Ground Loop

Connect all chasses together, so that you have one electrical point, use large guage wire. Now use one path to earth from the chassis - i.e. one wire. This should eliminate a ground loop problem.

in reponse to your question about connecting chasses - loosen a chassis screw on each item and connect via spade connectors. Earth ground would ideally be a ground rod - but the street side of the water pipe works fine or for that matter the electrical panel ground bus. The idea is to have only one path to ground. Make sure that all your chasses are connected to the ground pin of your ac socket (where your power cord plugs into the item). Cheat the ground pin on all power cords except one. That way you have one path to ground for all items. The only difference in resistance being the short high guage wire connecting the chassis - tighten the screws and this should be in the range of less than 50 milliohms. Just remember, if you later move your equipment around - uncheat the grounds. The only reason this is still safe is that you still have all chasses connected to ground via the interconnecting wires.

Note - by chassis I am referring to the metal case of each piece of equipment. Do not stick anything through the vents, to not connect anything to any component, do not insert anything into the interior of the equipment. Doing so is dangerous and will very likely end up with a "smokey" flavor to the music - i.e. you will fry the equipment. The connection I am referring to (to the chassis) is to a point on the case that you could touch by picking the unit up or moving it around - i.e. on the case.

Mordenmail - it is highly unlikely that you have anything wrong with any of your components. The solution of connecting all your chasses and having one wire to ground addresses the most common cause of ground loop hum - either one of your chassis is not really connected to the third prong of the ac connector or the ground from one of your outlets is loose at some point - likely through other connections at other outlets where it is looped through. If that doesn't work the next step is to disconnect any cable from cable television, the internet, or an antenna if you have such connected anywhere in your audio system. This is another common cause of ground loop problems, the shield of the cable is at a different "ground" than your household wiring ground. After that, the place to look would be the connection between signal ground and chassis ground inside each piece of equipment. This is likely made via a wire from the pcb or a metal connection where the pcb is mounted to the standoffs to the chassis. Simply tighten the screw or nut that makes the connection. After that, the cause would be a cold solder joint from one signal ground path to the wire or connection to the chassis for the pcb. Grounding the shields of balanced interconnects at more than one point can also cause the problem. One work around if you cannot find the problem is to use isolation transformers between the interconnects for the audio signal - but this would not be the place to begin. Remember, we are talking about a ground loop hum (sounds like 60 Hz) so the problem is caused by coupled ac currents - this is not unusual, you will have inductive and capacitive coupling of ac currents because you have current carrying wires and conductive plates all over your system in any system - for example normally operating transformers. Ground loop problems can be hard to track down because there is almost never anything wrong with any of the individual components - it is the different paths to ground that causes the problem - you end up with a resistance where there should not be a resistance and hence you develop a 60 hz signal - that signal gets transferred between the signal carrying wires connecting your components, gets amplified and you hear coming from your speakers. The way to troubleshoot this problem is to address the most common causes first and in the most cost effective manner. Let me know what you find.