Back check angle should be such that the hammer heel catches solidly, causing the back check wire to spring back momentarily as it absorbs the momentum of the hammer. As the key starts to release the backcheck wire springs back, shoving the hammer forward slightly which allows the jack a milisecond more time to get back under the hammer butt. This is very much like the function of the repetition lever/repetition spring in a grand action. Try setting backchecks so the catch hammers at the distance from strings recommended by Yamaha, and then (while looking for wear in back check felt, and hammer heel leather) make certain that backcheck angle is correct. This tip is derived from information from a class given by Bill Spurlock for our chapter a few months ago. Roland Kaplan, Santa Clara Valley Chapter (Calif).
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