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I had my contractor install 4 dedicated 20 Amp circuits on their own subpanel (about 50' from the outlets). Two are in the front of the room for the amps. Two are in the back of the room for the electronics and video.Each circuit home runs hot, neutral, and ground to to the electrical panel using 10 gauge wire. The outlets are PS Audio Power Ports which are isolated ground outlets.
I just hooked everything up tonight for the first time and had massive ground loop hum. My first step in identifying the problem was to leave just the preamp and amp hooked together. No such luck as that is the connection that is humming.
If I plug the amps in to the same outlet as the electronics, it obviously goes away.
If I lift the ground on my solid state amp, it goes away but this is obviously not good.
If I lift the ground on my tube amp, it still hums.
The one thing I did do that fixed it was to plug in a Jensen Isomax transformer right before the amp. However, I don't know what this will do to the sound quality and there is no way to A/B since the hum is so overwhelming.
I really am at a loss for how to solve this. I can't share a ground wire across all of the outlets because it is not code.
Any help is greatly appreciated. I already had a ton of problems with the general contractor's electrician so he will be no use diagnosing the problem.
Edits: 08/24/14 08/24/14Follow Ups:
Just curious what you have done to solve your ground loop hum problem.
and cut the third prongs. Paul, the P in PS Audio, recommended this to me when faced with the same issue from a power plant and a bi-amp. So much cleaner and lower noise after. Safety ground is a noise antenna.
OK so lets hear the usual objections like always based on safety. It's a good time for me to go visit all the audiophile graves of those from the 40's, 50's and 60's and later that died from not having safety grounds when there were no safety grounds to "protect us". (tongue inserted in cheek)
ET
"those from the 40's, 50's and 60's and later that died from not having safety grounds"
We were rugged in those days...
And I'm from them and I agree that at least for home audio the risk is minuscule.
Actually I think only my power amp has one now...
The common topology used to be only grounding your preamp and that to try and keep the phono preamp intact when you sparked the tonearm. Interestingly enough that also provided a "safety ground" on the side. Since all of the other devices were hooked to it with shielded cables any internal breakdown from powerline to case would cause fault currents to return to ground through the preamp and trip the breaker or blow the component fuse.
Look at AC/DC all-american five radios. One side of the line went right to the chassis and the plugs were completely unpolarized. But unless you did something totally stupid like pull off a knob (and somewhere there must be someone who didn't but we sure did) or touch a screw on the bottom what could go wrong?
Yet having spent my whole life in the radio/electronics arena I personally know of no one ever electrocuted. Shocked, yes. Killed, no. Ten minutes of training in electrical safety is of far more lifetime value IMHO. GFI's on the other hand are great, ah the grand march of tchnology, and likely a good choice for folks who want fault protection AND signal isolation.
Rick
The common topology used to be only grounding your preamp and that to try and keep the phono preamp intact when you sparked the tonearm. Interestingly enough that also provided a "safety ground" on the side. Since all of the other devices were hooked to it with shielded cables any internal breakdown from powerline to case would cause fault currents to return to ground through the preamp and trip the breaker or blow the component fuse.
The small gauge signal ground wire in a typical interconnect would never be able to handle the high ground fault inrush current in the event of a ground fault short circuit in a power amp. A typical 20 amp circuit breaker could pass 1000 amps before it could trip open. The small signal ground wire of the IC would melt, blow itself free at one end or the other of the connector. More than likely what would happen first is the component fuse in the amp would blow breaking the ground fault circuit. Of course if the ground fault were ahead of the fuse then the fuse would not be part of the ground fault circuit.
The point is ICs should never be used as an effective means for an AC power ground fault circuit current path.
Something else that should be considered is not all designer/manufacture of audio equipment connect the signal ground to the chassis equipment ground. Example, I have an ARC VT50 power amp. The signal ground is not connected to the chassis equipment ground. So if a ground cheater was used on the power cord plug and if an AC power ground fault were to happen any where in the power cord assembly or inside the amp the outer case of the amp would be HOT with respect to any other equipment grounded piece of equipment. A difference of potential of 120Vac would exist.
"The point is ICs should never be used as an effective means for an AC power ground fault circuit current path."
OK. Yet they typically will do the job just fine, especially the shielded ones which is why I expressed it that way. Remember the issue is the fusing current, not the long term load.
"Something else that should be considered is not all designer/manufacture of audio equipment connect the signal ground to the chassis equipment ground."
True, but that didn't used to be as common as now. And indeed the practice may be helping to contribute to the dismal RFI rejection many experience. Additionally in a stereo there will often be noticable hum or something where in, say, a floor lamp, a stray strand from the hot can touch the metal housing and still light just fine. The newer polarized plugs do help with that...
Rick
"The point is ICs should never be used as an effective means for an AC power ground fault circuit current path."
OK. Yet they typically will do the job just fine, especially the shielded ones which is why I expressed it that way. Remember the issue is the fusing current, not the long term load.
False Security.
As for shielded cables, a foil with couple of small drain wires was never meant to carry high ground fault currents. Also worth mentioning, who today connects both ends of the shield at each end? ( With the exception of a coax cable.)
Remember the issue is the fusing current, not the long term load.
I would agree for an AC power ground fault condition that occurs after the component power fuse. But what about an AC power ground fault condition ahead of the fuse? Say a homemade power cord or an aftermarket power cord that was made in some guy’s back room or basement. If a ground fault condition were to occur in the power cord assembly the chassis of the piece of equipment would become HOT and the equipment power fuse would not be part of the ground fault circuit.
Instead of cutting it off,just use a cheater plug for about a buck at any Walmart or Home Depot.
Maybe if someone makes an "Audiophile' grade cheater plug....
Please forgive me sir,I realize the era of my ways and shall do my best to amend my ignorance.
... and I know this because I've tried it before.Even if you were to attach the cheater plug to the plate (as you are supposed to), the weight of a heavy gauge powercord could rip the cheater plug off of it's screw mount. If you want to use a cheater plug with a heavy powercord, remember to support the cord with blocks or cable lifts of some kind.
I recommend the use of powercords with removable ground pins, such as those made by PS Audio. Their base models cost less than $100, AFAIK, and build quality is tops.
Edits: 08/26/14 08/26/14
Even if you attach the cheater plug to the plate (as you are supposed to),
LOL, you do know the cover plate 6/32 screw support in the receptacle is internally connected to the receptacle supporting back strap that is in turn connected to the safety equipment grounding conductor.
The 3 wire to 2 wire adapter only becomes a ground cheater when the ground tab of the adapter is not connected to the safety equipment ground.
Sorry if I wasn't clear. What I was trying to say is that the ground tab connection that is provided for "safety" is *supposed to be (or, meant to be) used*. Most of us who use cheaters know about the safety considerations but are mindfully choosing to ignore such warnings. Therefore, we do not use the ground tab connection.My point is that really heavy cords will often need some support, especially if you use cheaters. That's all I was trying to say...
Edits: 08/26/14 08/26/14
Nah, why take probably a decent power cord and degrade the quality with a one dollar cheater.
ET
PS Audio power cords feature removable ground prongs (at least mine do). Simply unscrew.
Correct, the newer ones do. I did have an older one that did not.
Cheers, your pal ET
I had my contractor install 4 dedicated 20 Amp circuits on their own subpanel (about 50' from the outlets). Two are in the front of the room for the amps. Two are in the back of the room for the electronics and video.
Each circuit home runs hot, neutral, and ground to to the electrical panel using 10 gauge wire. The outlets are PS Audio Power Ports which are isolated ground outlets.
* Isolated ground receptacles? Is the wiring installed in metallic conduit? If conduit, was the wire pulled into the conduit after installation of the conduit? If conduit, was an individual conduit installed for each Dedicated circuit?OR,
* Is the wiring MC cable with an outer steel or aluminum spiral armor around factory installed conductors.
http://www.afcweb.com/mc-metal-clad-cables/mc-lite-aluminum-armored-cable/OR.
AC cable with an aluminum corrugated armor around factory installed conductors.
http://www.southwire.com/products/ArmorliteTypeAC.htmOR,
* Is the wiring 10-2 with ground NM-B cable? (Romex is a trade name of NM-B cable). IF 10-2 W/GRD NM-B cable the outer jacket of the cable will be orange in color.
http://www.homedepot.com/p/Southwire-250-ft-Orange-10-2-Romex-NM-B-W-G-Wire-28829055/202316274
Are all the dedicated circuits fed from the same power Line, leg, in the sub panel? All from Line 1, L1, or all fed from L2?Don't know? Quick check is to look at the 4 breakers in the sub panel that are for your audio/video equipment.
If the breakers in the sub panel are mounted horizontally they are connected to L1 and L2 down each side as follows,
You will find numbers stamped into the dead front cover that covers the breakers around the handle and face of the breakers.
> > > > > > > > > > > left side - - right side
L1 .... breaker spaces 1 ...... 2
L2 .... breaker spaces 3 ...... 4
L1 .... breaker spaces 5 ...... 6
L2 .... breaker spaces 7 ...... 8
And so on down each side of the panel
Example are your 4 dedicated circuits connected to breakers in L1 spaces 1,2,5,6 or L2 breaker L2 spaces 3,4,7,8?
A sure way is with an AC volt meter. in your case you will need a piece of wire to extend one of the test probe leads of the meter.
Measure from one of each small slot contact of each dedicated circuit duplex receptacle to the other small slot contact of all other dedicated connected connected duplex receptacles. You should measure zero volts.
Edits: 08/25/14 08/25/14 08/25/14
There is a central junction box close to the room that attaches to the sub-panel via a piece of PVC that was buried ~18" in the ground (the house is on slab and very difficult to pull wires through). Flexible metal conduit was then installed from the junction box to the outlets. Much of the conduit has shared wires in them. The wires were pulled after the conduit was installed.
The metal raceway has its own ground as well per code.
The circuits share the same leg.
I will check the voltage when I get home
Flexible metal conduit was then installed from the junction box to the outlets. Much of the conduit has shared wires in them. The wires were pulled after the conduit was installed.
Induced voltage onto the safety equipment grounding conductors caused by the loosely installed current carrying conductors in the flexible metal conduit multiplied by more than one dedicated branch circuit sharing the same conduit. A true dedicated branch circuit does not share the same conduit or cable with other branch circuits.
Starting on page 31 of Link provided below.
Quote:
The “Conduit Transformer”
• This finally explains what drives 99% of all ground loops!
• Load current in line and neutral produces opposing magnetic fields
since instantaneous current flow is in opposite directions
• Imperfect cancellation magnetically induces voltage over the
length of the nearby safety ground conductor
• Strongly affected by geometry and proximity of wires
• Highest voltages with randomly positioned wires in conduit
• Lower voltages with uniform geometry of Romex®
• Voltage is directly proportional to load current, wire length, and
rate of change in current or ΔI/Δt
• Mechanism favors high-frequency harmonics of 60 Hz
• For constant current in L and N, induced voltage rises at 6 dB/octave
The “Conduit Transformer”
Wires randomly positioned in conduit
produce the worst possible results!
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
I eliminated the issue via a high quality Jensen isolation transformer.
Tried different cables. It's not the cables.
As another inmate suggested, try unplugging your video cable from the wall.
Why don't you just have the contractor come back and make it right? I would hope he stands behind his work!
Why don't you just have the contractor come back and make it right? I would hope he stands behind his work!
The electrician more than likely wired the sub panel and dedicated circuits per Local and NEC code. Per code the install is fine. I would assume an electrical inspector signed off on the job.
That is correct. It was installed per code and signed off.
I would think any reputable electrician would stop back and check it out. He has nothing to lose by making a phone call.
He will come back but I need to know what to tell him.
You don't say what kind of "problems" you had with the electrician, but substance abuse is rampant these days so I would suspect improper wiring and/or improper use of materials as the cause of your problems.At the very least, I would remove the faceplates from your receptacles and maybe even the receptacle units themselves to try to take a peek. Maybe there's a loose or faulty connection. If anything's amiss on the superficial level, a screwdriver may be all you need to correct things.
PS: Be sure to shut off the power before you go diggin' around...
Edits: 08/25/14 08/25/14
I'd take a look at the subpanel wiring. The "safety" grounds should all be connected next to each other and preferably on the tail end of the bar away from the input so that power current doesn't flow across them.
If you need to move things around be very very sure to turn the breaker for the subpanel off in the main box first and check for voltages with a meter before unscrewing things.
Of course this assumes that you weren't having the problem before rewiring. I agree with the poster who says to see if it the cable connection is part of it.
Good luck, Rick
Cable tv coax is disconnected along with everything else except for the amp and preamp.
If you have a voltmeter and some wire you may be able to measure the various voltages between your grounds. I agree with Jea48 that voltage differentials are the rub, the question is why and where. Even a $10 meter from Harbor Freight will probably do the job. Their AC LSD is .1V and your audio signals are around 1V max so if the hum is loud it's prolly < 20 dB down.
Good luck, Rick
Cable tv coax is disconnected along with everything else except for the amp and preamp.
Did you disconnect the incoming CATV coax cable from the CATV receiver box? If not the CATV incoming coax cable would still be connected to the safety equipment grounding conductor of the power cord of the CATV receiver box to the wall receptacle the preamp is plugged into. That is if the CATV receiver box uses a 3 wire power cord and plug.
What you are looking for is a reason/source why there is a difference of potential, voltage, somewhere between the safety equipment grounds of your 4) 20 amp dedicated circuits.
Edits: 08/25/14 08/25/14
To reiterate, there are only 2 things plugged in at the moment. The amp on 1 circuit. The preamp on another circuit. The preamp only has a interconnect running between it and the amp.
To reiterate, there are only 2 things plugged in at the moment. The amp on 1 circuit. The preamp on another circuit. The preamp only has a interconnect running between it and the amp.
When you plugged the amp and preamp into the same duplex receptacle, where you did not have the ground loop hum, did you use the same long interconnects as was used when the equipment was separated plugged into two different power circuits? This is important to establish a common base line to start from.
Welcome! M-B.
sounds frustrating, hopefully there is an EE or construction inmate that will be able to help you out. Keep us posted.
My ground loop problem was caused by the Comcast cable feed. When I disconnected the feed, the ground loop hum disappeared (everywhere...I have two separate systemes that were affected).
Common problem. You can use two baluns (75-300 ohm attached to 300-75 ohm) to isolate the cable. Better yet, call Comcast and inform them that the electrical code requires that the cable be grounded at the service entrance and have them come out and do the installation properly. If they hem and haw, tell them they have no choice. I suspect that there are millions of cable installations that are not to code and that Comcast doesn't want your city inspector doing an audit of their installations.
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