Bill Koenigsberg wrote in 160117 MMDigest about calibrating Duo-Art
reproducing pianos using test rolls. I have a test roll I got from
Klavier many years ago that says it is test roll #4 and it seems to
serve me well. I don't think they ever changed the response curve that
the pneumatic system was supposed to have to play the rolls properly.
I know I've commented before, here on the MMDigest, regarding the
calibration of the Duo-Art system. I think people tend to concentrate
on the section of the roll where it goes up and down the scale with the
damper rail on and off where the notes should sort of drop out with the
dampers on and play softly with the dampers off. I use a vacuum gauge
on this because when you get it right I look at the gauge to see where
it is as when you go to tighten the lock screw on the knife valve drive
shaft it changes the adjustment. If you watch the gauge as you are
tightening the lock screw you can avoid that.
Anyway, all that being said, the more important tests are the chord
test where they alternatively speak and don't speak at the different
intensity settings. If your Duo-Art is working properly they really
will do it. I think very often people have the intensity accordions
set up with way too much motion and therefore the chord tests fail.
The accordions are set correctly when they have a total travel from
"all off" to "all on" of 15/16ths inch. To check this, remove the
accordions from the expression box and see if you have the 15/16" of
total travel. If not, use drill bits of 1/2", 1/4", 1/8" and 1/16"
as your regulating tools. Roll the bits between the adjustable stop
screws and the stop felt, they should be pretty snug as you roll the
bits along the way. Duo-Arts have a reputation for playing too loud
and I believe that most often this is the reason why.
Also check the zeroing using a vacuum gauge. Set up the gauge and then
pull or push on the expression linkage to the stop point, not too hard,
just find the ambient rest point. Now, pull down on the linkage and
see if you get the same gauge reading after you release it. Very often
you will not, because very often there is friction somewhere in the
linkage. A typical friction point is on the knife valve drive shafts
themselves. Be sure to check them first by removing the connection
linkage to them and turning them by hand -- they should move without
any friction at all.
This work is best done with the expression box removed from the piano
and on a bench using a vacuum source. Hope this is a help to all the
Duo-Art lovers out there!
Ben Gottfried - Ben's Player Piano Service
Richfield Springs, New York