ST-PA18 Audio Power Amplifier
The audio power amplifier shall be an RDL ST-PA18. The unit shall provide one balanced line-level input, one output that duplicates the input terminals, one amplified output with integral audio compressor capable of driving speaker loads of 4 O or greater, a single-turn gain trimmer, an LED power indicator and an LED to indicate compression activity.

The line input shall be electronic balanced bridging with an input impedance no less than 20 kOhms and an input level of +4 dBu and shall be fully compatible with either an unbalanced or balanced audio source. The balanced input shall provide common mode rejection greater than 45 dB for frequencies between 50 and 120 Hz. A single-turn adjustable trimming control shall be provided to set the amplifier gain.  The input gain range shall be capable of producing an output level that crosses the compressor threshold for input signals from -16 dBu to +25 dBu.

The unit shall provide a frequency response of 20 Hz to 20 kHz (± 2 dB) with total harmonic distortion plus noise <1% and a noise floor exceeding 75 dB below the normal rated output level. 

The unit shall provide audio compression calibrated to the amplified output level, with a threshold 3 dB below full rated amplified output power. The compressor shall preserve aural dynamics by not acting upon average input signal levels with peak components that would not clip the amplifier stage at its rated power output. Higher average and peak levels shall be compressed according to two dynamic time constants that automatically adjust to correspond with the dynamic characteristics of the input audio signal such that the compression activity remains essentially inaudible.  The compressor shall be capable of preventing amplifier clipping for input overloads of at least 20 dB.  Compressor activity shall be indicated by a variable-intensity LED.

The unit shall provide an unbalanced mono amplified output at an output power of 18 W (RMS) into a load impedance of 8 O. The unit shall include automatic shut-down circuitry to protect the unit from potential damage due to output over-current. The unit shall otherwise operate normally following application of a momentary or sustained short to its output. The power amplifier stage shall be high efficiency, utilizing a pulse duration modulation (switch-mode) method capable of delivering a continuous sine-wave output at the rated amplifier output power. The unit shall be equipped with specialized audio circuitry to remove artifacts associated with Class D or similar class switch-mode amplifiers.

The unit shall be constructed in an electrically non-conductive, thermally conductive enclosure. Internal circuitry shall be protected from moisture and vibration using a thermally conductive compound that permanently secures the circuitry within the enclosure.

The face of the unit shall provide graphical labels identifying wiring connections and operating controls. Controls shall be oriented toward the face of the unit.

Connection to external wiring shall be provided using a fixed terminal block on the edge of the unit. The terminal block shall accept wiring gauges from 14 to 22 and shall include a positive electrically conductive mechanism to prevent wire abrasion by the terminal screws.

The unit shall measure 3” (7.6 cm) x 1.6” (4 cm) x 0.7” (1.7 cm) and be compatible with all RDL STICK-ON mounting accessories. The unit shall be supplied with a two part re-closable polypropylene fastener system equipped with a rubber adhesive that bonds to low surface energy materials.

Power requirements shall be 24 Vdc ground-referenced with a maximum current not exceeding 1000 mA. The unit shall utilize an external power supply. The unit shall be engineered, assembled and tested in the U.S.A. and be specified for continuous duty in professional installed systems. The unit shall be specified for operation in an ambient temperature between 0 and 30 degrees C. The unit shall comply with relevant EMC requirements and shall bear the CE marking.

The unit shall be an RDL ST-PA18.