buzzzzz, where did i go wrong?

I'm with Sean...I would also add to my previous post that if there is CATV involved some where in the system to use a g round breaker for it instead of tyring to make the ground common.

dedicated lines. what goes where?
Dedicated (meaning separate?) grounds that run to different ground rods...sounds like the beginning of trouble (ground loops, hum...etc). The whole idea is to have a single, common ground in a system. If each is at a different, even slightly, potential (voltage) you will have current flow through the ground causing who-knows-what... When all of the grounds are common (as in most all electrical wiring and systems), by definition they are all at the same potential (voltage) and no current will flow.

If you read through some old posts, you will find those reporting improved performance after opening up the electrical panel and re-tigtening all the ground and common line connections. Many connections leads to contact resistance. The resistance causes voltage drops and that causes unwanted current flow.

All grounds should be common and this include cable TV connects if that's any where in your system. Multiple ground rods are good, just tie them together with 10 gauge solid wire and make sure all connections are tight...
Rap 04-16-02

Thanks for all.
Update:
All grounds tied together with 10 gauge solid wire. slight improvement
All grounds and common line connections tightened. no effect
Switched out FIM880's.isolated ground outlets definitely less buzzy
Cable Tv disconnected, ground break was already in. no effect
Did usual routine...amps alone are quiet...but the minute I hook up the preamp the buzz is back.
Lifting the ground via cheater at the amps makes them completely quiet!
For Tomorrow: new ground rod...#3. reground main box to something more substantial than something from 1975.
By the way there is a 15 volt difference between the main ground and the circuit ground!

Question: is there any problem sonically or safetywise in leaving the grounds of the two amps lifted?
JD

I would question the ground of the house too. Which is way is the potential difference. Is the house ground lower or higher than the earth ground. There are also "salt" based chemical grounds that have better conductivity than driving a stake into the ground. - Dan

Jdwek: I'd find out which component is contributing the 15 volts and contact that manufacturer. Seems suspiciously high and may be indicative that service is needed.

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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