Ground loop problems and how to get rid of them …

1 Documents[ index ][ back ][ site search ] [ acronyms ] [ discussion ] [ mail to a friend ] [ post message ] Ground loop problems and how to get rid of themWritten and copyright by Tomi Engdahl 1997-2000 NOTE: The information presented here is believed to be correct and is made available here by the author. The author of this document is not liable for any effect this information or any use thereof may have. The documents have been used and recommended by many people and are belived to be accurate. So accurate that they have also been featured as GB AUDIO Ground loops DATA SHEET on their web pages (with permission from me).

2 BasicsA good power distribution system is essential for proper operation of audio system. Professional audio systems just doesn't work well with normal extension cords running hundreds of feet to a stage. Besides the power feed the good grounding of thw whole system is essential. Ground loop is a condition where an unintended connection to Ground is made through an interfering electrical conductor. Generally Ground loop connection exists when an electrical system is connected through more than one way to the electrical Ground . When two or more devices are connected to a common Ground through different paths, a Ground loop occurs.

3 Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent Ground loops , all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other. Usually Ground loops are an after-the-fact type of problem in which the end-user blames the installer, the installer blames the manufacturer, and actually nobody is at fault. Neither the manufacturer nor the installer can usually predict where a loop will occur. Only after the system is installed can it be determined if a problem will exist.

4 Ground loop problems can be corrected and avoided. It is important for the dealer, isntallee and the end user to be aware that this problem can occur. It is a good idea to design the system to avoid most obvious source of this kind of problems , and then be prepared still to face some problems when starting to use the system. A Ground loop problem may occur at several points in the system, and each occurrence of the problem must be corrected individually. Why grounding is so important ?Earthing of electrical systems is required for a number of reasons, principally to ensure the safety of people near the system and to prevent damage to the system itself in the event of a fault.

5 The function of the protective conductor, or earth, is to provide a low resistance path for fault current so that the circuit protective devices operate rapidly to disconnect the supply. The NEC, National Electrical Code defines a Ground as: "a conducting connection, whether intentional or accidental between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth." When talking about grounding it is actually two different subjects, earth grounding and equipment grounding. Earth grounding is an intentional connection from a circuit conductor usually the neutral to a Ground electrode placed in the earth.

6 Equipment grounding is to ensure that operating equipment within a structure is properly grounded. These two grounding systems are required to be kept separate except for a connection between the two systems to prevent differences in potential from a possible flashover from a lightning strike. The purpose of a Ground besides the protection of people plants and equipment is to provide a safe path for the dissipation of Fault Currents, Lightning Strikes, Static Discharges, EMI and RFI signals and Interference. Improper grounding can create a lethal hazard. Correct grounding is essential for correct operation nad safety of electrical equipments.

7 Grounding can solve many problems , but it can also cause new ones. One of the most common problem is called " Ground loop". What causes the humming in audio systems ?Audio and video systems need a reference point for their voltages. Generally referred to as common or Ground , although it may not be actually connected with the earth, this reference remains at "zero volts" while other signal voltages "swing" positive (above) and negative (below) it. Physically, the common may be a wire, a trace on a printed-circuit board, a metal chassis, virtually anything that conducts electricity. Ideally it should be a perfect conductor, but in any practical system it is not.

8 As the complexity and size of the system is increased, the imperfect conductivity of the common ( Ground ) conductor inevitably causes problems . Hum and buzz (50Hz/60Hz and it's harmonics) occur in unbalanced systems when currents flow in the cable shield connections between different pieces of equipment. Hum and buzz can also occur balanced systems even though they are generally much more The cable shield currents and Ground voltage differences are caused by several mechanisms. The second most common source of hum and buzz is the voltage difference between two safety grounds separated by a large distance or the voltage difference between a safety Ground and an "Earth" Ground (such as a grounded satellite dish or cable TV source).

9 This problem is usually called " Ground loop". This is the most common one in severe humming problems . Hum and buzz can also be magnetically induced or capacitively induced directly into signal cables. Or the noise current can leak from mains input through capacitance between the power transformer primary and secondary windings which causes that a portion of the line voltage will ALWAYS be capacitively coupled directly to audio circuit Ground . This capacitivly coupled power line signal will usually contain significant harmonics out to 1 MHz or more. These signals will cause currents to flow in the cable shields thus adding this noise directly to the audio signal.

10 Why grounding without problems is do difficult ?Virtually all data and broadcast construction projects run into problems of grounding. These problems occur primarily because there is a conflict between issues of safety ( Ground - ing to prevent electrical shock) and electronic noise reduction (using " Ground " as an electronic "dump" for noise and inter- ference.) These two uses are often not compatible and can sometimes be in direct conflict with one another. The ultimate purpose of good groundind scheme is he preservation and adherence to the safety aspects while obtaining the maximum noise reduction possible.