Unbalanced Audio Switcher-4x1

The RDL ST-SX4 is a 4×1 solid-state switcher for selecting one of four unbalanced audio sources. It provides unity gain, a 10 dBV input and output level, and remote source selection through a single control pair. The module can also operate as a slave for stereo switching, allowing coordinated source selection where a stereo configuration is required.

Ideal Use Cases

The ST-SX4 is suited to audio systems that require centralized source equipment with selection performed from another location. One control input and ground can select the desired channel, reducing the control wiring needed between the switcher and the remote position. Its four-input, one-output arrangement supports systems that need to route one of several unbalanced sources into a shared downstream signal path.

It can be remotely operated with the D SERIES-RC4ST remote control. Slave capability also allows the model to participate in stereo switching applications rather than limiting integration to an independently controlled mono signal path.

Why Choose This Model

All audio switching is solid-state, and the signal path operates at unity gain. The input impedance is 100 kΩ unbalanced, while the output impedance is below 50 Ω unbalanced. These documented characteristics give system designers concrete loading and output-drive information when incorporating the switcher into an unbalanced audio installation.

The ST-SX4 provides 23 dB of headroom and a frequency response of 15 Hz to 40 kHz within ±0.5 dB. THD+N is specified below 0.1%, with a typical value of 0.05%. Residual noise is below -70 dB when referred to -10 dBV, and crosstalk is specified as below the noise floor.

Installation and Integration

The switcher requires a ground-referenced 24 Vdc supply at 45 mA. The recommended supplies are the PS-24AS for the USA and PS-24AX for international use; the power supply is not included.

Remote selection uses a control input with a 10 kΩ pullup to +15 Vdc. The single control terminal is connected through the appropriate resistance to the ground terminal to select a channel. The supplied external resistors support this control method. The documented selection values are 2.7 kΩ for input 1, 6.8 kΩ for input 2, 22 kΩ for input 3, and no resistor for input 4. A 0 Ω short to ground corresponds to no input selected.

For installations requiring a dedicated user control, the ST-SX4 may be operated with the D SERIES-RC4ST. Its specified ambient operating range is 0°C to 55°C.

Performance Highlights

• Selects one of four unbalanced audio sources.
• Provides remote audio selection through a single control pair.
• Uses all solid-state audio switching.
• Supports slave operation for stereo switching.
• Maintains unity gain with a specified 10 dBV input and output level.
• Delivers a 15 Hz to 40 kHz frequency response within ±0.5 dB.
• Provides off-channel attenuation above 85 dB at 1 kHz, above 80 dB at 10 kHz, and above 75 dB at 20 kHz.
• Specifies crosstalk below the noise floor and 23 dB of headroom.

What Makes It Different

The ST-SX4 combines four-source unbalanced audio selection with a resistance-based remote control interface. Instead of requiring separate control conductors for every source, the selected resistance on a single control input determines the active channel. This arrangement is paired with solid-state switching and documented attenuation performance across 1 kHz, 10 kHz, and 20 kHz.

Its slave capability is also significant for systems that need linked switching. A second switching function can follow the control arrangement to support stereo source selection while retaining the model’s remote-control approach.

Final Assessment

The RDL ST-SX4 provides a focused solution for remotely selecting one of four unbalanced audio sources. Its unity-gain signal path, 100 kΩ inputs, low-impedance output, wide specified frequency response, and resistance-based control interface make its operating characteristics clear for system integration. With supplied control resistors, D SERIES-RC4ST compatibility, and slave capability for stereo switching, it addresses both single-channel and linked source-selection requirements.