40 W Stereo Audio Power Amp with VCA & Power Supply-Includes North American Power Cord

The RDL RU-PA40D is a VCA-controlled stereo audio power amplifier that delivers up to 40 watts RMS total into 8-ohm speakers. Its high-efficiency Class D output, balanced and unbalanced inputs, selectable stereo or summed-mono operation, and external level-control support provide a flexible foundation for audio systems requiring dependable amplification and remote volume adjustment. The included power supply accepts 100 to 240 Vac, and this model includes a North American power cord.

Ideal Use Cases

The RU-PA40D is suited to stereo and mono audio systems that need line-level source connectivity, external level control, and integrated output protection. Its selectable operating modes and multiple input formats accommodate systems built around balanced professional sources, unbalanced consumer sources, or a combination of the two.

• Stereo systems requiring 20 watts RMS per channel into 8 ohms.
• Summed-mono systems that need switch-selectable input operation.
• Installations using a remote potentiometer, 0 to 10 Vdc control, or an RDL remote level control.
• Audio systems where compressor-assisted clipping control and output-power management are important.

Why Choose This Model

The amplifier provides two defined output configurations: 20 watts RMS per channel into 8 ohms for 40 watts total, or 15 watts RMS per channel into 4 ohms for 30 watts total. A slide switch selects the appropriate 4- or 8-ohm output setting, while a second slide switch selects stereo or summed-mono input operation. This combination allows the amplifier to be configured around the connected speakers and the required channel format without adding an external summing device.

Its VCA section supports linear 0 to 10 Vdc control, a 10 kΩ linear-taper potentiometer, and compatible RDL remote controls. A 10 Vdc VCA reference output is also provided for external control arrangements.

Installation and Integration

Four line-level inputs are provided: balanced left and right inputs at +4 dBu and unbalanced left and right inputs at -10 dBV. The unbalanced connections use RCA jacks, while the balanced inputs use a detachable terminal block. VCA control is also available through a detachable terminal block. Two single-turn gain adjustments provide independent setup for the left and right channels.

The included power supply accepts 100 to 240 Vac at 50-60 Hz and 1.5 A, then supplies 24 Vdc to the amplifier module. The RU-PA40D version includes the North American cord. Its specified ambient operating range is 0° C to 40° C maximum, with 20° C recommended.

Performance Highlights

Frequency response extends from 20 Hz to 20 kHz within ±1 dB into either 4- or 8-ohm loads. THD+N is below 0.1% at 1 kHz with a 1-watt output into 4 or 8 ohms. It is below 1% from 50 Hz to 20 kHz when measured at the compressor threshold level, equal to 12 watts RMS into 8 ohms. Crosstalk is better than 60 dB at 1 kHz without compression.

Maximum input levels are +22 dBu balanced and +12 dBV unbalanced. Input impedance is 50 kΩ balanced and 20 kΩ unbalanced. Below 20 watts RMS, specified noise is below -80 dB with the VCA control at 6.25 V and the output level 6 dB below maximum; noise is below -70 dB with the VCA control at maximum.

What Makes It Different

A studio-quality, aurally transparent compressor/limiter is integrated into the amplifier. Its threshold is nominally 2 dB below rated output, with automatically adjusting attack and release times. The circuit controls clipping while producing maximized average output power, and compression is enabled through the input-level adjustments. A red THRESHOLD LED shows compressor activity, while a blue POWER LED confirms operation.

Thermal and short-circuit protection add protection for the amplifier during operation. Together with the Class D output circuit, selectable speaker-impedance setting, remote VCA control, and flexible input connections, these features distinguish the RU-PA40D as more than a basic two-channel power amplifier.

Final Assessment

The RU-PA40D combines 40-watt total stereo capability, balanced and unbalanced connectivity, external VCA control, stereo or summed-mono selection, and an integrated compressor/limiter in one amplifier. It is a strong fit when the system specification calls for 4- or 8-ohm operation, remote level adjustment, defined clipping control, and an included universal power supply with a North American cord.