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". |
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 |
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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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 |
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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you know, after lifting all the grounds with cheater plugs except for one (the preamp) I still have a small buzz as well as a hiss. I think after I finish the regrounding stuff I will have to shut off every breaker in the house testing each one, one by one to see if any of them are contributing. There are several halogens as well as several lutron dimmers about. If I throw the breakers with those lights and dimmers does that mean they can no longer be a problem?
Also, using a multimeter is there a way to test a cable to see if it is faulty as well as the expedident of listening to it? I am wondering if the problem isn't internal to my rig. what about other multimeter uses?
JD |
Dear all,
thanks for all your inputs. I am unfortunately on the graveyard shift but as soon as I get home I will examine my various panels and subpanels and try to figure it out. I am a bit unsure whether I should be examining high volatage electrical panels after having been up all night but what is life without a little risk.
Sean, on the email I sent you that I think you didn't get I mentioned that some friends and I will be in Chicago on May 8-10 and I think we are going to wrigley on the 9th. Maybe you would like to join us since I think that is where you are from! You can reply by email or whatever. Tix are I think $26 plus tixmaster's damn fee.
JD |
Hey JD.......Bob here.The reason I asked you about the neutrals or white wires is that these are also referenced to the same grounding nuetral bar in your main panel.You should have a grounding neutral bar in your sub-panel.Tell me if you fed your sub-panel with hot ,neutral and ground or if you just ran the hot wire to your fuses and did you install a breaker in your main panel to branch from.Back to the neutrals,the grounding bar in your sub panel has a bonding screw through it to ground the enclosure itself.This bond is NOT USED for sub-panels.Also one other very important item is your metal conduit connection if its functioning as your ground consider that the point that it connects to your main panel is likely inches away from the grounding neutral bar and being connected directly to the panel enclosure you will certainly pick up stray voltages.The best way to accomplish your outlet grounds is get the Hubbells or Leviiton Hospital outlets with isolated grounds and run separate wires back to your panel.You can then use your conduit as a shield by connecting it to the panel end only and using a plastic washer on the outlet box(if metal) to isolate it.One more great thing to finish off the grounding job is if you have room in your main panel install an additional grounding bar(these are readily available and designed to attatch to your existing bar) and connect all your new outlet neutrals and grounds to this bar.If you can install the bar as close to your service ground as possible(also you should connect your rods right next to the service ground) this gives your audio circuits the most direct path to earth and minimizes the reaction from the rest of your house wiring.I used to wire houses in my younger days and was close to becoming a journeyman electrician before deciding on another career.Hope this helps and feel free to email me if you like.... |
I think my fiance soon to be wife is starting to really wonder about me! |
one other supplemental thought. the three dedicated circuits should ideally be on the same bus in the panel to minimize ground differentials. also, if possible, this bus should be the one with the fewest amount of large 'noise' contributors from i.r.,dimmers, fridge, etc. this could involve some rewiring in the panel but is usally worth the effort. |
good night,...I am on the night shift!
jd |
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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Ok I think I am getting it. Let me be more specific. The panel and the two rods are separated by about 35 feet. The two rods are about 6 feet from each other. I am going to take one copper wire from each rod to the grounding bar in the main box.
The outlets are still FIM880's which do not have an isolated ground. The conduit is their ground. Should I also use their copper grounding wire and land it to the grounding bar?
About the fuses, they indeed are a subpanel but i am not sure what is meant by the neutrals being bonded to it or not. By the way...I do own a multimeter and I not afraid to use it!....maybe someone could tell me how?
Thanks JD |
Sean,
I mailed you but I don't think you got it. I think there is a problem. Could you mail me?
Thanks
JD |
I've done similar circuit and grounding uprades.The key as others have mentioned is your using the new rods to supplement your existing service ground lowering the overall resistance.Spacing of the rods is important,they should be at least six feet from the service ground and six feet apart and each rod must be tied back(with a separate wire) to the same point in your panel as the service ground.Don't tie the rods together as you want the rods connected in parallel not series.Also you should have an isolated ground on your outlets for each circuit and each ground wire should be connected back to the same point in your panel as your service ground and rods.This is the essence of a star grounded system with ONE low resitance pathway to earth.If your using your fuse connections as a subpanel in some kind of enclosure make sure none of your neutrals are bonded to it.If your using in-line fuses you won't have this concern. |
JD, drop me an email at your convenience. Sean
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Maybe you should take the preamp to a friends house and see if it does the same thing.... - Dan |
OK this is starting to drive me batty.
Today's events included changing the main system ground. We also tried all combos of grounding rods including none except for the main system ground, 2 supplemental rods tied together, all on one supplemental rod...you name it I think we have tried it. we also went through the whoel house flipping each circuit on sequentially but no single breaker added to the buzz effect. It seems to happen after the preamp and teh digital end are tirned on. It is there when only the preamp is on and is slightly greater wheen the digital end is turned on. I am actually starting to wonder if my cables are a problem . They are MIT and are singled ended. Still moving the cables around has no effect.
i notice that cheating the amps takes away teh buzz leaving a small hiss. Maybe this is noise coming in on the neutral?
When you tie the grounds together does that just mean passing a copper wire between them? Does anyone have anyo other ideas?
JD |
Hi Sean,
Actually when I said, "salt" I did not mean it that way I should have said electrochemical. The company that I have found that does this stuff grounds substations, towers and the like. Their system has a lifetime of fifty years and only requires a little ground moisture to work effectively. Of course this come at a price, but this is the real thing. Check out http://www.sgscorp.com/index.html for more info.
- Dan |
Good stuff so far, especially Sean and Rap. One thing is certain - having two separate ground systems (power system and ground rods) will cause trouble, especially with a 15v difference. It's not a component problem.
So pick your ground system. Either float everything and tie everything to the ground rod, or give up on the ground rods and use the power system ground. If you use three prong cords and tie to the ground rods then that 15v difference results in current flow through the ground paths (chassis, cabinent, etc) through the ground prong to the power system ground.
I don't know how old your house is, but I wonder if the power system ground is good. Sometimes you get corrosion in old electrical systems.
With your audio gear referenced to ground rods, you might get a slight tingle if you come into contact with a component chassis and some other appliance referenced to power system ground (like a metal lamp with a 3 prong cord) at the same time. |
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
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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. |
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 |
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'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 |
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. |
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 |
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? |
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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Have you tried putting 'cheater plugs' (lifting the ground) from all but one three pronged plug? If the buzz/hum goes away, you are good to go, since ALL components that are connected (via interconnects) to the grounded component will be safely grounded. Check out this Michael Elliott web site for more info:
http://www.altavistaaudio.com/hum.html
Hope it is as easy as that. |
