[sdiy] OT: home organ Leslie hacking

[Roy J. Tellason]

On Thursday 13 January 2005 11:02 am, Scott Gravenhorst wrote:
> <rkmoore at memphis.edu> wrote:

<...>

> >Don't try to get too creative with speed control.  The leslie in my
> >home organ is a little single phase induction motor.  I've seen people
> >put rheostats in series with the motor to vary the voltage in an
> >attempt to vary the speed.  This will damage the motor.  These motors
> >are only meant to run at speeds related to the frequency of the AC
> >source.  If you have an inverter for the motor then you can shange the
> >motor speed.  I have added a switch to turn the motor on and off
> >because in my organ the leslie rotates constantly otherwise.

> Years ago, I built an induction motor speed control.  It operated a
> phonograph motor.  The only way to get this working correctly is to vary
> the frequency of the input power to the motor.  There are (at least) two
> general ways to accomplish this, a variable frequency "push pull"
> inverter which uses a center tapped transformer and two power
> transistors (or SCRs if you want to go that route) OR it can be done
> single ended with one power transistor and no transformer.  The second
> method works for motors that expect a light load.  Heavier loads will
> require the first method.  Note that there are some limitations with
> this, one being that the motor's winding and core are optimized for 60
> Hertz, so there's a frequency range limitation.  Push it too far outside
> this range (which I cannot begin to guess at) and the motor will heat up
> beyond it's tolerance.

This is interesting,  do you have details of this online anywhere?

I remember an article some years back in Popular Electronics,  I think it was, 
where they offered some sort of a device you could build to *slightly* vary 
the speed of a synchronous motor.

I never considered using one of these in a Leslie speaker,  but thought it 
would be kind of nifty to add pitch bend to a Hammond!  :-)