Owner`s manual

®
3
Ground Loops
Ground loops are insidious. They are caused by the non-zero resistance of the wire used to inter-
connect the equipment. Typically, ground loops are created by a piece of equipment having mul-
tiple connections into the grounding system.
In autosound, this problem is exacerbated by the rather callous belief by auto makers and certain
other folks that the metal frame of the vehicle makes a good ground. While this may be true for
cigarette lighters and tail lights, applying this belief to audio systems is a gilt-edged invitation to
disaster.
Figure 1 shows what happens. Generally, the audio wiring has higher resistance than the power
wiring. Since the electrical system of the car uses the body/frame structure as it’s negative return,
the non-zero (yes, it’s small, but not small enough!) resistance of the car body allows small voltage
drops to be created between various points in the car body.
Figure 1. Anatomy of a ground loop.
The alternator in the battery charging system makes things worse because the frequency of it’s AC
output (alternating current...that’s why it’s called an alternator, not a generator) is easily within the
audible range. The low impedances involved (high available current means low impedances) make
filtering out alternator noise even more difficult. Anyway, these voltage drops occurring between
various points in the car body usually have alternator noise riding on them, which gets into a sound
system via a ground loop.
Until you’ve traced out a noise problem, and found it to be a cleverly concealed ground loop, the
phrase “ground isn’t Ground” just sounds like random noise from another audio fanatic. All it
takes is one good ground loop problem to turn the hardiest skeptic into a believer.
What is Noise?