Instability puzzler

[Alan Barnard]

Since it is at the break, see if you have separations in the bridge laminations or the bridge from the soundboard. Is there any change in tone on the notes that go flat? A lot of the Hamilton studios get this problem right at that break: It can get so bad that the notes have a sound to them like a drummers wood block being struck with the drumstick. Anyhow, movement in the bridge could/would in theory affect pitch.

Alan Barnard
Salem, MO




Original message
From: "Michael Kurta" 
To: Pianotech 
Received: 12/6/2007 8:43:50 PM
Subject: Instability puzzler


    Yamaha MX100 w/Disklavier (U1) 6 years old, in a H.S. vocal music room, never moved from there.  Climate controlled year around. At the tenor/treble break the F#5 and G5 go out of tune overnight!  We've had trouble with this piano since new being unstable, but its getting much worse now.  Lovely instrument, sounds great when tuned, but almost immediately goes flat around this brace.  Measured all the notes today after having pitch raised and tuned 9 days ago.  SAT says all notes within 2-3 cents except those mentioned and a few others here and there up to 15 cents flat.  Measured these again after finishing up today, and they're 5 cents flat within 45 min. 
    Strings look good, bridge, pins and hitch look fine, pins are tight and smooth, no plate separation from back, running out of ideas. 
    We called the dealer who will in turn bring Yamaha in now.  Any thoughts?
    Mike Kurta
    Syracuse chapter 
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