Mackie MDB-1P Passive Direct Box

The Mackie MDB-1P is a single-channel passive direct box designed to connect unbalanced, high-impedance instruments and sources to balanced audio systems. It converts the signal for a balanced XLR output, helping make long cable runs to a mixer or audio interface more practical. A 1/4-inch Thru connection lets the original source remain connected to an instrument amplifier or compatible effects chain.

This DI box is suited to guitars, basses, keyboards, media players, and similar sources with a 1/4-inch unbalanced output. It is useful for live sound, rehearsal spaces, recording setups, and installed systems where a source needs to feed both a local amplifier and a mixer. Its passive design requires no battery, phantom power, or external power supply.

The MDB-1P is engineered for a neutral signal path with a specified 20 Hz to 20 kHz frequency response and 128 dB dynamic range. Its 140 kOhm unbalanced input impedance is designed for high-impedance sources. A stated total harmonic distortion figure of 0.002% from 1 kHz supports clean signal transfer in a properly matched system.

A switchable -15 dB pad reduces the input level for high-output sources, including instruments with active electronics or high-output pickups. The rear-panel ground-lift switch separates chassis ground from signal ground at the balanced output when needed to address system ground-loop hum. These controls make the unit adaptable without adding active electronics or power requirements.

The MDB-1P fits easily into a stage or studio signal chain: connect an instrument to the input, run the XLR output to a mixer or audio interface, and use the Thru jack for an amplifier or instrument-level parallel device. Its compact steel chassis measures 5.8 inches deep, making it practical for pedalboards, stage cases, or desktop recording rigs. It is a focused interface component for systems that need a passive DI connection rather than a powered preamp or audio interface.

Key Features

• Passive Direct Box: Operates without batteries, phantom power, or an external supply.
• High-Impedance Input: Accepts unbalanced 1/4-inch instrument and source signals.
• 1/4-Inch Thru Output: Routes the source onward to an amplifier or compatible effects device.
• Balanced XLR Output: Connects the converted signal to a mixer or audio interface.
• -15 dB Pad: Reduces high-level input signals to help prevent overload.
• Ground-Lift Switch: Separates chassis and signal ground to help address ground-loop hum.

Design & Installation

The MDB-1P uses a heavy-gauge steel chassis and Mackie's Built-Like-A-Tank construction approach. It is a compact, single-channel DI box with front-panel 1/4-inch Input and Thru jacks, plus a rear-panel male XLR output and ground-lift switch. The enclosure measures 1.5 inches high, 3.4 inches wide, and 5.8 inches deep.

Use a shielded 1/4-inch instrument cable from the source to the Input jack, then connect a standard XLR cable from the output to a mixer or audio interface. Connect the Thru jack to an instrument amplifier, tuner, or instrument-level parallel effects chain when a local feed is needed. Start with the pad disengaged, engage the -15 dB pad for a source with excessive level, and try the ground-lift setting only if hum is present; do not connect an amplifier speaker output directly to the input.