ST-MA2 Muting Monitor Amplifier
The audio power amplifier shall be an RDL ST-MA2. The unit shall provide one balanced input, one muting terminal, two terminals that attenuate the output 3 dB, two terminals that attenuate the output 6 dB, and one amplified output 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 60 dB for frequencies between 50 and 120 Hz. A multi-turn continuously adjustable trimming control shall be provided to set the amplifier gain to a fixed value.  

The unit shall provide a frequency response of 45 Hz to 14 kHz (± 1.5 dB) with total harmonic distortion plus noise <0.5% and a noise floor exceeding 80 dB below the maximum rated output level.

Five control terminals shall be provided.  Each control terminal shall be active when externally pulled to ground using either a dry contact (switch or relay) or an open collector capable of sinking at least 0.3 mA.  One terminal shall mute the output of the amplifier by greater than 90 dB at 1 kHz and greater than 75 dB at 20 kHz.  Two separate terminals shall attenuate the amplifier output audio by 3 dB when either or both terminals are pulled to ground.  Two separate terminals shall attenuate the amplifier output audio by 6 dB when either or both terminals are pulled to ground.  The attenuation produced by the 3 dB and 6 dB terminals shall not be cumulative when one or both 3 dB terminals and one or both 6 dB terminals are simultaneously pulled to ground.

Audio switching for muting and/or attenuation shall be essentially inaudible and shall occur within 50 us.

The unit shall provide an unbalanced mono amplified output at an output power of 2 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 capable of delivering a minimum continuous sine-wave output of 1.75 W (RMS).

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 220 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 50 degrees C. The unit shall comply with relevant EMC requirements and shall bear the CE marking.

The unit shall be an RDL ST-MA2.