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Setting Up A Hum Free System
Every now and then, we might come across a sound, an irritating hum, in our systems. They are normally caused by bad grounds, or a ground loop condition. Usually, these can be avoided, if you know what you're doing.
Sometimes, in poorly designed sound equipment, ground loops occur inside the chassis, even when the equipment has balanced inputs and outputs. In this instance, there is little that can be done to get rid of hum.
Following these simple rules will help you avoid most correctable external causes of hum and you will save many hours of work and frustration, without the need for often useless and sometimes expensive "hum eliminators". A properly set up, quality system shouldn't have any hum to eliminate.
Single Power Feed
If your system power requirements are low enough, get your power only from one electrical outlet. This will avoid the potential ground difference problem, which can exist if power is taken from multiple power outlets. If distance and electrical code permits, it is a good idea to run a power extension cable from one feed to all subsystems connected to your audio system. Try to make sure that the outlet you're connecting into, does not also supply neon/fluorescent lighting, or refrigeration devices.
Wire All Audio To Same Phase
Use a dedicated power feed for your audio system. Wire all sound sources, musical instruments, effects and your mixer to the same, grounded and dedicated power feed. Do not connect any other equipment, other than your audio components to this power feed. This saves you from many sources of hum. It is a good idea reduce the number of power leads, and if that isn't possible, clearly mark leads, which are part of your audio power feed so that you don't accidentally connect any other equipment to them.
Never connect fluorescent lamps, dimmers, computers or video monitors to your audio power feed. Use a separate connection for these and make certain the cables don't run in close proximity to each other. If they must cross, do it once, at an angle as close to 90 degrees as is possible.
Balanced Connections
Balanced connections are much less sensitive to interference, which can cause hum.
Most professional audio devices are connected via balanced cables to minimize the pickup of stray electrical noise. Consumer audio devices use unbalanced cables and are very prone to picking up noise, especially at low signal levels from devices such as microphones. Balanced circuits have an inherent ability to only pass audio signals and reject unwanted noise.
Balanced refers to the fact that there are two symmetrical signal lines and one ground, while unbalanced uses just one signal line in reference to ground. Normally, XLR connectors are used in most balanced devices while unbalanced consumer gear normally uses mini-plug or RCA connectors.
Here lies a potential karaoke problem, since many components in use, for karaoke, are consumer grade. With the widespread availability of JVC/RSQ decks, they are commonly used in karaoke shows, yet are low end, home grade gear. If you're running a professional show with these decks, be prepared to use top grade cables, discarding the junk that comes with the decks. Even then, you may still run into some electrical noise that is unavoidable. How can you determine if a deck is of commercial quality? If it does not come in a rack mountable configuration, it is definitely consumer grade equipment. Even with this, you should know that just because that component is rack mountable does not guarantee it is commercial quality. Why does this matter? Home grade equipment does not need to handle the rigors of road shows, with the transportation needs, transformers and lighting found in commercial venues.
XLR Connectors
The recommendation here is not to ground the sleeves of XLR connectors. The reason is that XLR sleeves can easily come in contact with metal railings or other components, which are grounded, to something else. If your sleeves are not grounded, you'll not have a problem here. If you have grounded an XLR connector sleeve to an audio ground you may develop a hum, due to the introduction of ground paths or loops. Wrap the sleeves with something non-conductive, if necessary, and don't allow anything to ground to the cable, on either end.
Isolate Unbalanced Connections
If you have a mixture of balanced and unbalanced connections, use isolation transformers in every connection. When unbalanced lines cannot be transformer isolated, there are special cable assemblies available to help solve problems.
You should avoid unbalanced equipment in your system. The exception to the rule would be with equipment that will be very close together, connected to the same leg of the AC service, with a minimal run of audio cable to speakers, but even then, you’re risking noise.
Short Distances On Unbalanced Cables
If you must use an unbalanced cable, remember the length must be kept less than two meters. Cable lengths longer than this will pick up and amplify electrical interference.
Isolate Audio Cables
Power wires generate magnetic fields around them, which can cause a hum through the audio cables. Avoid placing your audio cables near your main power cables or any cables feeding lighting systems. Once again, fluorescent and neon are the worst culprits, but all lighting can be trouble, especially if you're using stage lights with dimmers or other controllers.
Keep the audio cables at least a meter away from power cables. If the audio cables must cross power cable then they must cross them as close to 90 degrees, as you can, to keep the hum potential to a minimum.
Isolate Grounds From Separate Power Feeds
If your power amplifier is connected to different power feed than your mixer, then use a balanced connection between your mixer and the amplifier. If you can't use a balanced connection, use an isolation transformer in the audio line.
If you are running a video monitor and/or computer equipment, run a separate power feed to each. Use audio isolation transformers in all audio connections between your computer or video monitor and your mixer. Computers and video equipment typically have unbalanced audio connections, so isolation transformers are the only proper way to get rid of a humming problem.
Keep Transformers & Power Panels Away
Audio equipment and wiring can easily pick up a hum from various magnetic fields. Avoid putting any sources of magnetic interference near your system. This applies to power transformers, video monitors, computer monitors, electric motors, fluorescent lights and any wiring, which may carry large amounts of current.
Do Not Coil Cables
Coiled cables can cause a magnetic field around them and/or pick up magnetic fields. If your power cables are coiled, they can cause large magnetic fields and heat up under load. Use the shortest cable required to get the connection made. If you must gather up excess cable runs, lay them on the floor, in a figure eight form. This will greatly reduce the possibility of magnetic interference.
Star Grounding - One Path to Ground
Star grounding is the name audio and electrical engineers use to describe a wiring system where all the electronic signal grounds (cable braiding, jack sleeves or XLR Pin 1) either:
Flow in a serial manner without coming into contact with the electrical or chassis ground, or
Join the main power supply ground at only one point.
This removes the possibility of a potential difference between main grounds or the connection of main grounds being duplicated in an audio system.
With star grounding, the center that is usually chosen is at the mixer. The reason for this choice is that most systems only have one main mixing console and the vast majority of devices are connected to it. This grounding system will usually help ensure that your system will remain hum free.
Avoid Contacting Other Grounds
There are many other things, which can cause unwanted grounding. Audio connectors often have a metal shell, which can contact other grounded metals. The same thing applies to microphones and cable connection boxes. If there is anything exposed in your audio wiring, which can touch other ground, then insulate it. Avoid metallic parts in the floor or building, and if you can't, use a thick insulator, like carpet, between the metal and your equipment connections and rack, to provide necessary isolation.
Use Correct Gain Settings
By using the correct signal levels throughout the system, you will minimize hum, feedback, noise and distortion. Main gain controls should typically be set between halfway and fully up. Main amplifier gain controls set at lower positions require input signals to be set at higher levels to obtain suitable power levels, which can also amplify noise. Particularly with unbalanced input lines, the hotter your signal is, at the input of an amplifier, the more noise propagation you will have into your amplifier. Work the amplifier more and your channel gains less.
Grounding Safety
The main reason we ground a sound system is safety. Proper grounding can prevent lethal shocks. The next reason for grounding a system that includes AC powered equipment is that proper grounding may reduce external noise pickup.
The AC power cord ground (the green wire and the third pin on the AC plug) connects the chassis of electronic equipment to a wire in the wall power service, which leads to an earth ground. The earth ground, required by electrical codes everywhere, can contribute to ground loops.
Don't Break The AC Ground
With just one path to ground, there can't be a ground loop. Can there be a ground loop with one audio cable joining a mixer to a power amplifier? Of course there can be. A ground connection through the AC cables and the chassis of the two units completes the second ground connection.
One method, often used to break this ground loop is to lift the AC ground on one piece of equipment, typically the power amplifier. This removes the AC ground. The system now relies upon the audio cable to provide the ground, which is extremely hazardous! You also put at risk all components connected to that device. I do not endorse the use of AC ground lifts for any system.
Maximize Safety
Try not to lift the safety ground on any piece of equipment. Never defeat the AC safety ground on your mixer or any piece of equipment connected to your microphones, either directly, or indirectly. Microphones take priority in grounding safety because your performers will be holding them and may touch other grounded items.
Always plug your audio equipment into the same AC service leg. This not only reduces the potential of a ground loop, but also reduces the danger of electrical shock. If one circuit breaker controls both of those outlets, you're on the same phase. Always connect lighting, air conditioning, refrigeration, etc., to a completely different phase or leg of the main power distribution.
Remember to plan ahead and always think safety, while minimizing unwanted noise.
120 volt AC current will kill you. Play safe.
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The buzz/humm gets louder with an increase in the master volume and I have to keep the master pretty low so the buzz isn't that noticeable BUT ITS STILL THERE !
Found the problem! 
Seems the number 9 channel on the mixer was the cuase of all the hum & buzz. I turned that sucker off and all the NOIZE went away ...There was a little static and buzz from one of the other channels as I played with the Volume controls.
