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== Amplification ==The Realistic MPA-20 is a 20 watt Solid State PA Amplifier sold by Radio Shack at one time. This is a good choice as the unit can run constantly powered on for years without problem. A less reliable amp or standard home audio receiver would burn up after such extended use without being powered off. This unit must remain constantly powered on and ready to amplify whatever line level signal it receives.[[Image:realisticmpa20.png]]Originally there were only two speakers in the speaker system. These could be wired either series or parallel, thus doubling or dividing the total resistance rating.The back of the MPA-20 supports a single connection to the "com" common ground and any one of the positive posts. :*16 Ohms:*8 Ohms:*4 OhmsThere is a 70 Volt connector for using with line transformers.Originally there were only two speakers in the speaker system. These could be wired either series or parallel, thus doubling or dividing the total resistance rating. Two 8 Ohm speakers wired in Series can be connected to the 16 Ohm post on the back of the MPA-20 amp. Two 8 Ohm speakers conencted in Paralle thus would have to be connected to the 4 Ohm post on the back of the amp. A resistance value too low can cause damage to the amp. A resistance value too high will result in low volume audio.{||[[Image:mulspeakpubaddr2spor1.png]]| Series and Parallel Illustrated|[[Image:mulspeakpubaddr2spor2.png]]|} 1/2 WATT LINEAR TAPER POT 1/2 WATT LINEAR TAPER POT W/SPST SWITCHBe sure to use an "'''audio taper pot'''" for volume control.Be sure to use an "'''audio taper pot'''" for volume control. This is a special kind of [[Potentiometers are Variable Resistors|Potentiometer]] designed for audio.==== Some popular audio Attenuators ====*ALPS RK27 (alias, "ALPS Blue")*Chinese made ALPS (clone) Stepped Attenuator*Panasonc EVJ*Radio Shack 271-1732*DACT CT2== Amplification ==The Realistic MPA-20 is a 20 watt Solid State PA Amplifier sold by Radio Shack at one time. [[Image:realisticmpa20.png]][[Category:Intercom Systems]]