[LAU] Terrible mic ground noise

[Gene Heskett]

On Monday 01 April 2013 08:08:15 Len Ovens did opine:

> On Sun, March 31, 2013 9:25 am, jonetsu at teksavvy.com wrote:
> >> From what you have said above and from looking up the HW you are
> >> using,
> >> you should not be getting any audio through the mic at all. So if you
> >> turn
> >> the gain up high enough you might get hum.
> > 
> > That must be the problem then.  The higher the volume, the higher the
> > 'ground' noise.
> > 
> >>>    The electric plug has only two prongs.  I though of getting some
> >> 
> >> What electric plug?
> > 
> > The one to which the computer stuff is connected.  The house plug.
> > Which is not a plug, but a box. That one does not have a ground wire
> > as others do.  The two-AC plastic socket unit has no ground wire.
> 
> Is this the way the whole house is wired? (or garage or whatever) This
> may very well be some of your problem. It would seem that your whole
> setup is floating.

I doubt if it is 'floating', and we've had something resembling the NEC 
codebook for more than half a century now.  What I would be concerned with 
in a house with wiring old enough to not have the 3rd, round pin in its 
duplexes, would some folks, and I have found this before in my travels, 
that the wider of the two slots in the duplex, which was supposed to be 
connected to the white wire which in post knob & ball wiring days, was 
always assumed to be the neutral side of the wiring.  The black wire was 
supposed to be connected to the narrower slot, and was assumed to be the 
hot side of the line.  By electricians...

I can drive to what was a greasy spoon about a  mile from here, in an old 
frame building, where every appliance in the kitchen was hot enough to buzz 
the help,  the whole damned building is wired backwards!  She finally moved 
her business about 2 years ago, into a much more modern building.

THE IMPORTANT PART of this msg:

At the lumberyards, like Lowes or Home Depot, in the electrical aisle, they 
have shirt pocket sized electrical 'Sniffers" not much bigger than a pen or 
pencil.  Often their power switch is the pocket clip, you grab the end and 
squeeze the clip shut, then the other end has a plastic coated blade, and 
it will trill like a canary & blink an LED you can see when that blade is 
within 1 to 2 inches of a live wire.

They sell for something in the ten dollar range, very cheap for something 
that can save your life by finding hot stuff that isn't supposed to be, 
like your refrigerator, often installed within reach of the usually well 
grounded stuff of the kitchen sink?

So please get one ASAP.  If not sooner.

/THE IMPORTANT PART.  The rest is optional but hopefully educational.

I have 2, and they have saved me from many a potentially lethal shock over 
the last 25 years from stuff that was wired by folks who claimed to have 
known what they were doing.

If you find a reverse wired duplex, where the wider slot is the hot side, 
it was probably wired bass-ackwards and has been since a roll of wire came 
on the premises 65 years ago.  Yes, its been that long since I wired my 
parents house for electricity as it was being built in 1947.  I was then 13 
yo.  Not knowing the white was ground by convention in the electrical 
trade, and already used to a grounded wire in a radio being black since I 
was already doing radio service for smoking money back then, I did it 
backwards & had to go back and fix it a month later when we were wiring the 
crawl space dugout for a water pump, the pump was a people buzzer when 
turned off.

One of the steps in the education of Gene, who has now chased electrons to 
make therm do useful work all his life since, the last 50 in broadcasting. 
Oh, and I haven't had a cigarette now for 25 years. quit cold turkey, sick 
of being half sick with a cold that seemed to have hung on for more than 
its allotted 2 weeks.

> I would feel comfortable fixing the wiring to make
> sure I had proper grounding even if it just meant running one wire for
> that purpose. If there are any grounded outlets in the building
> (washing machine for example), I would run an extension cord from
> there. I have not had hum like that from a mic. If you have no grounded
> outlets at all in your house... In North America that would be over 50
> years old... then running a good thick wire (14 gauge would be good) to
> the chassis of your computer from the cold water pipe if you are on
> city water and it is metal all the way out of the house... or a 6 foot
> piece of re-bar pounded into the ground would work too. If you are on
> well water the whole water system may be above ground or plastic. Also
> check the main power panel as the power company may have that grounded
> regardless of the rest of the house. A friend who is an electrician
> would be a great asset at this time :) They could probably figure
> things out in less time than it took you to read this.
> 
Maybe.  One of my boyhood best friends followed in his fathers footsteps 
and got his Journeyman's card by the time he was 20.

I had a problem & called him in on it (somehow life had put us back in the 
same town) when he was about 45, because I was at the time up to my butt in 
alligators as I had just become the CE at a tv station & the wiring to the 
studio lights was being a smoking problem child.  Electrical stuff letting 
out the smoke usually means keeping fire extinguishers handy...

He came in, we made all sorts of measurements & did a lot of head 
scratching for a couple hours one afternoon, then sat on the back stoop & 
had a beer, still playing what if games but reached no consensus as to why 
were were measuring many times the expected current in the neutral wires of 
one electrical box but not the other, the source of all the smoke & sparks.  
He was stumped as was I ATT.

So I went home to dinner, still thinking about it, and the lights came on 
while I was scarfing up a hamburger steak.  I went in about 5AM Sunday 
morning & verified the error.  One of those 2 boxes was miss wired.

Hard to fix as there wasn't a big breaker to kill the whole box that was 
miss wired, so I had to work on it hot. NBD to me.

The problem was related to it being a 3 phase system.  There was about 50 
kw worth of lights in the studio in those days so there was 2 boxes full of 
15 amp breakers.  One box was a Federal, one box was a Square-D.  I forget 
now which was which, but one box ran one phase A down the column of 
breakers on the left, and phase B down the 2nd column of breakers on the 
right, and one boxes bus was formed like a pair of combs teeth facing each 
other positioned between the teeth of the other phase, so that the top row 
was fed by phase one, the next row by phase 2, the 3rd row back on phase 1 
etc to the bottom of the box.

The electricians? who wired it weren't cognizant of the differences that 
would make and blindly wired both boxes so that the lamps, 1500 watt 
halogens, were wired up with a pair of 12 gauge wires to the hot side, and 
a single 14 gauge wire bringing the neutral back for BOTH lamps.

So one box had 29 amps coming back up the flea weight 14 gauge neutral 
because both lamps were on the same phase, where the other box only had 
about 3.5 amps on this same neural wire because thats about what you get 
when you do the vector math for 2 legs of a 3 phase system.  So the 
solution was to remove the right hand top wire, move it to the left hand 
side at row 2, take that wire back to the top right breaker, and basically 
do a step & repeat till I got to the bottom of the box.  The breakers 
themselves could have been moved, easier, except that would have tangled up 
the wires even worse & the connections needed tightening anyway.  Just good 
practice IMO.

Problem solved for the life of the facility.  Wrong boxes in the first 
place, should have been 3 phase boxes, but it was built by idiots working 
on the cheap & they would probably have had to special order the correct 3 
phase boxes.

A good electrician should have grokked that little detail instantly.  But 
the vector math for a 3 phase system was not in his knowledge banks at all 
even if he was working days at one of the coal fired power station 
facilities being expanded that light up Los Angeles at the time, time being 
the late 1970's, place being Farmington NM.

I never had the heart to tell him that his education was incomplete.

Life leads folks down an infinite multitude of paths, always according the 
the Peter Principle I think.  Or is that Parker?  Never could (shrug) keep 
those 2 guys straight.

[...]

Cheers, Gene
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