If you've got an MP3 player and a decent car stereo, it's easy to get by without an equally powerful home setup. If you're in that position, you might occasionally want to use your car amp in the house to drive a set of speakers. Car amplifiers run on 12V DC power and your wall outlet puts out 110V AC, so making them play together nicely takes a bit of persuasion.
Power Supply Amperage
An easy way to calculate the amount of amperage you'll need from a power supply is to add up the fuses in your amplifier, and divide that total in half. For example, if you've got a pair of 15-amp fuses in your amplifier, you'll need approximately 15 amps of continuous power from your 12V power supply. You can buy units with 15 to 20 amps of current at retailers such as Radio Shack. Higher-current power supplies are commercial products, but can often be found used or online.
Connecting Your Amp
Most amplifiers connect to power through a set of screw terminals. This makes them easy to move back and forth between your home and car. Just unscrew the terminals, unmount the amp, and you're off. To connect your amp in the house, buy the same gauge of wire you use in the car. Most installations use red for the "hot" or positive wire, and black for the negative. If your wire is larger than the power supply's terminals can accommodate, crimp or solder banana plugs to the wires at that end. For added safety, you might also install an inline fuse on the red wire. Use the same amperage as the amp's fuses.
Most home stereo speakers are rated for 8 ohms of impedance, or electrical resistance. Most car amplifiers are rated for 4-ohm speakers. You can use 8-ohm speakers without any problem, though they won't put out as much volume. Boxed car speakers are your best choice. If your amplifier is rated for 2-ohm speakers, use those to get better volume at any power setting. Your speakers' sensitivity, expressed in decibels, is another factor. Every 3 dB of sensitivity doubles your speakers' volume, so speakers rated at 90 dB will generate twice the volume of a set rated at 87 dB.
Testing Your Setup
Connect an MP3 player or other audio source to the amplifier. Turn on the power supply, adjust the amp to a low volume setting, and power it up. If you hear a loud hum, that means you're plugged into an outlet with a bad ground. Turn off the power, and try again from a different outlet. If the hum is gone, turn up the volume slowly until you reach a normal listening level. Check the amplifier and power supply frequently, to make sure they aren't overheating. If the amplifier overheats, you need higher-impedance speakers. If the power supply overheats, the amp is drawing too much current.
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