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buzzzzz, where did i go wrong?

The setup:
spectral monoblock amps
spectral preamp
theta front end

The NEW DEDICATED CIRCIUTS
4 separate circuits each with fuses jumped off the main box and grounded to the main box
one circuit for each monoblock
one for the preamp
one for the digital front end (MIT power conditioning)

the amps and preamp each share a supplemental grounding rod. The digital end has its own supplemental ground rod
The outlets are all FIM880. These do not have an isolated ground (could that be the problem?)

I still have a buzz.low but audible; it goes away when I lift the ground from my amps. I assume I have a ground loop but I am not sure how or what I do about it. I assume I have made some awful basic error but not sure how.
I know for instance from the posts that Garfish uses three supplemental grounding rods. Maybe I should have tied all those together? any other ideas
jdwek
jdwek OP
84 posts
 
Although I am armed and with a multimeter I am rather one the level of one who has just enough knowledge to get himself in trouble. So, in order to check resistance, do I simply turn the meter to the ohm symbol and touch the rods with the red and black probes?
DOes the power have to be off to those circuits? Since teh rids are quite a bit distant from each other I assume I can attach jumpers of copper wire to the rods and touch those.
I actually today tried to check teh resistance at the outlet level by putting the red and the black into the common and the ground hole on the outlet. I was not sure if the power should have been on or off to the outlet but I got a number less than one.
It also turns out they use in California something called harmonic transmission which I may have to investigate.
jd
sean
6,231 posts
 
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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jdwek OP
84 posts
 
Tomorrow I will install plastic spacers at the mounting bracket of the FIM's to the metal receptacle. Then I will attach the supplemental grounds to the grounding bar at the main service panel. Thanks to both Mar00 and Sean for their help in the continuing great struggle in which I am engaged...someday they will write a book on this...Jerry and the ground loop....maybe some dr. suesslike illustrations
scottshannon
42 posts
 
No one has touched on this yet. So try this: 1st hook up the amp to the speakers ONLY. Do not hook the preamp to it. Is hum still present? If so, the amp has a noisy transformer. If not, connect the pre to the amp but dont hook anything else to the pre. Got noise? Proceed on in this way to find out what component is actually causing the ground loop if there is in fact one. I have had a similar problem and found that there was no ground loop at all...I would try this trick before you go any further with the grounding to find nothing is "wrong".
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