32-2003.fm Page 1 Tuesday, March 28, 2000 10:45 AM Please read before using this equipment.
32-2003.fm Page 2 Tuesday, March 28, 2000 10:45 AM ˆ Contents Features .................................................................................................................................. 3 Preparation ............................................................................................................................. Presetting the Controls ...................................................................................................... Presetting Audio Input Devices ...........
2-2003.fm Page 3 Tuesday, March 28, 2000 10:45 AM ˆ Features Your RadioShack MPA-125 100-Watt PA Amplifier gives you the versatility and power you need in a professional sound system. Its wide frequency response easily handles amplification of voice and music. Use it in meeting halls and auditoriums, at sports events, in schools, and in the office for paging systems – anywhere you need to deliver special announcements with excellent sound.
32-2003.fm Page 4 Tuesday, March 28, 2000 10:45 AM ˆ 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.
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 standardsized audio equipment rack or on a desk, shelf, or table. Be sure you place it in a location with adequate ventilation. Do not put it on thick carpeting (which can restrict air flow) or near a heat source such as a heat vent or radiator (which can cause it to overheat). Speaker placement depends on your room’s size and arrangement.
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.
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.
32-2003.fm Page 8 Tuesday, March 28, 2000 10:45 AM CONNECTING THE SPEAKERS Determine the total impedance of speakers you want to connect in series by adding up the individual impedances of all the connected speakers. For example, if you want to connect two 8ohm speakers in series, add 8 (the impedance of one speaker) plus 8 (the impedance of the other speaker) for a total speaker impedance of 16 ohms (see “Connecting Two Speakers In Series” on Page 9).
32-2003.fm Page 9 Tuesday, March 28, 2000 10:45 AM You can achieve a proper total impedance by combining series and parallel connections. Preparing the Speaker Wire Use the shortest length of wire possible to connect the speakers. After placing the speakers, use this table to determine the wire length and choose the appropriate gauge size: Wire Length Connecting Only One Speaker Connect the speaker’s negative (–) terminal to COM (common) on the back of the amplifier.
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 8Ω Ω Speakers 8Ω Ω ___________ = 4Ω Ω 2 Speakers 8Ω Ω 8Ω Ω 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.
32-2003.fm Page 11 Tuesday, March 28, 2000 10:45 AM 3. Connect the two pairs of speakers in parallel. If you connected 8 ohm speakers 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 the combined series/parallel connection described above is also 8 ohms. Likewise, the total speaker impedance is 4 or 16 ohms if the speakers are 4 or 16 ohms, respectively. 4.
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 the amplifier to the transformer’s desired primary tap (10, 5, 2.5, 1.25 or 0.62 watts). USING YOUR AMPLIFIER Note: Usually, each speaker in a system uses the same wattage tap. If you want a particular speaker to have a higher volume level, connect the wire from 70V RMS to a higher wattage tap on the transformer. Start the input sound source.
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.
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.
32-2003.fm Page 15 Tuesday, March 28, 2000 10:45 AM ˆ Troubleshooting We do not expect you to have any problems with your RadioShack MPA-125 100-Watt PA Amplifier, but if you do have a problem, this chart might help. If not, take the amplifier to your local RadioShack store for assistance. Symptom No power. No sound. Feedback. Possible Cause Suggestion The fuse might be blown. Check the amplifier’s fuse and replace it if necessary (see “Replacing the Fuse” on Page 17).
32-2003.fm Page 16 Tuesday, March 28, 2000 10:45 AM ˆ Care and Maintenance Your RadioShack MPA-125 100-Watt PA Amplifier is an example of superior design and craftsmanship. The following suggestions will help you care for your amplifier so you can enjoy it for years. Keep the amplifier dry. If it gets wet, wipe it dry immediately. Liquids might contain minerals that can corrode the electronic circuits. Use and store the amplifier only in normal temperature environments.
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) 3amp, 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.
32-2003.fm Page 18 Tuesday, March 28, 2000 10:45 AM ˆ 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) ....................................................................................................................... MIC (XLR Jack) .................................................................................
32-2003.
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 workmanship under normal use for one (1) year from the date of purchase from RadioShack company-owned stores and authorized RadioShack franchisees and dealers.
