us know and love). As you move the limiter control clockwise the effect comes on sooner and the clipping becomes steeper, yielding more distortion in the output.

In addition to the two front panel controls, the PRO-3's internal circuit board has slotted potentiometers that can be tweaked with a small screw driver to alter the treble and bass rotation speeds, rotor acceleration/deceleration times, bass rotor effect center, and bass rotor L/R balance for stereo use. The PRO-3 owner's manual describes how to take the PRO-3 apart (there's a trick to it) and also describes the internal adjustments in detail.

There is common disagreement on what the "correct" acceleration and deceleration speeds are for good Leslie simulation and so the ability to tweak this value on the PRO-3 is important. Motion Sound says that the default settings were chosen to match the characteristics of a Leslie 147 in peak maintenance operation. But older Leslies or those having less frequent maintenance often have slower accel/decel times so it is difficult to characterize typical accel/decel times and individual tastes vary widely. After initial production had begun and partly because of feedback on the Hammond list, Motion Sound made a great move in adding the accel/decel internal adjustment. Also, using the PRO-3's rotation speed internal adjustments one can achieve the various rotation speeds available with the 147 (and similar units) through belt/pully seating.

The PRO-3 comes with a footswitch box containing two foot switches and a cord with a 1/4" TRS plug. One switch toggles the rotors between fast and slow and the other switch is a "brake" which allows the rotor to spin down to a stop when not in fast mode. This simulates a two rotor Leslie whose slow motor has been unplugged, a favorite technique of some organists. Alternatively, the PRO-3 can accomodate a typical guitar amp footswitch with a standard mono 1/4" plug to control fast/slow operation only (no brake).


So what's a PRO-3 sound like? Well, it sounds more like a Leslie than any electronic simulator I know, which of course is no surprise given it's physical properties. To my own ear, when mated with a high quality amplifier for the bass rotor simulation, it's comparable to any of the solid state Leslies and better than some of them. It falls a little short of the "gold standard" tube driven screaming Leslie 122/147, but still in all the PRO-3 is a very impressive sounding product.

Treble Tonality

It is a point of controversy that in the PRO-3 design Motion Sound has chosen a crossover point of 700Hz between the treble rotor and bass rotor simulation, rather than the traditional 800Hz crossover point used in Leslie amps. In addition, the crossover circuit has a slope of 18db/octave, rather than the less steep 12db/octave found in Leslie amplifiers. When questioned on this point, Motion Sound says they chose the crossover numbers that sounded best given the PRO-3 driver and horn characteristics. They felt the driver sounded better when sent signal down to 700Hz rather than the traditional 800Hz, and the steeper 18db/octave slope was then needed to keep damaging bass out of the horn.

The driver chosen is made by Eminence and has a fairly bright high end. This maybe desirable for guitar players, but organists interested in emulating a classic B-3/Leslie sound should consider placing an 15 band equalizer between the organ and the PRO-3 to filter out some of the highs above, say, 4-6kHz. This is especially important if you're playing a B-3 clone (such as the XB-2) as many clones have more highs than the B-3 and while this is less noticeable through a classic Leslie, the PRO-3 may make your clone sound a bit shrill.

The crossover characteristics and the choice of driver combine to give the PRO-3 a tonal personality that's a little different from that of a Leslie. I find that the top octave of my XB-2 has a little less punch with the PRO-3 than with a Leslie, perhaps because the bass rotor signal doesn't go as high in the frequency spectrum as it does in a Leslie due to the 18db/octave drop-off centered at 700Hz rather than 12db/octave at 800Hz. My XB-2's high end output is faithfully reproduced by the Eminence driver, but the XB-2 high end (and that of other clones) is considerably shriller than that of a B-3 so this is not an advantage. Still, the shrillness is pretty easily cured with an EQ or tone adjustment on the organ and the lack of punch in the top octave is not pronounced enough to be considered a major flaw.

The PRO-3 rotor uses a flared eliptical horn shape and is counter-balanced using a weight on a threaded shaft. This is different from a Leslie, which has a longer flared conical horn with a round opening and uses a matching horn as a counter-balance (only one of the Leslie horns actually works!). The PRO-3 horn is white in color (Leslie horns are black) and it can be easily seen spinning inside the PRO-3. Some people don't like the look of the white horn, but I like being able to glance at the PRO-3 in low gig lighting and see if it's going fast or slow.

The stock Leslie treble horns have conical diffusers stuck in the ends which are designed to increase the frequency modulation (doppler effect) of the sound coming out of them. Removing the diffusers decreases frequency modulation and increases amplitude modulation, a sound some people prefer. It is also said that removing the diffusers makes the Leslie a little louder. Whether a Leslie sounds better with the diffusers in or out is a matter of personal taste and a subject of endless debate. The unique shape of the PRO-3 horn is an attempt to increase frequency modulation while preserving the amplitude modulation heard from an open Leslie horn. I can notice that the PRO-3 has a bit more frequency modulation than my Leslie with the diffusers removed, especially when spinning slowly. I like this sound better, but your mileage may vary.

Bass Tonality

The PRO-3's requirement that you provide amplification for the bass rotor simulator is both its greatest strength and its greatest weakness. If you use a poor quality amplifier for the bass rotor simulation, the PRO-3 will sound poor, whereas if you use an excellent quality amplifier for the bass rotor simulation, the PRO-3 will sound excellent. This is because a wide range of the tone generated by an organ comes out of both the treble and bass rotors, making the quality of the bass rotor amplification crucial to good tone. If you disconnect the bass speaker and play only through the treble rotor of the PRO-3 or any Leslie, what you hear is tinny, honky, and unpleasant. Most of the warmth, body, and punch of the organ tone comes from the bass rotor, even though the treble rotor provides most of the audible rotational effect. Consequently, a good bass rotor amp makes the PRO-3 sound good while a poor bass rotor amp makes it sound poor.

With that said, you should get the idea that it's very important to mate the PRO-3 to a good quality amplifier for the bass rotor simulation. Some people have reported excellent results mating the PRO-3 to a Barbetta 32C, a high quality keyboard amp. I use my PRO-3 with a 400 watt Crown power amp and a very high quality JBL PA enclosure, as do some other hammond list members. Using this combination, my organ rig is louder, cleaner, and punchier than any solid state Leslie I know of; not because the PRO-3 has a better rotor/driver/amp than the solid state Leslies, but because the bass section I've mated the PRO-3 with has far more power and equal or better speaker quality than the solid state Leslies. In this way, I consider that the PRO-3 affords me the opportunity to assemble a killer organ amplification system from the components I choose. Were I using an integrated Leslie combo amp, I'd be constrained to the power and speaker choices made by the manufacturer, unless I had extensive modifications done to the Leslie.


To get the best sound from your a PRO-3, you have to find the proper volume balance between the PRO-3's treble horn, and your amplification of the bass rotor simulation. This is considerably trickier than you might expect, but with some practice I find I can do it quickly. Once you get the balance right you don't have to mess with it again until the next gig because the PRO-3's volume control adjusts the volume of both the treble rotor amplifier and the bass rotor simulator output signal. I find that different room conditions etc, cause me to make small adjustments in the balance between gigs.

When using the PRO-3 with a PA system, you can run the bass rotor simulation direct to the house and mic up the PRO-3, but consider running the PRO-3 bass rotor signal and mic(s) into your keyboard mixer and amp, then to the house board. This will give you control of the treble/bass balance, something I don't think I'd trust to the average sound guy.

Portability and Expense

Since the components of my system are separate modules, my rig is far more portable and storable than even the smallest Leslie. While the combined pieces of my component rig weigh an amount similar to that of the smallest Leslie, I carry the components of my system separately, which means a few more trips to/from the car at gigs than when I was using a Leslie, but my back is much happier for it. The PRO-3 itself weighs a mere 26 lbs, less than even my effects rack!

When considering the expense of a PRO-3, you need to evaluate the expense of the entire amplification system. You may already have a keyboard amplification system for other keyboards you use. If that system is adequate for your other keyboard needs and you have a spare channel (or mixer input), that system will probably be adequate for your PRO-3 needs.

If you need to get an amp to use with the PRO-3, you should carefully compare the PRO-3 plus an amp to a new or used Leslie according to your price and portability constraints. In the USA in 1995 the PRO-3 street prices were between $525 and $600.

Motion Sound

I believe that a key apsect of a product is the manufacturer's (and dealer's) attitude toward their customers. I try not to give my money to a company that is not very interested in my satisfaction and continued business. I was among the very first buyers of the PRO-3, and I realized at the time of purchase that Motion Sound was a tiny company made up of a few entrepreneurs offering their first product. Normally I would be reluctant to buy in such a situation, but the attractiveness of the product was great enough that I decided to take a chance.

I'm glad to say that in spite of some potentially serious "new product" type problems with my PRO-3, that I would not hesitate to buy again from Motion Sound and can enthusiastically recommend them on the weight of their highly ethical business practices, their readiness to make full disclosures about all problems they are experiencing, and their eagerness to go to extremes to correct all problems.

Motion Sound was having trouble with blown drivers among the first several hundred of their units sold. It turns out that there was a problem with the assembly of drivers at the driver manufacturer (Eminence) which has since been corrected by reinforcing the driver with a silicon bonding treatment. I had the displeasure of having both the original and replacement drivers blow. Motion Sound clearly understood that this was completely unexceptable. They replaced first the original driver, then when the replacement driver blew they replaced my entire PRO-3 unit, all at their expense. After correcting the driver problems, Motion Sound extended an offer of free trade-in to all holders of the old drivers (those drivers NOT labeled "MS") for new reinforced drivers.

While one might expect a manufacturer to go to such lengths to assure customer satisfaction, my experience is that normally they do not. And usually a manufacturer will refer all problems to the dealer, but Motion Sound was happy to deal with me directly which demystified the process for me and also gave me quicker turnaround.

In addition, several improvements were incorporated into the PRO-3 during the first several months of manufacture. These changes add an internal pot to control rotor acceleration rates and also to improve the treble rotor tonality and significantly increase the output level of the bass rotor simulator. Motion Sound has offered free upgrade kits to owners of the original units. Glitches and early improvements are common in new products being offered by small new companies, but Motion Sound's service and consideration of the owners of the early products is unprecedented in my experience.

Motion Sound principle John Fisher is a subscriber of the Hammond list and has announced all PRO-3 modifications and offers to the list readership. He also has occasionally asked for list member input on Motion Sound products. I appreciate this sort of open exchange with a manufacturer. Thanks John.


For my money, the PRO-3 is an excellent product that offers many advantages to those who want a high quality Leslie sound in a very portable package. As with any product, there are features I like and don't like and things I'd like to see improved, but the PRO-3 offers an excellent Leslie sound and a great alternative to lugging a heavy weight Leslie around to gigs, and at a reasonable price. Anyone in the market for a Leslie or a Leslie simulator should take a very close look at the PRO-3.

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