Harpsichord - Mechanism

Mechanism

Harpsichords vary in size and shape, but all have the same basic functional arrangement. The player depresses a key pivoted in the middle of its length, which causes the far end of the key to rise. This lifts a jack, a long strip of wood, to which is attached a small plectrum (a wedge-shaped piece of quill or, nowadays plastic), which plucks the string. When the key is released by the player, the far end returns to its rest position and the jack falls back. The plectrum, mounted on a tongue that can swivel backwards away from the string, passes the string without plucking it again. As the key reaches its rest position, the string's vibrations are halted by the damper, a piece of felt attached to the top of the jack.

These basic principles are explained in more detail below.

• The keylever is a simple pivot, which rocks on a balance pin passing through a hole drilled through it.
• The jack is a thin, rectangular piece of wood which sits upright on the end of the keylever, held in place by the registers (the upper movable, the lower fixed) which are two long strips of wood running in the gap from spine to cheek with rectangular mortises through which the jacks can move up and down.
  
• In the jack, a plectrum juts out almost horizontally (normally the plectrum is angled upwards a tiny amount) and passes just under the string. Historically, plectra were made of crow quill or leather. Most modern harpsichords based on historic instruments have plastic (delrin or celcon) plectra.
• When the front of the key is pressed, the back of the key rises, the jack is lifted, and the plectrum plucks the string.
• The vertical motion of the jack is then stopped by the jackrail, which is covered with soft felt to muffle the impact.
  
• When the key is released, the jack falls back down under its own weight, and the plectrum passes back under the string. This is made possible by having the plectrum held in a tongue which is attached with a pivot and a spring to the body of the jack. The bottom surface of the plectrum is cut at a slant; thus when the descending plectrum touches the string from above, the angled lower surface provides enough force to push the tongue backward.
• When the jack arrives in fully lowered position, the felt damper touches the string, causing the note to cease.