From las8323@rs175174.ks.boeing.com Tue Oct 30 11:57:29 2001
Subject:Re: Boston Smokin'.....Pitch-bend????

Hey Dave,,
You think *you* can stray from the charter? why, you ain't seen
nothin' yet :-)
>
> It's been a long time since I've heard Smokin, but the Hammond TG's pitch
> control is a feedback control loop. What that means to the happy organist
> is that if you turn the organ off and on again, the organ goes flat, then
> sharp, then flat, then sharp, etc, and eventually (maybe 5 - 10 seconds)
> the organ settles in at the correct pitch again. The start motor gets the
> TG going a little on the fast side.

Unless I'm mistaken (hey! it's happened :-) there's no "feedback control
loop" in a Hammond with the possible exception of including the 60Hz
servo motor as a "mechanical" version (sorta strechin' it) of this 'loop'.
But there are no electronic resolvers, as such.

The process you describe, however real, is small and cyclical. Turning
the motor off, or (more brutally) engaging the start motor, will result
in a change of main armature revs BUT the main servo motor is self
centering and does so so quickly that these unsettlings are almost
percieved as unilateral.

The fluctuation in pitch (phugoid, hysteresis... take yer pick) is *always*
occuring, albeit microscopically. If you notice, the main drive is axially
coupled to the shaft through a spring. Additionally, "slip clutches",
essentially low friction slip discs, are installed on each of the
countershafts. This has been known to mystify even the Great Hammond
Experts (on another list). Any mechanism that rotates will
encounter "phasing" from imperfection, however slight, in alignment,
angular velocities, or balances. Laurens Hammond doubtless learned these
dynamics from his clockmaking days: phasing, or resonance summation,
will result in "rumble", random (or periodic) vibrato, and could
easliy sum to failure. Thus all the slipping stuff. The servo motor
runs rock steady, but the TG itself does not and certainly doesn't
remain completely locked to even itself, though well within most
peoples' pitch perception. This also adds to the mystic "richness"
from the mechanical archetype that the purpose built electronics
STILL have a hard time (though not impossible) in duplicating.

Just FYI.

What this also means is that smooth, predictable pitch bend is not
the easiest thing to do because the TG is SO inclined for stability.

>
> I guess I've strayed far enough from the CloneWheel charter (again) so I'll
> shut up now. ;-)
>
> Dave
>

Guess I'll shaddup now, too.

Larry