ST-SH2 Stereo Headphone Amplifier
The stereo headphone amplifier shall be an RDL ST-SH2. The unit shall provide two balanced inputs, two amplified unbalanced headphone driver outputs and a provision for stereo remote volume control.

Line inputs shall be electronic balanced bridging with an input impedance no less than 10 kOhms and shall be fully compatible with either an unbalanced or balanced audio source.  A multi-turn continuously adjustable trimming control shall be provided for each input channel to set the circuit gain to produce the rated output level for a line input level between -20 dBu and +6 dBu.

The unit shall provide a frequency response of 20 Hz to 40 kHz (± 0.25 dB) with total harmonic distortion plus noise <0.005% (20 Hz to 20 kHz) and a noise floor exceeding 100 dB below the normal rated output level. Each line input shall provide common mode rejection at 100 Hz of greater than 50 dB. The unit shall provide a total dynamic range of at least 115 dB. Crosstalk between channels shall be less than 65 dB from 10 Hz to 20 kHz and shall be less than 80 dB at 1 kHz.

The unit shall provide an unbalanced stereo headphone audio output at a nominal rated output level of +4 dBu with an output impedance of 100 O. The unit shall be capable of producing a maximum output level of 250 mW into 8 O or 20 Vp-p into 2 kOhms at each channel output. The output shall be capable of driving headsets with an impedance range from 8 O to 5kOhms. The unit shall otherwise operate normally upon application of a momentary or sustained short to either output channel.

The unit shall operate normally in the absence of an external volume control.  There shall be a provision for connection of an external stereo volume control using a ground connection for the CCW rotation of each channel, left and right, of the external control and one connection from each wiper of the external control to a control terminal on the unit. The external control shall be an audio taper 10 kOhms stereo potentiometer. The unit shall not require any connection to the CW external potentiometer terminals. The unit shall operate normally with an external potentiometer connection up to 1 meter in length.

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 200 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 55 degrees C. The unit shall comply with relevant EMC requirements and shall bear the CE marking.

The unit shall be an RDL ST-SH2.