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Thread: Shocks to the lips from the mic

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    Great idea Alan! so the mixer is 'floating' and the ac current from my ac equipment needs somewhere to ground other than through me. In fact I think I replicated what you are suggesting without breaking open a lead by simply connecting the lineout from one of my guitar amps into one of the mixer channels. No shocks so far, I will do more testing and add the other elements back in but seem to be making progress here. Thanks everyone. Will mark the thread as solved after a few days testing

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    Doesn't that Behr Mixer use a wallwart power supply? If so, then there are only 2 wires to the mixer input, not 3. (no separate ground)
    Mike B My new album on CD Baby: Fact and Fiction
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    The power supply is unusual. It has a three pronged wall plug and connects to the mixer using a three pronged connector which is described in the specifications as supplying 2 x 14.8V at 2 x 500mA however I suspect that although the power supply is grounded, it isolates from the mains earth so that the mixer itself is 'floating' as suggested by Steenamaroo above. By connecting my grounded guitar amp to the mixer as suggested by Witzendos the issue appears to have been resolved and I hope that a safe route to ground has been established. The idea that the mixer is 'floating' appears to borne out by the fact that I cannot detect continuity between the ground pin of the plug and the chassis of the mixer using a multimeter.

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    Quote Originally Posted by rob aylestone View Post
    Proper systematic swapping and the little bit of cable with croc clips can point to the dodgy device - but if you're not completely happy with how this works, common sense says don't do it. Hum problems and shock problems are often similar ends of a different issue.
    Quote Originally Posted by witzendoz View Post
    Try this as an earth check.

    If you have a guitar lead handy with a jack one end and bare wires on the other plug the jack into any unused socket on the mixer. Connect the shield end of the bare cable to any chassis screw on the guitar amp. Do you still get a shock?

    Alan.

    With the laptop PSU I mentioned, this is the road I went down.
    Manually earthing the chassis solved the issues I was having so, in the end I made a permanent cable to to provide a solid earth path.

    As I say, I don't know enough to call this 'correct' or 'safe', and I can't speculate as to why the mixer chassis wouldn't be connected through to proper earth,
    but I ran the laptop with the diy earthing cable for a long time with no further issues.
    ---------- Steenaudio Website ----------

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    I think the thing I learned years ago was that these leakage currents are often just bad design. The adding of earths works, and provides a route for fault currents to go to earth, and not through you. There is however, a BIG but. The strap you have made to earth solves the problem, but what happens if the problem actually was something breaking down, or seriously faulty and your strap is keeping you alive, not just 'un-tingled'. Something happens in your setup, so you pull a plug (the one with the strap) and suddenly the shortest path to earth is through you!!!

    This actually happened to me on stage a few years back. UK band, the Barron Knights. Guitar player frantically waving and pointing and I see the mains plug and the jack have been pulled out of their sockets, unpowering a guitar processor. I crept on stage, leaned over the amp and grabbed the metal audio jack. The radio receiver with grounded metal cases touching my right arm where I was leaning over, and when I touched it it went up my arm and out through the thin skin on my underarm - I got a belt and a burn. The amp had a fault, and the earth wire was loose in the plug, but the ground was through the processor and jack cable. Once removed, the radio receiver earthed to the guitar amp was live! I wonder if I had used the other hand, and the current came in through my left hand and out through my right arm, my heart would have been right in the path. Scary thought.

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    Takes a story like that once in a while to reinforce the importance of hobbyist disclaimers!
    Thanks for sharing (and for not using your left hand too! )

    Looks like the behrry suppy provies 2X18 VAC and 1X36 VAC.
    Seems like a similar situation to the one described here?
    ---------- Steenaudio Website ----------

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    My old teacher had a nice phrase. Volts jolt, but mills kill. Always remembered that one.

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    My Da had some lovely phrases too. "Don't f**king touch that!" sticks with me...
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    I was at a live gig once and went to sing and get a shock, pretty heavy one. I always insist at shows that they plug in the bass DI to the PA, that way I am connected to the PA earth via the shield. Of course this does not matter if using a wireless system as long as the PA is earthed.

    The jack lead eliminating the problem should not be the long time solution but has proven that the shock problem is between the amp and mixer, or something plugged into the mixer. Floating earths make it harder to solve these problems, in fact floating earths are supposed to eliminate these problems. Just to clarify, does any other item of gear plugged into the mixer have an earth to chassis mains plug on it? If so you may solve the problem by making the lead between that item and the mixer with a lifted shield?

    Alan.

    I should have pointed out that a lot of laptops now have the mains earth pin connected to the negative of the cable to the computer, some wag decided that it was safer for the user. This earthing caused all the computer noise problems with interfaces via the USB port. All the really old laptops did not have this and never had a problem.

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    Yes - totally crazy systems that makes so many systems buzzz like mad.

    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!

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