[sdiy] Hammond Organ Query

[Tim Parkhurst]

Here's a little more information from

http://theatreorgans.com/hammond/faq/hammond-faq.html#SEC3
*******************
"The secret of the Hammond tone wheel organ lies in its method of tone
production. The tone generator assembly consists of an AC synchronous motor
connected to a geartrain which drives a series of tone wheels, each of which
rotates adjacent to a magnet and coil assembly. The number of bumps on each
wheel in combination with the rotational speed determines the pitch produced
by a particular tone wheel assembly. The pitches approximate even-tempered
tuning, (it's done with integer math after all)."
*******************

So it looks like perhaps there is a common drive shaft with a slightly
different diameter / tooth count gear driving each tone wheel. By varying
the drive ratios between the common shaft and each the tone wheel,
fractionally different frequencies can be derived.

Tim Servo

> -----Original Message-----
> From: Roman [mailto:modular at go2.pl]
> Sent: Friday, October 25, 2002 3:08 PM
> To: Tim Parkhurst; 'Tim Ressel'; synth-diy at dropmix.xs4all.nl
> Subject: Odp: [sdiy] Hammond Organ Query
> 
> but the teeth count cannot be fractional, so in order to have decent
> tempered scale, there has to be 100s of teeth, like divide ratios in top
> octave dividers. So if there's only one shaft, and all wheels rotate
> at one speed, the lowest note must have about 100 teeth, the highest...
> I'm affraid to even think how many.
> It must be done another, probably obvious, way. So? How is it done?
> 
> Roman
> 
> ----- Original Message -----
> From: Tim Parkhurst <tparkhurst at siliconbandwidth.com>
> To: 'Tim Ressel' <madhun2001 at yahoo.com>; <synth-diy at dropmix.xs4all.nl>
> Sent: Friday, October 25, 2002 8:00 PM
> Subject: RE: [sdiy] Hammond Organ Query
> 
> 
> > Hi Other Tim,
> >
> > Remember that the Hammond used a bunch of "gears" (really just toothed
> > wheels) all mounted on one common shaft. No gear ratios are involved
> since
> > the gears don't mesh together or drive anything. They just made each
> wheel
> > smaller or larger to give it the right number of teeth.
> >
> > Tim Servo
> >
> > > -----Original Message-----
> > > From: Tim Ressel [mailto:madhun2001 at yahoo.com]
> > > Sent: Friday, October 25, 2002 10:25 AM
> > > To: synth-diy at dropmix.xs4all.nl
> > > Subject: [sdiy] Hammond Organ Query
> > >
> > > Mass Brain Query:
> > >
> > > On the Hammond organ the tone generators were
> > > gear-tooth wheels ... so like, does it use
> > > just-intonation? Seems like it would have to so the
> > > ratios come out even. Equal temperment (an ironic term
> > > to use with this crowd :-) generates all these nasty
> > > irrational numbers that would be difficult to make
> > > with gear ratios.
> > >
> > > ?????
> > >
> > > --TR
> > >
> > >
> > > __________________________________________________
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> >
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