Pianotech

  • 1.  Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 16 days ago
    I recently serviced a Brodmann BU-128 vertical from 2009, which had some of the worst bobbling I've ever seen.
    I did some regulating, but this piano was especially stubborn. The jacks cleared the hammer butts with plenty of room--aftertouch was not the issue. The tops of the jacks look especially deep, so in a way I'm not surprised. It's kind of like walking through a screen door that closes quickly and nails you on the way out.

    Anyone encountered one of these pianos? I've sent an email to the company describing the issue, but no response. Hence my post.

    Here's a thought though: We can adjust the fore-aft position on grand jacks so that we get the fastest performance but without "cheating." Is it possible to somehow do the same with vertical jacks? Perhaps they lie at rest too deeply under the hammer butts, and if a thicker rest felt were installed, the back of the jack would clear the butt faster? Of course one would have to make sure the jack didn't cheat under a hard blow, just like a grand. What about experimenting by gluing a bit of felt on the back of the jack itself with just a small dot of glue? If it worked, would that extra mass impede the motion of the jack with too much inertia? One could of course replace all the rest felt if something of just the right thickness could be found.
    If the jack were tilted a small bit forward, I suppose it would compress the spring a tiny bit more. Hopefully there would be enough adjustment in the letoff screws to compensate.

    Any commentary on my thought experiment? Maybe I'm reinventing some square wheel that's already been left at the side of the road...

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    Scott Cole, RPT
    rvpianotuner.com
    Talent, OR
    (541-601-9033
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  • 2.  RE: Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 16 days ago
    Is there enough slack in the bridle straps? Is the action mounted correctly? Is the hammer blow correct?

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    Steven Rosenthal
    Honolulu HI
    808-521-7129
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  • 3.  RE: Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 16 days ago
    Paul and Steven,
    Thanks, I'll look at those factors as well.
    Scott

    --
    Scott Cole, Registered Piano Technician and Doctor of Music
    Serving Southern Oregon and Northern California
    (541)601-9033







  • 4.  RE: Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 16 days ago
    What about the checking? If it isn't catching the hammer close enough to the strings, the butt will bobble on the jack. I see this in older pianos with excess lost motion. There will be bobbling because there isn't enough dip to complete the full cycle of what happens in a keystroke. The jack ends up bobbling. This is helped by adjusting the capstans, or for just on problem note, you can move the back check in a little closer.

    In the regulation you did, did you begin with shimming the hammer rest rail to make blow distance correct? Then lost motion and the back checks?

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    John Formsma, RPT
    New Albany MS

    Something just ain't right with all this.
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  • 5.  RE: Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 16 days ago
    Another thought. Could the let off button rail have come loose or moved?

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    Steven Rosenthal
    Honolulu HI
    808-521-7129
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  • 6.  RE: Brodmann upright: bad bobbling

    Member
    Posted 16 days ago
    Check the jack springs- they could be too strong . Messing around by adding felt etc may backfire. Can you post some pictures as well ? I would concentrate on the worst
    bobbler and get it fixed. As LaRoy Edwards advises get it right once and duplicate it 87 more times. It would be helpful to go through a vertical regulation checklist so as not to miss things. That is get the blow set, let off etc Maybe the let off rail has shifted as Steve commented. How is the lost motion ? hammer return springs ? damper clearance and timing ?

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    James Kelly
    Owner- Fur Elise Piano Service
    Pawleys Island SC
    843-325-4357
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  • 7.  RE: Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 15 days ago
    Is the bobbling confined to the the section of the scale from the bass/tenor break to the treble break?

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    Edward McMorrow
    Edmonds WA
    425-299-3431
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  • 8.  RE: Brodmann upright: bad bobbling

    Member
    Posted 15 days ago
    I encountered something similar on an old upright and determined that it couldn't be regulated to spec without installing thicker hammer butt felts: jack buried too deeply into hammer butt. Someone had installed new hammers/shanks/butts but weren't careful.

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    Don Dalton
    Chester VT
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  • 9.  RE: Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 15 days ago
    I'm not sure if someone else mentioned this but overly strong damper springs could cause bobbling hammers.

    David

    David Weiss
    Registered Piano Technician
    (434) 823-9733
    davidweisspiano@gmail.com
    www.davidweisspiano.com

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    David Weiss
    Charlottesville VA
    434-823-9733
    davidweisspiano@gmail.com
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  • 10.  RE: Brodmann upright: bad bobbling

    Registered Piano Technician
    Posted 15 days ago
    This is true! Early lifting dampers with strong springs can contribute to bobbling.
    Also hammer return springs that are too weak: think Yamaha's with breaking spring loops. Combine strong jack springs and weak hammer springs and the jack may be able to push the hammer up towards the string on a slow release - kind of like a repetition lever on a grand.

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    Ryan Sowers
    Olympia WA
    360-705-4160
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