The Decimator


Spinning Wall of Leslie Death

I have recently put together the most awesome leslie rig of my musical career ("leslie" meaning "generic name for rotating speaker", not the brand.) This ends a 30+ year quest for "that sound". Read on for the details.

My Background

I have been modifying and building leslies since I bought my first Leslie 45 in 1968. I have experimented with changing drivers, speakers, crossovers, and amps. I have built my own cabinets, including a 2 piece system with JBL and Gauss components powered by Crown. I've tried deflectors off and on. For one reason or another, nothing has ever been a great solution for awesome tone, portability, and volume.

Criteria for my ideal leslie

  • Size and weight - a real leslie cabinet, whether short boy or tall boy, is a bulky awkward thing to move. I want something that is easily transportable.
  • Volume - it has to be LOUD enough to hear onstage. You can always put some in the monitor, but I prefer the sound straight off the cabinet.
  • Tone - I have had loud clean leslies before, but over the years I have come back to the classic overdriven tube leslie amp sound as the ideal. There is nothing like that warm thick fat sound for electric blues and rock organ.

The Problems

The Leslie 122 or 145 amp has the ideal tone. But at 40 watts, it can't cut a stage live, much to the dismay of rock and blues organists everywhere. I'm not up for carrying 4 leslies to a gig like some guys used to do. Go to a solid state amp for power, and you lose the tone. Shrink the cab too much, and you lose the bass.

My Rig

My rig consists of a Speakeasy Absolute Modelling Amplifier, a QSC PLX 1804 power amp, a Speakeasy Roadbox 3 rotary cabinet, and a Speakeasy Roadbox 3 Convertible cabinet. I have also added a dbx dual 15 band EQ for overall tonal shaping.

The Roadbox 3 cab has everything in one box and replaces the bottom rotor with a forward firing speaker, while the Convertible retains the rotor but moves the horn into a separate box for portability. They both use single lightweight motors with speed controllers instead of the heavier traditional 2 motor systems. My Roadbox 3 cab came with a 60W tube amp and a tube preamp which I have removed and am not currently using. Another mod I have made is replacing the stock titanium driver with the same high powered phenolic driver that comes with the Convertible.

To me, two leslies is the ideal number for a deluxe rig, as you get this amazing swirling sound on tremolo. I can use both for recording and for gigs on large concert stages, but I can take one or the other for smaller venues. While a real short boy leslie clocks in at around 130 lbs, these cabs are about 75 lbs, and are considerably more compact.

The amount of bass they project is amazing however! The combination of straight bass speaker and a rotor is also great. With the cabinets balanced in volume, I get a great solid bass along with the throbbing tremolo from the drum.

The QSC power amp delivers 600 watts to the 8 ohm Convertible, and about 330 watts to the 16 ohm RB3, for a total of close to 1000 watts of spinning leslie death!

I use the graphic EQ to fine tune the tone of the speakers and cabinets to match my real Leslie 142, and to bring out extra key click when I want it.

Disclaimer

I am not an employee or a compensated shill for Speakeasy Vintage Music. I AM a satisfied customer and enthusiastic endorser of their approach to tone.

The AMA

The heart of the system is the Absolute Modelling Amplifier. The AMA is the most amazing advance in high power leslies ever. Think of it as "instant classic leslie tone in a box". As of this writing, Speakeasy's own website doesn't have many details about the AMA, and there is a lot of confusion about this device on the web, so I'll go into a bit of detail.

The AMA is a 2U rack piece with a low powered leslie equivalent amp in it. However, the term "Amplifier" is kind of misleading, as it is used mainly like you would use an effects device.

And that is the magic solution right there - tube AMA for tone, high powered solid state amp for volume. Brilliant!

About Getting "That" Tone

Make no mistake. The classic overdriven leslie sound comes from the POWER AMP tubes being overdriven. Tube preamps alone are not sufficient to get this sound. I have done experiments with my AMA, and I would describe the preamp overdrive sound as somewhat fizzy while the power amp overdrive is smooth and velvety. When combining both, if I turn up the preamp overdrive too much, I get little episodes of "braaaap" intermodulation in the output.

Another interesting tone variant possible with the AMA/preamp combo is the severely overdriven guitar amp sound made famous by Jon Lord. For this, you throw the switch putting the preamp into high gain mode, and just crank.

Inside the Roadbox Convertible

The cabinets are built from birch ply, then covered in tough pickup bed liner skin.

This is the interior of the bass cabinet. Below, the wood rotor. From left to right: pouch with spare belt, motor, speaker input jack, Eminence Delta speaker, speed control back plate, MASSIVE crossover, speed control board and motor fuse.

The interior of the top cabinet contains the horn motor, driver, back plate, and pouch with spare belt.

AMA Details

The A channel in my unit has the preamp, with a high gain switch, preamp volume control and EQ pots. The PA Input jack bypasses the preamp and provides direct access to the power amp. This is where you would plug in a real Hammond console which has its own tube preamp.

The B channel is the power amp. The Power Amp Volume control is where you set the amount of overdrive (this corresponds directly to the volume control on a real Leslie tube amp), and the Lineout Level control is where you set your master volume.

On the back are jacks for power, a fuse holder, line output, and speaker output. Notice my crudely labelled 2nd Line Out jack, which I added myself to drive the second roadbox cabinet - I prefer that to making up a Y cable.

A multipin connector carries the line output signal and power to the roadbox cabinet. While 600 watt Roadbox cabinets use an external rack mounted power amp, the 250 watt cabinets have their solid state power amp built in.

Construction is first rate, starting with a heavy steel chassis and lots of metal shielding, and continuing with neat hand wired panel controls, high quality circuit boards, and tube sockets for the amp and preamp.

On the left you see the preamp, which models the AO-28 tube preamp in a Hammond console. On the right is the power amp which models the leslie amp.

The amp uses 10 watt 6V6 power tubes instead of the 40 watt 6550 tubes found in a real leslie amp, and has a speaker output that you could drive with those 10 watts if you wished. At the center back you can see the gold load resistor which absorbs the power in place of a speaker, when using only the line outputs.

Note all the extra transformers in the AMA. Each input and output is authentically transformer coupled, which helps capture true tube amp behavior when being overdriven.

Sound Recordings

Here are some recordings of rock riffs showcasing the overdriven tones you can obtain from the AMA. The organ used was a Nord Stage with all internal EQ, leslie sims, and amp sims turned off.

The fidelity of these recordings is not the greatest. It is recorded in mono from my digital camera's built in mic, and the resulting sound and video files don't have anything in the high end. Any hiss, warbling, or rattling sounds are coming from the recording gear or from vibrating objects in my basement! The leslie system itself is dead quiet.

Fortunately, a real Hammond and leslie don't reproduce anything much in the high end either, and these examples show the sound quality of the AMA very well.

Try to listen on some good headphones or a decent speaker system with some decent low end!

  1. Gregg Allman, Dreams. Just a touch of overdrive to sweeten it up. Vamp is 888000000 with percussion 3rd, soft, fast and C3 vibrato. Chorus is 8885030067 with no vibrato and fast leslie.
  2. Gregg Rolie, Mother's Daughter. That legendary dirty Santana organ that we love. Vamp is 888000000 C1 vibrato, and leslie stopped. Chorus is 888888888 with no vibrato and fast leslie.
  3. Tony Kaye, I've Seen All Good People. This is an example of medium overdrive on a brighter registration. 8885030067 with no vibrato, leslie chorale, and hall reverb from the Stage.
  4. Gary Wright, Waitin' For The Wind. Classic heavy Spooky Tooth riff with heavy overdrive. Vamp is 888000000 with leslie chorale. Chorus is 888888888 with C3 vibrato and fast leslie.
  5. Jon Lord, Space Truckin'. OK, now this is getting ridiculous! Emulating his famous Machine Head tone using Marshall amps, I have turned the preamp High Gain switch on, and cranked the Preamp volume and Power amp volume both up to about 75%. Registration is 888800222 but with this kind of heavy distortion, the registration doesn't much matter. Leslie is stopped.