Radio Design Labs ST-PA18
Power Amplifier


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List Price: $169.13
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Radio Design Labs' ST-PA18 features a balanced line level input that may be connected unbalanced. The gain control range will accommodate standard unbalanced levels as well as professional balanced levels. The module bridges the input signal. LOOP OUT terminals permit a balanced input to be fed to additional amplifier modules making the ST-PA18 an ideal component in distributed audio system design.

NOTE: Radio Design Labs' PS-24KS power supply is NOT included but is required in order to power this product.  Please see the "Accessories" tab or click here for more information on the PS-24KS power supply.

The LOOP OUT may also be used to feed a subwoofer amplifier (see RDL ST-CX2S Subwoofer Filter). The ST-PA18 output will drive an 8 ohm speaker or multiple speakers connected to present an 8 ohm load to the amplifier and it is capable of driving 4 O loads. A red COMP LED is provided to indicate the threshold of the integral compressor. Audio levels that could cause the amplified output to clip are compressed according to two dynamic time constants. Normal audio level signals remain unaffected by the compressor thereby preserving audio dynamics and preventing the compressor from increasing feedback potential when the amplifier is used for paging.

The compressor is designed to remain aurally transparent while maintaining clean, unclipped amplified audio for input overloads of up to 20 dB. The ST-PA18 produces average audio levels and audio clarity normally expected of amplifiers delivering much higher output power. The ST-PA18 operates from an external 24 VDC 1A power supply, sold separately. A POWER LED illuminates when the module is powered. The module provides thermal and output short-circuit protection.


  • 18 Watts RMS Audio Power Amplifier
  • Output for 8 ohm Speaker
  • Maximized Audio Level at Full Power Output
  • Superior Audio Quality at High Output Levels
  • Line Level Balanced or Unbalanced Input
  • LOOP OUT to Feed Additional Amplifiers
  • Integral Audio Compressor to Control Clipping
  • High Overall Audio Operating Level
  • LED to Indicate Audio Compression


  • Input: Line level (+4 dBu bal; -10 dBV unbal)
  • Input Impedance: 20 kohm balanced bridging; 10 kohm unbal
  • Gain Adjustment: Single turn
  • Minimum Input Levels: -16 dBu* balanced; -18 dBV*unbalanced
  • Maximum Input Levels: +25 dBu balanced; +22 dBVunbalanced
  • Frequency Response: 20 Hz to 20 kHz (+/- 2 dB)*
  • THD+N: < 1%*
    *Measured at compressor threshold level equaling 12 W RMS output power
  • Noise: < -75 dB (below 18 W RMS)
  • Compressor: Threshold 3 dB below rated output,automatic adjusting attack and release
  • CMRR: > 45 dB (50 Hz to 120 Hz)
  • Output Power: 18 W RMS into 8 O
  • Output Circuit: Class D
  • Ambient Operating Environment: 0° C to 30° C Max; 20° C Recommended
  • Indicators (2):
    Red LED: LED indicates compressor activity
    Green LED: Power ON
  • Power Requirement: 24 Vdc @ 1000 mA, Ground referenced
24V @ 1000mA Power SupplyRadio Design Labs PS24KS 24V @ 1000mA Power Supply

Typical Performance: Input: 100 to 240 VAC Output: 24 Vdc, 1 A (UL, CSA) Dimensions: 1.80" x 3.51" x 1.55" (4.6  x 8.9 x 3.9 cm) Efficiency: ENERGY STAR Level IV

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