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"Amp Up" Your Factory System

Get fuller sound by adding an amplifier

Heads up!

Welcome to this article from the Crutchfield archives. Have fun reading it, but be aware that the information may be outdated and links may be broken.

One of life's most embarrassing moments — you're mesmerizing your friends with your knowledge of musical lyrics, and one of them says, "Umm...that's not the way it goes."

Chances are you suffered this musical faux pas because you were listening to weak, ill-defined sound from a factory sound system and misunderstood a key word or a phrase.

The good news — there's no better way to dispel muddy sound than with an amplifier. An amp can help you get the most from your factory system — especially in a larger van or SUV, where it's really tough to achieve clean, powerful sound.

Speaker-level inputs let you connect an amplifier to your factory stereo system.

The value of speaker-level inputs

Factory radios do not have dedicated outputs for amplifiers (preamp outputs). So you'll want an amplifier with speaker-level (often called high-level) inputs; these inputs enable you to tap into the factory speaker wires for a signal flow.

They're called high-level inputs because the voltage level is significantly higher than with a standard preamp output connection. These inputs convert the high voltage to one the amplifier can handle. Once connected, you'll hear clean, well-defined sound (including the lyrics to your favorite song).

Speaker-level inputs are a standard of many two- and four-channel, and mono subwoofer amplifiers.

A 2-channel amp will power two speakers (or a subwoofer); a 4 channel-amp provides a few more wiring options.

Which amp is right for me?

As a rule, there's no reason to buy more amplifier power than you need, and this is especially true with factory stereos and speakers. A monstrous 1600-watt, 4-channel amp will simply overpower your factory system.

Most factory receivers do not put out a lot of power — 8-10 watts RMS would be considered average. As a rule of thumb, you'll need to increase your amplifier power by a factor of 10 to double the volume level. So if you want the volume to be twice as loud as it is now, you'll need an 100-watt per channel amplifier (keep in mind that factory speakers won't handle this kind of power). However, even a relatively small outboard amp (with as little as 25 watts RMS per channel) will produce a noticeable increase in the clarity and impact of your speakers.

If you just want to power two speakers (or a subwoofer), choose a 2-channel amp. A 4-channel amp will drive four speakers, two subwoofers, or two speakers and a subwoofer (a common configuration, particularly with rear speakers for additional "fill").

Amplifier placement will depend on whether you are powering front and/or rear speakers, or a subwoofer, as well as the cargo space in your vehicle.

Check out our Learning Center articles for tips on choosing the right amplifier for your vehicle.

Installing an amp means routing cables for both power and audio signal.

Installation issues

The installation of an amplifier using speaker-level inputs does not differ significantly from one with preamp outputs. Before you do anything, you'll want to disconnect the negative terminal from your battery to protect against a possible short circuit.

Working from your car's passenger compartment, you'll run the red power wire from your amp kit through your vehicle's firewall, route it to your battery, and connect it to the fuse holder. Mount the fuse holder, and secure the connections to the radio and the battery. This will help you get power. You'll also route your red (power) and blue (turn-on) wires under door panels (or under seats) to your amplifier.

In addition to power, you'll need an audio signal. For each speaker, or subwoofer, that you plan to drive with an amp, strip back a small part of your vehicle's color-coded left and right speaker wires, then splice in the wires that lead to your amplifier. (Solder or crimp, and secure the connection for optimum performance.)

If your amp is in your trunk, it's a relatively short path to rear deck speakers or a subwoofer. Driving front seat speakers will require you to run wiring under a door jamb or the floor carpeting to reach the speakers. Likewise, if your amp is under a front seat, the front speakers are more accessible than the rear ones.

Be sure to check out our articles on step-by-step amplifier installation instructions, amplifier installation tips and tricks, and our installation video — it's a great teaching tool whether you're installing your first amp, or your 100th.

Another option: line output converters

You just got a neat gift from a relative — an amplifier for your factory stereo. Trouble is, it doesn't have speaker-level inputs.

There's no reason to be a "re-gifter." Simply pick up an inexpensive line output converter. This is a small device that converts the high-voltage, speaker-level signal to a preamp-level signal that's acceptable to your amp. An "LOC" consists of a transformer and a high-voltage resistor. The converter connects to your amp using a standard RCA patch cable. The transformer should be grounded; most line output converters have a wire for that purpose. They also usually have an adjustable gain feature for you to tweak the output.

Installing an amp can involve a bit of elbow grease. But a successful installation might well leave you grinning ear-to-ear the next time someone challenges you to "Name That Lyric."

Line output converters step down high voltage signals to preamp levels for connection to your amplifier with an RCA cable.