
2. Ground loops: Ground loops are the most common way radiated noise gets
into a mobile stereo system. This is especially true of multiple amp systems.
They have more ground points, and that means more possible locations for
ground loops to form. A ground loop is formed when any ground point in the
system is at a different potential that at any other ground point in the system.
3. Power Lead (+12V) Noise: Since true power lead noise is the only noise that
isn't radiated, and since the vehicle's battery (if in good condition) provides
adequate filtering for alternator noise, then only ignition and accessory noise
could enter the system through the power leads.
BUILT IN NOISE SUPPRESSION
The vehicle's battery forms a huge capacitor bank that does a fantastic job of
filtering noise. Unfortunately, batteries grow old and lose their ability to hold a
charge. At the same time, they lose their ability to filter noise; even corrosion on
the battery terminals will cause increased noise as it isolates the battery.
If the vehicle is in need of ignition repair or tune up, increased noise will result.
Specifically, check the condition of points and condenser, as well as the spark
plug leads. Don't forget to check for resistor plugs, too.
TROUBLESHOOTING NOISE
Once the type of noise has been determined, the entry method must be isolated.
The easiest place to start is the amplifier. Unplug the RCA jacks and listen for a
change in the noise level. If little or no change occurs, the amplifier's power is
contaminated. If the noise is gone, the possibilities are a ground loop or a noise
problem earlier in the system. If the problem is a ground loop, the best solution is
a better ground for the amp(s). Another solution is to carefully connect a wire
from the shield of the RCA connector, at the amplifier end, to a good ground on
the vehicle. This will effectively short circuit the ground loop.
The next check is for radiated noise. With the deck still electrically connected to
the vehicle, slowly remove it from its installation, and listen for a change in noise
level. Any reduction would indicate that noise was being radiated directly into the
deck while it was in the dash. If you are dealing with radiated noise, the only
solution is isolation. The easiest method is usually to move the contaminated
wiring away from the stereo's wiring.
The best way to eliminate power line noise is to install a filter capacitor across
the noise source. The best capacitors to use are .5mfd 25v bypass capacitors for
the coil, as well as any accessory motors, and .1mfd 100v ceramic disc
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