|
|
|
Ground Loop, a hum in analog audio usually caused by a difference of potential when cables are connected
between equipment. Ground loops defy logic, what would seem to be the correct way to ground audio equipment will in many cases not work. So the correct method of reducing ground loops is to do whatever works. There are a few suggestions that may help. For instance, all equipment should be grounded with a 3-prong AC plug, unless there is a ground loop. Then using a 3-prong to 2-prong AC adaptor that lifts the third prong ground, one by one insert the adaptor in series with each piece of audio equipments AC plug and if the ground loop gets better, leave the adaptor in place. The equipment will still be grounded via audio connector grounds. Sometime running a ground wire from equipment to equipment helps, but not always. If you try to ground the equipment to a water pipe or even an outside ground rod you may create a worse ground loop. Balanced audio lines, a truly balanced audio line does not need a shield. A shield is a good idea but a shield may also create a ground loop between equipment. Having the shield connected at one end only may help reduce ground loops. And as strange as it sounds, not having the shield connected at all may help. |
| Balanced audio lines do not need a shield. For years radio stations would feed audio from their studios to the transmitter over miles of unshielded telephone balanced audio wires. These lines would normally provide 60db signal to noise ratio and a flat frequency response of 50HZ to 15KHZ. Keep in mind that these unshielded wire pairs were in a bundle of regular telephone wires carrying telephone conversations and ringing current. Yes, a truly balanced audio pair does not have to be shielded. This means the amplifier output feeding the line and the input being used at the other end must truly be a balanced output and input. Balanced means both sides of the line are active and neither side is grounded. |
|
Unbalanced audio lines, you're screwed. The shield wire is part of the signal path and must remain connected. Another trick to reduce ground loops is to connect the shield wire through a capacitor at one or both ends of a cable. The capacitor allows a path to ground for AC signals, noise etc, but blocks any DC current flow that might result from different voltage potential between equipment chassis. The vaule of such a capacitor is usually .1 mfd. If you are working with equipment that has a 2-prong AC power plug, try turning the plug 180 degrees. If the plug has one prong bigger than the other you can not do this. A word of caution, equipment that has a 2-prong power plug has the potential of causing a shock due to current leakage in circuits and an ungrounded chassis. Is your hum really a ground loop. If nothing you do seems to help you might want to try moving your equipment around and reposition stuff. Sometime hum fields from power transformers get into audio circuits if close enough to each other. And do not cable tie all your cables together with audio and AC power together. Keep all the power cords away from audio cables. Of course if you are using fiber optic cables on a digital output/input, none of this is a problem. But then chances are you wouldn't even be interested in any of this. |
GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING
GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING
GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING
GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING - GROUNDING