Owner`s manual

Figure 4. Bypassing the alternator output.

Grounding practices

CAUTION

Ground Isn’t Ground!

Remember those words. Any time that you think that grounding is a trivial matter recite those three

words.

The basic reason that we ground anything at all is to supply a negative return for the electric

current that operates a device. If you’re an auto maker, basically anything that is metal and some-

how associated with the vehicle body is fair game. If you’re a state-of-the-art autosound installer,

that belief is the first and last mile on the road to ruin.

A second reason that things are grounded is so that their metal enclosures can act as a shield for

incoming EMI. Remember...the metal enclosures only act as a shield when they are grounded. This

helps keep portions of the circuitry that weren’t designed to be radio receivers from becoming radio

receivers.

Ground loops cause problems by allowing multiple paths into the grounding system. This wouldn’t

be such a problem if it were not for the finite and measurable resistance of the ground system.

When you combine the multiple current paths into the ground system caused by the auto maker’s

indiscriminate definition of the word ground and the finite resistance of the ground system you get

voltage drops. These voltage drops cause trouble when they get into an audio system via a ground

loop. What happens is that the audio system tends to amplify any noise present in the ground

system. The net result is noise.

Here’s some (heh-heh) ground rules:

1. There should be one and only one path to the negative side of the vehicle electrical system. If

you elect to use the vehicle body as this point, scrape the paint from under the contact point, and

use a lockwasher on both sides of the terminal lug.

In extreme cases, you may need to run a heavy gauge wire to the battery’s negative terminal.

Alternatively, you could use the point where the battery negative hits the vehicle frame. Again,

clean everything and use lockwashers. If the connection point is subject to vibration (like on the

engine), then be sure to use stranded or braided wire (braided is better) and leave enough slack

so that the entire length of wire can vibrate. This will help keep it from breaking.

Minimizing Noise in Autosound Systems