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32-2003.fm Page 1 Tuesday, March 28, 2000 10:45 AM
MPA-125 100-Watt PA Amplifier
Owner’s Manual
Please read before using this equipment.
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32-2003.fm Page 2 Tuesday, March 28, 2000 10:45 AM Contents Features .................................................................................................................................. 3 Preparation ............................................................................................................................. 4 Presetting the Controls ...................................................................................................... 4 Presetting Audio Input D
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32-2003.fm Page 3 Tuesday, March 28, 2000 10:45 AM Features Master Volume Control Your RadioShack MPA-125 100-Watt PA — lets you adjust Amplifier gives you the versatility and power the overall sound level. you need in a professional sound system. Its EQ IN/OUT Switch — lets you connect and wide frequency response easily handles am- use an equalizer with the amplifier. plification of voice and music. Use it in meet- ing halls and auditoriums, at sports events, in Push-Terminal Connectors
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32-2003.fm Page 4 Tuesday, March 28, 2000 10:45 AM Preparation PRESETTING THE CONTROLS Before you begin making connections or using your amplifier, preset the audio input source’s and the amplifier’s controls to avoid over-driving a channel or producing sudden unexpected loud sounds. Presetting Audio Input Devices Set the audio input sources’ controls to these levels: Audio Device Control Setting Turntable Power Off Tape Deck Power Off CD Player Power Off Amplifier/Receiver Power Tone Off F
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32-2003.fm Page 5 Tuesday, March 28, 2000 10:45 AM MOUNTING THE AMPLIFIER PLACING THE SPEAKERS You can mount the amplifier in a standard- Speaker placement depends on your room’s sized audio equipment rack or on a desk, size and arrangement. We recommend you shelf, or table. Be sure you place it in a loca- play a wide-range recording and experiment tion with adequate ventilation. Do not put it with speaker placement until you find the lo- on thick carpeting (which can restrict air flow) catio
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32-2003.fm Page 6 Tuesday, March 28, 2000 10:45 AM Notes: • If your microphone’s cord is longer than 20 feet (6.01 meters), we recommend that you connect it to a balanced jack to reduce signal hum. • If you connect a microphone to both jacks for MIC 1, MIC 2, MIC 3, or MIC 4, the microphone you connect to the unbalanced jack has priority. • If you connect a microphone to either MIC 4 jack, set PHONO/MIC 4 on the back of the amplifier to MIC 4. Connecting a Turntable Turntable GND PHONE/MIC 4
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32-2003.fm Page 7 Tuesday, March 28, 2000 10:45 AM Connecting an Auxiliary Sound Source You can connect any high-level sound source, such as a CD player, tape deck, or tuner, to the CD/AUX jack on the back of the amplifier. CD/AUX Connecting the MIX BUS Jack You can connect another MPA-125 to this jack to double the size of your PA system. This lets you use up to eight microphones (or six microphones and two turntables), and two auxiliary sound sources. Use a shielded cable with phono plugs a
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32-2003.fm Page 8 Tuesday, March 28, 2000 10:45 AM Determine the total impedance of CONNECTING THE speakers you want to connect in series SPEAKERS by adding up the individual impedances of all the connected speakers. For You can connect one or more 4-, 8- or 16- example, if you want to connect two 8- ohm speakers to the amplifier, with or with- ohm speakers in series, add 8 (the out transformers. To ensure equal volume impedance of one speaker) plus 8 (the from each speaker, all connected sp
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32-2003.fm Page 9 Tuesday, March 28, 2000 10:45 AM You can achieve a proper total impedance Connecting Only One Speaker by combining series and parallel connec- Connect the speaker’s negative (–) terminal tions. to COM (common) on the back of the amplifi- er. Then connect the speaker’s positive (+) Preparing the Speaker Wire terminal to the speaker terminal (4WWWW , 8WWWW , or 16WWWW ) on the back of the amplifier that match- Use the shortest length of wire possible to es the speaker’s impeda
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32-2003.fm Page 10 Tuesday, March 28, 2000 10:45 AM Connecting Two Speakers In Parallel Follow these steps to connect speakers in parallel. Two 8 Speakers WWWW 8 WWWW ___________ = 4 WWWW 2 Speakers 8 WWWW 8WWWW Speaker 1 Speaker 2 1. Connect both speaker’s negative (–) terminals to each other, then connect both wires to the COM terminal on the back of the amplifier. 2. Connect both speaker’s positive (+) terminals to each other, then connect both wires to the speaker terminal (4WWWW , 8WWWW
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32-2003.fm Page 11 Tuesday, March 28, 2000 10:45 AM 3. Connect the two pairs of speakers in Line transformers have several connectors parallel. If you connected 8 ohm speak- called taps. ers the total impedance of both pairs is 8 ohms (16 ‚ 2 = 8). Note: If each of the four speakers is 8 ohms, the total speaker impedance of Taps the combined series/parallel connection described above is also 8 ohms. Like- wise, the total speaker impedance is 4 or 16 ohms if the speakers are 4 or 16 ohms, resp
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32-2003.fm Page 12 Tuesday, March 28, 2000 10:45 AM Follow these steps to connect speakers using a transformer. Connect a wire from 70V RMS on the back of USING YOUR AMPLIFIER the amplifier to the transformer’s desired pri- Press in POWER to turn on the amplifier. mary tap (10, 5, 2.5, 1.25 or 0.62 watts). Start the input sound source. Note: Usually, each speaker in a system uses the same wattage tap. If you want a Rotate MASTER VOLUME to its mid-position. particular speaker to have a higher
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32-2003.fm Page 13 Tuesday, March 28, 2000 10:45 AM SAFETY INDICATORS Your amplifier has two indicators that warn you of potential damage to the amplifier. CLIPPING Indicator PROTECTION Indicator The CLIPPING indicator lights when a sound source’s signal exceeds its mixing control setting. If this happens, reduce the level of the appropriate mixing control or reduce MASTER VOLUME until the indicator flickers only at peak volume levels. The PROTECTION indicator lights if the amplifier gets too
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32-2003.fm Page 14 Tuesday, March 28, 2000 10:45 AM USING THE FEEDBACK FILTER The FEEDBACK FILTER control lets you reduce or eliminate squeal and other noise caused by feedback. After you adjust MASTER VOLUME, MIC 1, MIC 2, MIC 3, MIC 4/PHONO, and CD/AUX, turn on the amplifier and any connected sound source. If you hear any feedback, turn FEEDBACK FILTER clockwise until you reduce or eliminate the feedback. Note: The FEEDBACK FILTER control decreases feedback frequencies by up to 12 dB. If it
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32-2003.fm Page 15 Tuesday, March 28, 2000 10:45 AM Troubleshooting We do not expect you to have any problems with your RadioShack MPA-125 100-Watt PA Am- plifier, but if you do have a problem, this chart might help. If not, take the amplifier to your local RadioShack store for assistance. Symptom Possible Cause Suggestion No power. The fuse might be blown. Check the amplifier’s fuse and replace it if necessary (see “Replacing the Fuse” on Page 17). Sound source or speakers not con- Chec
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32-2003.fm Page 16 Tuesday, March 28, 2000 10:45 AM Care and Maintenance Your RadioShack is an example of superior design and MPA-125 100-Watt PA Amplifier craftsmanship. The following suggestions will help you care for your amplifier so you can en- joy it for years. Keep the amplifier dry. If it gets wet, wipe it dry immediately. Liquids might con- tain minerals that can corrode the electronic circuits. Use and store the amplifier only in normal temperature environments. Temper- ature ext
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32-2003.fm Page 17 Tuesday, March 28, 2000 10:45 AM REPLACING THE FUSE If the amplifier does not operate, you might need to replace the fuse on the back of the amplifier with the supplied (or another) 3- amp, 250-volt fuse. Important: Let the amplifier cool down and see if it starts again before you assume a fuse needs to be replaced. Caution: Do not use a fuse with ratings other than those specified. Doing so might damage your amplifier. 1. Unplug the amplifier. 2. Use a Phillips screwdriver
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32-2003.fm Page 18 Tuesday, March 28, 2000 10:45 AM Specifications Output Power at THD 2%, 8 Ohm Load 1 kHz ................................................................................... 100 W Total Harmonic Distortion (at 70 Watts, 8 ohms, 1 kHz, with Band Pass Filter) MIC (Phone Jack) ....................................................................................................................... 0.25% MIC (XLR Jack) .............................................................
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32-2003.fm Page 19 Tuesday, March 28, 2000 10:45 AM Notes 19 Notes
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32-2003.fm Page 20 Tuesday, March 28, 2000 10:45 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
