A sustaining device is provided for prolonging the vibration of a string of a stringed musical instrument having a first magnetic pickup means responsive to the vibration of the string. The sustaining device includes a magnetic string drive capable of inducing a vibration in the string. A first amplifier amplifies the output of the pickup to a level that provides sufficient energy to the driver to prolong the vibration of the string. A switch is coupled to the driver for selecting the mode of operation of the driver between the pickup mode of operation wherein the driver functions as a second magnetic pickup, and a driver mode of operation wherein the driver functions as a magnetic string driver. An output changing device is provided that is responsive to the switch for changing the output of at least one of the first pickup and a driver in response to a change in the mode of operation of the driver.
