3 Line Input Mixer-Line Out

The RDL ST-MX3 is a three-input line-level mixer with a single line output. It is designed to add line-level inputs to an existing mixer or combine multiple sources before a line output. All three inputs are individually adjustable and support balanced or unbalanced bridging connections. The specified design provides isolation between input signals together with low-noise and low-distortion performance.

Ideal Use Cases

The ST-MX3 is intended for systems that need to mix three line-level signals into one output. It can expand the available line inputs on an existing mixer or combine signals before they enter another line-level connection. The inputs can accommodate sources with different levels, impedances, or balanced and unbalanced configurations. This flexibility is useful when the connected sources do not share the same output arrangement or when separate input-level adjustment is required for each signal.

Why Choose This Model

Each of the three inputs is independently adjustable, allowing the connected signals to be set individually before being mixed. Every input is specified as a 30 kΩ balanced or unbalanced bridging input. The listed adjustable gain range for each input is 14 dB to +24 dB. Isolation between the input signals is part of the stated feature set, while the output is designed to drive both low- and high-impedance balanced or unbalanced lines.

Installation and Integration

The ST-MX3 supports balanced and unbalanced connections at both the input and output, simplifying integration where wiring configurations differ. Its output impedance is 400 Ω. The nominal output level is +4 dBu and is adjustable; when the output is used unbalanced, its level is 6 dB below the balanced line level. Power may be ground-referenced or floating through the RDL SupplyFlex power input configuration. The module requires 24 Vdc at 55 mA. Recommended power supplies are the PS-24AS for the USA and PS-24AX for international use, and the power supply is not included. The specified ambient operating environment is 0° C to 55° C. The provided 2 x 2 x 4-inch dimensions apply to the cardboard package.

Performance Highlights

The specified frequency response is 10 Hz to 20 kHz within ±0.5 dB. THD+N is less than 0.03% from 10 Hz to 20 kHz. Noise is specified below -80 dB with all inputs at 10 dB gain and referenced to +4 dBu. The mixer provides 18 dB of headroom, while common-mode rejection is greater than 50 dB from 50 to 120 Hz. These published measurements define the model’s operating bandwidth, distortion, noise, headroom, and rejection performance for line-level signal mixing.

What Makes It Different

The defining feature of the ST-MX3 is its ability to combine three independently adjustable signals even when their levels, impedances, or balanced and unbalanced configurations differ. Its bridging inputs, isolated input signals, adjustable output, and compatibility with low- or high-impedance lines address several integration requirements in one unit. The SupplyFlex power arrangement also supports either ground-referenced or floating 24 Vdc power. Together, these features make the model specifically focused on flexible line-level expansion and signal combining.

Final Assessment

The RDL ST-MX3 provides a focused solution for mixing three line-level sources or adding inputs to an existing mixer. Its three adjustable 30 kΩ bridging inputs, 400 Ω output, +4 dBu nominal balanced output level, 10 Hz to 20 kHz response, and 18 dB headroom provide clearly stated operating parameters. It is particularly relevant when a system must combine balanced and unbalanced sources or signals with differing levels and impedances. A compatible 24 Vdc power supply must be obtained separately.