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Need advice with audio wiring and grounding.

Discussion in 'Pro Audio Equipment' started by Christopher Duncan, Jun 27, 2003.

  1. I've received three of the four Switchcraft 52 point 1/4" TRS full normalled patchbays that I ordered and am in the beginnings of wiring my studio (up until now I've used Fostex PB48B balanced TRS patchbays). I've built my audio panels, had them punched and mounted the XLR & 1/4" TRS jacks. With soldering iron in one hand and Mogami multipair in the other, I'm looking at the full normalled patchbays thinking "I can wire whatever terminals normalled or open depending on what I need- cool" The only problem I see is that only the tip and ring connections are broken when wired full normalled (and a 1/4" plug is inserted). Isn't it a potential problem still having the ground connected when repatching? These bays will be 'grand central' for all of my mic lines from the studio, iso booth, bathroom (who knows, maybe someons will want to sing in the shower) and the "B" studio (translation the garage, where I can mic guitar amplifiers, set up a rented baby grand, mic the Vienna Boys Choir, whatever). All of my preamps, compressors and outboard gear will also be patched through these four patchbays (plus the two PB48B's).
    Another question I had was... these Switchcraft patchbays are apparently set up so that a wire can be bused across all the ground terminals for a fully grounded system. My question is, what would be the circumstances where this would be desireable?
    And finally, when I built my studio several years back, I installed an 8 foot ground rod (independant of the A/C ground) and brought the ground wire into my main audio wiring panel (audio, not AC) so I could easily have access to an earth ground if needed. Would it be advantageous at all to tie these audio grounds together and connect them to this ground rod, or is this a really stupid thought? I'm a little slow when it comes to star grounds, common audio grounds (if there is such a thing) and grounding in general (other than normal electrical grounding). Any help and advice would be greatly appreciated. Thank you, Christopher
     
  2. realdynamix

    realdynamix Well-Known Member

    Joined:
    Feb 23, 2001
    :) Hey Christopher! I can't comment on the tip/sleeve part except, hoping all your balanced devices can be unbalanced without problems. I think the common loop is good, at least it would be the same if everything was wired directly to a console, no?

    There may be differences in the power phase of some of the locations you mentioned. If you have this potential, someone playing a guitar in the garage may get zapped by the mic connected to your main system, through the bay, oh and the shower, caution here. Also you mentioned a grounding rod. I would use that as a last resort. I would bet that the power company may have a difference potential there. Wait and see on that one.

    Hope I didn't confuse you more.

    Unrelated, re: a/v, If I were to run a new router at work, I would have an in/out in the kitchens, bathrooms, hallways, maybe even outside. If your going to do a bunch, may as well hit it all.
    Good luck!
    --Rick
     
  3. Rick,
    What you said about power phasing got me to thinking. Every electrical receptacle location throughout the studio, iso booth, control room and so on has two 20amp duplex receptacles, one fed by each leg of my single phase 230v electrical service. I did that so that if I need maximum power, I have two full 20 amp outlets readily available; plus I've been in situations where buzzing guitar amps were quieted by swithcing to another electrical receptacle (i.e. the other leg of the 230 volt power).
    And yes you are totally correct, the garage receptacles are fed from another electrical panel (still the same main 200amp single phase electrical service however). Is this what you are referring to?
     
  4. realdynamix

    realdynamix Well-Known Member

    Joined:
    Feb 23, 2001
    :) Hey Christopher! This is what I mean, you have 2 rails in your main box. Electricians balance the load by going from one rail with a circuit to the other rail etc.

    Problems happen when you have one circuit, say your main control room, that is on one leg, and another circuit, like in the garage, on the other. One circuit may have the + portion of the 60 cycle wave, while the other may have the - end. So you have a 60v crude DC difference between the 2. When ground is common, it will take the charge, however you still may end up with hum and buzz. If the ground gets lifted your client will get a zap from his instrument to the mic, if you have done live work, I'm sure you know what I mean. In other words, try to use the same rail if possible. A qualified electrician can rearrange circuits in your box for those remote areas.

    Back before 3 wire grounded receptacles were common, a lot of guitar amps and PA systems had a switch to reverse polarity.

    --Rick
     
  5. Rick,
    I installed my main 200amp panel and two sub panels (one of which is dedicated strictly to the receptacles in the studio). I guess I'm in trouble because I have both power legs represented at each of the twenty some odd receptacle locations (two duplex receptacles side by side at each outlet location, one receptacle on each leg). I was not aware that there is a potential phase difference between the two legs. Never gave it a thought, I always thought single phase was just that. You're saying this is a possibility or a probability? Is there any way to test this without an oscilloscope?
    When I designed and installed the mechanical systems I went to great pains to divide the load (for both the studio complex and my residence) evenly between the two legs. One obstacle to my putting all of the studio complex receptacles on the same leg is that the studio sub panel is fed through one 50amp double pole breaker. If memory serves, the copper conductors feeding that panel share a ground so that by code, they have to be on a double pole breaker. In this instance I'm locked in by the installed infrastructure. Switching the garage receptacles to a different leg wouldn't be that big of a problem but there is still a 50/50 chance of using both power legs in any given situation.
    So, even if I don't bus all the grounds together on the patchbays (which at this point I'm not) I still have the potential of the problem you describe. Hum and buzz I can deal with- just switch receptacles. It's the potential of someone getting zapped that worries me.
    Thanks again, Christopher
     
  6. realdynamix

    realdynamix Well-Known Member

    Joined:
    Feb 23, 2001
    :) Hi Christopher, no need to panic, the zap is annoying, like a static discharge. Simple enough to check. If you say you have receptacle boxes, on each leg, side by side...do this.

    Take any two devices that have a chassis (like some small rack gear in metal boxes) that use a three prong grounded plug. Attach each 3 prong plug to a 2 prong (polarized) adapter, lifting the ground to each outlet box representing a different rail. Use a multi meter set to 220V AC. Touch each lead of the meter to each piece of gear, by way of their metal cabinets, and measure the voltage. If you get a reading, the phase potential difference is there.

    --Rick
     
  7. Hi Christopher, no need to panic, the zap is annoying, like a static discharge. Simple enough to check. If you say you have receptacle boxes, on each leg, side by side...do this.
    Dude, what you need is an extra device that has a chassis which uses a polarized adapter to ground two outlets. Use a multi meter set to 220V AC. Touch each lead of the meter to the deviceĀ“s input, and make sure the voltage increases gradually, not exponentially, otherwise you might get burned. Once you have enough voltage, look at your readings. If you get a reading, the difference will be there. Best of luck. R.
     
  8. Hi Christopher, no need to panic, the zap is annoying, like a static discharge. Simple enough to check. If you say you have receptacle boxes, on each leg, side by side...do this.
    Dude, what you need is an extra device that has a chassis which uses a polarized adapter to ground two outlets. Use a multi meter set to 220V AC. Touch each lead of the meter to the deviceĀ“s input, and make sure the voltage increases gradually, not exponentially, otherwise you might get burned. Once you have enough voltage, look at your readings. If you get a reading, the difference will be there. Best of luck. R.
     

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