Of course, the U3 you're working with is apparently new, but I encountered the same "Multi" striking problem on a U3; but it was about 30 years older. The reason: Broken hammer butt spring cords, in addition to needing many points of regulation, including backchecks too far from catchers. But then again, sometimes the hammer butt spring simply gets disengaged from the cord, causing bubbling. Terry Peterson ----Original Message Follows---- From: Richard Brekne <Richard.Brekne@grieg.uib.no> Reply-To: Pianotech <pianotech@ptg.org> To: Pianotech <pianotech@ptg.org>, College and University Technicians <caut@ptg.org> Subject: Re: "Bobbling" hammers on a new Yamaha U3. ( Please help! ) Date: Tue, 13 Apr 2004 14:06:46 +0200 gordon stelter wrote: >Ladies and Gentlemen of the List, > I maintain a Yamaha U3 for a church here, which >is only one year old, yet has developed "bobbling" >hammers on about 25 notes. The immediate cause is that >the front edge of the jacks are not all escaping from >under the butt buckskin on letoff, althouigh the >keydip is "at specs", and the letoff is much more >generous than "spec": varying from 5 to 10 mm! > > Sounds like somethings either amiss, or someone has tried to deal with this problem before you.... or both. 5 mm letoff should be PLENTY to establish plenty of jack clearance with at specs keydip. > My first effort at correcting this problem will be >to meticulously regulate this piano to Yamaha factory >specs, although I believe that this will only make the >"bobbling" worse. I believe that this will occur, as >the strange, current "regulation" on this little used >instrument ( besides the aforementioned "letoff" >distances, the hammers are checking at an inch or more >from the strings ) seems to have been effected to >overcome some inherent design flaw ( or flaws ) which >does not allow the jacks to readily slip out from >under the hammer butts. > > If you regualte to ALL the Yamaha specs... you should have no troubles.... yes ?? Certainly tho if you just regulate letoff in closer your problem will be exhasperated. But starting with a 10mm dip, proper blow distance, and correct checking distance then the jack should show itself to be well clear of the knuckle when the key is held forcefully down. If thats the case and you still have bobbling problems then you need look closer at a few other things. Could be there is something slowing or inhibiting slightly the last bit of key travel so that on light play you dont really bottom out. Could be the jack stop rail is in just a bit close, or even return springs that are set too strong. Could even be the damper stop rail in just a hair too close. I am sure others can think of more things that end up causing bobbling when jack clearence looks correct for the static test above. > The percieved design flaw to which I refer is a >very sharp edge on the plastic jacks' front edge, which seems to >catch on the buckskin, causing the butt >to bounce upon it repeatedly rather than allowing the >jack to fully slip out. This problem may also be >exacerbated by the use of an overly "nappy" buckskin, >and an unusually sharp angle on the hammer butt >buckskin face, at the point where where the jack would >normally "trip out". > > Yes... but regulating the jack travel so tight that it is pushed out by the knuckle is a borderline regulation trick anyways.... you should be able to eliminate bobbling by playing it a bit more safe and allowing for more (and earlier) jack travel. Again... Yamaha regualtion specs SHOULD give you enough jack travel. > It seems that a tiny bevel, were it filed on the >front edge of the jacks, would be efficacious in >remedying this "bobbling". I may also try sanding down >the butt buckskin and lubricatinmg with some microfine >Teflon. > > Well.. you never know of course... you COULD try smoothing the leading sharp edge on a few to see if it helps. Cant do any harm as long as you dont over do it. You may have a set of jacks that have a production fault and there is some undo friction problem involved.... but I'd be mildly suprised to hear that was the case. > My first efforts, however ( after regulating the >action ) will be to reduce the hammerstroke, and >perhaps increase the keydip by 1 mm. > > I'd leave key dip where it is, regulate letoff to 3-4 mm, and bring in the hammer stroke to assure proper jack clearance at the fully depressed key before doing anything else. > If you please: Have any of you encountered a >similar problem on a piano of this model and, if so, >how did you approach its remedy? > > Worst bobbling problem I ever encountered on an upright was a Steinway. Turned out that someone had changed the whippens and used non factory parts that were'nt quite the same dimmensions and ended up with a too steep jack angle. Even with severe cheating on the regulation the jacktop would bounce the butt back for different types of touch. Only fix was to get the right whippens. I find that too strong a jack return spring is a frequent problem tho. > Your advice will be gratefully recieved, > Sincerely, > Gordon Stelter > > > Cheers RicB _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives _________________________________________________________________ Free up your inbox with MSN Hotmail Extra Storage! Multiple plans available. http://join.msn.com/?pgmarket=en-us&page=hotmail/es2&ST=1/go/onm00200362ave/direct/01/
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