[pianotech] Bobbling hammers and jack spring pressure?

[Paul McCloud]

Hi, Gregor:
    Check the damper spring tension also.  Too much tension will produce the same symptoms.  I found this while trying to diagnose a similar problem with a Chinese upright piano we were selling.  
    On another American brand, their new Schwander (loop type) action had bobbling problems.  I had to increase the letoff distance a bit to reduce the problem.  I figured that the return springs were too "weak" and soft play would not be hampered if I did that.  It seems that some pianos are prone to this even when new.
    Paul McCloud
    San Diego


----- Original Message ----- 
From: Gregor _ 
To: pianotech at ptg.org
Sent: 01/21/2009 8:23:17 AM 
Subject: [pianotech] Bobbling hammers and jack spring pressure?


List,

is there a way to ease the jack spring? I have problems with a Yamaha P121N upright that has bobbling hammers. The hammer butt is dancing on the jack tip. All regulation measures are okay and there is enough aftertouch. I suspect the jack spring being too strong. Any thoughts how to get it right? 

There is no lost motion, check is about 15 mm, aftertouch is okay and I gave some talkum powder to the jack tip and the let off button. The only thing that helped was to set the let off to 10 mm, but that´s not a satisfying solution. The strange thing is that one could play without bobbling hammers but something makes the player stop pressing down the key before the let off point. A very subtile resistance gives the player a hint that the key is pressed down now, but that´s not right. The player could and should press further on. The strange thing is that this problem is new for a few days. I should mention that we had very dry air last weeks and the customer has a floor heating. Therefore I suspect a connection between this problem and the dry air.

Any comments?

Gregor



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