Yamaha bobbling

[Ron Nossaman]

>I've find that the hammer bouncing problem is mostly due to a
>synchronization problem between the bottoming of the key and the
>checking moment.

Not unless you're accustomed to having hammers check before letoff. Or am I 
misunderstanding you?


>The hammer bounce on the jack before the jack have traveled enough to
>be out of the way in fact, even if, when moving slowly you can see the
>jack out of the leather.

Yes, that's obvious.


>Yes it is a lack of acceleration oàr move at the end of the jack's
>path that look like the most probable cause, but also the fact that
>the buckskin (ecsaine) groove , making the letoff occurring faster,
>the hammer is yet bouncing while the move is in its regulated letoff
>moment possibly ?

It's not a lack of acceleration. The high ratio between jack length and toe 
length insures plenty of acceleration if the key is just pushed through 
letoff, but takes more force to do it because of that high ratio. And it 
isn't grooved Ecsaine. This always happens (in my experience) in new pianos 
to players who are just beginning, or had an old worn out, 
sloppy-actioned  piano before - or both.


>It occur even when playing normally.

I've never seen it happen under normal play. It's always been from someone 
trying to play very lightly, and I've seen it dozens of times.


>Extra heaviness at the end of the
>stroke is another problem, , but may certainly add something to the
>first.

I think that extra heaviness at the bottom of the stroke, with the player 
not pushing through it, is the primary problem.

Ron N