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MMD > Archives > December 1997 > 1997.12.05 > 13Prev  Next

An Adjustable Bleed System for Duo-Art
By Ian McDonald

Description and object of an adjustable bleed block operating in a
Duo-Art upright piano.


Aim for the fastest repetition and most even operation of stack valves,
by adjusting the amount of bleed to each valve.  (in a way which could
be restored without trace.)


To, as far as possible,

  Compensate and even valve speed where cross valve plates have been
replaced by round.

  Even the effect of varying porosity of pouch leather.

  Even the effect of slight variations in valve weights.

  Move towards evening the effect of varying piano action tensions.

I am unable to back up my logic with actual tests, so I open this up
to those who may have test results.


By passing the existing bleed via its tracker tube to a larger bleed
hole fed with regulated stack vacuum and restricted on a variable basis
by a pointed adjustable screw.



Dressed pine, Bleed board  413x58x15mm; Spacers cut as required 7mm;
Screw board 413x58x10. (this is for 80 notes.)

Bleeds 80 - 9mm diameter brass washers with center hole (bleed) twice
the size of the stack bleed. (brass to wood glue.) (center attach using
screw point.)

Pointed screws, 80 - 20x4mm with Allan key heads. (self tap into holes
in screw board.)

Elbows, 80 each of 90 degree and 45 degree Y junctions.

2 - 7mm OD connectors, and 2 - 7mm OD elbows.  (vacuum supply.)

Pneumatic cloth seal for top of box.

Contact me for detailed assembly instructions.


Cover the small channel ( that feeds vacuum to stack bleed) above and
in front of the bleed.  Y junction into the tracker tubing at the back
of the spool box at the level of the tracker bar.  Design a clip
arrangement to hold the adjustable bleed block on top of the spool box.
Fit an elbow into the back of the left and right stack to supply
regulated vacuum to the bleed block.


Fit test roll, use note test at beginning of roll;  remove drive chain;
tempo to 0;  lever to play;  Duo-Art on;  manually advance roll; use
finger to rapidly open and close each tracker bar hole ( play each
note); adjusting bleed screw to optimum repetition.  Further adjust
over periods of roll playing,  generally the adjustment is to open the
bleed about 1/8 of a turn at a time.

Hoped for outcome, every note plays with all the tracker bar holes
open.  Every note repeats with the fastest roll speed.

Ian McDonald

 [ Editor's note:
 [ I just celebrated (?!) 25 years of employment at Lockheed Corp., and
 [ many of those years were in Research & Development, mostly for U.S.
 [ Government projects.  We proposed the projects, and reported the
 [ progress, using this strict outline.  I've 'filled it in' with what
 [ I think Ian is writing about:
 [ PROBLEM - Notes play unevenly at low intensity
 [ OBJECTIVE - Develop a simple adjustment method such that each note
 [    can be adjusted individually to a consistent, even loudness.
 [ APPROACH - Substitute, for the existing bleed, an adjustable bleed
 [   which exhausts the pouch to a regulated supply.
 [   BACKGROUND & THEORY - (The practical experience and/or theory
 [     which justifies the proposed approach.)
 [ BUDGET & SCHEDULE - (There's never enough of either one. ;)
 [ PROGRESS - (reported weekly to the boss, annually to the government)
 [ RESULTS & CONCLUSION - (only in the final report)
 [ I invite constructive comments and suggestions from our readers
 [ about this proposal which Ian has kindly submitted for our review.
 [ -- Robbie

(Message sent Thu 4 Dec 1997, 07:43:11 GMT, from time zone GMT+1000.)

Key Words in Subject:  Adjustable, An, Bleed, Duo-Art, System

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