40 W Stereo Audio Power Amplifier with Power Supply-Includes NA Power Cord

Ideal Use Cases

The RDL TX-PA40D is suited to audio systems that require two-channel amplification from unbalanced line-level sources. It drives 4- or 8-ohm speakers and can operate in stereo or summed-mono mode, making it adaptable to systems that need independent left and right channels or a combined mono signal. Its 3.17-inch-wide chassis also provides a compact option where installation space is limited. With 20 Hz to 20 kHz frequency response, the amplifier supports both voice and music program material.

Why Choose This Model

The TX-PA40D delivers 20 W RMS per channel into 8 ohms for 40 W RMS total output. When configured for 4-ohm speakers, it supplies 15 W RMS per channel and 30 W RMS total. A slide switch selects the appropriate 4- or 8-ohm output impedance, while a second switch selects stereo or summed-mono input operation.

Its studio-quality, aurally transparent compressor/limiter controls clipping while allowing normal audio signals to retain their dynamics. Increasing the input level can engage full compression to maximize average output power. A red front-panel threshold LED provides a visible indication of compressor activity.

Installation and Integration

Two left and right unbalanced phono jack inputs accept nominal -10 dBV line-level signals. Each channel has a dedicated single-turn gain adjustment, allowing input levels to be set independently. Input impedance is 10 kΩ unbalanced, the listed minimum input level for crossing the compressor threshold is 18 dBV, and the maximum input level is +15 dBV.

The included external power supply accepts 100 to 240 VAC at 50 to 60 Hz through an IEC C14 input and provides 24 Vdc to the amplifier. This TX-PA40D version includes a North American power cord. The recommended ambient temperature is 20° C, with a specified maximum operating range from 0° C to 40° C. A blue power LED confirms that the module is receiving power.

Performance Highlights

Frequency response extends from 20 Hz to 20 kHz within ±1 dB when driving either 4- or 8-ohm loads. THD+N is below 0.1% at 1 kHz and 1 W into 4 or 8 ohms. The published 8-ohm measurement is below 1% from 50 Hz to 20 kHz at the compressor-threshold level corresponding to 12 W RMS output.

Crosstalk is better than 60 dB at 1 kHz without compression, while noise is specified below -75 dB relative to 20 W RMS. The compressor threshold is nominally 2 dB below rated output and automatically adjusts its attack and release times. These operating characteristics provide defined performance data for both standard amplification and compressor-assisted operation.

What Makes It Different

The compressor/limiter can be used in two ways through the channel gain settings. It can function primarily as a limiter for clipping suppression, or it can operate as a full compressor/limiter to increase average output power. The red threshold LED flashes when limiting prevents output clipping. When compression is more continuously active, the LED remains dimly illuminated between peak flashes.

High-efficiency Class D output stages produce minimal heat across expected voice and music modulation levels. Integrated thermal and output short-circuit protection further safeguards the amplifier. Continuous full-power operation with audio tones will not damage the unit, although that operating condition is not recommended.

Final Assessment

The TX-PA40D combines selectable stereo or summed-mono operation, clearly specified output for 4- and 8-ohm speakers, independent channel gain controls, and active clipping management in a compact enclosure. Its included 24 Vdc power supply and North American power cord provide the required power components for this model, while visible power and compression indicators make operating status easy to identify.