I read Eliyahu Shahar's post about his Duo-Art piano:
> ... both the repeat and rewind pneumatics are operated by
> holes on the extremes of the tracker bar -- thus if we want
> to repeat the roll, they will be fighting against each other.
Usually, the hole in the take-up spool is used to trigger the
repeat function. That hole is uncovered near the end of the rewind
cycle, but before the rewind hole at the left side of the tracker bar
is exposed. Thus, the two function don't work against each other.
What is interesting and little known, is that through simple tubing
changes, the rewind and repeat functions can be triggered simultaneously
with the result of putting the transmission into neutral. This is
precisely the scheme of controlling the Duo-Art piano when used with
The rolls used in these demonstrations have a rewind perforation at
each spot on the roll where the piano part is "paused". The conductor
cues the piano to start playing again by pushing a button that
momentarily disables the "rewind" pneumatic, and the "repeat" pneumatic
throws the transmission back into the play position. The roll starts
moving forward instantly. This is because while "paused", the air
motor is still running and the entire stack is under vacuum.