buzzzzz, where did i go wrong?

My guess is that the two seperate ground rods need to be tied together. If the FIM's have a common ground, then all of the grounds are tied back to the other system via the conduit. As such, you may need to tie the two isolated system ground rods back to the main house ground or go to isolated ground outlets.

As it is right now, you have the potential for multiple levels of ground within your system. Besides each ground rod that you have going, each circuit can have slightly varying levels of conductivity to ground. This is due to differences in resistance, especially if you have multiple connections along the way. If you used straight runs of wire without tying in anywhere else ( that is what a dedicated circuit is ), this should not be a problem though.

I would also take steps to weather-proof / seal the ground rod connections once you've got everything straightened out. No matter how good of a connection was made, moisture, dew and corrosion will find a way to get in there and gradually diminish all of the effort that you've put forth. Sean
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did you tie the two audio ground rods to the house ground rod ? If so, that should negate the differences in ground potential so long as you have a good connection on all of them.

As to Dan2112's comments, treatment of the soil to increase conductivity is a temporary band aid at best. The soil has to be treated on a regular basis. Besides that, the chemicals are typically somewhat corrosive to metals and may cause premature rotting of the ground rods themselves.

As to floating the grounds of the amps, i don't see a problem with this. In Laura Dearborn's book "Good Sound", she comments on this. One "expert" said that he typically experiences better performance by floating the amp grounds than by floating anything else. Others state that you should select one component ( commonly the preamp since all components inersect there ) and ground it, letting all of the others float. This puts them all at the same ground potential. Others say that digital gear should all be grounded due to the amount of trash that they generate. Personally, I think it all boils down to trial and error.

Have you checked to make sure that the circuitry that the amps are on are of the same polarity as the other outlets ? I know you just had them professionally installed, but mistakes do happen. Also, have you checked to make sure that all of your gear is electrically oriented the same way ? This might help you also. Sean
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http://forum.audiogon.com/cgi-bin/fr.pl?htech&1014011751&read&keyw&zzhum

JD, drop me an email at your convenience. Sean
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JD, i'll drop you a line in the morning, kind of late and i'm beat now : )

To start off, try grounding ALL of your ground rods together. That should get rid of your hum. If it does, you either need to replace the FIM's with outlets that isolate the grounds, leave all of the ground rods tied together or move the ground rods to within a few feet of each other.

If tying all the rods does correct the problem, you can also try removing the connection from one rod at a time and see which rod has different potential from the others. It is possible that each rod is different and that you would need to leave them all tied together to solve the problem. Once again, the only way to get around this is to isolate the audio grounds from the house grounds via different "floating" outlets. Sean
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JD, you can try to measure the resistance between the various grounds. You can go from the ground on the breaker box to each individual rod and see what resistance that you get. If you get readings that are all very close, that is a good thing. The further apart the readings are, the more potential for hum and ground loops. This will also verify that you have a good connection from the box to each individual rod.

Another test is to measure from one ground rod to another ground rod. This will measure the conductivity of the soil around each individual rod. Obviously, the lower the reading, the more conductive the Earth. It is possible to have rods located within just a few feet of each other and have VERY different levels of conductivity. I recently did some digging around my house and found that i had a very high clay content in one section. Moving over just a few feet showed very little to no clay. Obviously, this would make a BIG difference in terms of conductivity and ground potential. Sean
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JD, i would first try isolating the conduit from the audio system as you mentioned. If that does not solve the problem ( which i think it might ), then let's take it from there. Having ground rods spaced out quite a distance lends itself to different levels of ground conductivity as mentioned above. One would have to work on either equalizing the ground potential or tying them together so that they share a common path in order to minimize any differences. Sean
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