4 Mic or Line Input Mixer-Mic and Line Out

The RDL FP-MX4 is a four-channel audio mixer built for balanced microphone and line-level signal management in the compact RDL FLAT-PAK format. It combines balanced inputs with balanced microphone and line outputs, selectable 24 V microphone phantom power, three selectable microphone gain ranges, and low-noise performance. Four individual gain adjustments provide control over each source, while a dual-LED VU meter displays the line-level output.

Ideal Use Cases

The FP-MX4 is suited to audio systems that need to combine as many as four microphone or line-level sources. Its selectable microphone gain ranges accommodate different incoming mic levels, including signals below -50 dBu, while the line inputs are specified for +4 dBu operation. The two balanced output formats support systems requiring either a +4 dBu line-level output or a -45 dBu microphone-level output. Balanced signal paths make the mixer appropriate for installations designed around professional balanced audio equipment.

Why Choose This Model

Each microphone input presents a 2 kΩ balanced impedance and offers switchable 24 V phantom power compliant with IEC 61938:2013. Microphone input ranges are switch-selectable from -30 to -40 dBu, -40 to -50 dBu, or below -50 dBu. Each line input has a 10 kΩ balanced impedance, may also be wired unbalanced, and is rated for a +4 dBu input level. Per-channel adjustment extends from off to 65 dB of microphone gain at the maximum gain range, or from off to 6 dB of line gain.

Installation and Integration

The FP-MX4 measures 1.42 inches high, 3.25 inches wide, and 8.14 inches long, equivalent to 3.61 by 8.26 by 20.68 centimeters. Its specified operating environment is 0°C to 50°C. Power requirements are 24 Vdc at 160 mA with a ground-referenced supply. The power supply is not included; the specified recommendations are the PS-24AS for the USA and PS-24AX for international use.

Four balanced microphone inputs, four balanced line inputs, and two balanced outputs provide the electrical interfaces for integration. The line output is rated at +4 dBu with a 150 Ω balanced impedance, while the microphone output is rated at -45 dBu with a 150 Ω balanced impedance. A dual-LED VU meter provides visual monitoring of the line-level output.

Performance Highlights

Microphone frequency response extends from 10 Hz to 30 kHz within ±0.25 dB. Line frequency response extends from 10 Hz to 45 kHz within the same ±0.25 dB tolerance. With four line-level sources at unity gain, residual noise below the +4 dBu output is specified at less than -84 dB wideband.

At 40 dB microphone gain, the listed microphone noise value is -90 dB; with all four microphone-level sources, noise is less than -82 dB wideband and less than -84 dB A-weighted. At 50 dB gain, the corresponding values are -86 dB for the microphone, less than -72 dB wideband, and less than -76 dB A-weighted with all four sources. At 60 dB gain, they are -80 dB, less than -65 dB wideband, and less than -67 dB A-weighted.

What Makes It Different

The FP-MX4 combines four-channel mixing, mic and line input compatibility, and separate balanced mic- and line-level output formats in one FLAT-PAK unit. Its input flexibility extends beyond basic source selection: the microphone path includes three gain-range choices and selectable phantom power, while the line path can accept balanced wiring or be wired unbalanced. Individual gain adjustment on all four channels and line-output VU indication provide direct control and monitoring without adding unsupported processing features.

Final Assessment

The RDL FP-MX4 is a focused analog mixing solution for installations requiring four controllable microphone or line sources, wide frequency response, selectable microphone gain ranges, and balanced output choices. Its documented electrical specifications, compact dimensions, phantom-power capability, and dual-LED output meter make it a precise choice when both microphone- and line-level integration are central requirements.