Installing Your Own Car Amplifier

Installing an amplifier calls for a little more skill and creativity than installing a receiver or a pair of speakers. But it's not necessarily all that difficult. If you know what to look out for before you start, you'll save a lot of troubleshooting time after you're finished. 

Carefully plan each step and allow plenty of time. If you run into a little engine noise, don't be discouraged. It's usually not that hard to get rid of. Remember, if you bought your amp from Just Kenwood, you can get free technical advice by phone and email. 

Whatever it takes, we're sure you'll be thrilled with the end result. With the extra power, you'll get more volume and much cleaner, more dynamic sound, even at low volume. 

Finding the right spot 

An amplifier can be securely installed with just a few screws. But since amplifiers can be sensitive to electrical and motor noise and because interference from the amplifier may affect your radio reception, try to mount it at least 3 feet away from the radio tuner. Good locations include:

• Under a seat 

  • Pros: Closer to the receiver, so you can use shorter control and signal cables. Closer to the front speakers, so running a wire to them will be easier. No luggage space lost.

  • Cons: You may have to remove the seat to do the installation. Larger amps may not fit. 

• On the firewall (passenger side) 

  • Pros: Short wires can be used. You won't have to remove a seat or climb into the boot. 

  • Cons: Only very small amps fit here. Closer to some common noise sources (heater fan motor, flasher unit etc). 

• In the boot or hatch area 

  • Pros: Lots of room for large amps. Near the rear speakers. 

  • Cons: You sacrifice some boot space. Longer signal and power wires required. 

  When working inside the boot, tape over the catch, so you won't become trapped inside accidentally. 

Don't mount an amplifier or other car stereo components such as electronic crossovers or equalizers directly onto steel bodywork - you will invite noise problems. Instead, mount the amp on a non-conductive board and mount the board to the car body (or use rubber grommets under the mounting screws to isolate the amp). 

Before you drill the screw holes to mount your amplifier, connect it up and give it a test run. If the amplifier is operating correctly, with no engine noise, then proceed with the installation. There is also a safety issue here - components that aren't securely mounted could break loose during an accident and injure someone as they fly through the passenger compartment. Use nuts and bolts to secure amplifiers and other components to their mounting locations. 

If you have a subwoofer box in your vehicle, you can mount the amplifier on the outside of the box. If you are mounting the amplifier on the floor, check beneath the car to be sure your screws won't puncture a brake or fuel line. 

Wiring for safety and good sound 

Most amplifiers do not come with power and earth cables or audio leads to carry the signal from your receiver. For most single-amplifier installations, the best way to buy these is in an amp wiring kit that also supplies a thin piece of wire for the turn-on lead, a fuse or circuit breaker, and all the connectors you need. 

The main power lead should be thick — nothing thinner than 12 gauge will do. It draws power directly from the positive battery terminal. An in-line fuse or circuit breaker must be fitted near the battery. Without one, an accidental short circuit could pose a fire hazard and damage your amp. 

Thicker wire — 10, 8, 4 or 2 gauge — might be called for, depending on the length of wire you want to use, the power of your amplifiers and how you plan to use them. For more information see the cable gauge selection chart. 

For amps that put out up to (50 w x 2) channels or (25 w x 4) channels, 10 gauge power cable will usually suffice. Step up to 8 gauge or 4 gauge cable if you're running the wire all the way to the boot and you like your music loud with a lot of bass. 

Thicker wire delivers more current 

If you're planning to use your amplifier to power a subwoofer, install thicker wire. Amplifiers require a lot of current to handle loud, low bass notes, and the thicker the wire, the more current it can deliver. To attach the power lead to the battery, crimp a eyelet terminal onto the end of the wire (most wiring kits come with the ring terminal already attached). 

Unscrew the nut that secures the positive (+) battery clamp to the battery post, slip the power lead terminal over the bolt that secures the battery clamp to the battery post and replace the nut. Do not attach the power lead terminal directly to the battery post. 

How and where to earth your amplifier

The earth wire should be the same thickness as the power cable and must make direct contact with bare metal of the car. 

Look for an existing bolt or screw that makes contact with the car body near the amplifier. Remove the bolt or screw, and scrape away any paint or grease. A star washer will help your earth wire maintain tight contact with the car body. Crimp or solder a eyelet terminal onto the end of the earth wire, slip it underneath the washer, and replace the bolt or screw. 

If you can't find a convenient earth screw or bolt, drill a hole for one. Again, be careful not to drill into the fuel tank or a fuel or brake pipe. 

Earthing multiple components 

If you're installing several components, try to earth each one separately, with about a half-inch of space between each of the earthing points. If you'd rather use a single bolt, place the earth for the component that draws the most current (probably your biggest amplifier) closest to the car body. Put the earth for the component that draws the least current (probably the electronic crossover) on top. 

Wiring for automatic turn-on 

Most amplifiers turn on automatically when a positive 12 volt signal is applied to the amplifier's turn-on input. Since this is a very small amount of current, a convenient method of sourcing this signal is via the electric aerial output from your head unit. Connected this way, your amplifier will be powered up as soon as you turn on your head unit. 

Most amplifier cable kits come with 15-20 feet of thin blue wire that is meant to be used for the turn-on connection. If your receiver doesn't have an electric aerial lead, or if it only works when you actually use the radio, you'll have to make use of another ignition-switched 12 volt power feed. 

Turning on multiple components 

If you have more than one amplifier or other components in your system, you can, in most cases, link the turn on leads together. If you have four or more components in your system, you may need a relay to protect your receiver. That's because the receiver's electric aerial feed can only supply a limited amount of current. 

If the components in your stereo system ask for more current than the receiver can supply, you can burn out that circuit in your receiver. Call our telephone advice t if you need advice on building a relay network (have your invoice handy). A relay network connected to the power antenna lead draws a small amount of current from the receiver, but supplies enough current to simultaneously turn on all your other components. 

Feeding the audio signal to your amplifier 

Most receivers provide preamp output from RCA sockets. If both your receiver and amplifier use RCA connectors, they easily plug together. Preamp output signals vary in strength, depending on manufacturer. If you bought both your amplifier and your receiver from Just Kenwood, you can be sure their signals are compatible. If one of your components was purchased elsewhere, make sure the amplifier's input requirements match the receiver's preamp output level. 

Some amplifiers can also take their input signal from the receiver's speaker leads. But if your receiver has preamp outputs, use those instead. You'll get a cleaner signal. Make sure the cables supplying the audio signal to the amplifier are kept well away from potential sources of noise, such as brake light, heater blower or rear window demister wires.  If the amplifier is located in the boot, run the input signal leads down the same side of the car as any speaker wires you've installed. Run the power and turn-on leads down the other side of the car to avoid interference.

Most amplifiers can accept a choice of line-level or speaker-level input signals

Can your vehicle handle the current demands of a multi-amplifier system? 

Your vehicle's electrical system is designed to  supply the car's different components (headlights, wipers, etc.) with the needed current and voltage to operate properly. 

Some cars' systems are designed for additional current loads (caravan or trailers, for example), but most of them are not. Luckily, most manufacturers design their cars' electrical systems with a reserve capacity that is well-suited to supplying power for a sound system. Look at the label on the vehicle's alternator. This tells you how much current (expressed in amperes or amps, for short) the alternator is capable of producing. 

Most alternators are capable of producing 55-65 amps. This is adequate for sound systems producing up to 350 watts RMS. Some more modern vehicles have alternators rated up to about 120 amps. This will be sufficient for systems of up to about 600 watts. Some pre-1985 cars, on the other hand, have alternators only rated for 35 amps. This will only support about 125 watts in amplifier power. 

If you want more power than your alternator can supply, you will have to consider exchanging your alternator for one of a higher output. This is a specialist job and outside the scope of Just Kenwood. Installing a second battery won't help. The only reason to do that is to play your stereo for long periods with the engine turned off. How you use your system (in terms of usual listening volumes) can make a big difference in current drain. 

The above discussion assumes that you will not be listening to your sound system at three-quarter volume all day long. Any system playing at one-third volume is drawing considerably less current than the same system at three-quarter volume, you probable won't need a charging system upgrade if volume levels are kept reasonable.

On the other hand, you could be asking for trouble if you do keep the volume cranked up. If your system needs more current than the alternator can supply, it can grab current from the battery up to a point. Here are a couple of warning signs to look for: 

• your headlights dim in time to the music when you turn it up loud after dark

• your bass sounds great when you first turn it on, but gets mushy and less powerful within a minute or so

One easy, effective solution is installing a capacitor. Heavy-duty capacitors connect to the power cable (just before it reaches your amplifier) and act as a buffer zone between your amp and your car's electrical system. They store up a reservoir of power which can supply the amplifier's peak demands (like a bass drum beat) without having to draw current from the battery. 

Estimate amplifier current demands 

It's tricky to relate amplifier wattage directly to current consumption. To see how you can figure out what you have, see the page 'frequently asked questions' for amplifiers. 

How to estimate your electrical system's reserve current capacity 

Take your alternator's output rating in amps and multiply it by 40%. This approximate figure will give you a baseline for about how much reserve capacity your car's electrical system has. 

If, for instance, your alternator is rated at 90 amps:
                       90 amps x 40% = 36 amps left to power your sound system.
A hypothetical sound system drawing 33 amps would just work with this car's electrical system:
                       (system draw = 33 amps, car's reserve = 36 amps)
The car's battery would supply the reserve current necessary for the music peaks that are capable of drawing 60-70 amps. Remember, these figures are not scientific estimates!