Radio Design Labs TX-PA40D
20W RMS Per Channel @ 8 Ohms Stereo Amplifier with Power Supply


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Radio Design Labs' TX-PA40D features two unbalanced line level inputs on high-reliability gold plated phono (RCA) jacks. A front-panel recessed gain control trimmer permits setting the desired amplifier output level for each channel. The gain range accommodates the range of typical unbalanced audio signal levels. Each of the two TX-PA40D outputs will drive a 4 Ohm or 8 Ohm speaker or multiple speakers connected to present a 4 Ohms or 8 Ohms load to the amplifier. The output impedance is switch-selectable on the front panel of the module.

A front panel switch is provided to sum the audio inputs to mono. In the stereo mode, the TX-PA40D independently amplifies each audio channel, left (L) and right (R). If speaker placement in the specified installation is incompatible with stereophonic amplification, the input mode switch may be set to 'summed mono'.

The TX-PA40D includes a stereo analog compressor/limiter for audio fidelity noticeably superior to conventional class D amplifiers with digital limiting. The input GAIN settings determine whether the limiter alone is used for clipping suppression, or if the full compressor/limiter will be used to substantially increase the average output power beyond that of a standard 40 W amplifier. A red front panel LED flashes when the limiter is preventing output clipping. Normal audio level signals remain unaffected by the compressor thereby preserving audio dynamics. If the input level is increased so the compressor is active, the LED remains dimly lit between peak flashes. The audio is compressed according to three dynamic time constants providing aural transparency while maintaining clean, unclipped amplified audio for input overloads of up to 20 dB. The TX-PA40D, with compression, is capable of producing average audio output levels and clarity normally expected from stereo amplifiers with a much higher output power rating.

A blue power LED illuminates when the TX-PA40D is powered from its external 24 Vdc power supply. The module is equipped with both thermal and output short-circuit protection. The high efficiency Class D output stages produce minimal heat for all levels of expected voice or music modulation. Continuous full power operation with audio tones will not damage the amplifier, but is not recommended.

The TX-PA40D is the ideal choice in many applications where a high quality, high-efficiency utility amplifier is needed to drive a pair of 4 Ohm or 8 Ohm speakers. It is designed for fixed gain amplification applications where gain is controlled by other equipment. Examples include projectors with variable audio outputs used in classrooms, boardrooms and video conferencing.

Radio Design Labs TX-PA40D Features:

  • Stereo Audio Power Amplifier
  • 20 Watts RMS per Channel into 8 Ohms – 40 Watts Total
  • 15 Watts RMS per Channel into 4 Ohms – 30 Watts Total
  • Left and Right Unbalanced Phono Jack Inputs
  • Switch-Selectable Stereo or Mono Operation
  • Studio Quality, Aurally Transparent Compressor/Limiter
  • Compressor/Limiter Controls Clipping
  • Compressor Produces Maximized Average Output Power
  • Compression Enabled Using Input Level Adjustments
  • LED to Indicate Audio Compression Threshold
  • Outputs Drive 4 or 8 Ohm Speakers
  • High-Efficiency Class D Operation
  • Thermal and Short-Circuit Protection
  • TX-PA40D includes North American Power Cord

Radio Design Labs TX-PA40D Specifications:

  • Inputs (2): Line level (-10 dBV nominal unbalanced), Left and Right
  • Input Impedance: 10 kOhms unbalanced
  • Gain Adjustments (2): Single turn, one per channel
  • Minimum Input Levels: -18 dBV (to cross compressor threshold)
  • Maximum Input Levels: +15 dBV
  • Frequency Response: 20 Hz to 20 kHz (± 1 dB, 4 or 8 Ohms)
  • THD+N: < 0.1% (1 kHz, 1 W, 4 or 8 Ohms); < 1% (50 Hz to 20 kHz, 8 Ohms) (measured at compressor threshold level equaling 12W RMS (8 Ohms) output power)
  • Compressor: Threshold nominally 2 dB below rated output, automatically adjusting attack and release times
  • Crosstalk: Better than 60 dB (1 kHz, no compression)
  • Noise: < -75 dB (below 20 W RMS)
  • Selectors: Slide switches: Output Impedance 4 Ohms or 8 Ohms; Input Mode SUMMED MONO or STEREO
  • Output Power: 20 W RMS into 8 Ohms per channel,40 W RMS total; 15 W RMS into 4 Ohms per channel, 30 W RMS total
  • Output Circuit: Class D
  • Ambient Operating Environment: 0° C to 40° C Maximum; 20° C Recommended
  • Indicators (2):
    • Red LED: THRESHOLD LED indicates compressor activity
    • Blue LED: POWER on
  • Power Requirement (Supply Included):
  • Input: 100 to 240 VAC, 50 to 60 Hz, 1.5 A, IEC C14; Output to module: 24 Vdc
  • Package Type: Cardboard Box
  • Package Dimensions: 5.125" x 2.5" x 5.875"
  • Shipping Weight: 1.655 lbs.
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Radio Design Labs' PS24V2A is a 24 volt DC Switching Power Supply, with North American cord, 2 Amp output and DC Plug. Input:  100 to 240 VAC Output:  24 Vdc, 2 A (UL, CSA) Dimensions:  2 in. (5 cm) x 1.33 ...

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