Duo-Art Repetition problems in a particular section of the piano
(provided we can rule out the piano action itself), are usually caused
by a problem either in the expression cutouts (note cutouts) or the
Duo-Art expression box.
Few rebuilders take the time to open an expression box and restore it
thoroughly. If this hasn't been done, then there's no telling what it
could be. Instead of going into detail here, I would ask Mario
Solimbergo if he knows what I speak of, and if he has first checked the
MMD Archives. It's hard to guess what he already understands about
this process, and what information he yet needs. But for a Duo-Art to
be responsive, this must not only be done correctly, but must also be
tested, and it cannot be done (at all) with carpenter glues. You have
one chance, and one only, to get the two halves of the box back together
again in an airtight fashion, and so only hot hide glue, which sets by
gelling, is capable of assuring you of an airtight bond throughout --
the first time -- since it's difficult to doctor and test the joints
The first and most obvious problem to look for in the expression box
would be a leaky bass flap valve. If these aren't sealing perfectly
and quickly, then one side of the box will favor the other during soft
solo passages. But there are other problems about the expression
joints that will cause a similar problem, not to mention the pouch
valves, one of which may not seal properly.
The note cutouts are sneaky little culprits which few people seem to
mention. They are taken for granted. But if you want to hear the
difference momentarily, just bypass them with brass nipples and a short
length of tubing to take the place of the 4" or so through the cutout
box, and quite often you will hear an amazing difference.
The reason is because what is called a "note cutout" selects the four
expressions holes on either end of the trackerbar. With just one
resistive path through the box, a certain combination of intensities
will be missing. Since it was the treble that was weak, it may be
found that the problem is only in the solo side of the box, and only
when very light accents are used, we'll say. If it misses these on
occasion, then you have an intermittent problem with expression,
actually. This almost always shows up in the treble, since more often
the faint solo expressions will be up there, instead of in the bass,
and because one notices a missed treble note more than a missed
incidental note in the bass.
However, there is always the possibility of a stack problem of course.
A progressive error of pneumatic placement, stiff hinges, tight striker
guides, and other mechanical problems from end to end will contribute.
For example, I have found that as simple a thing as loosening the
bottom (captive) leather nut on the pneumatic finger fixed a similar
problem for one or two notes. While I have never run into a whole
section like that, it isn't too unlikely.
[ Mario, could you connect a water-tube manometer to the player, and
[ compare the suction data, of bass vs. treble? This data will help
[ to determine if the problem is pneumatic or mechanical. -- Robbie