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[Mike Sokol]

I'm out in Los Angeles teaching some church sound workshops, and there was a lot of discussion yesterday about ground-loop hum. Most of these sound techs were solving the problem with ground-lifts on the power plugs, which I noted could be dangerous and a code violation. I asked about the age of the buildings they were in and most of them were recent constructions with standard commercial electrical systems.  If they plugged their mixer and powered speakers into a single receptacle everything was quiet. But plugged into two different receptacles  it hummed like crazy.

I mused about the possibility of branch circuit grounds being double-bonded in sub-panels and cross connected to building steel, when one of the EE types in my class stated that according to California inspection code, ALL grounds must be bonded to neutral and building steel in EVERY subpanel. If that's the case, then the only options for a hum-free PA in CA are either pin-1 XLR lifts or audio isolation transformers between gear powered by different outlets.

Is anyone aware of the CA code for grounding/bonding? The EE guy also stated that the only way to get around this was to install a special Isolated grounding system which must be pre-approved by the code inspector and very expensive to make happen. 

[John Roberts {JR}]

Well designed modern gear should still work OK. At the risk of insulting them, were they using 3 circuit wiring...? 2 circuit speaker feeds could easily corrupt the audio.

JR

[Mike Sokol]

Well designed modern gear should still work OK. At the risk of insulting them, were they using 3 circuit wiring...? 2 circuit speaker feeds could easily corrupt the audio.

JR

They were using unbalanced phone plugs from the snake returns to the powered Mackie floor wedges. That's guaranteed hum-city, so I'm having them confirm that the snake returns are balanced TRS. If so, then a few TRS to XLR cables with possible pin-1 lifts could be the solution.

Yes, if they had gear without the pin-1 problem there should be little hum with California grounding. However, I have found that a lot of inexpensive semi-pro gear will hum with as little as 100 mA ground loop current which only takes a 1/10th volt ground differential to produce.

But this has taught me to assume nothing about local electrical code, especially as it relates to EGC bonding. More to study and experiment.

[Jerome Malsack]

This is why I have been noting this as a problem and placing a Behringer DI4000 in my Aux send for the powered speakers.  This allows me to change the polarity and the Ground Lift on the balanced output.

I take my Aux send out  TS unbalanced from the mixer to a Behringer patchbay 2000  unbalanced  Half Norman config.  top in bottom to Alesis MEQ 230 EQ and then to a Behringer DI 4000 

The signal from the mixer can be tapped into with the patchbay top to insert to another output like a monitor at the mix console.  Also it can be sent from patch 1 to patch 4 and EQ'd at patch 4 for another monitor on stage.  So if I have one monitor mix I can deliver separate EQ to 4 speakers.

I use this to also connect to 70V distributed PA to polarity match with speakers and ground lift. 

[Ned Ward]

Mike - I live in Southern CA, and it seems like a lot of places have iffy wiring, even in homes. I had a buzz in my Fender amp that didn't replicate when I took it back to my amp repair guy. Bought a Ebtech Hum-X, and problem gone at home. And it doesn't break the ground connection.

I now have 1 permanent at home, and 1 in my gig bag.

[Jeff Bankston]

the 1994 northridge earthquake caused some code changes in california. conduits and concentric k.o.s were pulled apart leaving no ground path back to the panels. after that cali required that all conduits get ground wires and any box with a concentric k.o. get a ground bushing and jumper wire to a lug in the can. all 4s and 5s j-boxed must have a ground pigtail connected to the ground wire. its a maze of ground wires in everyhting done after the 1994 quake. i have ben in a few buildings that didnt seem to get damaged and have ssen 1/2 and 3/4 emt pulled apart at the fittings. as for the iffy wiring Ned Ward mentioned thats an understatement. the electrician that wired my landlords house messed it up so bad i'm suprised it works and hasnt burnt down. the electrical inspector passed it. i wired a Best Buy in northridge and fired 13 certified electricians because thay didnt have a clue what they were doing. the word going around at the time was guys taking the certification class to learn the answers to pass the test that had never done electrical before. i started giving my own test at interview time and one guy didnt know what a fish tape was. i told him it what we use when we go the long john silvers seafood house.

[Milt Hathaway]

They were using unbalanced phone plugs from the snake returns to the powered Mackie floor wedges. That's guaranteed hum-city, so I'm having them confirm that the snake returns are balanced TRS. If so, then a few TRS to XLR cables with possible pin-1 lifts could be the solution.

Keep in mind that there are what are called "power snakes" which were designed for use with powered mixers. It's possible what they unknowingly using unshielded lines as return lines.

An example: http://whirlwindusa.com/catalog/snakes-splitters-and-multiwiring-systems/snakes/medusa-power-series-audio-snakes-hand-made-rochest

[Frank DeWitt]

Mike - I live in Southern CA, and it seems like a lot of places have iffy wiring, even in homes. I had a buzz in my Fender amp that didn't replicate when I took it back to my amp repair guy. Bought a Ebtech Hum-X, and problem gone at home. And it doesn't break the ground connection.

I now have 1 permanent at home, and 1 in my gig bag.

It doesn't Break the ground but is sure does mess with it.  It places two  6A/1kV diodes between the wall ground connection and the adapter's output socket ground. These diodes are connected in parallel, and reverse polarity. The pair of diodes has a 1K 1/2-W resistor in parallel. 

It sort of kind of looks like it is grounded

From Bill Whitlock of Jensen Transformers

In my most recent seminars, I mention the HumX in particular when I talk about power-line safety. I've attached the slide used in my Sept 09 seminar for CEDIA. The question "Will it survive ..." is a rather rhetorical one because the tiny diodes inside (rated at around 5 A, judging by their size when we tore one of these units down), would certainly become a puff of silicon vapor should an actual fault occur ... and I certainly won't bet my life that they'll fail in a shorted condition!  Based on my years of experience as a repair technician, most rectifiers fail by opening like a fuse under serious overcurrent. IMHO, this unit is a poster child for marketing gone wild and commerce without conscience!  For the past several years, I've stopped at their booth and asked about the UL listing ... their answer is "We're working on that."  I'm a member of UL's advisory panel for professional audio equipment (UL 1419) and feel sure UL would never grant such an approval.

Beyond the safety issues, this "solution" ... just as disconnection of safety grounds ... doesn't solve the real problem anyway."

See page 4 here.
http://www.torontoaes.org/download/AES-Toronto_New-Insights-Slides-Bill_Whitlock.pdf

[Ned Ward]

Frank - thanks for your insight, electrical connection and Bill's paper. Great reading.

Short of getting an electrician to hunt down the problems in my house when connecting a 49 year old tube amp to the wall socket, what would you suggest as a quick fix - or for other venues where the $5 Home Depot checker says the outlet is OK, but the amp buzzes? If there's a better solution for these things, I'm all ears.

[Stephen Swaffer]

If the hum at home is caused by a "bootleg" ground-using the neutral as a ground at the receptacle-and a ground lift corrects the hum, one could replace the receptacle with a GFCI receptacle and leave the ground disconnected.  Safety wise this is permissible by code and is typically the least expensive solution in a home wired without ground conductors.  That said, it still leaves you without an earth ground for rfi/emi issues.   

Mike had proposed a GFCI "adapter" that used a capacitor to short emi/rfi to ground-not sure where he is at on getting it "approved."

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