545SD – Classic Instrument Microphone. The instrument microphone delivers an exceptionally uniform cardioid pattern to minimize feedback. It features a silent magnetic reed on and off switch with a lock-on option and selectable dual-impedance operation. Shipped connected for low-impedance operation, the 545SD features a silent magnetic reed on/off switch with a lock-on option. A favorite for instrument pickup and recording, the 545SD can also be used on lecterns in public address systems.