Power Amplifier-20 W 25 V Outputs

The RDL FP-PA20B is a 20 W RMS constant-voltage power amplifier designed around a 25 V output. It accepts either a +4 dBu balanced or -10 dBV unbalanced line-level input and provides plug-in terminal-block connections for straightforward system wiring. An integral audio compressor controls clipping while supporting a high overall operating level and maximizing the available output level.

Ideal Use Cases

This model is suited to audio systems requiring 20 W RMS of output power at 25 V. Its balanced and unbalanced input compatibility allows it to work with line-level sources operating at common professional and consumer reference levels. With a chassis measuring 2.3 inches high, 3.25 inches wide, and 6 inches long, it can be considered for integrations where equipment space is limited and terminal-block wiring is preferred.

The FP-PA20B is particularly relevant when the system design calls for a constant-voltage amplifier with controlled clipping behavior. Its specified input range accommodates balanced levels up to +23 dBu and unbalanced levels up to +15 dBV, while the single-turn audio-taper gain adjustment provides local level control.

Why Choose This Model

The FP-PA20B combines a defined 20 W RMS output at 25 V with an integral compressor that begins operating 6 dB below rated output. Attack and release are adjusted automatically, allowing the amplifier to manage signal peaks without requiring separate compressor controls. A red PEAK LED indicates compressor activity, while a green LED confirms that power is on.

RDL specifies this model for a high overall operating audio level, maximized audio level for the available output power, and audio quality superior to standard amplifiers. These characteristics are supported by detailed frequency-response, distortion, noise, and common-mode rejection specifications.

Installation and Integration

Audio input and output wiring use plug-in terminal blocks. The line input supports +4 dBu balanced and -10 dBV unbalanced sources, with a 20 kΩ balanced bridging impedance or 10 kΩ unbalanced impedance. Minimum levels required to cross the compressor threshold are -26 dBu for balanced input and -28 dBV for unbalanced input.

The amplifier requires a ground-referenced 24 Vdc supply, which is not included. Current requirement is 1650 mA for continuous RMS power output or 1000 mA for normal uncompressed audio. Listed recommended supplies are the PS-24V3A and PS-24KS for the USA, along with the PS-24V3 and PS-24KX international models. The specified operating environment is 0°C to 30°C maximum, with 20°C recommended.

Performance Highlights

Rated output power is 20 W RMS at 25 V. Frequency response is specified from 50 Hz to 18 kHz within ±3 dB. THD+N is less than 0.1% at 1 kHz and less than 0.5% from 50 Hz to 20 kHz. These distortion measurements are taken at the compressor-threshold level, corresponding to 4 W RMS output power.

Noise is specified below -80 dB relative to 20 W RMS. Common-mode rejection is greater than 55 dB from 50 Hz to 120 Hz. Together with the compressor and supported input levels, these specifications provide a clear performance profile for matching the amplifier to a 25 V audio system.

What Makes It Different

The defining feature is the interaction between the 20 W RMS constant-voltage output and the built-in compressor. Its threshold is fixed 6 dB below rated output, and its automatic attack and release behavior is designed to control clipping while retaining a high operating level. The dedicated PEAK indicator makes compressor activity visible during setup and operation.

The amplifier also supports balanced and unbalanced sources without requiring separate input versions. Published limits for impedance, minimum compressor-threshold levels, maximum input levels, distortion, noise, and CMRR give integrators concrete values for system planning.

Final Assessment

The RDL FP-PA20B is a focused 25 V amplifier for applications requiring 20 W RMS, flexible line-level input compatibility, terminal-block connections, and integral clipping control. Its compact 2.3 by 3.25 by 6-inch enclosure, single-turn gain control, automatic compressor, and dual status indicators provide the essential controls and feedback needed for integration. A compatible 24 Vdc power supply must be selected separately according to the required operating level.