Universal Audio Mixer-3 Mic or Line x 1 Mic or Line

Ideal Use Cases

The RDL ST-UMX3 is a compact three-channel audio mixer for combining mic-level or line-level signals into one output. It suits systems that need three independently managed sources consolidated before the next audio stage. Because every input has its own MIC/LINE switch, the three channels can be configured for microphone sources, line sources, or a combination of the two. This makes the unit useful when the central requirement is focused 3×1 mixing in a compact format.

• Three-source audio systems that need one combined feed.
• Installations using balanced line inputs and either a balanced or unbalanced output.
• Signal paths that require separate gain adjustment for every input.

Why Choose This Model

Each channel accommodates either a 600 Ω microphone input or a 50 kΩ balanced line input. The input gain range is adjustable from OFF to 60 dB in mic mode and from OFF to 21 dB in line mode, allowing each source to be attenuated fully or raised within its specified range. Maximum input signal is -18 dBu for mic and +25 dBu for line. At the output, the mixer supports 150 Ω balanced or 75 Ω unbalanced connections.

Line output is +4 dBu nominal, while mic output is specified at 50 dB below line level. That combination of per-input mode selection, independent gain range, and output connection choices gives integrators specific electrical targets for matching the mixer to surrounding equipment.

Installation and Integration

Set the MIC/LINE switch on each channel to match the connected source, then adjust that channel’s gain for the required contribution to the mix. Observe the stated input limits and select the balanced or unbalanced output arrangement needed by the receiving device. The unit requires ground-referenced 24 Vdc at 55 mA. The recommended power supply is PS-24AS for the USA or PS-24AX for international use; the power supply is not included.

Mic inputs are not protected against phantom voltage. Do not feed phantom voltage directly into the ST-UMX3 mic inputs. When phantom microphone powering is required, use an ST-MPA24 or ST-MPA48 mic phantom adapter. The specified ambient operating range is 0° C to 55° C, which should be considered when choosing the installation location. Package dimensions are 2 x 2 x 4 inches; the listed shipping weight is 0.175 pounds.

Performance Highlights

In mic mode, frequency response is 50 Hz to 100 kHz within ±1 dB. In line mode, it is 10 Hz to 100 kHz within ±0.05 dB. THD+N is below 0.006%. IMD is below 0.04% for mic at 50 dB gain and below 0.008% for line. The specified 18 dB of headroom provides a clear reference for system gain planning.

Noise for each input is below -70 dB in mic mode at 50 dB gain and below -82 dB in line mode at unity gain. CMRR is greater than 60 dB for mic and greater than 50 dB for line from 50 to 120 Hz. These published figures make it possible to evaluate the unit against a system’s response, distortion, noise, and rejection requirements before installation.

What Makes It Different

The ST-UMX3 places a MIC/LINE choice directly on all three inputs rather than limiting the mixer to one source level. Each channel also has its own gain range, including an OFF setting. The single output can be wired balanced at 150 Ω or unbalanced at 75 Ω, and its specified mic and line signal levels provide defined parameters for downstream integration.

Its operating information is concrete for a compact utility mixer: input impedances, maximum levels, gain ranges, output impedances, frequency response, distortion, noise, headroom, and CMRR are all stated. That detail helps an installer make compatibility decisions from published values.

Final Assessment

The RDL ST-UMX3 is a focused choice for three-to-one mixing when sources may be microphone level, line level, or a combination. Its main strengths are per-input MIC/LINE switching, independent gain adjustment, balanced line-input capability, balanced or unbalanced output wiring, and documented performance figures. It requires an external ground-referenced 24 Vdc supply, and installations involving phantom-powered microphones must include the specified ST-MPA24 or ST-MPA48 adapter because the mixer’s mic inputs are not phantom-voltage protected.