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The Realistic MPA-20 is a 20 watt Solid State PA Amplifier sold by Radio Shack at one time. 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.Be 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.[[Category:Intercom Systems]]