18 Watt 8 Ohm Audio Power Amplifier

The RDL ST-PA18 is a compact, professional-quality mono audio power amplifier designed to deliver 18 W RMS into an 8 Ω speaker. It accepts line-level signals in either +4 dBu balanced or -10 dBV unbalanced form and uses a Class D output circuit. An integrated compressor helps prevent clipping, with its threshold positioned 3 dB below rated output and automatically adjusting attack and release.

Ideal Use Cases

The ST-PA18 fits audio systems that require a dedicated mono amplifier for an 8 Ω speaker and already provide a line-level source. Its balanced and unbalanced input options support integration with either +4 dBu balanced equipment or -10 dBV unbalanced equipment. Because the amplifier is rated for 18 W RMS output, it is best matched with applications whose speaker impedance and required output power correspond to that specification.

Why Choose This Model

This model combines a compact format with a focused set of professional audio features. Its integrated compressor responds before the amplifier reaches rated output, helping control signal peaks that could otherwise produce clipping. Automatically adjusting attack and release allow the compressor to respond without separate timing controls. A red LED indicates compressor activity, making engagement visible during operation, while a separate green LED confirms that power is on. Gain is adjusted through a single-turn control.

Installation and Integration

For balanced connections, the input is designed for +4 dBu line level and presents a 20 kΩ balanced bridging impedance. For unbalanced connections, it accepts -10 dBV line level with a 10 kΩ input impedance. Published minimum input levels are 16 dBu* balanced and -18 dBV* unbalanced, while maximum input levels are +25 dBu balanced and +22 dBV unbalanced. These specifications provide clear limits for matching the amplifier to the source equipment.

The ST-PA18 requires ground-referenced 24 Vdc power at 1000 mA. Recommended power supplies are the PS-24KS for use in the USA and the PS-24KX for international use; a power supply is not included. The specified ambient operating range is 0° C to 30° C maximum, with 20° C recommended. These power and environmental requirements should be confirmed before installation.

Performance Highlights

Rated output power is 18 W RMS into an 8 Ω load through a Class D output circuit. Frequency response extends from 20 Hz to 20 kHz within ±2 dB. THD+N is specified at less than 1%, and noise is listed as below -75 dB at levels below 18 W RMS. Common-mode rejection is greater than 45 dB from 50 Hz to 120 Hz. Together, these published figures define the amplifier’s frequency coverage, distortion, noise, and balanced-input rejection performance.

The compressor threshold is set 3 dB below rated output, directly relating its operation to the amplifier’s available output level. Automatic attack and release adjustment manage how the compressor responds, while the red activity indicator provides immediate confirmation when compression is taking place.

What Makes It Different

The ST-PA18 brings mono amplification, balanced bridging input capability, unbalanced input compatibility, and output-level compression into one compact amplifier. Its feature set is centered on the requirements of a single 8 Ω speaker rather than multichannel operation. The combination of single-turn gain adjustment and separate compressor and power indicators gives installers direct level control and straightforward operating feedback without adding unrelated functions.

Final Assessment

The ST-PA18 is a precisely specified choice for systems requiring mono operation, 18 W RMS into 8 Ω, line-level input, and 24 Vdc power. Its balanced and unbalanced input support broadens source compatibility, while the compressor adds automatic control below the rated output threshold. Before installation, confirm the speaker load, source level, available DC power, and ambient temperature. For fulfillment reference, the source lists cardboard-box packaging measuring 2 x 2 x 4 inches, a shipping weight of 0.225 pounds, and a WEEE weight of 0.165 pounds.