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32-2002.fm Page 1 Friday, February 11, 2000 11:36 AM
MPA-50 40-Watt PA Amplifier
Owner’s Manual
Please read before using this equipment.
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32-2002.fm Page 2 Friday, February 11, 2000 11:36 AM Contents Features ................................................................................................................... 3 Preparation .............................................................................................................. 4 Presetting the Controls ....................................................................................... 4 Choosing a Location ...............................................
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32-2002.fm Page 3 Friday, February 11, 2000 11:36 AM Features Your RadioShack MPA-50 40-Watt PA Your amplifier is ETL listed to UL stan- Amplifier gives you 40 watts of solid dards and meets all applicable FCC power for your public address (PA) sys- standards. tem. The built-in three-band equalizer enables you to tailor the sound to fit your WARNING: To reduce the risk of fire or environment. Its wide frequency re- shock hazard, do not expose this product to rain or moisture. sponse easily
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32-2002.fm Page 4 Friday, February 11, 2000 11:36 AM Preparation Notes: PRESETTING THE CONTROLS • Place the speakers so they are mounted slightly above the listeners’ Warning: A sudden high output from the heads and pointed toward them. amplifier could damage your hearing or the speakers connected to the amplifi- • When using more than one speaker, er’s output. overlap the projection areas of the speakers to prevent “dead” spots. To avoid accidentally overdriving a channel or prematurely a
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32-2002.fm Page 5 Friday, February 11, 2000 11:36 AM Making Connections Important: Connect all auxiliary equipment and speakers before connecting power. PHONO L (Left) and R (Right) Input PHONO/AUX/CD Switch — Select the Jacks — Connect a turntable with a input source. Even if you connected magnetic cartridge. To avoid distortion, auxiliary equipment to both the PHONO do not connect a high-level audio input and AUX/CD input jacks, you can use source to these jacks. Even though the only one
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32-2002.fm Page 6 Friday, February 11, 2000 11:36 AM Speakers minal that does not have the wire SPEAKER PHASING attached to it. Phasing is the direction the speaker 4. Touch the negative end of the bat- cone moves with reference to the polari- tery with the lose end of the wire ty of the connection wires. Proper phas- attached to the other speaker termi- ing is important when you use more than nal. Note the direction of the cone one speaker in the same room or area. movement — inward or out
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32-2002.fm Page 7 Friday, February 11, 2000 11:36 AM determine if your speakers are connect- mum impedance (16 ohms) or fall ed in series, parallel, or series/parallel below its minimum impedance (4 combined. ohms). Note: We recommend that you use For example, if you connect four 8- speakers that are rated the same (for ohm speakers: example, all 8-ohm speakers) for all se- – In series, the total impedance is 32 ries or parallel connections. ohms (8 + 8 + 8 + 8 = 32). This • Speakers are conn
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32-2002.fm Page 8 Friday, February 11, 2000 11:36 AM Speakers in Series One Speaker 8WWWW Speaker Connect the speaker’s negative (–) ter- minal to the amplifier’s COM (common) terminal. Then connect the speaker’s Two 8WWWW Speakers positive (+) terminal to the amplifier’s terminal that matches the speaker’s im- 1. To determine the total impedance of pedance. For example, if you have an 8- speakers connected in series, add ohm speaker, connect the speaker’s the impedance of all the speakers. p
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32-2002.fm Page 9 Friday, February 11, 2000 11:36 AM Speakers in Parallel Series and Parallel Combined Two 8WWWW Speakers Four 8WWWW Speakers 1. To determine the total impedance of If you must hook up more than two speakers connected in parallel, speakers, you might have to use a com- divide the impedance of one bination of series and parallel connec- speaker by the number of speakers. tions to get a total impedance that matches one of the amplifier’s terminals. For example, if you want to co
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32-2002.fm Page 10 Friday, February 11, 2000 11:36 AM 4. To determine the total impedance of • You can add or remove a speaker speakers connected in serial and without having to recalculate the parallel combined, divide the imped- entire system’s impedance. ance of one pair of speakers by the • You can reduce signal loss when number of pairs. you use speaker wire over 50 feet For example, if you want to connect long. four 8-ohm speakers in serial and You need a separate transformer for parall
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32-2002.fm Page 11 Friday, February 11, 2000 11:36 AM Cautions: • Before you connect the speakers, be sure the total wattage of the primary taps you intend to use does not exceed the amplifier’s maximum 40-watt output power rating. • Avoid multiple connections to the amplifier’s 70V and COM terminals. Follow these steps to make the connections. 1. Connect a wire from the amplifier’s 70V terminal to each transformer’s primary tap that matches your speaker’s wattage rating. For example, if you
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32-2002.fm Page 12 Friday, February 11, 2000 11:36 AM Controls and Operation MICROPHONE 1 and 2 Inputs — Con- 150Hz Equalizer Control — controls nect any standard dynamic microphone output for instruments in this very low 1 with a /4-inch plug. range (such as an organ or a contrabas- soon). Too much bass makes music POWER Switch and Indicator — Press sound muddy and boomy, while too little the bottom half of the switch to turn on makes it sound hollow and thin. Rotate the amplifier. The ind
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32-2002.fm Page 13 Friday, February 11, 2000 11:36 AM Troubleshooting If you should run into difficulties, check the wiring of the system. Are there any short circuits in the speaker wiring? Have you provided adequate ventila- tion? Did you calculate speaker imped- ance correctly? Be sure microphones and connecting cables are not defective. Be sure you are using large enough speaker wire. You should always use 16-gauge (or larger) wire. The longer the run of speaker wire, the heavier the ga
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32-2002.fm Page 14 Friday, February 11, 2000 11:36 AM Care To enjoy your MPA-50 40-Watt PA Am- terclockwise until the fuse holder plifier for a long time: pops out. • Keep the amplifier dry. If it gets wet, 3. Remove the fuse holder and replace wipe it dry immediately. the fuse. • Use and store the amplifier only in 4. Slide the fuse holder back in place normal temperature environments. then, using a flat-blade screwdriver, push and turn the fuse holder’s cap • Handle the amplifier gently a
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32-2002.fm Page 15 Friday, February 11, 2000 11:36 AM Specifications Output Power at 1 kHz, 10% THD ............................................................................... 40 Watts Power Bandwidth at 1W, 10% THD, Auxiliary Input ............................................ 70 Hz–20 kHz THD at 2W, 1 kHz MIC1 .............................................................................................................................. 1% MIC2 ...........................................
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32-2002.fm Page 16 Friday, February 11, 2000 11:36 AM Limited One-Year Warranty This product is warranted by RadioShack against manufacturing defects in material and workman- ship under normal use for one (1) year from the date of purchase from RadioShack company-owned stores and authorized RadioShack franchisees and dealers. EXCEPT AS PROVIDED HEREIN, Ra- dioShack MAKES NO EXPRESS WARRANTIES AND ANY IMPLIED WARRANTIES, INCLUDING THOSE OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE,
