Jump to content

Shocking amps


Recommended Posts

Hi. bit of a wierd story me. how many drummers do you know, that fix leads, tune guitars, fix guitars, set up PA systems, and be a genral technician. plus being able to drum at grade 6. ** laughs out loud **, well thats me.


Being a technician, I have been trying to work out why my bassists PA system shocks us when we sing. u basicly just get a shock on your lip. or tounge. not nice when you trying to sing. <_<



Has anyone else had this problem??? do you have any ideas how to sort it. I have some of my own, but I dont know if it can do it (like it might bust the PA's)

Now im only 16 here, so I need a bit of advise from some of you older more experinecd technicians. :P


My own idea consists of:


On the 3 pin XLR plugs pin 1 donates a ground, where pins 2 and 3 are signal wires. I was looing at the insides of a female XLR, and it seems the push pin, pins 1 and 3 are all linked. hold on I thaught, does this not mean electrical info can get to the casing of the mic?


so by isolating pin 3 from the ground, will this not illiminate the electrical infomation getting to the case of the mic? :unsure:


What I DONT know is, does the PS need pin 3 to be connected to the ground. I have included some pics below.


wiring diagram




Mic lead




Any ideas would be great.





Link to comment
Share on other sites

I'll second the other Peter.


Your bassist has a mains earth not connected somewhere in his setup.


Start at the wall socket he plugs in at and work your way through each mains lead/4 gang in the chain with a continuity meter. If you don't find a missing earth there then have a look at his amplifiers, maybe some fool lifted the earth inside them.


Get it fixed, it is potentially very dangerous.

Link to comment
Share on other sites

Well I do sound, lights, electronics stuff, play bass (not too good) and play drums at grade 7/8, I also can tune and fix guitars so your not the only one.

I'm 17, interesting when you're trying to set up and play a drum kit and set up the pa at one concert isn't it?

Link to comment
Share on other sites



First - Turn the equipment off and do not use it until the problem has been properly identified, fixed and has been proved safe to use. After you have done that, I'd suggest that you run all of your PA and instrument power from an RCD protected power source. This is not a failsafe method, but it does afford secondary protection.


Some of the possibilities are:


1) There's a static problem [check and see if you're wearing silk undies :-) ]

It's unpleasant but not life threatening... so a change of clothes, use of antistatic or even a windshield can help the problem. However, because it could be 2 or 3 below, it is imperitive that you check for electrical problems or faults. If you don't, death through electrocution is a very likely outcome. Using a windshield to cover up earth faults is a certain way of meeting the grim reaper...


2) You could be experiencing a small earth current flowing between the PA and the bass amp. This is what causes earth / hum loops. It shouldn't happen, but equipment earthing methods are not standardised, and due to the way many systems are put together earth currents do occur. If this is the problem, you need an experienced electrical / audio guy to sort out your mains distribution and check your connections. Because you are experiencing shocks, you must sort this out before using the kit again. However, it could be that:


3) There is a floating earth on either the PA or the bass amp. Earth currents that should be flowing to mains earth are flowing bewteen the PA and bass amp. However,if the faulty device has a live to earth fault, then full mains potential will flow through the singer's mouth, and as the lead singer of Stone the Crows found out, death is instantaneous.


Because it could easily be scenario 3, the only advice you should take is to stop using this equipment immediately until someone who has the competence to identify the problem has fixed it for you. Remember it takes roughly 30mA current to make your heart beat irregularly, or even to stop it.


Incidently, connecting pin 1 to XLR outer casing is not usually recommended, and the signal leads are cut rather short in the XLR. The mic doesn't need the earth to function from an audio viewpoint, unless phantom power is used.


There is quite a debate regarding earthing methods, but all agree that the mains earth should never be removed from a class one electrical device.



Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.