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32-2001.fm Page 1 Friday, February 4, 2000 7:53 AM
MPA-40 20-Watt PA Amplifier
Owner’s Manual
Please read before using this equipment.
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32-2001.fm Page 2 Friday, February 4, 2000 7:53 AM Contents Features ................................................................................................................... 3 Preparation .............................................................................................................. 4 Presetting the Controls ....................................................................................... 4 Choosing a Location .................................................
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32-2001.fm Page 3 Friday, February 4, 2000 7:53 AM Features Your RadioShack 20-Watt PA Amplifier Your amplifier is ETL listed to UL stan- gives you 20 watts of solid power for dards and meets all applicable FCC your PA system. Its wide frequency re- standards. sponse easily handles amplification of voice and music. It operates on either WARNING: To reduce the risk of fire 120 volts AC or 12 volts DC power so or shock hazard, do not expose this you can use it anywhere you want to de- product
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32-2001.fm Page 4 Friday, February 4, 2000 7:53 AM Preparation To avoid sudden audio from the input PRESETTING THE sources, be sure all audio devices are CONTROLS turned off before you connect them to the amplifier. Warning: A sudden high output from the amplifier could damage your hearing or the speakers connected to the amplifi- CHOOSING A LOCATION er’s output. Choose a location with adequate venti- To avoid accidentally overdriving a lation. Do not place the amplifier on thick channel o
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32-2001.fm Page 5 Friday, February 4, 2000 7:53 AM PHONO/AUX/CD Switch — select the cable’s barrel plug to this jack if you input source. Even if you connected want to temporarily power the amplifier PHONO auxiliary equipment to both the from your vehicle’s 12-volt battery. Then AUX/CD and input jacks, you can use connect the cable’s other end to your only one source at a time. vehicle’s 12-volt accessory socket (such as a cigarette-lighter socket). Speaker Push Terminals — press the Cauti
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32-2001.fm Page 6 Friday, February 4, 2000 7:53 AM 3. Touch the positive end of a 1.5-volt ed in series, parallel, or series/parallel flashlight battery to the speaker ter- combined. minal that does not have the wire Note: We recommend that you use attached to it. speakers that are rated the same (for 4. Touch the negative end of the bat- example, all 8-ohm speakers) for all se- tery with the lose end of the wire ries or parallel connections. attached to the other speaker termi- • Speakers a
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32-2001.fm Page 7 Friday, February 4, 2000 7:53 AM • If you connect more than two speak- You can connect one or more 4-, 8-, or ers using only series or only parallel 16-ohm speakers, with or without trans- connections, the total impedance formers, between the amplifier’s output might exceed the amplifier’s maxi- and the speakers’ input. To ensure mum impedance (16 ohms) or fall equal volume from each speaker, all the below its minimum impedance (4 connected speakers should have the ohms). sa
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32-2001.fm Page 8 Friday, February 4, 2000 7:53 AM Speakers in Parallel you can make the correct connection. The total impedance of all the speakers 1. To determine the total impedance of must match one of the amplifier’s output speakers connected in parallel, 4W 8W 16W ) terminals ( , , or . divide the impedance of one Speakers in Series speaker by the number of speakers. 1. To determine the total impedance of For example, if you want to connect speakers connected in series, add two 8-ohm sp
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32-2001.fm Page 9 Friday, February 4, 2000 7:53 AM impedance of one pair of speakers) by 2 (the number of speaker pairs) for a total speaker impedance of 8 ohms. 5. Connect the negative (–) terminals of all pairs of speakers to the ampli- COM fier’s terminal. 6. Connect the positive (+) terminals of Four 8W Speakers all pairs of speakers to the ampli- fier’s terminal that matches the total If you connect four 8-ohm speakers in speaker impedance (8W , in this series, the total impedance is 32
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32-2001.fm Page 10 Friday, February 4, 2000 7:53 AM Cautions: • Before you connect the speakers, be sure the total wattage of the pri- mary taps you intend to use does Taps not exceed the amplifier’s maximum 20-watt output power rating. • Avoid multiple connections to the amplifier’s 70V and COM terminals. Follow these steps to make the connec- tions. You need a separate transformer for each speaker. 1. Connect a wire from the amplifier’s 70V terminal to the transformer’s pri- Line transform
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32-2001.fm Page 11 Friday, February 4, 2000 7:53 AM 3. Connect a wire from the speaker’s 4. Connect a wire from the speaker’s positive (+) terminal to the trans- negative (–) terminal to the COM tap former’s secondary tap that on the transformer’s secondary matches the speaker’s total imped- side. ance (4, 8, or 16 ohms). Controls and Operation MICROPHONE 1 and 2 Inputs — con- the two microphones to get the proper nect any standard dynamic micro- volume and balance. phones. PHONO/AUX Source
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32-2001.fm Page 12 Friday, February 4, 2000 7:53 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 gau
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32-2001.fm Page 13 Friday, February 4, 2000 7:53 AM Care and Maintenance To enjoy your amplifier for a long time: Amplifier • Keep the amplifier dry. If it gets wet, The power fuse protects your amplifier wipe it dry immediately. from power (voltage or current) surges when operating it from an AC power • Use and store the amplifier only in source. If the POWER indicator does not normal temperature environments. light when you press POWER, check the fuse and replace it with one of the same
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32-2001.fm Page 14 Friday, February 4, 2000 7:53 AM Specifications Output Power at 1 kHz, 10% THD ............................................................................... 20 Watts THD at 1W, 1 kHz Low-Pass Filter MIC1 .............................................................................................................................. 1% MIC2 .............................................................................................................................. 1% AUX
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32-2001.fm Page 15 Friday, February 4, 2000 7:53 AM Notes 15
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32-2001.fm Page 16 Friday, February 4, 2000 7:53 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, AR
