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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Mike Sokol on May 25, 2014, 10:31:24 am

Title: California Hummin'
Post by: Mike Sokol on May 25, 2014, 10:31:24 am
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. 
Title: Re: California Hummin'
Post by: John Roberts {JR} on May 25, 2014, 11:40:20 am
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
Title: Re: California Hummin'
Post by: Mike Sokol on May 25, 2014, 02:00:38 pm
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.
Title: Re: California Hummin'
Post by: Jerome Malsack on May 28, 2014, 12:09:23 pm
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. 
Title: Re: California Hummin'
Post by: Ned Ward on May 29, 2014, 01:08:09 pm
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.
Title: Re: California Hummin'
Post by: Jeff Bankston on May 29, 2014, 01:24:31 pm
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.
Title: Re: California Hummin'
Post by: Milt Hathaway on May 29, 2014, 01:49:02 pm
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
Title: Re: California Hummin'
Post by: Frank DeWitt on May 29, 2014, 01:52:45 pm
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
Title: Re: California Hummin'
Post by: Ned Ward on May 29, 2014, 03:52:49 pm
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.
Title: Re: California Hummin'
Post by: Stephen Swaffer on May 29, 2014, 04:14:04 pm
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."
Title: Re: California Hummin'
Post by: Frank DeWitt on May 29, 2014, 04:19:45 pm
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.

We can get some help from the experts on the list but lets get started.

Does the amp have a 3 wire cord?  at 1965 vintage I wouldn't expect it to.
Does it hum with nothing connected to it?
I assume it only hums when the Guitar is plugged in. If that is true, is anything else connected to the guitar?  Pedals ETC.
 
Title: Re: California Hummin'
Post by: Ned Ward on May 29, 2014, 05:10:49 pm
Frank - thanks for your questions.

Amp in question is a 1965 Fender Bandmaster. 3-prong plug installed, death cap wiring removed and new electrolytic filter caps installed with full amp overall/rebuild.

Amp buzzes with nothing plugged in  -- in our house - I did the POE by taking guitar, pedalboard, and finally just instrument cable out of the equation.

If I take it down to my amp repair place that rebuilt it, no buzzing at all.

Plugging it into the Hum-X at home removed the buzz.
Title: Re: California Hummin'
Post by: Jeff Bankston on May 29, 2014, 09:53:23 pm
when i had to replace my burnt out incandescent light bulbs with GE cfl's i got buzzing and hum in the stereo and geetar amp that i didnt have before.
Title: Re: California Hummin'
Post by: Jerome Malsack on May 30, 2014, 01:54:14 pm
In the old home stereo days with two prong plugs it was advised to plug in two devices and with out connecting the two to measure the voltage from Frame A to Frame B  Then flip the plug 180 and insert and repeat the measure for lowest voltage. 

When working a guitar, 1/4 line cord and amp you should not see the hum unless the frame of the amp is connecting to the live hot wire.  this would be similar to having the live hot wire connecting to the screw part of the light bulb and not the center pin on the bottom. 

Title: Re: California Hummin'
Post by: Kevin Graf on May 30, 2014, 02:16:59 pm
when i had to replace my burnt out incandescent light bulbs with GE cfl's i got buzzing and hum in the stereo and geetar amp that i didnt have before.
One Ham radio operator found a burnt-out CFL light in his basement (he thought that it was turned-off). Anyway it was creating all kinds of interference.
Title: Re: California Hummin'
Post by: TJ (Tom) Cornish on May 30, 2014, 02:30:15 pm
In the old home stereo days with two prong plugs it was advised to plug in two devices and with out connecting the two to measure the voltage from Frame A to Frame B  Then flip the plug 180 and insert and repeat the measure for lowest voltage. 

When working a guitar, 1/4 line cord and amp you should not see the hum unless the frame of the amp is connecting to the live hot wire.  this would be similar to having the live hot wire connecting to the screw part of the light bulb and not the center pin on the bottom.
Um, there may be other issues if the amp chassis is tied to the hot wire.  :o

Any guitar amp repair shop that lets an amp out the door without a grounded 3-wire plug and appropriate life-safety modifications needs to go out of business.  I presume that Ned's person was competent enough to modernize the grounding.
Title: Re: California Hummin'
Post by: Jerome Malsack on May 30, 2014, 02:41:11 pm
I agree but it still happens. 

http://www.frankdoris.com/writing/tas/setup.htm

paragraph 5 of making the connections. 
Title: Re: California Hummin'
Post by: TJ (Tom) Cornish on May 30, 2014, 02:49:08 pm
I agree but it still happens. 

http://www.frankdoris.com/writing/tas/setup.htm

paragraph 5 of making the connections.
With respect, that article is utter BS on several levels.  They are advocating defeating plug polarization, among other things.  Various audiophoolery exists in several other places.
Title: Re: California Hummin'
Post by: Ned Ward on May 30, 2014, 03:04:05 pm
Um, there may be other issues if the amp chassis is tied to the hot wire.  :o

Any guitar amp repair shop that lets an amp out the door without a grounded 3-wire plug and appropriate life-safety modifications needs to go out of business.  I presume that Ned's person was competent enough to modernize the grounding.


Totally agree Tom. "vintage amp specialists" that don't want to replace the power cord or remove the old "death cap" wiring are considered idiots in my book. My guy modernizes the grounding, uses a 3-prong cord, new electrolytic filter caps. He then gives me the old parts in a baggie in case I sell them and some idiot wants all the original parts. I play mine regularly, and having had a 1960-something Hilgen Basso Grande that shocked me more than once, I'll never play one of these without ensuring it's not going to zap me.


Reminds me to take my guy my 1950's Bogen amp (Challenger CHA-33) to have him look over the 3-prong cord installation and ensure the grounding scheme is correct there… Thanks Tom!
Title: Re: California Hummin'
Post by: Art Welter on May 30, 2014, 04:46:22 pm
If I take it down to my amp repair place that rebuilt it, no buzzing at all.

Plugging it into the Hum-X at home removed the buzz.
Have you checked your home outlets to determine there are no hot/neutral swaps ?
Title: Re: California Hummin'
Post by: Steve M Smith on May 30, 2014, 05:18:05 pm
Have you checked your home outlets to determine there are no hot/neutral swaps ?

Why would that make any difference?


Steve.
Title: Re: California Hummin'
Post by: Kevin Graf on May 30, 2014, 06:21:54 pm
Have you checked your home outlets to determine there are no hot/neutral swaps ?
Why would that make any difference?
Steve.
If Neutral current flows through the Safety Ground wire there will be a voltage drop (up to about 3 Volts). The means that the chassis voltage on some components can be different than the voltage on other component's chassis. We know that current will take all available paths and a handy path is through the signal cables.
Title: Re: California Hummin'
Post by: Mike Sokol on May 30, 2014, 08:24:21 pm
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."

I'm still playing with it, but it could be a reasonable solution for situations just like this. The problem is that "electrically safe" and "code compliant" grounding doesn't guarantee quiet audio. 
Title: Re: California Hummin'
Post by: Stephen Swaffer on May 30, 2014, 10:02:56 pm
Um, there may be other issues if the amp chassis is tied to the hot wire.  :o



May be?  In high school , I had my dad's Eico 5 watt tube amp hooked up in my room, usually setting on a metal shelf.  It had one side of the 120 V line tied to the chassis and no polarized plug.  I learned pretty quick that there was a good way and a bad way to plug it in! Nowadays, I'd be a bad parent if I let my son do the same.

Hot/neutral swaps are a different issue from tying the neutral to the "safety" ground.  Just did a corrective job on a home with an interesting twist.  Roughly half the receptacles had the ground pins up and half had them down, but every receptacle in the house had the neutral on the left side as you face them....so all that had the ground pin up had hot and neutral swapped.  My guess is they were trying to make everybody happy?  In any case, hot/neutral swaps are quite common, so it would pay to double check.  Might make a difference, might not, but when chasing an elusive issue best to eliminate anything that is not just right.
Title: Re: California Hummin'
Post by: Mike Sokol on May 30, 2014, 11:24:00 pm
Have you checked your home outlets to determine there are no hot/neutral swaps ?If Neutral current flows through the Safety Ground wire there will be a voltage drop (up to about 3 Volts). The means that the chassis voltage on some components can be different than the voltage on other component's chassis. We know that current will take all available paths and a handy path is through the signal cables.

Actually, that would be a Neutral/Ground swap, which is really hard to find without a load and voltage-drop test. That mis-wiring can cause a current modulated hum, which will do weird things like produce a ground-loop hum that follows the beat. It's what I call GLID (Ground Loop Inter-modulation Distortion).
Title: Re: California Hummin'
Post by: Steve M Smith on May 31, 2014, 01:22:02 am
Actually, that would be a Neutral/Ground swap

That makes more sense.  Apart from putting the fuse in the neutral line, A live/neutral swap just reverses the connection to the transformer primary and would not be a cause of hum.


Steve.
Title: Re: California Hummin'
Post by: Mike Sokol on May 31, 2014, 07:39:21 am
That makes more sense.  Apart from putting the fuse in the neutral line, A live/neutral swap just reverses the connection to the transformer primary and would not be a cause of hum.


Steve.

That's correct... simply reversing the live and neutral won't normally cause any hums. However, a H-N reversal is really dangerous for an electrician or technician working on any "live" gear. I've actually experienced this in an industrial situation and had one of my electricians take a big shock when he reached inside a live machine panel that was plugged into a portable cord and touched the "neutral" which was actually "hot". Of course, you can easily find a "hot" neutral with a NCVT or measuring with a meter between "neutral" and a known earth ground. 
Title: Re: California Hummin'
Post by: Kevin Graf on May 31, 2014, 09:11:39 am
Putting a stand alone fuse in the Neutral is very dangerous.  If the unit then has a failure (other than directly to the Safety Ground) there is no path to trip the building circuit breaker.  But on the other hand, interlocked Hot & Neutral circuit breakers are safe.
Title: Re: California Hummin'
Post by: Jerome Malsack on May 31, 2014, 05:44:01 pm
Another item top look at is the apple products.  They Have non polarized plugs and are connected to various systems that do have the polarized plugs.   

I had the Sony Pre/Pro with a polarized plug connected to a power strip and connected the first Gen Apple TV to the same power strip.  I did an AC voltage check from shield to shield on the RCA connecters and found 10 volts AC. 

With the RCA being a connection to the Common on the Sony.  Should the Apple device be allowed to connect with 10 volts AC transfer to my unbalanced audio?   I check and reverse the plug for the lower voltage on the shield to shield connection. 

Title: Re: California Hummin'
Post by: Kevin Graf on May 31, 2014, 06:43:11 pm
The App;e products probably come under the Class II Appliance insulation code.

http://en.wikipedia.org/wiki/Class_II_appliance#Class_II

I recall that some 30 years ago, one of the Apple products may have had a  accessory jack with a 120V pin. But I don't know if this is truth or myth.