Leslie 122 Project - updated Mar 2005
Due to the large number of enquiries regarding this webpage...................
Please note - this project was put on my website to show how I aproached some of the difficulties of constructing a Leslie from scratch. It was never intended as a step by step construction project for others to follow. Because of this I am unable to supply plans or provide detailed help to other constructors.
On some alcohol enriched evening in 2002 I decided to build my own Leslie 122 - from scratch. Partly due to the fact that they are rare and expensive here in Australia, and fuelled with the desire to own "that" sound, I thought, why not? How hard can it be. Fortunately, there was a wealth of material available via sites on the Hammond Web Ring and on the Hamtech List archives, and I was able to do download schematics, pictures, dimensions, descriptions etc. I wouldn't recommend anyone attempt this without substantial woodworking & electronics experience. Having said that, it has been a challenging and rewarding experience so far.
Here are some of the specifications I decided on:
- Cabinet 19mm (3/4") high quality plywood
- Amp 40W class AB1 auto cathode biased output tubes, balanced XLR input +4 dBu
- Passive crossover 820hz, built as per original - coils hand wound.
- Treble driver - original Jensen unit supplied by Mel Music Australia
- Treble horn from Goff Professional
- Bass driver JBL 2205B 15" 16ohm.
- Bass rotor - constructed from 9mm ply, built from pictures !!
- Bass rotor pulley - alloy - from scrapped washing machine !!
- Bass and treble motors - both 12 DC - ex sagem teleprinter. These are precision low noise units.
- Rotor speeds individually adjustable via preset trimpots on rear panel. 5 Speeds - off, 2 slow & 2 fast speeds.
- Drive belts - Bass Rotor 8mm O-ring cord, Treble Rotor 6mm O ring cord. Joined with Loctite 401.
Cutting the Louvres, - the biggest challenge. Tip - run the grain crossways (I didn't) the louvres are easier to cut running with the grain !
It became apparent early on that the shape of the louvres was a critical element in the Leslie's sound. so it was important to get them right. Also, I learned that this had been a major stumbling block for other constructors. I had to build a special tool to cut the Louvres. After much trial and error, this is what I ended up with. The blades are High Speed Steel and shaped on a grinding wheel, then set in a piece of plain steel. The tool fits on a Ryobi 1300W cicular saw with 5/8" arbour. Cuts are made from both sides of the ply panel, the straight edge of the tool lining up at the same position on each side of the work. This gives the classic "scooped" louvre. Each louvre took 5 passes from each side, starting shallow and ending up about 3/32" from the opposite side.
Louvre Cutting tool on Circular Saw Louvre Cutting tool - profile Louvre Cutting tool - side view
Click this link for Specification Drawing of Louvres
Bass Rotor & pulley (from washing machine), upper and lower baffles, DC motor and "O" ring drive belt
Passive crossover, Jensen Treble driver, Treble horn from Goff.
Bass Rotor in cabinet - before cutting louvres.
Components - Class AB1 Power Amp, Jensen Treble driver, Treble Horn, DC motor. The Amp will be modified to 122 specs
The Panels and shelves in position for Assembly (don' know why the tennis ball is there)
Detail of upper horn after cabinet assembly and finishing
The drive belt is soft rubber o-ring material - from a pool shop-
they make the filter gaskets from it. Available in several thicknesses
about $1 per meter. Joined with loctite 401 - a good superglue.
Motor bracket slides to set belt tension.
Rear panel showing AC power cord, Five pin din connector to DIY half moon switch (attaches to organ with velcro)
There are 5 speeds - 2 slow, 2 fast and off in the centre, each speed for upper and lower rotor is fully adjustable
with the 8 trim pots visible on the panel. This is the big advantage of DC motors. Amp input is balanced XLR connector
on the chasis, Input level trim on the left. Click here for Revised Motor Control Circuit including Dynamic Braking. Half moon
switch is a 5 way single-ganged rotary switch. (Similar to a Strat 5 way pickup switch)
General view inside without back. That's an EV 15 " on trial in there. ( Now a JBL 2205B)
Decided to use a front-back brace. Heat sink is for motor control transistors.
Lower drive belt is 8mm soft rubber o-ring. Motor bracket is
Hinged with spring for belt tension. Bass Rotor takes about 5 seconds
to hit top speed of around 360 rpm.
Finished - kickboard timber is a little larger than original,- on castors - this thing weighs a ton.