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Interference?
9 Answers
I run a karaoke system at a local venue.When my equipment is attached to the tv on the wall(via a 10 metre lead) I get a lot of interference in the form of buzzing.Would attaching an earth onto the ground terminal of my mixer stop this?
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Could it be an earth loop hum? Are both the TV and karaoke machines power leads earthed? This will definitely cause a problem when the equipment are connected to different power points.
Even if the TV is not earthed by its own power lead it may be earthed by some other appliance plugged in via the outer shield of a signal input or output. For example an amplifier connected to its output. Disconnect any signal lead not required for you gig.
The outer shield of the signal lead from the karaoke to the TV completes a loop formed by the earth wiring to the wall sockets. This loop picks up noise. The bigger the area bounded by the loop the greater the interference. The noise is usually a mains hum but light dimmers will make a huge buzz in this situation.
Some mixers have an "earth lift" to disrupt the shield of the output sockets when this is a problem. Although it will stop the hum do not be tempted to disconnect any power earth. This is very dangerous.
If you cannot lift the signal ground run all the equipment from the same power point and keep the signal and power cables as close together as possible. This minimises the area of any ground loop.
Even if the TV is not earthed by its own power lead it may be earthed by some other appliance plugged in via the outer shield of a signal input or output. For example an amplifier connected to its output. Disconnect any signal lead not required for you gig.
The outer shield of the signal lead from the karaoke to the TV completes a loop formed by the earth wiring to the wall sockets. This loop picks up noise. The bigger the area bounded by the loop the greater the interference. The noise is usually a mains hum but light dimmers will make a huge buzz in this situation.
Some mixers have an "earth lift" to disrupt the shield of the output sockets when this is a problem. Although it will stop the hum do not be tempted to disconnect any power earth. This is very dangerous.
If you cannot lift the signal ground run all the equipment from the same power point and keep the signal and power cables as close together as possible. This minimises the area of any ground loop.
it's all true!!
unfortunately you can't avoid the stuff that's causing the problem.
keep leads as short as poss (as ghostbusters say) don't cross the leads.
you could try ferrite rings http://www.maplin.co.uk/free_uk_delivery/Ferri te_Rings_29788/Ferrite_Rings_29788.htm
which may help (at least they are cheap)
and of course ... the most expensive utp oxygen free copper cable you can afford
as for the ground ... ideally you want a fully bonded earthed loop to all your kit. (connected to mains earth AND a water pipe)
oh and testing the mains socket won't go amiss either.
I know that it's neither practical or possible to do all this .... a good earth is your best bet (if you can ... clip to a radiator as well)
unfortunately you can't avoid the stuff that's causing the problem.
keep leads as short as poss (as ghostbusters say) don't cross the leads.
you could try ferrite rings http://www.maplin.co.uk/free_uk_delivery/Ferri te_Rings_29788/Ferrite_Rings_29788.htm
which may help (at least they are cheap)
and of course ... the most expensive utp oxygen free copper cable you can afford
as for the ground ... ideally you want a fully bonded earthed loop to all your kit. (connected to mains earth AND a water pipe)
oh and testing the mains socket won't go amiss either.
I know that it's neither practical or possible to do all this .... a good earth is your best bet (if you can ... clip to a radiator as well)
"keep the signal and power cables as close together as possible."
NOT SO
try to keep them away from each other and Where unbalanced signal and mains cables must cross, make sure they�re at 90� to each other.
most of what has been said is true especially lighting circuits containing dimmers and chokes etc so try to use a socket that is on a different phase remember most commercial premises have a 3 phase supply, also use balanced leads wherever possible
right to your problem i have had this on a few occasions at work - the video ground on the TV will not be at the same ground potential as your audio equipment due to the fact that it has an isolated chassis this will cause problems if anything like a cable or sky box is also connected at the same time so next time you are there disconnect them and see if your him disappears and don't forget to reconnect after your gig
NOT SO
try to keep them away from each other and Where unbalanced signal and mains cables must cross, make sure they�re at 90� to each other.
most of what has been said is true especially lighting circuits containing dimmers and chokes etc so try to use a socket that is on a different phase remember most commercial premises have a 3 phase supply, also use balanced leads wherever possible
right to your problem i have had this on a few occasions at work - the video ground on the TV will not be at the same ground potential as your audio equipment due to the fact that it has an isolated chassis this will cause problems if anything like a cable or sky box is also connected at the same time so next time you are there disconnect them and see if your him disappears and don't forget to reconnect after your gig
ACtheTroll is way off the mark. The problem stems from multiple earthings. The entire system should have one earth only. Never ground in a loop.
Note that I said to keep the cables close together IF YOU CANNOT RUN ALL THE STUFF FROM ONE POWER POINT. This is the best you can do under this situation but the result is generally unsatisfactory. You might nearly get away with it using balanced signal cables.
Separating the power and signal leads further in a multiply grounded setup will make it worse.
Matt1es comment about the Sky box is probably exactly the kind of problem I was describing.
Note that I said to keep the cables close together IF YOU CANNOT RUN ALL THE STUFF FROM ONE POWER POINT. This is the best you can do under this situation but the result is generally unsatisfactory. You might nearly get away with it using balanced signal cables.
Separating the power and signal leads further in a multiply grounded setup will make it worse.
Matt1es comment about the Sky box is probably exactly the kind of problem I was describing.
Sorry. Brain fade. That came out wrong. Let me try again.
When the earth loop cannot be opened such as would be the case of an earthed television, the equipment should be run from the same power point with the power and signal leads run close to each other.
Matt1e is right that normally you try to separate the power and signal just as he describes to prevent the noise being induced into the signal lead. However where there is an unavoidable loop the idea of having them close together is to induce the same voltage into the signal lead shield as is induced into the power lead earth conductor.
It is unlikely to completely eliminate the hum but this helps to balance out the voltages induced in the loop. The further apart the cables get the more unbalanced the voltages and the larger the hum will be.
Hope this makes more sense.
When the earth loop cannot be opened such as would be the case of an earthed television, the equipment should be run from the same power point with the power and signal leads run close to each other.
Matt1e is right that normally you try to separate the power and signal just as he describes to prevent the noise being induced into the signal lead. However where there is an unavoidable loop the idea of having them close together is to induce the same voltage into the signal lead shield as is induced into the power lead earth conductor.
It is unlikely to completely eliminate the hum but this helps to balance out the voltages induced in the loop. The further apart the cables get the more unbalanced the voltages and the larger the hum will be.
Hope this makes more sense.
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