50 W Mono Audio Amplifier-70 V or 100 V-Includes North American Power Cord

The RDL SF-PA50A is a high-efficiency Class D mono amplifier designed for constant-voltage audio systems. It delivers 50 W RMS through a 70 V or 100 V output and accepts either a balanced mono source or an unbalanced stereo mini-jack source, with left and right channels summed to mono. Adjustable gain, dual-LED VU metering, external level control, and multiple protection functions provide the control and operating visibility required for an integrated audio installation. A 100 to 240 Vac power supply and North American power cord are included.

Ideal Use Cases

This model is suited to installations built around 70 V or 100 V distributed audio. Its UL 2043 plenum rating addresses projects that require equipment rated for plenum installation. The two input formats accommodate source equipment with a balanced terminal-block output or an unbalanced stereo mini-jack output. Because the stereo input is summed to mono, a stereo source can feed the amplifier without requiring a separate summing device. External level control also makes the SF-PA50A appropriate when adjustment must be available away from the amplifier.

Why Choose This Model

The primary reason to choose the SF-PA50A is its combination of 50 W RMS output, constant-voltage compatibility, and flexible analog input options. A single-turn audio-taper gain adjustment works with a dual-LED VU meter calibrated to 20 dB below full output power. Power, amplifier-mute, analog-input-level, and overload indications provide useful operating feedback. The amplifier also automatically limits supply current to protect against power-supply shutdown. Thermal and short-circuit protection add further safeguards during operation.

Installation and Integration

The balanced input uses a terminal block, while the unbalanced input uses a stereo mini-jack. Balanced input impedance is greater than 10 kΩ, and unbalanced input impedance is greater than 5 kΩ. The amplifier requires 24 Vdc at 2700 mA. Its included power supply accepts 100 to 240 Vac at 50 to 60 Hz through an IEC C14 connection and supplies 24 Vdc to the module. The included North American power cord completes the supplied power arrangement.

A detachable terminal block provides VCA control. Level can be controlled with a 10 kΩ potentiometer or a 0 to 10 Vdc control signal, and the amplifier is compatible with RDL remote level controls. The chassis measures 1.7 inches high, 5.83 inches wide, and 6.45 inches deep. The specified operating environment is 0°C to 40°C maximum, with 20°C recommended.

Performance Highlights

The power-amplifier output is rated at 50 W RMS for 70 V or 100 V operation. Frequency response is specified at +0/-3 dB from 50 Hz to 20 kHz, while THD+N is less than 1% at 1 kHz. The balanced input operates at +4 dBu nominal with adjustment, supports a -10 dBu minimum for 20 dB below full output power, and accepts up to +25 dBu before clipping. The unbalanced input is specified at 10 dBV nominal with adjustment, a -25 dBV minimum for 20 dB below full output power, and a +10 dBV maximum before clipping. Balanced common-mode rejection is greater than 60 dB from 50 Hz to 120 Hz.

What Makes It Different

The SF-PA50A brings together features that address signal connection, remote operation, monitoring, and protection in one amplifier. Its balanced mono and stereo mini-jack input choices reduce dependence on a single source format. The VCA interface supports both a standard control voltage and a 10 kΩ potentiometer, while compatibility with RDL remote level controls offers another integration path. Automatic supply-current limiting specifically protects against power-supply shutdown, complementing the amplifier’s thermal and short-circuit protection. UL 2043 plenum rating further distinguishes the model for installations where that standard is required.

Final Assessment

For a 70 V or 100 V system requiring 50 W RMS of mono amplification, the RDL SF-PA50A offers clearly specified audio performance and practical control options. Its analog input flexibility, calibrated VU metering, detachable VCA connection, operating indicators, and protection features form a focused installation package. The included universal-input power supply and North American power cord provide the required power components, while the published dimensions and environmental limits support advance installation planning.