Multiple circuits do not work (1 Viewer)

[Pete H]

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.)

 

[Ron Reda]

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???

 

[Brian Glaeske]

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

 

[Pete Mazz]

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

 

[brucek]

Pete H,

If you have connected equipment on different circuits you will have a ground loop

Sound like you've been having trouble, but I'm afraid I can't completely agree with your assertion.
The benefits of a dedicated circuit are many. I highly recommend it.
There's nothing magic about dedicated circuits. It just ensures a single run from your power panel to a wall receptacle, with no interconnections between and nothing else plugged into the circuit except your system.
The receptacles in your room now may have up to 12 lights and receptacles on the same circuit. At each receptacle that the wiring runs through, there is a set of twisted connections inside covered with marrettes that may be presenting a small resistance. The more of these connections, the more possibilities of poor, high resistive joints before the circuit reaches the receptacle that you are using.
Not to mention the myriad of things like motors, fluorescent lamps, and computers that may also be plugged into this same circuit besides your system.
All this can result in a loss of power and increased noise at the receptacle you're using for your system.
There's also a large possibility that if you are using more than one receptacle, that they may be on a different leg of the loadcenter.
These things are a recipe for problems of ground loops and other interference. This is the reason many like to install one or two dedicated circuits direct from the power panel to behind their system.
When you use a dedicated circuit, and noise is introduced on a different circuit in the house, even though they return to a common point at the loadcentre, this noise tends not to travel down your dedicated circuit because of the extremely low source impedance of the mains at the panel. It acts like a pass filter to this induced noise.
As you've already noted, if you place a particularly noisy light dimmer circuit on the opposite leg of your load center you can increase the noise rejection even further.
When you use two dedicated circuits you do have the added possibility of ground loops. The best solution for this is to run the two circuits together so they are identical lengths and paths traveled. This helps to ensure the potential of the safety grounds are at the same potential.
Ground loops are sometimes a difficult task to track down and remove because there are a million reasons for them to exist. The loop is caused by a difference in the ground potentials in your system. Breaking the safety ground almost as often clears the problem, and that is why it goes away with the use of two prong power cords or with the use of cheater plugs. This easy fix is obviously tempting, since it's so easy, but it's extremely dangerous and not recommended unless you enjoy getting a shock.
Generally a ground loop can be tracked down to its source, but removing the problem can sometimes be a little more difficult.
One of the other major culprits in creating ground loops is the use of more than one circuit in an HT system. The larger systems demand more power, so several dedicated circuits are sometimes needed. But even using a single circuit with different receptacles can cause a ground loop.
Residential houses use 240 volt "single phase" three wire power. The two "hot" legs are 120 volts and are 180 degrees out of phase. The loads in your house are balanced between these two legs at the service panel. It is advisable, if you do have two circuits powering your HT system, to ensure you are using a common leg. It is fairly easy to establish this.
Let me explain a bit about ground loops.......Even though the safety ground is a cold conductor, it can, and usually does, develop a small potential, through mutual inductance, wire resistance and various other reasons that can be different at each receptacle in your house.
When I plug a power amp into one receptacle and a preamp into another receptacle, the metal cases of these two units can have a small potential difference in their safety grounds which means that this equipment's metal cases are at a slightly different potential. When I connect a single ended (RCA) cable between these two devices, a small AC current can flow in the shield because of the potential difference. This signal is in the signal loop circuit and can cause a hum. An interconnect circuit has a loop path (completed circuit) that flows through the centre conductor of the interconnect cable and back on the shield. If there is an AC signal on the shield flowing because of the ground difference potential, you'll hear a hum. Breaking the safety ground of one of the two devices removes the potential and the path for the unwanted signal flow...
Exactly the same situation can occur, except usually worse, when you introduce a new ground into the system from cable TV or a satellite. Their ground on the shield may possess a different potential than the ground in your system and current will flow in all the interconnects. Usually by centralizing and bonding all external grounds to the common house ground you're at least giving yourself the best chance of reducing this problem.... To locate a ground loop you have to start with a minimal system and build it up cable by cable to find the cause.
So what can you do if your system is noisy.
The idea that there is always something fundamentally flawed with power from the wall is silly. Most AC power is fairly well regulated and generally free from noise.
The power supplies in our equipment will filter any small noise spikes and bypass most RFI to ground. The power supply regulators will make up for small line voltage changes. In fact the noise rejection from power cord to DC at the chip in any piece of equipment today is extremely high and doesn't need any help.
So I wouldn't particularly recommend any line conditioners or power plants.
I know many people swear by them but I'm not a huge fan power plants. They tend to generate a lot of heat. Basically these devices are AC to DC to AC converters. They take the AC from the wall and convert it to DC the same as the power supplies in all your audio equipment that you own. Then they feed a very high quality AC inverter to create a new AC signal to feed your equipment. Well, if the AC power in your home isn't a problem to begin with (and it usually isn't), what have you gained here? You already have a device in every piece of equipment you own to nicely convert AC to DC with a rather high noise rejection. Why do it again and then reconvert the DC back to AC and then feed it to a power supply and recreate DC again. Is the AC coming from the Power Plant going to contain less noise and harmonics from the wall? Maybe not - and as I said before, the noise rejection of a standard power supply in a piece of audio equipment is very high. And again, you'd be adding another device into the chain. How many times do you want to go back and forth from AC to DC?
And remember that most power plants are power limited. A standard 15 amp wall plug can supply about 1800 watts. Why would you want to limit the power to your equipment, particularly when most residential power is not flawed to begin with? I'm sure you'll read lots of anecdotal evidence of how someone's soundstage improved or any number of other stories regarding these devices. Believe them if you want.
Power conditioners are another questionable device that manufacturers make outrageous claims about. What can a power conditioner do?
It can filter some EMI/RFI noise. It can provide some local surge protection. Other than the power plant mentioned above it can't regulate the power. It can provide a convenient place to plug all your equipment, but a good power bar can accomplish this for a lot less money. Don't spend a lot of money on these devices.
One product I would recommend is a balanced power unit. The ones produced by Link Removed seem to come highly recommended by many uses.
Balanced power has some merit in the correct application, particularly in somewhat reducing reactive currents, but I feel standard residential power doesn't really benefit from being converted to common mode as much as using sensible electrical practices in wiring and grounding an audio system. I think it's essential that you try and remove all other sources of problems before trying one of these units.
I've seen too many poorly wired and grounded systems that produce a ridiculous amount of hum that the owners believe that throwing a balanced power or line conditioner at will solve. In your case where it seems you've installed a dedicated circuit and still have some problems, you might try one of these units.
Most noise in audio systems comes from ground loops, not from "dirty power". These are fairly easily solved, but it is a fairly time consuming task. Unfortunately, the safety system that is designed to save us from shock creates a lot of problems in the audio and video world.
brucek

 

[Kevin Deacon]

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?

 

[Wayne A. Pflughaupt]

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

 

[Pete H]

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.

 

[brucek]

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 Link Removed site and see what you think.....
brucek

 

[Wayne A. Pflughaupt]

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

 

[brucek]

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

 

[Bob_M]

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

 

[Pete Mazz]

is the neutral and ground bus isolated

This is important in a panel/sub panel setup. The main panel can have the neutral and ground together. In a sub panel they must be isolated from each other.

Pete

 

[Steve Berger]

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.

 

[brucek]

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.....
brucek

 

[Pete H]

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

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).

Brucek seems to be defining a ground loop. Doing this produces a small (ear within six inches of the speaker) amount of noise and not the loud noise heard when the CDP is inserted. Is this a ground loop? If not, I suppose it would mean I have had two "broken" CDP's in my system.

Bob and Pete, you both mention the ground and neutral wiring of the sub panel. I will look into this.

Thank you for your efforts.

 

[brucek]

Pete,

Doing this produces a small (ear within six inches of the speaker) amount of noise and not the loud noise heard when the CDP is inserted. Is this a ground loop? If not, I suppose it would mean I have had two "broken" CDP's in my system.

Well, not likely. Read the info above on this point. While not a permanent solution, don't rule out the use of a "cheater" for troubleshooting. Sometimes they're useful for finding a specific piece of equipment that is leaking noise into the ground system through a faulty capacitor.

brucek

 

[Pete H]

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.