Help with a DIY leslie

[mistercooper]

Hello all,

I just picked up a beautiful old tube powered turntable from goodwill for $2.  Its got a tweed covered speaker built into the front and its completely enclosed.  I believe It would make an excellent candidate for some sort of rotary speaker cab.  Most of what I'm hung up on is how to get a wire to the speaker on the platter if it will just keep twisting up every rotation?  How did leslie manage this?  Is there any easy way to get around it?

I would also be happy for any general rotary speaker advice in general if you have experience with 'em.

Thanks,

Coop

[R.G.]

For the woofer, the real leslies spun a baffle over a top-firing speaker, not the entire speaker.

The horns did spin, I think.

[Tubebass]

Actually the Leslie's high frequency section had a horn driver firing upward through a bearing into the rotating horn. The second horn was a dummy and was there only to balance the rotating mass of the working horn.
Trying to get Leslie-like sounds out of a record player could be challenging, though, as fast speed on a Leslie was 3 or 4 hundred RPM.

[RLBJR65]

Mark Hammer has some gut shots of a couple. http://hammer.ampage.org/
Here http://hammer.ampage.org/files/Spinner.ZIP and here http://hammer.ampage.org/files/Leslie.pdf

You could spin the speakers if you came up with some brushes and a couple slip rings to connect the wires to. Car alternators use them.
This is known to be noisy though since the slip rings and brushes will wear and the brushes can bounce. Might not be to bad?

[Mark Hammer]

There is something called a "commutator" which is essentially a continuous set of fixed contacts that another set of movable contacts can follow.  Electric trains use a largely straight version of this principle, though one can also have them in a rotary configuration.  I know we used to use them in a research lab, years ago when we needed to record from brain electrodes implanted in animals that had full free range of movement.  Sure we could use wires, but it wouldn't take too much trotting around sniffing the corners of the enclosure before the wires got all twisted, so the commutator allowed the contacts to move with the animal.

[Dean Hazelwanter]

One possibility for a DIY commutator is a 1/4" plug and jack, used as one of the pivot points. I don't know how well the contact points would hold up though. I wouldn't try it with a tube amp at first - they really hate being run with no load, which is what the amp would see if the connection were poor or intermittent.

[Headshot]

Leslie used something called a "Mercotac" to make the connection, while allowing it to spin.  Basically the contacts are suspended in Mercury and that allows them to spin.  Check out:  www.mercotac.com

[Dave_B]

There's some general info on the Wiki, along with some DIY links.

[idlechatterbox]

Some constant-speed propeller governors used on aircraft include a system similar to the commutator and brushes on motors, alternators, etc. The governors just need to maintain current flow (which is what you seem to need), whereas the commutator and brush arrangement has to take into account EMF, phase, etc. (which would not be a concern for you, if I understand what you're trying to do).

That's not to say that you need to get your hands on a prop governor (though in terms of coolness factor, that would make for a sweet stompbox gizmo!). But maybe looking at some of the designs would give you some ideas, since from an engineering standpoint, the goal is the same, to make sure that current flow is maintained while the axle turns.

Some things to bear in mind is that a lot of electrical applications (motors, generators, etc.) also have to worry about arc-ing (which can fry the small brushes and pockmark the surface of the cylinder) that you would not have to concern yourself with, unless you also WANT small lightening bolts (again, the cool factor).

In your case, some crude arrangment of something like a pizza wheel cutter, perhaps with 2 or 3 spaced evenly about the contact point, to pick up the slack in case there was a "bump," would work.

You could always combine the ideas: have Mark H rig up some rats with wires, put them onto one of those rat "exercise wheels" and have that connected to a pulley that rotated the speaker. On top of the speaker, put 3-4 prop blades.... Just kidding. 

It sounds like a really interesting project. Sometimes you end up with something really original when you try that kind of thing, even if what you wanted never really worked (though I think your idea should work). Either way, good luck and I'd be interested to see how it comes out. 



* The big "nipple" in the middle of most propellers houses the governor; current flow is needed to heat it for de-icing, among other things.