I am aware that a pedal Duo-Art is not held in high regard by owners
of full Duo-Arts, but in Tasmania these instruments are thin on the
ground, and I was lucky to find my Half D-A Steck upright.  However,
one question is niggling at me.

Unless I've got hold of the wrong end of the stick, in a full Duo-Art
both the Melody and the Accompaniment sides of the expression box are
fed the full vacuum being developed by the pump, and they modify it
according to the perforations along the sides of the roll.  In a pedal
Duo-Art, the melody level is generated by the pedaller, and this vacuum
is then modified by the single set of accordion pneumatics to deliver
the accompaniment level.

But doesn't this mean that the accompaniment level in a pedal D-A is
likely always to be less than that delivered by the same roll played
on a full D-A?  Then, in a soft passage, the accompaniment notes are
likely to drop out altogether on the pedal machine.

John Phillips

 [ Maybe the Accompaniment regulator outputs suction at a percentage
 [ of the Melody level.  If so, the coil spring will have been
 [ replaced by a "reference force pneumatic" connected to exhauster
 [ suction.  -- Robbie