Last edit by jolofboy, Professional edition user on Mon 17 Aug 09 @ 1:30 pm
Nine times out of ten, if you have a buzzing or humming problem on your speaker outputs, it's caused by what is known as a ground loop. This is where two pieces of equipment are operating, usually using different outlets, or in the case of a laptop, has no true earth (psu) The buzz or hum is caused by the mains potential trying to equalise using the only path it has, the earth line. Obviously it cannot equalise so it creates a loop. Hence "ground loop interference"
This is very common in laptops, you can easily tell if you have a ground loop. Using PSU, buzz and/or hum. Disconnect PSU (battery power) No buzz or hum.
There are many suggested ways of curing this problem, the most simple and safest for a DJ is simply to use what are known as "Ground Loop Isolators" These look like a little plastic case with inputs and outputs and are simply plugged in between equipment outputs and mixer inputs. All that is inside is a basic transformer that 'isolates' the loop.
There is no point in me adding a link to a supplier since there are VDJ users reading this from all over the world, just do a google for "ground Loop Isolator" and you will find what you want. You will need to buy one of these for each stereo channel going into the mixer.
WARNING WILL ROBINSON
Some people will advise you to remove the earth pins from plugs or use 3 pin to 2 pin converter plugs. THIS IS DANGEROUS! The earth line to a piece of equipment is put there as a safety precaution to prevent electric shock in the case of a fault. Putting this simply... DO NOT DO THIS! YOU COULD GET ELECTROCUTED! EVEN WORSE YOU COULD DIE!!
Ground loop isolators = cheap
Your life = whatever value you or your loved ones put on it. ie priceless!
NOTE, computers are very electrically noisy things anyway, you have cooling fans, GFX board fans, processors cycling, etc etc, ground loop isolators can eliminate a lot of that noise.
A ground lift is not the same as an earth lift, this may cause some confusion here as the words 'ground' and 'earth' do get transposed regularly in electrical discussion.
Please be aware that if you have a piece of equipment with a "ground lift" button. This IS NOT removing electrical earth, please DO NOT assume this.
Ground lift on audio equipment means lifting the AUDIO ground, that is, the outer core of your audio leads connecting equipment together, for instance the outer on your phono to phono leads.
Let me explain, and in this explanation the word EARTH means electrical earth, as the earth in a plug. The word GROUND means 'audio ground' that is, the outside wire on your phono and jack plugs etc which are usually in the form of a braid, wrapped around the inner core.
OK, imagine you have an amplifier and a mixer, both are plugged into the mains, now the GROUND is usually CONNECTED to the EARTH inside the equipment, most times this is fine and causes no problems, the reason they do this is that earthing the ground cable makes the ground act like a shield (and why outer cores are often called 'shield' as any interference absorbed by the cable will just leak to EARTH.
In a ground loop circumstance, there are two different electrical potentials in the two pieces of equipment. To simplify this, the connected equipment will work like a set of scales, it wants to balance, simplifying again, lets say there's 10 volts on an amp chassis and nine on the mixer (this is for illustration purposes only) The two voltages want to balance or equalise, the only route it has, is the one that connects the two pieces of equipment, that is, the GROUND of your audio leads, so it travels down those, the thing is, it never equalises as they are connected to the mains, so the difference in electrical potential doesn't change. THIS is a ground loop.
So, to stop that power leaking down the GROUND, you use the GROUND LIFT, which isolates GROUND from EARTH (sometimes completely, sometimes it just puts a resistor in line) This doesn't always work, hence needing ground loop isolators.
So endeth the lesson!
Trust me on this, it's all right and can be verified by searching on the net.
so again REMOVING "EARTH" FROM AN ITEM CAN RESULT IN DEATH!!!!!!!!!!!!!!!!
Something you should be aware of, VOLTAGE does not kill! It is the current that kills, there are huge transformers in some amplifiers that contain a huge amount of current. Bear in mind that UK mains is rated at 13 amp on the socket side (32 amp beyond that) now bear in mind that above 100 mA (0.1 of an amp) can be LETHAL