Pro 4 Input Mic/Line Mixer W/Phantom-Mic and Line Out

The RDL RU-MX4 is a four-channel audio mixer built for combining microphone and line-level sources while providing flexible output routing, individual phantom-power options and detailed level monitoring. Each channel includes a balanced XLR microphone input and an unbalanced phono-jack line input. The mixer also incorporates a switchable compressor/limiter, direct input and expansion capability in a 1.7-inch-high, 5.8-inch-long enclosure.

Ideal Use Cases

The RU-MX4 is suited to audio configurations that need to mix as many as four microphone or line-level sources. Its balanced 2 kΩ microphone inputs support switchable 24 V phantom power individually, allowing each microphone channel to be configured according to the connected source. Four 2 kΩ unbalanced line inputs accommodate line-level equipment through phono jacks.

Expansion capability and an unbalanced direct input provide additional integration flexibility. This makes the mixer useful when a four-channel mix must operate by itself or become part of a broader audio signal path. Its selectable output formats also support systems that require either microphone-level or line-level delivery.

Why Choose This Model

The RU-MX4 combines input flexibility, output selection and signal management in one mixer. Its balanced XLR output can be switched between microphone and line levels, while a separate unbalanced output operates at -10 dBV. An output attenuator provides adjustment from 0 dB to infinity.

A switchable integral compressor/limiter helps manage the combined signal when compression or limiting is needed. Operators can monitor every input through its own dual-LED VU meter and view the overall audio mix on an eight-segment LED level meter. Dedicated compression/limiting and power indicators make operating status immediately visible.

Installation and Integration

The mixer requires ground-referenced 24 Vdc power at 150 mA. The recommended power supplies are the PS-24AS for the USA and the PS-24AX for international use; the power supply is not included. The enclosure measures 1.7 inches high by 5.8 inches long, equivalent to 4.3 by 15.0 cm.

Balanced XLR microphone connections, unbalanced phono-jack line inputs, the switchable XLR output, the -10 dBV unbalanced output and the direct input provide several ways to connect the RU-MX4 within an audio system. Individual phantom switching prevents phantom power from having to be applied uniformly across all microphone inputs.

Performance Highlights

Microphone gain can be adjusted from off to 62 dB with phantom power off. With phantom power enabled, the high-gain setting also provides adjustment from off to 62 dB, while the low-gain setting provides adjustment from off to 46 dB. Line gain is adjustable from off to 27 dB.

The specified microphone frequency response is 80 Hz to 30 kHz within ±1.5 dB. Line response extends from 20 Hz to 30 kHz within ±0.25 dB. With four line-level sources at unity gain, residual noise is specified below -82 dB wideband relative to a +4 dBu output.

At 40 dB low gain and 50 dB high gain, microphone noise is specified at -79 dB. With all four microphone-level sources, noise is below -73 dB wideband and below -76 dB A-weighted. At 60 dB high gain, microphone noise is -70 dB; with all four microphone sources, it is below -64 dB wideband and below -66 dB A-weighted.

What Makes It Different

The RU-MX4 provides 18 indicators for detailed signal and operating feedback. Each input has a dual-LED VU meter, and the eight-segment mix-level display supports VU and peak readings. Its VU scale covers -20, -10, -6, -2, 0 and +3 dB, while peak readings are provided at +8 and +12 dB. On the mix meter, 0 dB corresponds to +4 dBu.

The combination of individual 24 V phantom selection, microphone and line inputs on every channel, switchable mic/line balanced output, unbalanced output, direct input and selectable dynamics processing gives the RU-MX4 more than basic four-channel summing capability. Its stated studio-quality, low-noise performance is supported by published frequency-response and residual-noise specifications.

Final Assessment

The RDL RU-MX4 is a focused four-channel mixer for installations requiring balanced microphone inputs, unbalanced line inputs and adaptable output levels. Individual phantom-power switching, adjustable gain, comprehensive LED metering and an integral compressor/limiter provide practical control over mixed audio. Expansion capability and the direct input further support integration beyond a standalone four-source mix.