Please read before using this equipment. 32-2002.
32-2002.fm Page 2 Friday, February 11, 2000 11:36 AM ˆ Contents Features ................................................................................................................... 3 Preparation .............................................................................................................. Presetting the Controls ....................................................................................... Choosing a Location .................................................................
2-2002.fm Page 3 Friday, February 11, 2000 11:36 AM ˆ Features Your RadioShack MPA-50 40-Watt PA Amplifier gives you 40 watts of solid power for your public address (PA) system. The built-in three-band equalizer enables you to tailor the sound to fit your environment. Its wide frequency response easily handles amplification of voice and music. Your amplifier is ETL listed to UL standards and meets all applicable FCC standards.
32-2002.fm Page 4 Friday, February 11, 2000 11:36 AM ˆ Preparation PRESETTING THE CONTROLS Notes: Warning: A sudden high output from the amplifier could damage your hearing or the speakers connected to the amplifier’s output. To avoid accidentally overdriving a channel or prematurely amplifying an audio input, set all the amplifier’s frontpanel controls to their lowest settings. • Place the speakers so they are mounted slightly above the listeners’ heads and pointed toward them.
32-2002.fm Page 5 Friday, February 11, 2000 11:36 AM ˆ Making Connections Important: Connect all auxiliary equipment and speakers before connecting power. PHONO L (Left) and R (Right) Input Jacks — Connect a turntable with a magnetic cartridge. To avoid distortion, do not connect a high-level audio input source to these jacks. Even though the amplifier has L and R input jacks, the output from the amplifier is monaural.
32-2002.fm Page 6 Friday, February 11, 2000 11:36 AM ˆ Speakers SPEAKER PHASING minal that does not have the wire attached to it. Phasing is the direction the speaker cone moves with reference to the polarity of the connection wires. Proper phasing is important when you use more than one speaker in the same room or area. Out-of-phase speakers can lose up to one-half of their potential volume, and can have a significantly decreased bass effect. 4.
32-2002.fm Page 7 Friday, February 11, 2000 11:36 AM determine if your speakers are connected in series, parallel, or series/parallel combined. mum impedance (16 ohms) or fall below its minimum impedance (4 ohms). Note: We recommend that you use speakers that are rated the same (for example, all 8-ohm speakers) for all series or parallel connections. For example, if you connect four 8ohm speakers: – In series, the total impedance is 32 ohms (8 + 8 + 8 + 8 = 32). This exceeds the maximum rating.
32-2002.fm Page 8 Friday, February 11, 2000 11:36 AM One Speaker Speakers in Series 8Ω Ω Speaker Connect the speaker’s negative (–) terminal to the amplifier’s COM (common) terminal. Then connect the speaker’s positive (+) terminal to the amplifier’s terminal that matches the speaker’s impedance. For example, if you have an 8ohm speaker, connect the speaker’s positive terminal to the amplifier’s 8-ohm terminal. Two 8Ω Ω Speakers 1.
32-2002.fm Page 9 Friday, February 11, 2000 11:36 AM Speakers in Parallel Series and Parallel Combined Two 8Ω Ω Speakers Four 8Ω Ω Speakers 1. To determine the total impedance of speakers connected in parallel, divide the impedance of one speaker by the number of speakers. For example, if you want to connect two 8-ohm speakers in parallel, divide 8 (the impedance of one speaker) by 2 (the number of speakers) for a total speaker impedance of 4 ohms. 2.
32-2002.fm Page 10 Friday, February 11, 2000 11:36 AM 4. To determine the total impedance of speakers connected in serial and parallel combined, divide the impedance of one pair of speakers by the number of pairs. For example, if you want to connect four 8-ohm speakers in serial and parallel combined, divide 16 (the impedance of one pair of speakers) by 2 (the number of speaker pairs) for a total speaker impedance of 8 ohms.
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.
32-2002.fm Page 12 Friday, February 11, 2000 11:36 AM ˆ Controls and Operation MICROPHONE 1 and 2 Inputs — Connect any standard dynamic microphone with a 1/4-inch plug. POWER Switch and Indicator — Press the bottom half of the switch to turn on the amplifier. The indicator lights. Press the top half of the switch to turn off the amplifier. The indicator goes off. MASTER VOLUME Control — Controls the overall loudness level of all sources.
32-2002.fm Page 13 Friday, February 11, 2000 11:36 AM ˆ 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 ventilation? Did you calculate speaker impedance 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 gauge should be.
32-2002.fm Page 14 Friday, February 11, 2000 11:36 AM ˆ Care To enjoy your MPA-50 40-Watt PA Amplifier for a long time: terclockwise until the fuse holder pops out. • Keep the amplifier dry. If it gets wet, wipe it dry immediately. 3. Remove the fuse holder and replace the fuse. • Use and store the amplifier only in normal temperature environments. 4. Slide the fuse holder back in place then, using a flat-blade screwdriver, push and turn the fuse holder’s cap fully clockwise to secure it.
32-2002.fm Page 15 Friday, February 11, 2000 11:36 AM ˆ 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 .............................................................................................................................. MIC2 ............................................................
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 workmanship under normal use for one (1) year from the date of purchase from RadioShack company-owned stores and authorized RadioShack franchisees and dealers.
