Ground loops occur when two components are grounded in locations with different ground potentials. That can create an unwanted current, which introduces the sort of interference that is often described as a hum or a whine. The right way to fix a car audio ground loop problem is to ground everything in the same place. If you can’t fix the problem the right way, the solution is to use an in-line noise filter.
Car Audio Ground Loops
Although there are a lot of things that can introduce unwanted noise in a car audio system, ground loops are the single biggest culprit. This noise problem can occur at any time two audio components in the same system are grounded in different locations. If those two locations have different ground potentials, an unwanted current flow, which can create noise, is introduced into the system. When the difference in ground potentials is removed, the unwanted current flow ceases, and the noise goes away. In-home audio systems, ground loops usually happen when two components are plugged into different outlets. Fixing the problem may be a simple matter of changing where you have things plugged in. Unfortunately, the matter of grounding is a little more complicated in-car audio systems. The chassis — and any metal that’s in contact with it — is the ground, but not all grounds are created equal. For example, grounding one audio component to the chassis and one to the cigarette lighter is a classic situation that can lead to the creation of a ground loop. Grounding a head unit to a cigarette lighter instead of the chassis also can introduce a ground loop. The right way to fix the problem is to tear down your sound system and attach the grounds from components like the head unit and amp directly to the chassis in the same place. That’s why it’s so important to make sure that everything is carefully plotted out during the planning stage of any new car audio system and then hooked up correctly during installation. This is a situation where an ounce of prevention is worth a pound of cure.
Isolating Ground Loops
While the right way to fix a ground loop is to deal head-on with the differential in ground potentials between different components, it’s not the only way. If the thought of tearing down your audio system, locating the grounds, and then putting everything back together doesn’t sound appealing, then you might want to look into an isolator. Ground loop isolators consist of an input, an output, and a transformer. The audio signal enters the isolator through the input jack, passes through the transformer, and exits through the output plug. Since there is no direct electrical connection between the input and output, the ground loop and any interference it generates is isolated from the signal. While these noise filters are technically just patches, and your underlying problem still exists, they’re patches that solve the immediate problem.
