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MMD > Archives > November 2014 > 2014.11.09 > 05Prev  Next

Regulating the Duo-Art Expression System
By Bob Taylor

This has been a good discussion and I would like to comment on
several of the points made by various contributors.  Using the test
roll, setting the optimum minimum intensity, notes that skip, reducing
the "too loud" problem, and understanding coding standards are issues
that have challenged most rebuilders.

It has been my observation that Duo-Art coding is inconsistent.  If
we are to believe the number three test roll, some skipping of single
notes is preferred during zero intensity while the sustain pedal is
off.  Yet, I have seen many rolls in which three notes are played at
zero intensity.  Clearly, this is a conflict of standards.

My recommendation is to partially ignore the test roll.  Keep a log.
When you notice the piano skipping, jot down the coding during the
event.  The next time regulation is required, refer to the log.  Set
zero intensity so that the piano consistently performs a very soft
pianissimo on your favorite rolls.

Some rolls are just have screwy coding and should not be used as
a standard for judging.  The perforator may have had a bad day when
the screwy roll was made, skipping snake bites or other coding holes.

The "too loud" problem occurs in most reproducing pianos.  Yes, the
late coding of pop Duo-Art rolls did reduce volume levels, but there is
more to this problem than that.  The real problem is one of regulation.
Ampicos, Duo-Arts, and to a lesser degree, Welte Licensees tend to play
too loud in the Mezzo Forte range.  Properly adjusting this range is
the key to a pleasing performance.

Regardless of the system, if the stack is above 10 or 12 inches of
vacuum, the piano will sound loud.  Usually, the pump spill valve can
be adjusted to aid in achieving a pleasing mezzo forte level.  Attempt
to get the pump pressure at its lowest level at zero intensity and
still yield reliable performance of sustain and soft pedal pneumatics,
or accordions.  Of course, the air motor must be running when this
setting is made.

Those of you familiar with the Ampico B system know that it introduces
air leaks through bleeds in several locations.  While we all ascribe
to the "air tight" rule, leaks are absolutely essential to regulate the
stack pressure.

As Julian Dyer likes to say, "You cannot regulate nothing".  What he
means by this, the expression system is a valve that allows air flow at
some degree.  If the stack is 100% air tight, with no notes being
played, there would be no flow to allow the valve to regulate properly.

Duo-Art knife valves do need a fair amount of flow to yield a good,
stable zero intensity.  If the stack is extremely tight, the knife
valve open area is very small.  Since that system has limited feedback,
transients can result in large drops in stack pressure.

Earlier contributors have mentioned that later Duo-Arts have atmosphere
bleeds in the expression system.  Those bleeds help the knife valve by
keeping them in a more open position, allowing for stable regulation.
It also helps correct for leaking knife valves.  If the knife valve leaks,
the valve may be totally closed when you set zero intensity.  In this
condition there is no compensation for transients.

Be flexible in finding what works best for you.  The Duo-Art system
can work beautifully.  It needs thorough understanding to get the best

Happy regulating!

Bob Taylor

(Message sent Sun 9 Nov 2014, 20:41:03 GMT, from time zone GMT-0700.)

Key Words in Subject:  Duo-Art, Expression, Regulating, System

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