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Push Terminal
RCA Connectors
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Maximum Power Handling
20 Watts
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Beginner (Installs < 10 minutes)
Radio Design Labs
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High Quality, High Efficiency Amplifier for a Pair of 4 or 8 Ohm Speakers
Radio Design Labs TX-PA40D 40W Stereo Audio Amp
Radio Design Labs TX-PA40D 40W Stereo Audio Amp
Radio Design Labs TX-PA40D 40W Stereo Audio Amp
Item# 77982
Price: Normally $291.49 
Hot Deal $190.25
Free shipping on orders over $175 - See Details


  • Stereo audio power amplifier
  • 20 W RMS / channel into 8 Ohms - 40 watts total
  • 15 W RMS / 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 controls clipping

Essential Info

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 specifically suited to 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.

The 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 Ohm or 8 Ohm 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.

For a 40W stereo amp with VCA, please see the Radio Design Labs RU-PA40D.


What's Included

  • TX-PA40D
  • Power supply
  • Specifications

    • Inputs (2): Line level (-10 dBV nominal unbalanced), Left and Right
    • Input Impedance: 10k Ohm 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,)*
    • 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 O per channel, 40 W RMS total; 15 W RMS into 4 O 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 Supply (included): 100 to 240 Vac, 50-60 Hz, 1.5A; 24 Vdc output to module
    *measured at compressor threshold level equaling 12 W RMS (8 Ohms) output power


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