Hello Ron. I don't know if my thanks to you came through the CAUT forum or not, but I thought I'd contact you at your email to let you know that this problem was resolved. At your suggestion, we considered the possibility of recapping the bridge or respacing the bridge pins. Since we willing to ultimately try that we decided to try some other experiments first. Your statement about the bridge pins not being able to support side bearing forces inspired us to first try replacing the bridge pins with longer, thicker pins for more support. And it worked, the noise is gone. It's interesting that the original clues was the noise could also be caused by plucking the string from the side, but it never occurred to me that there would be a design flaw in such an otherwise wonderful piano. Anyway, thanks again for your insight. Robert Callaghan Another possibility, if the Grotrian was made around the seventies, is that the bridge was designed with insufficient spacing between the unisons. This problem results in insufficient wood around the pins to properly support the side bearing forces. With an example I have experienced, several unison strings are so close to the pin of its neighbouring unison that noise (metallic in character) is generated at the bridge during heavier playing. The source of this noise can be confirmed by holding a blade screwdriver between the suspect bridge pins. In 1988 one of my clients purchased a new bridge cap from the factory for his Grotrian 223 grand when he visited Germany. In hindsight, I wish we had ditched the replacement cap and laid out a new design. But its easy to be wise after the event. When my clients son inherits the piano there are plans to recap the bridge again, but the board is starting to exhibit symptoms of failure, so it could end up being a total board redesign. Ron O.
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