Ground loop hum nonsense

[Dude111]

Originally Posted by jr_spyder

Do you have a ground wire between the TT and the preamp? Is it connected? This is a very common problem for older TTs if the ground wire is not connected, and that's what you have.

I dunno whats inside but to be frank I DONT KNOW HOW IT WOULD BECOME LOOSE! (The player sits in 1 spot)

Could it be caused by a problem with the house wiring??

Last summer when my air conditioner was on MY RADIO STARTED HUMMING (On the same plug) but stopped after a few minutes (I thought it might be LOW VOLTAGE) I dunno........

[chessman]

Ground loop hum occurs when the ground potential of one alternating current powered device is different than the ground potential of another alternating current powered device when the two (or more) devices share a pysical connection of some kind (power, signal, chassis ground, or other). It is a system issue (i.e. how the components and power circuits relate to each other), not an individual component issue.

There are three common responses. First, the "I don't want to have this issue" refusal to address the issue. Second, the lazy (and perhaps unsafe) "cheater plug, ground pin removal" technique. I confess I have reverted to the lazy technique more than once. And third, the "hunt down the problem, connection by connection no matter how long it takes, then really fixing it" technique. Dan and others have explained how to do the third technique.

Ground loop hum is a fact of life like gravity. You cannot wish it away, you can only manage it. And yes it is very hard to understand how it can erupt when all you did was swap one component for a similar component, but the cause is still a difference in ground potential. That is why you always see advice to have all audio dedicated cicuits on the same "phase" in the circuit breaker box, or to use "star grounding" or other techniques designed too minimize differences in ground potential.

As has been said by others before, the most common culprit is poor grounding of the cable TV. Oh, you say the problem is your stereo, even with the TV turned off? Go unplug the cable from the back of the TV anyway. If the hum stops, the cable TV ground is the problem. Ground potential differences can occur in a stereo system when a TV is connected to a DVD player that is also connected to a pre/pro that is connected to a sub. House current puts out a beautiful 60 H sine wave that gets subs humming when there is a ground potential difference in connected gear.

Of course, the above is but one example. It does, however, show how insidious a problem ground loop hum can be.

[jdandy]

Originally Posted by jr_spyder

I certainly believe the right wiring can do the trick, but alas I live in a 160 year old farm house with wiring that would have an electrician run away screaming. I know that's my problem.

John.......In a house that old you may still have some knob and tube style wiring in the walls and attic. In those old installations the hot and the neutral are physically separated and installed exposed as single wires pulled between porcelain insulators. Junctions (splices) in the circuits were usually made by twisting the bare copper end of a wire around a stripped section in the home run back to a panel. Knob and tube wiring did not have a ground. It is not uncommon for wiring down walls in a knob and tube installation to have the hot and neutral reversed at the receptacle. Couple that common wiring mistake with the absence of any grounding from receptacles to the service panel or earth driven ground rod, there can be all sorts of issues and hazards. In many older homes the original two prong receptacles were replaced with three prong receptacles so that modern plugs can be inserted but no ground wire exists at the ground terminal on the receptacle. This is quite common in older houses that have not had the entire home's circuitry brought up to modern code standards and regulations.

If you have not done so already, you may want to remove the receptacles from the wall to check that they have a ground wire landed on the correct terminal. Use a volt meter to measure hot to neutral and hot to ground. You should have 120 volts for both measurements. Measure neutral to ground. You should have no voltage. As a final test of ground integrity attach a long wire to the ground rod at your meter and then measure between that wire and the receptacle grounds for voltage. There should be no voltage. Also, using the resistance setting on your meter, measure for continuity between receptacle grounds and your separate wire back to the ground rod. If they show continuity to the ground rod then it is a true ground wire.

Sometimes, in the absence of ground wires in older installations, a shoddy electrician will installed a jumper wire from the neutral to the ground terminal. This is dangerous because the neutral is a current carrying conductor. A ground wire is a non-current carrying conductor. The practice of bonding a neutral and ground at a receptacle does not meet code but can fool a home owner into thinking the receptacle in question is grounded when it is not. The only place a neutral and ground can be connected by code requirement is at the point of first disconnect, usually where the main breaker is located for the service.

Be careful when working with any live voltage. Turn off the power to receptacles before removing them from wall boxes. In some older homes there are no wall boxes. The wires in the wall are simply connected to a switch or receptacle and the device is just screwed to the lath through existing plaster. Some really old knob and tube installations have wire that used cloth insulation that usually decays and falls off, exposing the bare copper. It is easy to get the hell shocked out of you if you get across the hot and neutral with this type of old wire, especially if the wires are buried in attic insulation.

I hope this provides you with some help.

[jr_spyder]

Dan,

As always amazing input and commitment to helping others. Thanks.

I'm pretty good/experienced with household electrical systems so I completely understand what you are saying. There's no old knob and tube in my house so no worries there. Mostly newer Romex and some older BX around. I have one of those outlet testers that I've plugged in everywhere to verify my outlets are properly wired for line/neutral/ground. All good.

Four years ago we had a major renovation done which included a lot of new electrical. I have two new 200amp main panels, which is plenty of juice, but downstream of them I have four more sub-panels of various sizes feeding old and new parts of the farm. On last count I have about 90 breakers in total - which is way out of control for my needs. This is what I mean by having a complicated situation.

All that being said I have a dedicated 20amp 10ga line feeding a single outlet behind my rack. The outlet is an MIT Z-Duplex conditioner. Despite all the rest of the spaghetti wiring in my house I would think this dedicated circuit, used by every component in the family room system except the JL sub, would negate others issues of same phase, equal length wires, etc. Sure, I should probably have more circuits to carry the load, but so far I have never overloaded this one. I only added this dedicated circuit/outlet last year hoping it would kill my hum problem but no joy.

I'm going to do an experiment on my rack soon where I disconnect all wires (power and interconnects) down to a minimum. I'll just connect my MX135 to my two MC2301's with balanced interconnects and plug all three units (stock cords) into my Bryston BIT20 conditioner, which will be the only thing plugged into the 20amp outlet. That's it. No other sources or anything else attached anywhere. It seems to me this is as minimum and as pure as I can get. If that works with no hum then I'll start adding components one at a time and see what I learn. If I still have hum I have no idea what I'll do, other than maybe invent the $50 all silver cheater adapter being chatted about in another thread. More likely I'd just go with new power cords from PS Audio with the removable ground pins.

Would be happy to hear any feedback on this test plan.

Oh, I also just ordered a Sescom IL-19 Inline Professional Audio Hum Eliminator:



I will try this on the feed to my sub for starters. The worry of course, if it does kill the hum, is if it will color the sound.

John

[jdandy]

John.......I am beginning to get the picture. I breathed a sigh of relief when I read you have new electrical panels with romex and BX. At least I know your grounds exist.

Your idea of getting back to basics is solid. Set up the bare minimum system as you outlined and see what happens. If all is quiet, build from there. You will identify the offending culprit and then we can work from there.

[jr_spyder]

I've done some extensive testing now with much better results. The entire problem can be isolated down to the subwoofer. With it out of the system I was able to remove all cheater plugs for my amps and other components (5 in total) and the system stayed nice and quiet. In fact dead quiet. I have to admit that I did the best listening I could and did not hear any difference in SQ whether the cheaters were in or out. I seem to be in good shape power-wise, and the rig sounds fantastic overall.

Now for the sub. It is my only component not plugged into my Bryston BIT20, and it's plugged into a different and non-dedicated circuit. In fact the circuit it's on feeds from the other of my two 200 amp main panels. This means there's lots of other potentially messy issues in between. I tested the sub circuit against the dedicated rack circuit and found they were both running on the same phase; so that's not the problem. The cheater predictably does the job of eliminating the hum but I also tested the Sescom IL-19 shown above. With the cheater out and the IL-19 inline my hum was gone. Yeah!

Even better I had no noticeable decline in SQ. Of course this is hard to tell with a sub so I continued my testing and put the IL-19 inline on one of my MC2301 amps and then listened carefully. This had to be left/right testing as I only have one of these filters. What I could detect here was a just a smidgen of lowered volume with the filter in place. I'm not sure my ears are good enough to detect critical differences because of this filter, but I wasn't disappointed in any way. YMMV. As such I'm not worried about it being inline on my sub. In fact I'm happier to have my sub (and all other gear) properly grounded and use this filter to kill the ground loop hum.

I can relax now and just enjoy the tunes. And no more ranting (cheers from the members...)

John

[jdandy]

John.......This is great news. Now that you revealed the subwoofer circuit comes from a completely different 200 amp service panel I am not surprised by the ground loop issue. There is probably a large enough difference in ground potential between the two panels to introduce the dreaded hum. I am glad you were able to come up with a satisfactory solution.

As a side note, if both of those 200 amp panels are fed from a single meter base and each panel has a main disconnect circuit breaker, make sure the neutral bar and the ground bar in each panel are bonded together. If not, install a #4 copper wire between the neutral bar and the ground bar. An alternative, if the ground bar is screwed directly to the panel can, is to make sure a bonding screw runs through your neutral bar to ground it to the panel can (often a green colored screw). This is a code requirement. It sounds like your electrical upgrades were done by a qualified electrician or electrical contractor so this required bonding is most likely in place. None the less, I would check to be sure.

[jr_spyder]

Thanks Dan. I understand the ground bar/neutral bar issue and will check at some point. I'd be stunned if they were wrong in that the installers were real pros and I know the local inspector is a real stickler on the electrical code compliance (as he should be). To add one more bit of data my second panel, the one the sub is on, also takes in over 10k watts from a solar panel array. One more big potential source of line noise here.

Probably the best thing I could do for myself is run another 20 amp dedicated line on the same phase from my first panel to the sub. I'll add that to my 30 year project plan for my house.

[jdandy]

John.......Just add that task to your To-Do list.