Noise and your new Amplifier

You've installed a new amplifier, only to discover noise in your system that wasn't there before. Don't panic — just run down this checklist, eliminating possibilities until you find the culprit.

An amplifier can introduce noise into your system through a bad ground or through a poor mounting. Rubber grommets or feet can help isolate the amplifier from the chassis of the vehicle, a potential source of noise.

Where is the amp mounted?

Is it near something that could be radiating noise, like a rear-mounted tuner or computer? If so, unbolt it and move it away to see if the noise stops. Remove your patch cables. If you still hear noise, check to see if your amp is isolated from the vehicle's chassis. Any contact between your amp's metal casing and your vehicle's body could cause noise problems.

Check your ground wire

Is it securely attached to the vehicle's chassis with a good contact to clean metal? Your ground wire should ideally be 18" long at most — a longer ground wire can cause noise problems. Improper grounding causes most system noise problems.

Check your gain structure

After you've set the gain on your amplifier, check for system noise (or hiss) with the engine off. Insert a blank tape (or put your CD player on pause), and turn the volume way up. If you hear an unusual amount of hiss, reset your gain structure by reducing the gain on your amplifier so that your receiver is supplying more signal in order to reach the same volume level. Experiment until you eliminate the hiss or reduce it as much as possible. A tiny bit of hiss is OK. You won't hear it while driving.

Are you hearing engine noise?

Any amp installation can be prone to engine noise. You may hear a whining or clicking sound (its pitch will vary with engine speed). Since most noise problems come from a poor ground, always make sure your ground wire is connected firmly to bare metal in the event of a noise problem. You can also try isolating your amp from the chassis of your vehicle by mounting it on a board or using rubber grommets or feet; using a different brand of patch cables; or, only if all else fails, installing a noise suppressor . The tricky part is figuring out which step or steps to take. Please read the rest of this section and try some of the simple tests.

Noise in the patch cables

Noise can be picked up by the RCA patch cables connecting your components. To test this, detach the cables from your amp. (Note: A small number of amplifiers mute themselves when patch cables are removed. To defeat the automatic mute, insert one side (left or right) of a spare patch cable into the amp's left and right input jacks.) Turn on your system and engine. If the noise is gone, reconnect the cables to the amp, and disconnect them from your receiver. If you hear the noise, your patch cables are definitely picking it up. Try re-routing them, taking care to separate them from your power cable by at least 18 inches. Also, newer cars may have a cable that provides power to computers and lights in the rear of the vehicle — make sure that your patch cables aren't too close to this cable.

You should also switch to higher-quality patch cables. The inexpensive RCA cables many people use to connect their components don't have the shielding or conductivity necessary to deflect noise in the metallic, highly-conductive automobile environment. Twisted pair RCA patch cables excel at rejecting noise generated by your vehicle. As a last resort, a ground loop isolator (like PAC's SNI-1) can be installed between the receiver's preamp outputs and your amp to minimize this problem.

Noise picked up by your antenna

If it's not in the patch cables, the noise may be coming from a ground loop caused by your antenna. Plug all your patch cables back in and unplug your antenna. If the noise goes away, try an antenna noise suppressor (like American International's AS100). This filter plugs in-line between your receiver and your antenna, breaking the ground path between them.

Noise picked up by the power or ground cables

If you still have noise after unplugging the antenna, it may be coming in through the amp's main power cable. Noise can be created by cable of insufficient gauge, so you might try thicker cable.

If you cannot find the faulty ground in your multi-amp system, a ground loop isolator can help minimize the problem.

Multiple amplifiers can also create ground loop problems, which can usually be solved by grounding each amplifier with its own separate wire. If you are unable to locate the cause, a ground loop isolator (like PAC's SNI-1) can be installed between the receiver's preamp outputs and the amplifiers to minimize this problem.