Repetition and Lost Motion
By Richard Moody
Greetings Robbie and MMD. You asked "why can't the vertical piano action repeat as well as a grand action?"
The reason is that grand pianos have repetition levers, and verticals don't. The repetition lever allows the note to be repeated when the key has only come back half way. On an upright the key must come back all the way. (That's the theory, and I have seen some uprights repeat before the key comes all the way up, but that is the exception rather than the rule.)
The only way to further understand this is to look at a drawing of the action, to familiarize yourself with the parts and the concepts, then watch the actual mechanism work. There are excellent diagrams in the Arthur Reblitz book, "Piano Service, Tuning and Rebuilding"
The "grand repetition action" or "double escapement action" was patented in 1821 by Sebastion Erard (Dolge, "Pianos and their Makers"). With some minor refinements this is the action of the grand piano today.
In regards to the Disklavier on Yamaha uprights, the regulation should be to factory specs. The lost motion should be checked after the player unit has been played a while to make sure there is no "negative lost motion" (for lack of a better term), i.e., the solenoid rods at rest should not be pushing up on the keys even a hair. (I am assuming the Disklavier pushes up on the backs of the keys a la the old Marantz Pianocorder.) If one runs a thumb down the keys at the capstans, glissando style, and sees some hammers wink or nod, this is an example of "negative lost motion".
There can be no sluggishness in the action. If the soft pedal is depressed then released all of the hammers should come back at the same time. If there are slow hammers, you will see them lagging behind. Lost motion and slow hammers are something the owner can and should check for if so inclined. To check for lost motion, (in uprights only) the hammer should move when the key is ever so slightly depressed.
To get an idea of extreme lost motion, depress the soft pedal, then depress a key and see how far it goes down before the hammer moves. That's why the upright feels different in playing when the soft pedal is used. If the owner can detect lost motion (without the soft pedal depressed of course) there is way too much, or the solenoid operating the soft pedal is out of adjustment.
On the player unit, the solenoids themselves have to be repeating and not binding. Also they should not push up too far on the keys in the on or play position. Does the Disklavier have a stop rail on top of the keys towards the rear?
Richard Moody
[ Thanks for the tip, Richard -- Art Reblitz's description is very
[ good, and I understand the problem now. -- Robbie
|
(Message sent Sun 9 Mar 1997, 16:16:26 GMT, from time zone GMT-0600.) |
|
|
Mechanical
Music Digest™ Archives
