User manual ALESIS RA500

[. . . ] REFERENCE SERIES TM TM TM POWER AMPLIFIERS REFERENCE MANUAL ©2000 Alesis Corporation Alesis RA150-500 Reference Manual © Copyright 2000, Alesis Studio Electronics, Inc. "RA150/300/500" and "Reference Series" are trademarks of Alesis Studio Electronics, Inc. ALESIS CONTACT INFORMATION Alesis Studio Electronics, Inc. 1633 26th Street Santa Monica, CA 90404 USA Do not use this address for repair service. Telephone: E-Mail: Website: 800-5-ALESIS (800-525-3747) support@alesis. com http://www. alesis. com CONTENTS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] Disadvantages: Requires power, generates some noise. To feed the same source to several different amplifiers: The input impedance of the Alesis amplifiers is 20 k in balanced and 10 k in unbalanced configuration. Thus, the inputs of several amplifiers may be connected in parallel if desired. The maximum number of amplifier channels will depend on the minimum output load impedance of the device feeding the amplifiers. For example, if the minimum output load impedance of the source device is 600 , up to 30 amplifier channels may be connected to it in parallel without overloading the source device's output. However, use of a distribution amplifier is recommended in large systems. To use the amplifier in Bridged Mono mode: Connect the input signal to Channel A/Left only. Move the recessed slide switch under the right input connectors to the Bridged Mono position. See page 20 for output wiring in Bridged Mono configuration. RA150/300/500 Reference Manual 17 Connections: Chapter 2 OUTPUTS Warning: Be sure that the AC power is off prior to connecting or disconnecting any signal wiring. SPEAKER CABLES The cables you use between the RA150/300/500 and its speakers are very important. Speaker cables must deliver large amounts of peak current to a speaker. To complicate matters further, a speaker represents an inductive load, and is more difficult to drive than a purely resistive load. Any resistance between the amp output and speakers will degrade the damping factor, efficiency and ultimately, the sound quality. Alesis recommends stranded, rather than solid, cables for flexibility and ease of installation. Because they lack sufficient current-carrying capacity, the amp and speakers will not perform properly and the sound may be degraded. WHAT'S THE LOAD IMPEDANCE? Alesis amplifiers can reliably drive 4 loads in Stereo mode and 8 loads in Bridged Mono mode. However, the impedance of a loudspeaker varies with frequency, and its nominal rated impedance is not necessarily its minimum impedance. Some loudspeakers carry both nominal and minimum impedance specifications, and some are supplied with impedance curves. When connecting multiple loudspeakers or systems to any amplifier, care should be taken that the actual load impedance does not drop below the amplifier's rated output load. The RA150/300/500 amplifiers will not be damaged by excessively low output load impedances, but they will not be able to provide full output power and their protection circuits may automatically cut off their outputs until the low load condition is removed. CONNECTORS Each channel features a standard binding post connector (red = "hot" output, black = ground). The binding post or "banana" connectors are the preferred choice for permanent installations. There is greater surface area contact than with phone connectors, thus promoting a better electrical connection between the speaker wire and amplifier. If you make your own cables, use electrical zip cord, which is designed to handle several amps of current, or heavy-gauge speaker cables if possible. In any event, the thicker the cable, the lower the resistance and the better the current-carrying capability. Thin hookup wire is not acceptable; the minimum acceptable wire type is the common "zip cord" used to connect AC to appliances. The table below relates the wire gauge to the how many feet of cable will lead to a 1 dB power loss at different impedances. For cables run up to about 25 feet, 16 to 18 gauge wire is satisfactory. Cable length that produces 1 dB of power loss wire gauge 6 8 10 12 14 16 18 20 22 feet 1200 800 475 300 190 120 75 50 30 at 4 meters 366 244 145 91 58 37 23 15 9 feet 2425 1600 950 600 375 240 150 100 60 at 8 meters 740 488 290 183 114 73 46 30 18 18 RA150/300/500 Reference Manual Chapter 2: Connections In recent years, expensive audiophile cables of high current capacity have appeared. [. . . ] The power output of the amplifier shall be 75 watts per channel (RA150), 150 watts per channel (RA300) or 250 watts per channel (RA500) into a 4-ohm load, with no more than . 02% total harmonic distortion. The units shall be capable of 150 watts (RA150), 300 watts (RA300), or 500 watts (RA500) into an 8-ohm load when operated in bridged mono mode with no more than . 05% total harmonic distortion. The amplifier shall be an Alesis RA150/300/500 Reference Series power amplifier. RA150/300/500 Reference Manual 33 Index INDEX 120-volt to 230-volt conversion, 10, 22 AC cord, 9 AC power, 10 balanced inputs, 14 balanced lines, 16 banana plugs, 19 Bridged Mono mode, 17, 20 cables shielded input, 15 speaker, 18 class AB, 7, 33 cooling, 7, 11 direct box, 17 Fuse, 10 gain setting, 25 ground audio, 9, 14 ground lifter, 24 ground loop, 24 grounding, 3 headphone amplifiers, 23 heat sink, 11 high-temperature operation, 11 impedance input, 17 speaker, 18 input clipping, 26 Inputs, 13 magnetic fields, 12 Maintenance, 28 Meters, 22 Mono. See polarity phone plug inputs, 14 polarity, 20 how to test, 22 power output, 30 Power cable, 3 power loss in speaker cable, 18 protection, 7 Rack Mounting, 11 RCA/phono input jacks. [. . . ]