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Re: hum on audio lines (strangness indeed)



trying to find the needle in a heystack ... here's some more advice to avoid hum in racks ( besides what's already been said ):
 
- find out which of your rack units causes the hum ( ... it sometimes helps to put it in another place inside the rack, because of the position of the transformers inside the units ... )
- insulate the rack units chassis from each other and from the rackrail they're connected to ( by using tape to keep the front plates apart from each other, and "humfrees" or plastic rings for the screws )
- keep wallwarts inside the rack as far away from each other as possible, as well as from the transformers of non-wallwart units and from line cables
- the whole rack, together with the other gear u're using, needs only one ground connection / should have only one and the same mains connection ( if u're rich, use a power conditioner ... i.e. Furman et. al. )
- when using a mixer and it's aux lines this may cause a doubling of ground connections ( "humloops" ) ... if so, u need special patch cords with the ground/shield disconnected ( the equipment inside ur rack maybe seen/connected as ONE unit ) - but better talk to a pro before u start disconnecting grounds, always keep in mind that u need ONE GROUND CONNECTION TO BE SAFE ! ! I will not take any responsibitity if u make a mistake and grill either urself or ur equipment !
- u may also use special transformers which separtate the ground ( in a way almost like a DI box ) for each of ur rack units.
this is the best solution, but expensive ...