GROUND LOOPS IN THE AV WORLD – By Brian Morris, CTS
Ground Loops in the AV World?
There’s no such thing, right? Wrong. Ground loops are a leading
cause of equipment failures and signal complications in the
AV world. A ground loop is created when a current (either AC
or DC) connects the grounds of two devices that should have
the same ground potential but are different. This current can
cause symptoms that can vary anywhere from signal noise, to a
floating “video hum bar,” to an audio “buzz,” to a total equipment
failure, and even electric shock. There are many cases in which
integrated circuits or printed circuit boards inside affected
devices are visibly damaged or burned due to ground loops.
solve a ground loop problem in a system. Doing this will remove
the ground from the device, thus increasing the risk of electric
shock. The ground on electrical devices is intended as a safety
feature to protect the users and the devices.
When using a twisted pair transmitter and receiver system in an
AV application test for ground loops in the same way as above,
being sure to test the shield of the cable that will connect the
twisted pair receiver to the display device.
As seen in the example below, many systems – simple or
complicated can utilize multiple different ground potentials.
This is a common occurrence because the AV source and the
display device are quite often in two different locations, and
thus using different electrical outlets. The problem occurs when
the ground potential of V1 is different than the ground potential
of V2. When the AV source and the display device are connected
together with a copper or aluminum cable, the two different
ground potentials create a ground loop using the shield of the
cable. This cable could be a video cable, audio cable, or any other
type of metallic conductor cable.
Other Ways to Prevent and Solve Ground Loops
One way to prevent ground loops is to transport the video and
audio signals over fiber optic transmitter and receiver systems.
Fiber optic solutions prevent ground loops by avoiding the use
of any metallic conductors. As previously discussed, the metallic
conductor in AV cables is the glue that ties the system devices
together, enabling ground loops.
The shield of the connection cables are generally connected to the chassis of the
device which is an unprotected surface, introducing the risk of electric shock to
the user and damage to the equipment.
Testing for and Solving Ground Loops
Systems can and should be tested for ground loops before
connecting the two sides of the system with the copper or
aluminum cable. This is done by using a multi-meter or voltmeter. For example, when setting up the system above, place
one probe from the multi-meter on the shield of the coppe