In the last letter of this thread, Robbie was wondering,
>[ 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.
The reason I didn't mention pressures is because that is almost never
the case. Weak valves are very seldom seen in just one section of the
stack, and not throughout. Mechanical resistance is more often seen
in one section than another, but that is found fairly easily underneath
the piano at the stack by just feeling the differences. Lost motion
is also easy to detect by raising the striker and feeling it touch the
When a problem with a weak section arises, it is almost always in
connection with roll play. Mario said they were the same notes which
were weak on the test roll. That gave me the clue-- probably theme
(solo). But I should have asked also if it was during accompaniment
or theme tests, or both? If it was primarily at low intensities?
And how the chord build-up tests performed at low intensities?
When a Duo-Art plays, the intensity of the note at the lower pressures
is dependent upon how many notes play at one time. The dependency
decreases as the pressure is raised. Everything is controlled by the
roll, so performance is determined entirely by the roll. If the
weakness is the expression box, then a manometer would probably never
catch it because the time required to react would be during a faint
(low pressure) theme accent perforation.
However, you can test one note at a time by removing the sustain pedal
control tube, thus raising the dampers, and running the single note
test with the expression on the full length of the note compass,
slowly. Each note should play evenly at zero intensity. Do the same
test again by first pulling off the bass theme tube at the theme valve
box, and then the next run, pull off the treble theme TB tube, same
box, then remove both. The themed side of the stack in each case
should be very slightly louder. When you remove both tubes from the
tracker bar, both sides should be the same. If, for some reason, your
treble side of the stack is not louder but the bass is, the problem
is definitely in the expression box.