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MMD > Archives > December 1997 > 1997.12.23 > 18Prev  Next


Duo-Art Adjustment and Missing Notes
By Craig Brougher

Bernt W. Damm was commenting on the export Duo-Art pianos he sees in
Africa, and in particular, the inadequacy of the test roll.  Good
Point!  I too have always wondered why Duo-Art didn't cut an
appropriately comprehensive test roll for concert regulation.

As it is, the test roll gets a technician in the "ball park," so to
speak.  After that, it takes many rolls to fine-tune the piano into
proper regulation.  Which means, you had better understand music, and
know what to listen for and how to achieve the effect you want, or
you're going to be in trouble with a Duo-Art.  This is because the
instrument relies totally on its roll for compensation,  which
presupposes that all Duo-Arts be up to factory specs.

Regarding the exceptions to that, however, I will relate that a friend
of mine who had rebuilt many Duo-Arts once found one whose expression
box theme valve hole in the bass had never been drilled!  (Pouch was
there-- just no hole above it!) So it does make one wonder just how
well they were all set up, doesn't it?

The way I have regulated the "zero adjustment" on Duo-Arts now for
decades is to use the note test and a piece of chalk.  By pulling the
sustain pedal trackerbar tube and turning on the Duo-Art On switch, the
note test will test every playing note for sensitivity and proper
operation, as Bernt has noted.  You can operate the rewind from under a
grand, and go back and forth over a particular part of the roll until
you catch the offending note or notes.

Then after you have done that and adjusted the sensitivity of the
notes, your theme arpeggios won't be a problem, since they respond
identically to weak playing notes.  You don't need a full compass on
theme arpeggio, once you've adjusted the piano to play accompaniment
intensity zero well.

Regarding the skipping notes when you replace the sustain valve's pouch
tube (which is better than depressing the pedal because it utilizes the
player), all the notes do not have to skip, of course.  What it means
is that the extra weight of the dampers should cause the marginal notes
to skip, which is normal.  You'll always have them.

The trick is to know how to adjust weak and strong notes out-- how to
even the player response to the piano touch.

If you have an overly strong note, there are two ways of weakening it
down.  You can start by placing a thick felt center rail punching under
its lifter finger and readjusting the striker rod nuts.  That causes
the pneumatic to start up from half-closed cloth, weakening the strike
a bit.  Or you can tighten the leather nuts on the striker finger a
bit, adding some resistance to the pneumatic that would be felt at the
lowest intensities only.

However, the differences between notes are greatly exacerbated when the
valves are set too close to the critical throttle-point (between .032
and .035 or so, depending on the leather used).  When Duo-Art valves or
valves in ANY reproducer player piano are set with small gaps (by a
rebuilder who wrongly believes that the valves will then play faster,
and with less travel losses), all they are doing is making life
miserable for themselves when it comes time to regulate the player
action to the piano.  To say "it can't be done" is very close to the
truth-- if not right on!

The idea of adding spring tension with a hammer butt spring and
increasing jack spring tension may be tempting but is not necessary,
and affects hand play.  That is not the way pianos should be regulated
in my opinion, just for the sake of getting a Duo-Art evenly regulated,
player-wise.

Bernt is at a decided disadvantage, I know, because of where he lives,
and because he probably feels that he is sort of a "sparrow on a
rooftop", a one-of-a-kind rebuilder who is trying to figure these
things out with what he has to work with.  So I can truly appreciate
his predicament.  I also suspect that most of his Duo-Arts are
uprights, which are much more difficult to fine-adjust.  I have at
times been at my wits' end with them!  So when I tell people I am
actually in the "aggra" business, I'm really talking about aggra-vation!

The basic overriding premise of all piano work is that if these
instruments were endorsed by concert artists without the need of
special hardware and helper springs (Hofmann owned a Weber Duo-Art
upright), then we can rebuild them the same way.  It isn't necessary!
The margins provided in the strength of the pneumatic at zero intensity
is sufficient to lift all but the toughest unregulated note at that
intensity (about 1/2 lb.) unless (usually) your jacks are set too far
under the knuckles, the knuckle is deformed, or your valve travel is
set too close.

When rebuilding the upright Duo-Arts, it is very important to use the
correct jack rest felt under the knuckles, or the action will be
extremely uneven and difficult to play.  Too thin a jack felt places
the tip of the jack too close to the butt center, to where a very small
difference of only a few thousandths creates huge differences in
playing force at the key.  Also, in upright Duo-Arts with a repetition
rail, it is very important to re-regulate that rail and fine-tune the
action to the new felt depressions gained, especially after new hammers
have been installed and the action re-regulated to them.

One other thing has also been a problem-- around here, at least.  Piano
tuners in this area had (and maybe still are) been using WD-40 to free
up stiff actions.  That works for just as long as it takes the oil to
penetrate and swell the wood around the centers.  (One tuner said, in
his own defense-- "Says right here on th' can, it ain't no grease and
it ain't no oil, so there." I should have asked, "Then why did you use
it to begin with?").

Forget the fact you end up with a terrible action to try to resurrect!
The only way I have been able to fix these actions is to laboriously
and steadily run a large, heavy-duty heat gun over the action parts,
boiling out the lubricant without burning the wood.  Then while
everything is still hot, displacing the remaining WD-40 with PROTEK
lubricant, waiting an hour, and soaking the action again.  I use a
large syringe to do this, now.  That way, I am able to put it where I
want it.

(Freshly applied PROTEK will always seem to free up an action, with or
without the heat, but it won't stay freed up without concentrated heat
applied.)

If we, as rebuilders, will discount a need for special modifications,
and rebuild that piano thoroughly so it can be regulated to a concert
touch, with a well-voiced sound, then there is no reason that our
player actions cannot be beautifully regulated to a piano like that,
unless-- there is an inherent problem with the player we have
completed.  And if there is, then there is no quick and dirty fix.

You have to pull that player out and re-regulate or repair it as many
times as necessary to get it right, and frankly no one will really ever
learn this art any other way.  As you do it, you gain knowledge.  We
can write books and talk about it, but that's just a starting point for
understanding it.

When it is felt that we should start modifying and redesigning the
pianos or revoicing the hammers extra soft to make up for other
problems that we don't understand, then we are, in effect, changing the
action and the tone in deference to a defective or maladjusted player
action.

Craig Brougher


(Message sent Tue 23 Dec 1997, 15:28:10 GMT, from time zone GMT.)

Key Words in Subject:  Adjustment, Duo-Art, Missing, Notes

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