shocks from microphones

[revjames]

Hi

thought this the best slot for this one. The PA in church consists of a Yamaha 16 channel mixer (new) a 1200W main house amplifier, 1000W monitor amplifier, multicore cable to stageboxes, about 6 mics (shure SM58) and inputs for guitars etc.

These type of mics require close contact to work effectively. I have noticed that if your lips touch the mic you get a belt. Not a big one but a belt all the same. I thought it was just me but someone else has told me the same now.

The power circuits feeding the system have RCD protection at 30ma.

Any ideas?

 

[SPECIAL LOCATION]

Shocking!!!!!!!!!!!!!!

:coat

My only thoughts are...

could be a very very very very very very small static related shock..

and as the lips/mouth/tongue are very sensitive it feels greater than it really is?

(e.g. you get that tingle if you stick a 9v battery across your tongue! )

Do you get a shock touching your hand onto the mic?

have you tried putting a volt meter between the mic and a suitable earth point?

 

[revjames]

no shock when you touch with hands etc. Will take a multimeter down tomorrow if I remember. Also I was soldering a new jack on to the lead feeding one of the monitors and every time the iron touched the cable it was making a speaker hum - even though the amp was off!

 

[revjames]

Tested from the mic to a screw on a switch which I knew was earthed. Seemed to be fluctuating and my meter doesnt read true RMS so set it to AC and it showed a steady 19V AC - bit of a worry? Now is this coming from the amp or the mixer I wonder? will do more tests later on when I have someone to switch various things off and on while I test.

 

[NozSpark]

Sounds like some sort of EMI or maybe static from you??

 

[danny7299]

Is the 48v phantom power is off on the desk , you don't need that for sm58's , is you have a faulty mic Or lead it could be that

For an explanation of phantom power look here

 

[revjames]

Thanks fo the replies, Danny I understand about the phantom power. I did some more tests today. everything switched on 19V, turn main house amp off - 17V, turn monitor amp off - 16V, turn desk off - 14V, turn power off at wall switch ( whole console including computer, projector supplies etc) - 8V. ?????

There is a multicore screened cable containing 16 pairs, plus speaker feeds for monitors etc. The multicore is terminated in 2 stage boxes one either side of the stage. They are metalclad. I was thinking perhaps bonding to nearby pipework or something?

Its all very strange must be an induced voltage I suppose?

 

[steptoe]

remember rev

volts jolt

current kills

for my pennies worth it deffo sounds like an induced voltage at no amps.

maybe you need one of meggermarks new fangled milliamp meters..

 

[revjames]

Just been at Church again, bent down to pick something up and my forehead touched the mic and I had a tingle. Got the meter out and there was about 13V ac present. I am thinking of taking a cable from the stagebox (only contains signal cabling remember) and earth it with a self tap and run a small cable to the nearest pipe and pick up an earth there.

Should I use 6mm green/yellow and the usual DO NOT REMOVE tag. What I am asking is should I treat it like an extraneous conductive part or can I add a small earth cable which will serve as reducing hum from the speakers and also (hopefully) remove the annoyance of tingly mics.

 

[Andy™]

or tell them to stop licking the mic.

maybe replace it with an ice cream?