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MMD > Archives > April 2001 > 2001.04.22 > 01Prev  Next


Duo-Art Adjustment Tips
By Randolph Herr

I choose not to take any sides in the recent discussion on Duo-Art
expression boxes.  Of course, Confucius say "Man who walk in middle
of road get hit by carriages going both ways," but I am still going
to take my chances.  One good sign is that there are still people who
care about these things.

On the constructive side, I want to offer two tips on Duo-Arts that
I have not seen published.  The first is a simple and foolproof way
to measure the two regulator springs, without having to break out the
micrometer.  Simply connect the two springs by their hooks, and pull
them apart by the adjusting collars (assuming that both collars are in
the same position on both coils).  If you see one spring stretching
twice as much as another, you know its rate is half that of the stronger
spring, and so on.

The second tip is something I borrowed from the Model B Ampico.  One
thing that all less-than-perfect rebuilds have in common is some notes
that do not play at a whisper quiet level.  The only solution is to
raise the entire zero level of the piano, and now you have lost all
of the pianissimo and probably much of the next higher level as well.
The whole piano suffers because of this "lowest common denominator"
adjustment.

Even when these pianos were new they were not perfect, although the
tolerance between notes was a lot lower than the average rebuild today.
It appears that Aeolian tried to compensate for this by putting a weak
phosphor bronze wire spring in the hinge end of each pneumatic.  When
the piano was undergoing final regulation at the factory, notes just
a little weaker than their neighbors had the spring removed, thereby
making the pneumatic a little stronger.

This is where my system comes in: It is a method to give a Duo-Art
stack the note-compensating feature.  This method is totally reversible
and non-destructive, so here goes: You will notice that all three tiers
of the D-A stack rest on a red felt about 1/4" thick.  This felt must
be removed.  Next, place a leather nut and two thick balance rail
punchings directly under the wooden poppet at the top of the brass
threaded wire used on each note.

By careful adjustment, each pneumatic will seem to float 1/4" above
the wood where the red felt was previously glued.  It can't open any
further because of the new leather nut under the wooden poppet.  Now,
when you have a note that is weaker than its neighbors, you can adjust
the two leather nuts above and below the finger sticking out from each
pneumatic.  By making the pneumatic just a little stronger, you can get
the entire range of notes to play at pianissimo.

Incidentally, my previous article about "Goof-Off" as a "cure" for
Steinway  verdigris had some feedback from readers who felt it was
not a permanent solution.  Well, taking an aspirin for a headache,
or getting a Novocain shot from a dentist is not a permanent solution,
but it sure helps when you need it.  Putting in a completely new action
will not last forever, either.  It has been two months since I tried
the Goof-Off and the action is still loose-as-a-goose.  I have used
Protek in the past, and not had as good a result as with the Goof-Off.

I suspect that the reason is that the Goof-Off actually softens the
junk, and then allows the motion of the part to polish the pin in the
bushing.  All the Protek does is to act as a lubricant, without cleaning
and polishing the pins.  If the action gets sticky ten months or ten
years from now, just spend a few minutes re-applying the Goof-Off.  If
there is an easier or better solution, I would like to hear about it.

Randolph Herr


(Message sent Sun 22 Apr 2001, 16:39:28 GMT, from time zone GMT-0400.)

Key Words in Subject:  Adjustment, Duo-Art, Tips

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