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MMD > Archives > December 2003 > 2003.12.16 > 09Prev  Next


Duo-Art Regulation
By Pete Knobloch

Ray Fairfield wrote in MMD 2003.12.14

> Per Pete Knobloch's suggestion I put in weaker springs, and reset the
> accordion pneumatics to the prescribed 1/16" increments and 15/16"
> total travel.  Now it does very well on the play/no play test, but
> my maximum vacuum at level 15 is 17" WG.  Bottom line is I get good
> expression at low volumes, but I lack the power I should have.

What I talked about in 031205 MMDigest just may not be a good procedure.
Like I said at the end of the message, "I don't know if this procedure
works but it is something to shoot holes in and discuss".  That is why
I as asking for feedback in the first place.

It may be that you just have to ignore the no-play portion of the
adjustment and make a compromise between ramping up to quickly and the
test roll no-play adjustments.   What I mean is bring the vacuum levels
up until you are satisfied with the louder passages.  17" of vacuum is
much too low.

> The only thing I can figure is to run with my weak springs as
> presently installed, and add "secondary" springs to each regulator.

I wouldn't do this since the original regulator was not intended to
operate this way.  There are many Duo-Arts that work fine without this
type of modification.

> Mike Kitner's pamphlet, "Rebuilding the Duo-Art," says to adjust the
> expression control arms for 1/16" regulator motion, and then adjust
> for 5" vacuum with the regulator springs.

What you are doing here is setting the relationship of the regulator
pneumatics to the knife blades.  I am not sure by the description you
gave that you are doing it right.  The pneumatic should deflect about
1/16".  You can do this in the piano by turning the pump ON and OFF.
Remember that if you turn the zero adjust screws too far back, the
knife blades might open up on the wrong side of the sliding valve and
actually cause the vacuum to decrease as the springs are tightened.
Try doing this adjustment again.  When you pull down on the spring, it
should always increase the vacuum going to the stack.

Once you know vacuum does increase, turn the pump ON and OFF and notice
how far the accompaniment pneumatic is pulled up.  Change the zero
adjust screw until it only changes by that 1/16".  Once this is done,
go ahead and try adjusting the spring tension again to set the zero
intensity level to around 5" vacuum.   You might find that you have to
choke the adjustment ring 1/2 the total length of the spring.   Just
don't go too far and over stretch the spring.  You may even need to
change back to the original springs to get this to work.

If you just can't get this adjustments to work properly, try increasing
the travel to 1/8" between pump ON and OFF and adjust the spring
tension again.  This may be bad advice but it is a way to bring the
spring tension down for the zero adjust.

I do know that the smaller this deflection is between the pump ON and
OFF, the more spring tension is needed to bring the piano up to the
proper zero intensity of 5".  I don't understand exactly what is going
on here but it relates to the outside cloth being tight and the
affective area of the regulator pneumatic.   I have always heard that
the graph should be linear but setting the regulator this way would
seem to make it non-linear at the lower levels.  This in affect would
give a larger change at the lower levels and would seem to compress the
higher level changes.  This could be exactly what you may need.

The other advantage about doing the above procedure is that the
regulator pneumatic is now allowed to travel its maximum distance
without bottoming out at the higher vacuum levels.  Of course your low
vacuum levels of 17" could be that the spring you selected should be a
little tighter or larger than it currently is.

In Ray's first message in MMD 2003.12.3, he wrote:

> But when installed in the piano, the vacuum levels ramp up much too
> rapidly, and playing the test roll reveals that each succeeding level
> is too loud.

I am wondering what you meant about this statement.  If you were
talking about the play/no-play tests, then they will ramp up too
quickly as far as playing volume.  At least they do on mine.   The real
test for the ramp up volume is the "Dynamic Build Up Test" which has 5
levels.  They build up from kind of soft to very loud.  These are the
ones that should sound as though they ramp up evenly.

I should add that I have a QRS roll that has problems in the SOLO build
up test (DA-1002-C).

The same test on an original Duo-Art test roll, which is a very old, is
2, 5, 9, 12, 16

The DA-1002-C roll level progression goes like this: 2, 5, 1, 12, 16
It should progress to level 9.

The #8 punch seems to be missing.  It really isn't missing, the #8 punch
is seen for just a short time and disappears before the accent note is
to play.  Maybe it is to test how tight the seal is for the solo pouch
chamber area?  Does anyone know for sure?

Pete Knobloch (Tempe Arizona, USA)


(Message sent Tue 16 Dec 2003, 23:29:51 GMT, from time zone GMT-0800.)

Key Words in Subject:  Duo-Art, Regulation

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