Multiple circuits do not work

Discussion in 'Archived Threads 2001-2004' started by Pete H, May 8, 2002.

  1. Pete H

    Pete H Stunt Coordinator

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    You have seen it before. "You need a dedicated circuit for all that high dollar equipment", "you really have a powerful amp, I would run a separate 20 amp circuit for that baby", "I've got (pick your number) two, three, four dedicated circuits for my equipment". Closely following these comments is the proverbial "make sure all your equipment is on the same phase (leg) of the panel" and "make sure those dimmer aren't sharing a circuit with your equipment, matter a fact, the dimmer circuit should be on the opposite leg".

    Well, it doesn't work. If you have connected equipment on different circuits you will have a ground loop. It may be something you can live with or maybe it will drive you nuts. This is the conclusion I have come to after year, three electricians, consulting with two "experts" in building home theater rooms, and more money than is reasonably sane.

    Any comments to the contrary? I hope.

    (Keeping dimmers off your equipment circuit help to reduce one form of noise but does nothing to eliminate the buzzing you will hear from your lights or the dimmer itself.)
     
  2. Ron Reda

    Ron Reda Cinematographer

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    Pete H,
    I've been praising the PS Audio Power Port for the past two days, so why stop?!
    I had a pretty bad ground loop hum issue when I installed my power amp for my fronts. I don't have a dedicated circuit (I'm living in a townhouse) and I have a dimmer on the same circuit so I was thinking that all hope was pretty much lost until I moved into a new place. Well, I installed a PS Audio Power Port the other night to replace an $0.89 receptacle and noticed that the audible hum that I was hearing from my fronts decreased significantly to the point where I could only hear a hum by putting my ear up to the speaker (I used to hear the hum from 14 feet away). Hey, after all you said you've spent, what's another $40???
     
  3. Brian Glaeske

    Brian Glaeske Stunt Coordinator

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    Not to mention that if you're not drawing more than 20amps (i.e. the circuit breaker never trips), you're not doing buying anything with multiples.

    Brian
     
  4. Pete Mazz

    Pete Mazz Supporting Actor

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    I've got dimmers all over the house, mostly X-10 stuff, and have zero problems.

    Do you have a single panel box, or a panel/sub panel?

    Pete
     
  5. brucek

    brucek Second Unit

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    Pete H,
     
  6. Kevin Deacon

    Kevin Deacon Second Unit

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    Somebody once mentioned that if you run a single wire from the pre/pro to the amp and connect the two chassis, the ground loop hum would disappear. Is this safe?
     
  7. Wayne A. Pflughaupt

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    Kevin,
    That would eliminate the ground loop only if it was between those two pieces.
    brucek,
    Perhaps you could take a look at this thread – you’re probably the only one here who can help this fellow with his electrical problem:
    http://www.hometheaterforum.com/htfo...365#post676730
    Regards,
    Wayne A. Pflughaupt
     
  8. Pete H

    Pete H Stunt Coordinator

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    Ron, I do use a Power Port in conjunction with a 20 amp Ultimate Outlet and a Juice Bar. These were purchased after I failed to incorporate a second circuit in my system. They allow me to plug everything into one circuit. I have tried using the UO on the second circuit. It made no difference. I will be purchasing a second Power Port for my projector so maybe I will try your suggestion then.

    I agree with Brian and would guess that most systems do not require the use of a second circuit to reach their potential. Honestly this includes my current setup. I want a useable second circuit for three reasons. First, my 2 channel amp (Rotel RB-1090) sits between the fronts and the second circuit was put in when the house was built to accommodate this. (The rack closet is in the left wall so I have to run the amps power cord across the room into the front of the closet.) Second, I knew the time would come, and it's here, when I would upgrade the amp. Not all of the amps on my short list would require the use of a second circuit but at least one, the Pass Labs X350, would. If it is preventable I do not want my choice of amps impacted by the lack of a second circuit. Third, I want what I have paid more than enough money to have.

    Pete, I have eliminated all dimmers. I can control ambient light in other ways. The house has two breaker boxes. The first takes in the electric company feed and controls things like the air conditioners and dryer. It also supplies current to the second box. Everything else in the house uses this box. I would put in a sub to this box if I knew it would allow me to use the second circuit or allow for stable expansion.

    Brucek, where do I start? First, thanks for the response. The a/v room was designed and wired for three separate dedicated lines. Each line connected to the panel at its own breaker. The breakers were on the same leg of the panel. (This was verified by four different people excluding myself.) The wires went from the panel to a single receptacle (outlet) with no stops on the way. I'm sure the wires are different lengths. All other receptacles and the lighting use a different circuit, which by chance, are on the opposite leg of the panel. Even based on what you have said I don't see how I could have done anything different. This has led me to the conclusion that using multiple circuits will produce a ground loop.

    I admit I could be wrong and I keep hoping somebody will point out the error of my ways. I doubt it. Part of the reason threads like this don't really take off is that people can't add a whole lot more than has already been said. Brucek said it even better "there are a million reasons for them (ground loops) to exist" and "even using a single circuit with different receptacles can cause a ground loop". This much I do know. One dedicated circuit means no ground loop.
     
  9. brucek

    brucek Second Unit

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    Pete H,
    I sympathize with your situation, and it's all too common. Many people read the forums and follow all the correct advice and when they create their theater, direct the electrician to install two, three, four dedicated circuits on the same leg assuming that there'll be no problems. The electrician follows the instructions and runs four cables all over hell half acre and puts one on the ceiling for a projector and one in the rear and maybe a couple in front. Then you hook up all up your equipment and it hums like heck. What a bust. Usually it doesn't happen, but it can, and if you've done everything correctly as it appears you have, it's a perfect situation to try the balanced power route I suggested earlier. I see no other solution.
    I was lucky with my equipment. I installed two dedicated lines to my system and I have no problems (not that it matters). I ran them the same route from the same leg and terminated them side by side. The impedance path and subsequent potential on each ground of these circuits is identical and it results in no ground loops with the equipment I use. But not every one is so lucky.
    If I did experience noise problems after going to this trouble I wouldn't hesitate to convert this power to common mode and purchase one or two balanced power units. I don't own any because I have no problems and my noise floor is very low, but I know how they work and the theory is sound (pardon the pun). This isn't a tweak.
    A balanced power unit is basically a very high quality isolation transformer with a center tapped low impedance secondary. So instead of a hot of 120 volts and neutral return, you have two 60 volt lines with a center tapped ground. Across the 60 volt lines which are 180degrees out of phase you have your 120 volts, with each 60 volt lead referenced to the ground at the center tap. There are a lot of benefits in this configuration. Any reactive currents developed in the load arrive at the common center tap and are cancelled. Any noise that would normally travel on the safety ground are cancelled at the center tap.There's not much chance of a ground loop.
    The other benefit can be a lower noise floor.
    I think this could be a good solution in your case. The cost isn't really prohibitive and I think it would allow you to use several dedicated lines without hum. A 15amp unit is around $900. Maybe visit the www.b-p-t.com site and see what you think.....
    brucek
     
  10. Wayne A. Pflughaupt

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    Pete,

    I know brucek has said that you can do everything “right” and still end up with a ground loop, but I think he would agree that it would be a fairly rare occurrence. This leads me to explore other avenues in your situation.

    I notice that you’ve given us much detail on how carefully you set up you electrical, Pete, but virtually nothing else. Like your system, for instance.

    In the rush to blame everything on the electrical you may have missed some of the most obvious and common causes ground loops, like a CATV feed or a poor DSS installation. I’ve seen very few DSS installs that impressed me – they all seem to be “let’s get this puppy in the air and blaze of here in an hour or less.” It is not uncommon for them to do a “quick and dirty” ground to anyplace but where it should be - namely all the way back to the house electrical ground. Instant ground loop potential if they do that.

    Again, it would be rare, but it is possible the telephone connection to a DSS receiver could be a problem. Phone service is supposed to be properly grounded at the service panel, too.

    Also, as brucek alluded, it is possible that bad cabling in your system can cause problems. A faulty piece of equipment can, too.

    At this point, Pete, I would examine every cable and every piece of gear, both audio and video, in your system.

    First make sure your are using decent-quality, well shielded cables. I’ve seen some “tweak” audiophile interconnects that do not use a shield, but rely on independent twisted conductors for noise rejection, which I expect is inferior to shielding if EMI is bad enough (perhaps brucek can clarify this).

    In some cases where high EMI is an issue, cables with an inadequate shield could be a problem. For instance, most people have good luck with Radio Shack’s Gold series cables. However, I have opened them up and their shield is rather poor, IMO - a very loose, rather sparse braid.

    Disconnect everything but the pre-amp and amplifier and see if the noise goes away. If the noise is still there, replace the cables between them and see if that makes a difference. If it doesn’t help, check them out separately. You can check the pre-amp by plugging a source component like a CD player directly into the amplifier (be careful of high volume levels if you decide to play a disc!). If you can give the pre-amp a clean bill of health, swap out the amp for a test. Perhaps a friend or the store you shop at can loan you one, or you can buy one at Best Buy or Circuit City long enough to test (a receiver with “Main In” jacks will do if you can’t find a power amp).

    Once you’ve cleared the pre amp, amplifier and their cables, all you need to do is add each piece of gear to the system one at a time until the problem returns. If a piece of equipment appears suspect, again try swapping the patch cables before you pronounce it culpable.

    I’m fairly confident, Pete, that since you’ve done your electrical right the problem with your system is elsewhere, and a little digging will find it. It would be a shame to drop a grand on balanced power if the problem was nothing more than a cable TV feed or a set of bad patch cables.

    Regards,

    Wayne A. Pflughaupt
     
  11. brucek

    brucek Second Unit

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    Wayne,

    I completely agree with you Wayne - I assumed Pete had already flogged all the equipment possibilities to death, so I passed over it fairly quick in my answer.

    Certainly if he has a power amp between his mains with an extension cord over to his equipment so it doesn't hum, it's not a permanent solution. I hope Pete has gone through the usual minimum system method you suggested.

    Plugging "only" the amp with speakers into the second circuit and "only" the preamp into the first, with a single set of interconnects between should yield no-hum. If it does, his loop source from different ground potentials is assured, assuming the equipment is not faulty (and subbing other equipment can reveal this as you've suggested). If it doesn't hum he can begin to add equipment until it does. This will at least give a clue as to the source of the problem.

    I assume Pete has established that the cable/DSS is not the offender. When I installed my satellite, I put an eight foot grounding rod outside, that I grounded the antenna and cabling to. Being lazy, I thought that would suffice. It didn't. It introduced a small hum into my system. I'm such a fanatic, even with my ear jammed up to my speaker, I won't accept any noise. So I then bonded the satellite grounding rod with a #6 wire to my house ground system and the problem went away. My point is that many installations do not bond the DSS ground to the house system as you've said. It's a good source of ground loop problems.

    Also as you've said, even bad IC cabling can cause hum that may be falsely blamed on electrical problems. A single ended connection requires it's shield for a completed circuit, but if a shield is broken, the signal will usually find another path through another shield or interconnection. The broken shield in this case is not revealed, but a hum begins. Tough to find.

    The woven cables you spoke of still have the same signal path with associated return ground. I tend to avoid unshielded twisted wire cables, they usually have slightly higher capacitance figures which tends to roll off the upper frequencies. They act like a low pass filter. To make an unshielded pair of wires usable on this high impedance interface, companies have to incorporate an interweaving technique of the insulated conductors. This usually works to reduce noise and can be almost as effective as a shielded coax but the technique also causes the capacitance per foot to rise. The parallel reactance resulting from the cables high capacitance figures starts to become a player in your impedance equation. Why bother.

    Anyway, I think it's important if people have a pesky hum that they've tried willy-nilly to repair, it requires a wholesale taking apart of the entire system and beginning with a single amp and speakers and then build the system cable by cable to find the source.........

    brucek
     
  12. Bob_M

    Bob_M Stunt Coordinator

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    Wayne,

    I was just going to comment on the cable TV and DSS issue. Thanks for pointing that out. Like Bruce said I am sure he has gone down the avenue but you never know. The other thing to check out is that sub panel. Is properly wired from the Main? For example, is the neutral and ground bus isolated, does it have a #6 wire or better going back to the ground bus at the main panel, Is a ground rod present or some other secondary grounding causing a problem at the sub panel?

    Bob
     
  13. Pete Mazz

    Pete Mazz Supporting Actor

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  14. Steve Berger

    Steve Berger Supporting Actor

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    I know this is going to sound pretty simplistic but they do make various isolation devices to break ground loops. There are audio, video, and coax isolators. I send signals all over my house from various devices and found my PC-DVD (about 65 feet away from the amp) would hum. An automotive isolator (intended for power amp hookup) cured it completely for about $10.
     
  15. brucek

    brucek Second Unit

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    Isolators are great for ground loops caused by cable TV. Simple, cheap fix. Most isolators are transformer based and as such aren't useful for DSS which requires a phantom DC signal to be passed. Transformers don't pass DC.
    Isolators for audio have impedance matching and frequency response issues that most people in audio aren't willing to accept..... [​IMG]
    brucek
     
  16. Pete H

    Pete H Stunt Coordinator

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    Sorry this reply is so long in coming. It has taken me some time to digest what you all have said. Also, I am trying to be careful in my response so I don't mislead any of you. It would be my hope that many people will benefit from this thread.

    Brucek, it is a big help to me to know that I have done things the way they should be done. I have read about BPT products in the past. I had never pulled the trigger on one because it is not where I would prefer to spend my next equipment dollar. Would you recommend one for each circuit or can I get by with just one? (I will ask BPT the same.)

    Wayne, the responses here do have me looking at my equipment. The ground loop was clearly evident the day we moved in. Since that time I have added or replaced a couple of key pieces that did not alter the problem. For this reason I have not considered this to be an equipment problem. My current setup consists of the following:

    CDP - Carey Audio 303/200 (new)

    Pre - SimAudio P-3 (new)

    Amp - Rotel RB-1090 (unchanged)

    DVD - Sony S7700 (unchanged)

    A/V receiver - Yamaha RX-V995 (unchanged)

    Projector - Sanyo PLV-60 (new)

    Speakers - B&W N802's, HTM1 and SCM1's (unchanged)

    I/C's are mostly from Better Cable. The only thing slightly unusual here might be the 20 something foot run from the preamp to the amp. All of these are single ended. I did try replacing the long run with a balanced set of something made by Alpha-Core. It didn't do anything for the noise. I do have one pair of "tweak audiophile I/C's" between the preamp and the a/v. (The P-3 has a home theater pass through.) Speaker cables are Kimber Bifocal XL's.

    I do not have CATV or DSS located in or near the room. The dvd player is my only video source. The signal goes straight from the player to the projector.

    As brucek already guessed I have flogged all the equipment. (I did this before calling in the experts.) I discovered the noise was much greater when the CDP was connected through the external decoder inputs on the av receiver. I added the preamp and, if anything, the noise got worse. My CDP at that time was a Rotel 991. I had already decided to upgrade the CDP so I moved the purchase forward and acquired the Cary 303/200. It made no difference to the noise I was hearing. I might be able to believe the system noise was caused by Rotel in some fashion. But problems in both the Rotel and Cary? The odds start getting a little long. Additionally, with everything plugged into the same circuit the system sounds fine. If some piece of equipment needs to be repaired or replace I can't tell it from the sound.

    Brucek made an interesting statement

     
  17. brucek

    brucek Second Unit

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    Pete,

     
  18. Pete H

    Pete H Stunt Coordinator

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    I will consider the Bryston. The Theta Dreadnaught also separates the signal ground from the chassis ground. I never thought of it as a selling point. As a side note, I described my situation to the Cary people. They were of the opinion I should lift the ground on the preamp and could do so without creating a hazard. (I'm pretty sure I understood them correctly.) Tonight I am going to run the analog signal straight from the Cary to the amp utilizing the digital volume control of the Cary. What the heck.

    Thanks for all your help.
     

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