A sustaining device is described for prolonging the vibration of the strings of a stringed musical instrument, such as an electric guitar having two or three electromagnetic pickups. The pickups are all low impedance transducers that can function either as pickups or driver transducers, depending on whether they are connected to the input of the instrument pickup amplifier or to the output of the sustainer amplifier, respectively. When a transducer is being used as a sustainer driver, it cannot be simultaneously used as a pickup. Different methods of selecting transducers to function as pickups or drivers are described. The transducers, having only hundreds of wire turns instead of the usual thousands of turns for common pickups, have a flat audio frequency response that can be modified to produce a multitude of common pickup sounds by manipulating the transducer resonance frequency, bandwidth, and amplifier gain.