The Mackie MDB-1A is an active direct box designed to connect a single instrument such as a guitar, bass, or keyboard to a microphone preamp for musicians and audio engineers in recording sessions, houses of worship, and live stage applications. It converts a high-impedance, instrument-level signal via its 1/4" TS unbalanced input to a low-impedance, mic-level output via its balanced XLR 3-pin jack. A 1/4" thru jack allows simultaneous connection to an amplifier or pedalboard.

A -20 dB pad reduces the input level to prevent distortion when using a high-gain source, and the ground-lift switch inhibits hum caused by ground loops. Additionally, there are switches for polarity and a 120 Hz high-pass filter. The Merge function allows the Thru jack to be used as a second, simultaneous input. Due to its active design, the MDB-1A operates on phantom power. A sturdy steel chassis enables confident use in the studio or on the road.