Radio Shack MPA-125 owner manual Connecting Speakers, Determining Total Speaker Impedance

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CONNECTING THE

SPEAKERS

You can connect one or more 4-, 8- or 16- ohm speakers to the amplifier, with or with- out transformers. To ensure equal volume from each speaker, all connected speakers should have the same impedance rating.

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.

Most speaker terminals are color-coded or have a mark that indicates the terminal’s po- larity. Usually, terminals with positive polarity are red or have a plus symbol (+), and termi- nals with negative polarity are black or have a minus symbol (–). Phasing is correct when you connect + to + and – to –.

Determining Total Speaker Impedance

Before you connect speakers to the amplifi- er, you must determine the total speaker im- pedance.

Caution: A total speaker impedance higher than 16 ohms or lower than 4 ohms can damage your amplifier or speakers.

In determining the total speaker impedance, you must first determine if you are connect- ing the speakers in series, parallel, or a se- ries/parallel combination.

Note: For the best results when connecting speakers (in series or parallel), only use speakers that have the same impedance.

•Speakers are connected in series when the first speaker’s positive terminal is connected to the next speaker’s nega- tive terminal.

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 8- ohm 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).

•Speakers are connected in parallel when all the speakers’ negative termi- nals are connected together and all their positive terminals are connected together.

Determine the total impedance of speakers you want to connect in parallel by dividing the impedance of one speaker by the number of speakers. For example, if you plan 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 (see “Connecting Two Speakers In Parallel” on Page 10).

•If you are connecting more than two speakers using only series or only paral- lel connections, the total impedance might exceed the amplifier’s maximum impedance (16 ohms) or fall below its minimum impedance (4 ohms).

For example, if you connect four 8-ohm speakers:

•In series, the total impedance is 32 ohms (8 + 8 + 8 + 8 = 32). This exceeds the maximum rating.

•In parallel, the total impedance is 2 ohms (8 divided by 4 = 2). This falls below the minimum rating.

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Contents MPA-125 100-Watt PA Amplifier Contents Features Master Volume Control lets you adjustPresetting the Controls Presetting Audio Input DevicesPresetting the Amplifier PreparationConnecting Input Sources Connecting MicrophonesConnections Mounting the AmplifierConnecting a Turntable Connecting an Equalizer Connecting an Auxiliary Sound SourceConnecting the MIX BUS Jack Connecting Speakers Determining Total Speaker ImpedanceConnecting Two Speakers In Series Preparing the Speaker WireConnecting Only One Speaker Connecting Two Speakers In Parallel Connecting Four Speakers In Series/Parallel CombinationConnecting Speakers with Trans- formers Transformers offer these advantagesUsing Your Amplifier Connecting PowerSafety Indicators Using AN EqualizerMonitoring the Sound Sources Listening SafelyUsing the Feedback Filter Troubleshooting Symptom Possible Cause SuggestionCare and Maintenance Replacing the Fuse FCC Wants YOU to KnowSpecifications Fm Page 19 Tuesday, March 28, 2000 1045 AM Limited One-Year Warranty

MPA-125 specifications

The Radio Shack MPA-125 is a versatile and powerful amplifier that was designed to meet the demands of audio enthusiasts and professionals alike. Renowned for its robust performance and reliability, the MPA-125 has garnered a reputation as a dependable choice for a variety of sound applications, from home audio systems to live sound reinforcement.

One of the standout features of the MPA-125 is its impressive power output. With a rating of 125 watts per channel at 8 ohms, this amplifier ensures that audio signals are delivered with clarity and precision, making it suitable for driving a wide range of speakers. The 2-channel design allows for stereo applications, providing a rich and immersive listening experience. Additionally, the MPA-125 can operate at a low impedance, ensuring compatibility with various speaker configurations.

The MPA-125 is equipped with several advanced technologies that enhance its performance. The built-in thermal protection circuit safeguards the amplifier from overheating, allowing it to operate efficiently even during extended use. The amplifier also features a soft clipping circuit, which prevents distortion during peak output levels, ensuring that audio quality remains consistent and clear at high volumes.

User-friendly design is another hallmark of the MPA-125. The front panel includes easy-to-use volume controls, indicator lights, and speaker output terminals. The amplifier is designed for straightforward integration into existing audio setups, making it accessible for users of all experience levels. The balanced XLR inputs provide a secure and noise-free connection, ideal for professional audio applications.

Constructed with high-quality components, the MPA-125 is built to last, ensuring longevity and sustained performance over time. Its compact form factor makes it easy to incorporate into various environments, from home theaters to portable sound systems.

Overall, the Radio Shack MPA-125 is a reliable and powerful amplifier that brings out the best in audio equipment. Its combination of solid performance, user-friendly features, and advanced technologies makes it an excellent choice for anyone looking to elevate their audio experience, whether for casual listening or professional use.
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