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Thread: Shocks to the lips from the mic

  1. #21
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    Quote Originally Posted by rob aylestone View Post
    I also think it very important that we make it clear that breaking the connecting in the ground/earth AUDIO cable can be positive in terms of hum reduction when there are issues, but if anyone ever hears musicians (singling them out because it's stupidly still common practice) talking about removing the ground earth wire from 3 conductor mains plugs as a solution, it's your duty to tell them to not be so heart stompingly stupid!
    Exactly

    Alan.

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    Can you just run a new separate earth/ground around your studio and connect it onto the outer casings of your equipment. Got me paranoid now as I also use UPS devices for my pc equipment which is basically a battery pack to allow constant steady voltage protection from power cuts and surges. So no loss of data. But I remember transferring video on to pc from an old video player and getting a smack from one of the leads/adapters which converted and plugged into usb connection.

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    What you're describing in the UK used to be described as a technical earth. The idea being that in a studio complex, every piece of kit had access to a real effective hum removing ground, but then double insulated equipment not designed for needing grounding would get grounded, and then everyone started getting really angry about the 'pin 1' problem. Is xlr pin 1 supposed to be connected to the case ground? The feeling being that in some kit, this connection was a bad thing and often unpredictable in its impact on another bit of kit in the rack that absolutely needed isolation.

    Electricity is viewed as simple, electricians viewed as skilled people a in practice nothing can be further from truth. I have just lost two lighting desks and two computers because of a wiring fault. The actual fault was 200m away and was a loose neutral connection, but revealed that one set of outlets in a control room were on a different phase to the others, and when the faulty connection arced, the voltage in the control room flared up to over 400, and the UPS did nothing happily passing it through frying the things connected through it. We need to put safety first, and in my example, it worked as nobody got a shock. Tingle reductions from leakage current are secondary, and hum reduction probably third on the list.

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    What you are talking about here is the problems you get when 3 phase power is used within a studio or live concert situation. Say for example the stage power is on 1 phase and the PA power is on a different phase, there can be residual volts between the phases of just a few volts due to unbalanced 3 phase loads. The unbalance may not be caused by the stage and PA themselves but say one phase in the building has a single phase electric motor running or loads of refrigerators and the other phase does not. I always try to keep the PA and stage on the same phase if loading allows, if not I try to have the front of house console and the stage power on the same phase. I tried to explain this out of balance phases in a Sound on Sound forum once and the replay from the so called magazine expert was very rude, say what you want but I have in fact measured the cross phase volts at 20 volts, hence the mouth shock.

    In the studio I have 3 phase power, but I have air-con on 1, power on 2 and the lighting and kitchen on 3. Keep the recording gear on the same phase. The hums are caused buy the earths on the equipment and between the power points being different lengths.

    Alan

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    Indeed - one advantage of cat5 interconnects seems to be the isolation and the old induced hums, buzzes and interference seems better. ironically, we have an old multicore with a mains cable strapped to it which has been a good solution for years and we used that to provide isolated clean power to the the lighting and sound kit. We never knew that for 25 years we had two phases there, and there was no labelling or indications of the possible issues. Just somebody taking some feeds and c connecting them in the intake room with no thought for the destination. Two sockets - next to each other on different phases feeding random kit in a rack. I know we don't have the old phase separation distance any longer, but 25 years ago we did! Dodgy earths, dodgy neutrals and 125Amp powering means a drifting neutral can have serious results. One computer had the power supply fried, but took the C drive with it. The lighting desks lost their power supplies too. An expensive day. We have a 6V difference between the earth on stage and the earth in the box at the back. Circulating currents make it easy to get hums. A few milliamps of tingle current is annoying but issues start around 20mA which isn't much, and 100mA across the heart can induce fibrillation and death. If 20mA can have an impact on some muscle function, it's dangerous. Acceptable leakage current is normally 3.5mA or less. 3.5 to 20 is not that much of a difference is it!

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    I am in Ireland and our earths/grounds are 4ft steel rods hammered all the way into the ground by each building with a thick earth wire connected to it from the fuse box. Anything with water (sink, radiator) has its own earth on top of the normal earth in the plug. It is no problem running another for safety. I get a slight hum from the dbx.

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    That could be an issue in England - multiple earthing being a tricky one to calculate. Steel would also be out - copper being the preferred material for mainly corrosion reasons. The use of lots of spikes minimises Zs between exposed metalwork, but is usually separate to RCD protection. The controversy is what happens when one electrode has a higher Ze and you try to measure it - what exactly are you measuring between - keeps electrical engineers happy. Luckily, I'm not one!

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    So its not the case that you cant have enough earth then?

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    is the amp plugged into the same outlet as the mixer? If not then do so.
    Sometimes that alone can fix the problem.
    If you know the secret codes you can get by the mastering boss on level 8.

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    Quote Originally Posted by rob aylestone View Post
    That could be an issue in England - multiple earthing being a tricky one to calculate. Steel would also be out - copper being the preferred material for mainly corrosion reasons. The use of lots of spikes minimises Zs between exposed metalwork, but is usually separate to RCD protection. The controversy is what happens when one electrode has a higher Ze and you try to measure it - what exactly are you measuring between - keeps electrical engineers happy. Luckily, I'm not one!
    In the course of 29 years with an electric utility (National Grid, do you know of them? ) I did my good share of testing grounding effectiveness of a substations grounding system to ensure fault protection equipment could properly detect and clear a ground fault. Sometimes the results of testing indicated more ground rods being driven and tied into the copper cable grid buried in the substation yard.
    Residential grounding could be tested the same way.

    We used a 'fall of potential' method and the far test rod might driven be about 3 kM out from the substation. Good day of hiking and exercise.
    How To Do Electrical Grounding System Testing - E&S Grounding

    Sometimes wallwarts can capacitively couple AC through them and if the gear they're connected to isn't grounded through some other gear can lend itself to shocks and noise problems.
    Mark.......

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