US 4075921 A An apparatus for initiating and sustaining
vibrations of a string in a musical instrument. A hand-held (or
permanently mounted) device senses the vibration of the string
and provides an output driving signal for sustaining the
vibrations. 1. An apparatus for initiating or sustaining the
vibration of at least one string of a musical instrument having
a plurality of generally parallel, spaced apart, coplanar
strings comprising: a housing adaptable for being hand-held,
said housing defining a channel; at least one pair of coils
disposed within said channel of said housing; guide means
comprising a pair of parallel guides defined by said housing and
disposed on opposite edges of said channel such that when said
pair of guides engage alternate strings said channel straddles
at least one intermediate string; and, amplifier means having an
input coupled to one of said coils and an output coupled to the
other of said coils; whereby said intermediate string may be set
in motion by said amplifier means and