Unstable Yamaha C7

[Farrell]

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Is the heat/AC blowing directly on the piano? From which direction? Have =
you sat a thermometer on the belly area and observed any temp swings =
during one (or more) of these pitch-drift cycles?

I would say that if the pitch cycles as the temperature cycles, then =
that is likely the cause. You would need to stabilize temp.

I once tuned a Yamy grand for an outside concert. The sun/clouds was =
playing peek-a-boo on the soundboard/strings. Pitch would rise and fall =
wildly 10 cents or more! Sounds like your situation might be the same =
thing - only from a vent.

Terry Farrell
  ----- Original Message -----=20
  From: Mark Dierauf=20
  To: pianotech@ptg.org=20
  Sent: Wednesday, June 16, 2004 10:26 PM
  Subject: Unstable Yamaha C7


  I take care of an older Yamaha at a recording studio that has a tuning =
instability problem that I've never encountered on any other piano - the =
pitch fluctuates by as much as 3 or 4 cents over the course of only a =
few minutes. It took me quite a while to realize that this fluctuation =
ran in sync with the forced hot air heating system. Now that it's =
summer, the air-conditioning from the same vents is having the same =
effect. The piano has a complete DC unit installed with a bottom cover, =
is tuned at least 20x annually, and is very pitch-stable in the long =
term. It is not located in direct sunlight and the temperature doesn't =
vary much, certainly not within seasons. In the winter there is a =
humidity control system adding moisture through the hot air ducts. The =
studio is in an old New England barn that had several hundred thousand =
dollars worth of renovation, and so is very well finished and insulated, =
but in the time that it takes me to work through the temperament the =
first notes tuned have already moved substantially. Once after chasing =
the pitch all through a tuning I repeated A4 for several minutes and =
watched the pitch rise about 2 cents above the starting point then fall =
about 2 cents below. This cycle kept repeating as I watched. Has anyone =
ever seen such a problem? Did you find any solutions?

  =20

  - Mark

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