From "Tom Driscoll" <tomtuner@verizon.net>
Subject: [pianotech] Regulation specs for Yamaha U3
Greetings,
Would anyone have the regulation specs for a Yamaha U3 upright?
Thanks in advance,
Julia Gottshall
Reading, PA
Assuming the action has been prepped cleaned and lubed.Hammers reshaped .Possibly butt spring cords replaced. Etc.
Also assuming no drastic action geometry problems and the U series yamaha should be fine in this regard.
Adjust key height to satisfy a good fit with the fall strip,the keyslip and the front rail keypins.
With the action in the piano start with a sample dip of 10 or 11 MM. (3/8ths "- 7/16ths")
Adjust letoff on sample to .125 mm (1/8th " )
Play with key dip (10 mm -11mm) and blow on sample to get correct aftertouch. How much aftertouch ?( I just looked it up and the reference said .025-.060.) I don't know but I know it when I feel it and I expect you may also.
Remember correct aftertouch allows the top of the jack to move away from the butt so the butt does not bounce off the top of the jack.
Adjust checking
Check damper timing with the key (spoons) and adjust to have damper movement at half the blow distance.
Test for bobbling hammers especially on a light blow .
Usually this is a sign of insufficient aftertouch ,but the U series Yamahas are notorious for this problem.
Damper springs that are too strong or lift that is too early have been suggested on list as a problem on these actions.
Even with more aftertouch (which can be achieved with shorter blow and/or more dip and /or increased letoff , these actions can still bobble.)
This is more likely to happen with 'Timid" players or those with weakness in their playing. They just don't power the key through it's full stroke and the hammer bobbles.
I think Ron has mentioned that this is a design problem with the jack size.
Aside from the Idiosyncrasies of this action the point here is that the piano case tells you where key height should be. You want clearance under the fall strip from the top of the key. You don't want the key so high that you can see between the bottom of the key and the top of the slip and you want the front rail key bushings to be engaged with the front rail keypin.
Then standard keydip with some variability as described and letoff as described ( Maybe a little closer if you don't live too far away from the piano)
Then the blow takes care of itself when it's adjusted to achieve proper aftertouch.
If you had a 1900 Ivers and Pond upright there ain't no place to get specs, but the piano case and reasonable common settings of dip , letoff and aftertouch will guide the way.
Just my take,
Best wishes,
Tom Driscoll