From harjoy@elknet.net Wed Jul 13 07:48:53 2005
Subject:Re: A little Leslie history - motors spinning in opposite directions

From: joek1000
> I started thinking about replacing the upwards pointing motor in the
330 with a motor that points downward. >I
asked Harvey Olsen about it and here is his response. BTW, Harvey is
a retired tech who was personal friends with Don Leslie.

>I thought it might be interesting to some readers on the list....

Subject: Re: Leslie question

<< I have another Leslie question! I have a 330 that works fine
but I'm not crazy about how the top and bottom both spin in the same
direction. I noticed a dramatic difference in the sound compared to
the opposite rotation of the 147. >>

Joe:

>For starters this is not a defect. I once asked Don Leslie about this
"problem" but he thought any discussion of rotor direction was
silly. The fact that some models have rotors that spin in the same
direction, and others where the direction is reversed was
unintentional. No one even thought about rotor direction when these
Leslies were designed.

>The direction that a Leslie rotor spins is entirely dependant on how
the motor is mounted in the cabinet. Very early Leslies like the
original "30 series" (30A. 31A, 31W, and 31H) had their lower
motors flipped around so the drive pulley was underneath. As a
result, the rotors spun in opposite directions.

About a dozen years ago Keyboard magazine in an article about Hammonds and/or Leslies related an experience Al (?) Goff had had in that he was trying to determine why two Leslies sounded so different from each other. He had used a scope, etc. and was not gainining on any cause. Then he happened to notice looking into the backs of the Leslies that one of them had same direcction of rotation on both motors, the other had opposites.

This is simple to change by reversing the stator in the motor relative to the rotor. The idler should be reassigned to the slack side of the belt.

It apparently didn't "bother" Don Leslie nor much bother Leslie manufacturers. However, after customers pointed out that the 122A first mode;s were being built with same rotation on motors, they switched to providing opposite rotation standard. It would be interesting to know if the Motion Sound MS 1771 uses opposite rotation.

Obviously there are some variables- including different ears. It is very easy to fool oneself on any A- B comparison. I am sure anyone that changes from same direction to opposites will say it's better- I though so.

The other things people have opinions on are wood or foam rotors- with or without cloth (probably about no effect), and cotton filter in or out of horn (probably no effect), and cabinet materials IMO some effect.

Also there is a matter of the "baffles" in the treble rotor, which will change the amount of frequency modulation and amplitude modulation.

Then there is the matter of back panels:
the center panel should be on and tight for good bass response. The top and bottom panels may reduce "engine noise" (motors, belts). Also to quote Tony Monaco the cov
ers keep you from getting some fingers mashed in the spin!

BTW the Leslie speaker does a very unique job on sound and even with some pretty good mimics out there in the VK-7, Electro, etc. most of these have to rank as a substitute, not a preference.

Harold

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