Owner`s manual

2. If you mount everything on a board, connect the chassis of each component to a good, solid

electrical ground. The vehicle body is a good choice here because what you want is a good RF

(radio frequency) ground. The wire running to the negative side of the electrical system has

inductance which raises it’s impedance at high frequencies. In effect, at radio frequencies, the

impedance could be high enough that the wire would look like an open circuit. Braided wire

works best here because it has low inductance.

3. It’s good insurance to use an ohmmeter to make sure that the chassis of each component isn’t

already tied to its internal electrical ground. Sometimes the case is tied to circuit ground through

a low to moderate value resistor. If the case to negative wire resistance is greater than 10 ohms,

then it’s you can connect the unit’s case to the auto body ground without causing a ground loop.

Some manufacturers put a switch on the unit to allow you to pick where the chassis is grounded.

If you supply the connection to the chassis of the unit make sure that the switch doesn’t supply

one too.

4. Some premium connecting cables have oversized connectors. Make sure that the shell of the

connector doesn’t inadvertently contact the chassis of the unit that it is plugged in to. If this

happens, you’ve got a ground loop on your hands.

5. When you think that you’ve got everything right, turn everything on, and disconnect the antenna

and the negative connection to the vehicle’s electrical system. If everything quits, you’ve got a

single point ground.

Remember: Ground isn’t ground!

Wiring Practices

After grounding, the rest is relatively easy. Here’s a few hints:

• Avoid running audio wiring along (parallel to) with high-current power wiring. The improve-

ment in noise pickup is proportional to the square of the distance between the wires. This is

more important when applied to line level audio wiring rather than speaker wiring.

• For high-powered systems, run heavy gauge wires directly to the batter for the power amplifiers.

How heavy? That depends on the distance of the run, and the current demands of the amplifiers.

You can’t err by making the wire too big.

• It may help to add an RF bypass capacitor at the amplifier end of the power cable to auto body

ground. It may also help to add a second bypass capacitor from the positive side of the cable to

the negative lead that runs back to the electrical system ground.

• Bad cases of alternator noise interference will probably require series chokes in the positive

power lead into the system. It may be easier (economically as well as electrically) to filter each

unit in the system separately than to try to find an interference choke with enough current

capacity to handle an industrial-strength power amplifier.

• Don’t use the auto body ground as the ground return for the speakers. They should connect to

ground via the power amplifiers output connections.

Minimizing Noise in Autosound Systems