Robbie, You note that "Mike Ames mentions that the DC output polarity
of the converter can change from one starting to the next.  A diode
bridge could be added if needed, to ensure consistent polarity."

The converter starts up in CW or CCW rotation randomly.  I suspect that
this was an accident when they were first designed it but they didn't
change for this reason.  Randomly applied DC prevents the electromagnets
from seeing the same polarity all the time so they don't develop
residual magnetism.

In practice, I don't think it matters too much, providing that you
switch the polarity occasionally.  In fact, I think Mike's MIDI Violano
system  has fixed polarity, so it probably doesn't matter at all.  So
Mike, what would happen if someone decided to reverse the polarity on
a MIDI-fied Violano?

Regards
Craig Smith near Rochester NY  USA