buzzzzz, where did i go wrong?

I agree with Sean. Having two separate ground systems in your rig is an open invitation to hum problems. Tie the rods together.

BTW, just for fun, before you tie them together, hook a voltmeter across your two grounds (with nothing else attached). Set it for AC and try a low voltage range. I'll bet you see a potential difference!

Also, are you running balanced or single ended interconnects?

Dear All,
Thanks for the responses. I am using single ended runs but have a balanced run that a friend made me that I would like to try. This morning I have been sitting with my electrician and working with it. The FIM 880 seemed to be part of the problem since when we swapped that out for regular hubbels on the preamp and digital circuit it helped a bit. I am going to next swap out the other FIM's. There is still a buzz now so I will try to tie the rods together.
jd

Jdwek- Unless you're using a metal duplex box, I don't see how the change in outlets would affect the buzz unless the ground wire connections weren't clean and tight. In any case, once you have the buzz corrected, be sure to give the 880 outlets a chance. You may find they provide a nice sonic upgrade to the hubbels. They certainly did in my system.
Good luck.

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