CAUTION AVIS RISK OF ELECTRIC SHOCK RISQUE DE CHOC ELECTRIQUE DO NOT OPEN NE PAS OUVRIR To prevent electric shock, do not remove the cover. There are no user-serviceable parts inside. Refer all servicing to qualified service personnel. Warning: This apparatus must be grounded. This product is a safety class 1 product. There must be an uninterruptible safety earth ground from the main power source to the product’s AC input. Whenever it is likely that the protection has been impaired, disconnect the power cord until the ground has been restored. Caution: To prevent fire or shock hazard, do not expose this appliance to rain or moisture. Note: Line Voltage Selector Switch You will find the line voltage selector switch on the bottom panel. Before your model is shipped from the factory, the switch is set to the power requirements of the destination. Nevertheless, you should check that it is set properly before plugging the power cord into the wall outlet. If the voltage requirements differ, adjust the selector switch as follows. Before adjusting, disconnect the power cord. 1. Provide yourself with a medium size screwdriver. 2. Change the position of switch to the proper voltage for your area. Caution: For continued protection against fire hazard, replace only with same type/rating of fuse. Warning: There are some sharp edges inside. To reduce the risk of injury, do not remove cover. Introduction Please Note! This manual assumes use of microphone-level inputs and line-level output, the most typical SmartMixer application. However, all inputs and the output may be individually switched internally to achieve any combination of mic- and line-level input/output. See page 10 for details. What is a SmartMixer? The AT-MX351 SmartMixer® is a microprocessor controlled, automatic switching, five-channel mixer. The four microphone inputs are XLRF-type balanced, with 48-volt phantom power available on pins 2 and 3. The Aux input is an RCA jack accepting auxiliary-level input from sources such as tape decks and VCRs. There is no signal processing of the Aux input. The mixer output is XLRM-type balanced, non-inverting. All AT-MX351 and AT-MX341a SmartMixers can be daisy-chained via the included AT8325/1.0 Link Cable and special connectors on the rear panel. The control bus and the audio are carried between mixers by the link cable. The result is that all microphones on a multi-mixer system can be controlled by one microphone connected to any mixer. Since all of the mixers are independently powered, there is no practical limit to the number of SmartMixers that can be daisy-chained. Features The AT-MX351 provides an independent gain control on the front panel for each input channel. Substantial gain reserve and adjustment range permit microphones of widely differing sensitivities to be used together successfully. Automatic threshold setting on all mic/line channels ensures proper gating levels for existing ambient sound conditions. Priority Pre-select To custom-tailor conferencing needs, the mode of each microphone channel can be independently switched via the front panel “Priority Pre-select” DIP switches. The combination of switch settings results in three different modes of priority selection/operation. In any of the three modes of operation, when everyone stops talking, the last microphone “on” will remain “on.” In a teleconferencing, recording, or broadcast application, this feature will provide continuous room ambience. This feature is cascaded throughout all linked mixers so that only one microphone in the entire system will remain on. When a microphone is “off,” its input is only attenuated. This attenuation is factory set at 8 dB. The amount of “off ” attenuation can be internally adjusted between 6 dB and 40 dB if desired. (See page 12, “Adjusting ‘Off ’ Attenuation.”) If automatic switching is not desired, a “manual” DIP-switch setting on the front panel bypasses the AT-MX351’s automatic switching and attenuation functions, causing the unit to behave like a conventional mixer. In this mode, the relative level of each microphone is strictly a function of the position of its respective front-panel gain control. NOMA (Number of Open Microphones Attenuated) The NOMA system helps control feedback by allowing for the increase in system gain that occurs when the number of open microphones increases. A built-in matrix in the AT-MX351 recognizes exactly how many microphones are on and automatically adjusts the gain accordingly. Because use of NOMA is not always appropriate or desired, the AT-MX351 is shipped with the NOMA function switched off. AT-MX351 Front Panel 1. Power switch. 2. Power “on” indicator. 3. Input Gain controls. Adjust inputs for microphone sensitivities and/or operating conditions. 4. Selected Channel LED indicators. Indicate which channels are “on” or “active.” 5. Aux In control. Adjusts input for source output level and/or operating conditions. 6. Output Level LED meter. Indicates RMS output level of the mi...