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Big Daddy · 05-07-2009, 12:08 AM

GROUND HUM

Generally, a ground loop is formed when an electrical system has more than one path to the electrical ground. The path between these points form a loop that works like an antenna and picks up noise. Grounding problems are normally found because you are using 2 prong and 3 prong power cords and plugging them into different wall sources.
You need to find the source of the problem. The only way is to unplug them one by one to see what is causing the hum.
Usually, the most common sources are cable TV boxes and computers that are connected to an A/V receiver. Unplug the cable box and/or the computer and see if it improves the hum.
Sometimes, changing the wall outlets solves the problem.
Don’t run interconnect and speaker cables parallel to power and extension cords.
Don’t coil up the excess length of a cable. If you have excess cables, instead of coiling them, you should make a figure 8 with them.
Use an RG6 digital coaxial subwoofer cable and move it away from the other cables. This may help.
Buy a good power conditioner/surge protector and plug all your equipment into that one, including the subwoofer amp. Make sure the coax cables for the cable TV also go through the conditioner. This may solve your noise problem.
Buy a ground loop isolator.

http://www.partsexpress.com/resources/subwoofer.html

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When I hooked up the RCA cable to my receiver from my subamp, it began to make an audible hum. Is it defective? Likely it is NOT defective. What you are hearing is called a "ground loop" and is caused by uneven ground potentials at various locations in your audio system. These potentials cause small levels of electricity to flow through the ground paths, which will often be amplified as a 60 Hz hum.
How do I stop it from humming? One of the first things to try is changing the outlet into which the subwoofer power is plugged. Since often a subwoofer is located away from the rest of the equipment, many times the outlet will be on a different circuit or have a different grounding point. Try connecting the subwoofer to the same outlet as the rest of your equipment via an extension cord or power strip. The next thing to check is the cable TV feed going into your system. While this at first seems like a silly idea, if you consider the web of connections in your A/V system, it begins to make sense. Temporarily unhook the main cable connection and see if the hum stops or is reduced. If it does, the easiest solution is to purchase a coax isolation transformer such as our #180-075. If this does not completely solve the problem, try unhooking the connections of different components in the system and see if the problem stops. If it does, consider using a line-level ground loop isolator in that location. Our #265-012 works well. If nothing seems to quite eliminate all hum, the #265-012 can be used directly on the subwoofer line-level feed and generally will solve most problems.
What if the subwoofer hums when it is not plugged into anything but the wall outlet? If there are mechanical hums or consistent loud hums coming from the speaker when nothing is connected, then it is likely defective. Contact customer service for assistance.
What if I hear a buzzing noise? This is usually from external sources such a fluorescent lights and light dimmers. Fluorescent lights radiate electro-magnetic interference (EMI) that can get into a bad or cheap RCA patch cable. Low voltage light dimmers often put noise directly onto the house electrical wiring. Test by turning these types of lighting off, making sure that the dimmer has a complete "off" position. Many of the "slider" or "rotary" dimmers do not have a completely off position even when at their lowest setting. If this is determined to be the source of the problem, try changing the circuit into which the subwoofer is plugged. As a last resort a line level ground loop isolator has been seen to improve this problem on occasion.
What if I hear a radio station? This is almost always a bad patch cable with leaks in the shield. Replace with a new or known good cable.

http://www.audioholics.com/education...-interconnects

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First, we want to minimize the common-mode voltage difference between the interconnected devices. If possible, plug everything into the same AC power outlet, or power strip. If that is not possible plug the interconnected equipment into power outlets that are on the same branch circuit (same circuit breaker). Another possibility would be to run an additional heavy gauge (low resistance) ground wire between the chassis of the two devices to divert some of the common-mode cable shield current.

Second, we want to minimize the resistance of the interconnecting cable shields. Use cables with a copper braid (or even spiral copper) shield instead of a foil shield. Use cables with the heaviest shield possible, or with double shields in order to minimize cable shield resistance. Do not use cables with aluminum foil shields, since their resistances are much higher. (Note: A foil-braid combination shield is fine, as long as the low resistance copper braid is present). Also keep cables as short as possible, since this will also reduce the total shield resistance.

http://www.epanorama.net/documents/g...oop/index.html

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Ground loop problems and how to get rid of them
Written and copyright by Tomi Engdahl 1997-2006

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).

Basics
The dilemma is that solving "noise" problems is an art within itself. Since it doesn't come up every day, we all have limited practical experience. This has spawned an industry for those who are now specialize in solving noise problems.

A 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 the 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. 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.

The bottom line is that a perfect "quiet" ground does not exist. The basics of all noise problems on the grounding system boils down to what is objectionable current. With the exception of hospital systems, the definition is vague at best. The standard electrical grounding system throughout the building isn't designed to have current constantly flowing through it--and yet it does, you cannot stop it. The reason a ground will not and never be perfectly noise free is that the grounding electrode conductor is nothing more than a long wire from point A to point B. And the longer the wire the more noise it will pick up.

Sound and video people are referring to the type of noisy ground with term like ground loops: current running the equipment grounding conductor, metal within the building, and grounding electrode conductor. Use of any of today's standard 120-volt or 230-volt single-phase AC systems mean potential problems for audio equipment. Computer guys have the same problem in their line of work and so forth.

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.

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. 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. 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 and safety of electrical equipments. 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. 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). 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 A.C. power transformer primary and secondary windings which causes that a portion of the A.C. 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 1MHz or more. These signals will cause currents to flow in the cable shields thus adding this noise directly to the audio signal.

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. That is not usually an easy task to do.

Why ground loop is a problem?
Ground loops are a mystery to many people. Even college-trained electronic engineers may not know what ground loops actually are. Engineers have either concentrated on power distribution (for the electric company) or on equipment that happens to plug in to the power distribution system. Not much thought has been given to power distribution and equipment as a single entity where ground loops arise.

Ground loops are the most common cause of AC line frequency hum in sound systems. Ground loops can be geenrally identified by a low hum (60Hz in the US, 50Hz in Europe) through the sound system. A ground loop in the power or video signal occurs when some components in the same system are receiving its power from a different ground than other components, or the ground potential between two pieces of equipment is not identical.

Ground loop is a common problem when connecting multiple audio-visual system components together, there is a good change of making a nasty ground loops. Ground loops commonly cause humming noise to audio signals and interference bars to picture. Ground loop makes the system sensitive to pick up interference from mains wiring which can lead to erratic operation of the quipments or even damages to the equipments. Some articles claim that wiring and grounding problems account for up to 80 percent of all power quality related problems related with sensitive electronic equipments like audio/video systems.

The audio/video and power industries have each designed their systems and equipment independently. As a result, there's a degree of incompatibility. Usually which is pwefectly adequate in power distribution and operation safety sense is not good enough for AV-systems. Ground loop interference problem is a consequence of this.

Always when operating with grounding issues remember that there is no absolute ground. There is a certain amount of resistance to electrical current between all grounding points. This resistance can change with humidity, temperature, connected equipment and many other variables. No matter how small, the resistance can always allow an electrical voltage to exist across it when there is any current flowing between those grounding points (and there is some current flowing almost always).

Audio-frequency groundloop problems are typically in the low millivolt range, so it does not have to be much interference in grounding system to cause problems in audio systems.

Remember that there is no absolute ground. There is a certain amount of resistance to electrical current between all grounding points. This resistance can change with humidity, temperature, connected equipment and many other variables. No matter how small, the resistance can always allow an electrical voltage to exist across it. The ground wires between wall sockets and power company transformers are not perfect conductors and neither is the shield of your coaxial video cable. If they were, ground loops would not be a problem. Effects of ground loop in video pictures are in the form of a black shadow bar across the screen or as tearing in the top corner of a picture. This is caused by different earth potentials in a system.

http://www.rane.com/note110.html

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Ground Loops
Almost all cases of noise can be traced directly to ground loops, grounding or lack thereof. It is important to understand the mechanism that causes grounding noise in order to effectively eliminate it. Each component of a sound system produces its own ground internally. This ground is usually called the audio signal ground. Connecting devices together with the interconnecting cables can tie the signal grounds of the two units together in one place through the conductors in the cable. Ground loops occur when the grounds of the two units are also tied together in another place: via the third wire in the line cord, by tying the metal chassis together through the rack rails, etc. These situations create a circuit through which current may flow in a closed "loop" from one unit's ground out to a second unit and back to the first. It is not simply the presence of this current that creates the hum -- it is when this current flows through a unit's audio signal ground that creates the hum. In fact, even without a ground loop, a little noise current always flows through every interconnecting cable (i.e., it is impossible to eliminate these currents entirely). The mere presence of this ground loop current is no cause for alarm if your system uses properly implemented and completely balanced interconnects, which are excellent at rejecting ground loop and other noise currents. Balanced interconnect was developed to be immune to these noise currents, which can never be entirely eliminated. What makes a ground loop current annoying is when the audio signal is affected. Unfortunately, many manufacturers of balanced audio equipment design the internal grounding system improperly, thus creating balanced equipment that is not immune to the cabling's noise currents. This is one reason for the bad reputation sometimes given to balanced interconnect.

A second reason for balanced interconnect's bad reputation comes from those who think connecting unbalanced equipment into "superior" balanced equipment should improve things. Sorry. Balanced interconnect is not compatible with unbalanced. The small physical nature and short cable runs of completely unbalanced systems (home audio) also contain these ground loop noise currents. However, the currents in unbalanced systems never get large enough to affect the audio to the point where it is a nuisance. Mixing balanced and unbalanced equipment, however, is an entirely different story, since balanced and unbalanced interconnect are truly not compatible. The rest of this note shows several recommended implementations for all of these interconnection schemes.

The potential or voltage which pushes these noise currents through the circuit is developed between the independent grounds of the two or more units in the system. The impedance of this circuit is low, and even though the voltage is low, the current is high, thanks to Mr. Ohm, without whose help we wouldn't have these problems. It would take a very high resolution ohm meter to measure the impedance of the steel chassis or the rack rails. We're talking thousandths of an ohm. So trying to measure this stuff won't necessarily help you. We just thought we'd warn you.

http://www.ethanwiner.com/dimmers.html

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Kill Studio Hum and Buzz at the Source

HUM 101

Hum derives from the fundamental frequency of the AC power line, which in the USA is 60 Hz. However, most hum also contains harmonics of that fundamental frequency: 120 Hz., 180 Hz., and so forth. In fact, the only real difference between "hum" and "buzz" is that buzz has more harmonics, and those harmonics extend to a higher audible frequency.

There are three basic ways that hum and other power line-related noises can get into an audio system. One is through radiation in the air, such as when you bring an electric guitar close to the power transformer in an amplifier. In this case the guitar's pickup acts as an antenna that receives the 60 Hz. energy being radiated by the transformer. The whole point of using shielding to surround the center conductor on guitar wires and studio patch cords is to keep radiated hum from impinging on the wire inside the shielding.

The second way hum can be induced into an audio system is when a voltage difference exists between the common ground connections of two or more pieces of equipment. Third, clicking and buzzing noises can get into an audio device through the power wires. Every time an electric motor is turned on or off, the motor's coils "kick back" into the power line a brief but high-level voltage spike. The large motors used in refrigerator and air conditioner compressors are a common cause of audible clicks and pops. The power supplies used in most audio gear are unable to block these high-frequency impulses, and they pass right through the power supply into the audio circuit.

Similarly, solid-state light dimmers can create havoc with audio gear. These devices work by changing the amount of time the full power line voltage is applied to the light being controlled, as opposed to actually raising and lowering the voltage. Although AC power is supplied by the power company as a pure sine wave (having no harmonics), the dimmer's sudden switching of the voltage on and off actually generates harmonics which extend to very high frequencies. And these high frequency harmonics can get into audio gear both by radiation through the air and also by traveling through the power wiring directly into the audio circuitry.
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READ THE REST OF THE ARTICLE BY CLICKING ON THE LINK.

Jensen makes a high end isolator for subwoofers, but it is expensive.

Instructions For Xitel Isolator: