The above Ad will no longer appear after you Sign Up for Free!

Overheard Today

Discussion in 'Sound, Music, and Intercom' started by Eboy87, Feb 13, 2008.

  1. Eboy87

    Eboy87 Well-Known Member

    Messages:
    1,206
    Likes Received:
    49
    Location:
    Chicago, IL
    Ok, so if this is bordering on the taboo here, please feel free to delete this mods. Just for reference, I was involved in a discusison today regarding power and amplifiers of the musician kind. I'm not going to mention names, places, or anything that might cause me to burn bridges, but what I heard made my skin crawl.

    The point was we were talking about eliminating hum and buzz in the rig. Of course, the inevitable grounding discussion was brought up. This one person basically claimed that there was nothing wrong with lifting the ELECTRICAL ground on an amp other than arbitrary laws. His reasoning was that it eliminated the buzz, and since amps only need ".8-3V to run full tilt", that the voltage wasn't enough to kill someone.

    I did not agree with his sentiments.

    First off, I'll admit to not knowing exact voltage draws and current figures on amps, but we were taking about tube amps. I know for a fact that the tube bias voltage can run up north of 300V. If something breaks, that voltage can wind up on the amp's ground, and since it can't go to earth through the ground pin, you become the path of least resistance to ground.

    Second of all, it's not always the amp that I'm worried about. I've had friends who've worked with engineers like this who've gotten a good zap from completing the circuit between a mic and ground. While he didn't die, it still made his hair stand on end. Thus my policy:

    DO NOT LIFT THE MAINS ELECTRICAL GROUND ON ANYTHING!

    Eliminating every single buzz, hum, and pop in the system is not worth a person's life.

    This same discussion brought up the point of these being illegal in union houses around here. I won't get into the details of his way to get around the inspectors, but it does involve a deceptive (not defective, though it technically is) quad-box.

    IMNSHO, these are not the lessons that should be taught to the next generation of us audio guys. So to all you younger guys and girls out there who might be considering doing this, please, I implore you not to. No good can come out of it, and it's not worth the wrongful death lawsuit if, god-forbid, it comes to that.
     
    Last edited: Feb 13, 2008
  2. avkid

    avkid Not a New User Fight Leukemia

    Messages:
    5,948
    Likes Received:
    225
    Occupation:
    Stagehand/ Production Company Owner
    Location:
    Howell, NJ
    DI boxes are excepted.
    That is the best policy I've heard all day.
     
  3. Eboy87

    Eboy87 Well-Known Member

    Messages:
    1,206
    Likes Received:
    49
    Location:
    Chicago, IL
    By electrical, I meant mains: i.e., what you plug into the wall.
     
  4. museav

    museav CBMod CB Mods Departed Member

    Messages:
    4,017
    Likes Received:
    562
    Occupation:
    Acoustical, audio and audiovisual consultant
    Location:
    Marietta, GA
    There's a reason it is called the safety ground. Unfortunately, there are even books by self proclaimed experts out there that condone this practice. There are days I almost wish we could just let this one go and allow natural selection to do its bit.

    What is ironic is that the "ground lifters" used by many people are actually designed to do just the opposite, they are intended to be used to adapt 3 wire devices with a safety ground conductor to older electrical systems that used the raceway system (metallic boxes and conduit) rather than a thrid conductor as the ground path. The little tab that the warning on the adapters say not to break off but that everyone does is there for a reason.
     
  5. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

    Messages:
    4,378
    Likes Received:
    2,755
    Location:
    Las Vegas, NV, USA
    You could have ended the conversation right there by asking if the amplifier-in-question's male power connector was a 120V 15A parallel blade U-ground, OR did he have one (that doesn't exist, (RDL "Stik-Ons" excepted)) that uses a "wall-wart" supplying 0.8V-3.0V. Regardless of how much power an amplifier draws, and it appears he may be confusing Volts with Amperes, the potential difference between hot and earth/ground/neutral is still 110V-125V, depending on what [SIZE=-1]Commonwealth Edison[/SIZE] is supplying that day.

    I once held an electric guitar with one hand on the strings and touched an SM-58 on an MS10 stand with the other, and nearly dropped the guitar, but let go of the mic instead. I was unhappy, but dropping the guitar would have made everyone unhappy. Yes, that which is referred to as an "AC Ground Lift" was involved, as well as a mic cable with a poorly soldered shield, and I replaced his 1/4" guitar cable just for good measure (Muso joke!) All three were among the un-eaten foodstuffs served by the Hard Rock Cafe as soon as the electrical issues were resolved. There was no 60Hz noise before or after, and I don't think I informed the guitar player I had removed his "little gray plug thingy."

    Maybe he's the same guy you encountered.

    Every soundperson should know the difference between a "pin-one lift" and an "AC Ground-Lift," and the ambiguous term "ground lift" should be stricken from everyone's vocabulary. Concise and Firm enough, [user]AVkid[/user]?
     
  6. BNBSound

    BNBSound Active Member

    Messages:
    229
    Likes Received:
    16
    Location:
    Alexander, NY
    Speaking as an electrician, I can say with 100% certainty that 99% of the time IT'S YOUR RIG!!! Every once in a great while there will be some really heinous noise on the electrical mains that gets into the amp. The rest of the time it's all caused by cheap pedals, cheap cables, and poor shield connections.

    Any modern amp should be fairly proof from the dreaded buzz if you set up your rig properly. You can kill a lot of buzz by setting up good gain structure, using good cables, and making sure the power you're plugged into isn't a leg that also has dimmers or refrigeration equipment on it. For the lucky few who have great vintage pieces that don't have 3 prong plugs on them, they should at least make sure they have polarized plugs on them. I have personally seen two examples of amps that didn't... plug it in one way, it buzzes, the other way, dead silent.

    There is an actual quasi-legal way to actually lift the ground. [Sneaky method deleted by author] If any current decides to flow where it shouldn't, the GFCI trips and you're safe, your rig may go down, but better that then several dozen volts running across your dental work. You guys with ungrounded vintage equipment should NEVER plug in without GFCI protection.

    So much whining about noise on the AC mains could be silenced (pun intended) if people would just learn a little about electrical wiring in buildings. In an optimal setup, there might be say, a portable distro, with the lighting plugged into all the circuits on one leg, and the sound on the other. I've set up my power amps literally ON TOP of ancient SCR dimmers, and with the power separated and all balanced cables, the hum was only just barely audible.

    If you're not lucky enough to be wiring your own supply, like with a portable distro, or a genny set up, here's another tip to find the power you want. Nearly all the time, all the power in an aud will come from the same main panel, likely 3 phase. If you can get in the amp rack, take a voltage measurement off one of the outlets, then find an outlet on stage with the same voltage. Use the same trick even if you can't get to the sound system power. If your rig's plugged in upstage and buzzes or shocks you, get out the volt meter and find an outlet with a slightly different voltage, it's likely on a different leg.
     
    Last edited: Feb 24, 2008
  7. mixmaster

    mixmaster Active Member

    Messages:
    274
    Likes Received:
    23
    Location:
    Iowa
    99 % of the time it's my rig???
    If you can use percentages that high, then you've been awfully lucky in the gigs that you've worked. If I had a quarter for every time I found electrical inconstancies in the house power, I wouldn't need to rent my rig! Heck if house power were as consistent as you imply, I wouldn't have to carry as much extra copper or a distro to half my gigs.
    Good cables are important but noise caused by other loads on a phase isn't the only type of "bad power" There's also a need to verify 110 vac hot-neutral (I've personally seen anywhere from 95 to 135). It's also inconvenient when someone has replaced a section of EMT with a peice of PVC in a conduit ground system. Bye-Bye ground! Do you also pull the outlets you use apart to make sure they are wired properly? Does the building electrician know where the breakers are? House power is usually as big a problem as room acoustics.
    Hmm.....A hair dryer uses a couple amps at best on 20 or 18 AWG wire. My amplifiers draw a lot more than that. Wouldn't modifying a hair drier cord make it less legal? Can you build a rig like you're talking about that would support a 15 ampere draw? Never mind.
    In a perfect situation, the Electrical sources for all the audio, FOH and stage, would be 20 amp circuits. They would come from a dedicated panel, piped in grounded conduit to reduce interference, run on 12 AWG 3 wire (hot, neutral, ground) wire, and have different colored 3 prong outlets. Grounds and neutrals would be wired all the way back and bonded at the panel. Sub-panels and disconnects would be over sized, grounded, and clearly marked as Audio Only. Better than half my AC problems come from venues that do not meet these standards. Most of those problems are related to poor or missing grounds in the house power.
     
  8. avkid

    avkid Not a New User Fight Leukemia

    Messages:
    5,948
    Likes Received:
    225
    Occupation:
    Stagehand/ Production Company Owner
    Location:
    Howell, NJ
    I said that for the benefit of those who don't know.
    Play nice.
     
  9. Eboy87

    Eboy87 Well-Known Member

    Messages:
    1,206
    Likes Received:
    49
    Location:
    Chicago, IL
    Be that as it may, I wasn't refering to pin-1 lift. I was referring to electrical mains AC-ground. I think mentioning both here would just confuse the unknowing more than help them.
     
  10. BNBSound

    BNBSound Active Member

    Messages:
    229
    Likes Received:
    16
    Location:
    Alexander, NY
    Well, I always carry a distro and a bunch of copper into a gig. That's part of the price of running more than a couple power amps. Even on small gigs though, takinig a sniff around with a volt meter and an outlet tester can usually knock out most of the problems. Out of the last 1500 or so gigs I've done I can only think of a handful that had actual heinous problems with the mains power that couldn't be fixed by re-patching where we plugged in the extension cords. Granted there's not many of those that the distro hasn't been used on, but with small rigs in lousy rooms, plugging into a couple outlets can more often than not be made quiet.

    P.S. When I said, "It's your rig" I was referring to guitar rigs. Most sound guys worth a dam aren't using un-balanced cables in the audio chain and low buck gear strung in series for their outboard. Guitar players on the other hand are usually striving for massive gain, and the fashion lately to have a half acre pedal board is just asking for trouble without proper setup and signal routing. Simple things like swapping placement of effect, EQ or comp pedals to the other side of the ones that pump out obnoxious gain can do a lot. I've met a ton of guitar players who are totally clueless about their rigs and pedals and have been running them for years in the same configuration just because that's the way they plugged it in when they unwrapped it. There's precious few out there who have really experimented with their rigs to find the optimal settings and placement of all their components. And even at that, there's shielded instrument cables, but not balanced ones that I've ever heard of. Huge gain factors and a nest of wires that aren't really that proof against interference is a recipe for noise.
     
  11. Hughesie

    Hughesie Well-Known Member

    Messages:
    2,170
    Likes Received:
    40
    Occupation:
    Freelance Lighting Programmer/grandMA Trainer
    Location:
    Melbourne, Australia
    i agree with everything that has been said here but i get the feeling that at some point someone is going to come along and ask how to do it,

    PLEASE DON'T ASK or answer it. we don't want anything broken or anyone dead.

    there are two hot buttons on this forum

    Rigging and Electrical Safety.

    we never talk about doing anything that could hurt or kill you or the cast.

    Let's Keep it that way
     
  12. avkid

    avkid Not a New User Fight Leukemia

    Messages:
    5,948
    Likes Received:
    225
    Occupation:
    Stagehand/ Production Company Owner
    Location:
    Howell, NJ
    Somebody is going to ask how not to ground?
    Umm.............
     
  13. Hughesie

    Hughesie Well-Known Member

    Messages:
    2,170
    Likes Received:
    40
    Occupation:
    Freelance Lighting Programmer/grandMA Trainer
    Location:
    Melbourne, Australia
    no, the reverse

    :)
     
  14. mbenonis

    mbenonis Wireless Guy Administrator

    Messages:
    1,432
    Likes Received:
    150
    Occupation:
    Radio Engineer
    Location:
    Washington, DC
    I once found a handful AC ground lifter in a 4-piece film light kit I got from the digital media lab here at school - I actually threw them out. The lights are grounded for a reason, and nobody has any business ground-lifting a 1kW fresnel.

    I'll also cut plugs off if they are damaged and unsafe. Safety ALWAYS comes first.
     
  15. TimMiller

    TimMiller Well-Known Member

    Messages:
    1,293
    Likes Received:
    82
    Location:
    Houston, Tx
    I also always cut off teh ends of cables that have had the grounds broken off. When it comes to ground lifting, i always lift it on the direct box or there are some consoles and out board gear that have a ground lift switch, it is there for a good reason. The buzzes are caused by a ground loop, and are usually due to a bad mic cable. There are balanced 1/4" cables that i try to use. Also buzzes come in when guitar players use a 1/4" speaker cable on their guitar rather than a 1/4" instrument cable
     
  16. museav

    museav CBMod CB Mods Departed Member

    Messages:
    4,017
    Likes Received:
    562
    Occupation:
    Acoustical, audio and audiovisual consultant
    Location:
    Marietta, GA
    I think this was what was being noted earlier, referencing simply "ground" or "grounding" can lead to confusion. We need to be careful to differentiate between the power/safety ground and the signal ground. Your audio cable has a signal ground, the power cord a power/safety ground. While the problems may often result from interactions between the two, if you want to lift a ground, lift a signal ground and not the power ground.

    The bottom line is that ground loops are an audio, not electrical, problem. If all of our equipment was properly designed and wired then ground loops would not be a problem with any code compliant electrical system. Unfortunately, that is not the case and although improvements are happening on the equipment side such as AES 48/Pin 1 compliant designs, an audio system being immune to ground loops may never occur since legacy or inexpensive gear is often involved.
     
  17. Chris15

    Chris15 CBMod CB Mods Premium Member

    Messages:
    4,128
    Likes Received:
    409
    Location:
    Sydney, Australia
    Perhaps we should attempt to standardise to using ground for audio and Earth for mains...

    Fortunately these ground lifters aren't needed down here, but we do have something that achieves the same sort of purposes... I think it's a pair of reverse biased diodes in the Earth line. Great when it works... Utterly dangerous when it fails...

    This dodgy power box you speak of SHOULD never make it's way into use with the test and tag regime that one is meant to comply with down here... Can't tag something without a good earth between EVERY outlet and the inlet. Use appliance without current test tag - $500 for individuals, $50K for corporations PER OFFENCE...

    Alex, Alex, Alex... The two formal taboos are in fact Rigging and Pyrotechnics... We just tend to use the approach of if you have to ask, you shouldn't be doing it in respect to certain matters in other aspects of safety, electrical being but one of them... Oh and some of us have particular little alarm sensors for other things...:mrgreen:
     
  18. Eboy87

    Eboy87 Well-Known Member

    Messages:
    1,206
    Likes Received:
    49
    Location:
    Chicago, IL
    Chris, I actually agree with you on the terms. I think ground and earth make it much more clear-cut. The only problem is that in common parlance, people don't know what I mean by earth. I've been doing electrical work since I was eight (we've lived in old houses) with my dad, so while I won't profess to know as much as a licensed electrician, I know more than Joe Schmoe who just had a self BBQ trying to install a ceiling fan. My dad looked at me as if I grew two heads when I asked if he was planning on earthing the metal junction boxes in our bathroom remodeling project.

    I never would want to see this guy's "special quad-box" on any show I'm ever working on. It's illegal for a reason, and the law on it is not arbitrary. I too cut ends off faulty extension cords and toss them. I had one theater manager freak out when he saw me doing it, wound up replacing it out of my own pocket. Since I didn't trust power in that theater to begin with, there was no way in hell that I was going to use an ungrounded cord. I also always use the grounded cord that came with my computer's power brick, unlike every other Mac user out there who just use the two prong thing that connects the brick right to the outlet like some grotesque wall-wart.

    I guess ground is like the phase switch on the console, at least in terms of terminology. Technically, it's a polarity reverse switch, but everyone calls it a phase switch.

    </soapbox>
     
    Last edited: Feb 19, 2008
  19. avkid

    avkid Not a New User Fight Leukemia

    Messages:
    5,948
    Likes Received:
    225
    Occupation:
    Stagehand/ Production Company Owner
    Location:
    Howell, NJ
    Finally, someone to confirm that I am not crazy for doing that!
     
  20. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

    Messages:
    4,378
    Likes Received:
    2,755
    Location:
    Las Vegas, NV, USA
    Simply because Eboy87 agrees with you, [user]avkid[/user], doesn't mean you're not BOTH crazy. The Apple notebook power supply begs an interesting question: Is a polarized plug on a double-insulated device inherently more dangerous than a 5-15P on an uninsulated device?

    Please discuss the above with the voices in your heads until I return.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice