Hello, It has come to my attention recently - after using computer communications voice software that I can reduce the hum of the microphone recording by lightly touching my pc case. I was always under the impression that the earthing worked in my room. However, I have bypassed the psu earth temporarily simply by connecting a wire from a clamp in the pc case(unpainted surface) to the earth contact hole of the mains socket. This does not reduce the hum at all. However, by touching the case and touching the floor with the other hand I can reduce the hum on the signal. Therefore, is the earthing failing at some point in the house or is there something that I am ignorant of?
I can supply any information if you require more detail. thanks goodbye
I may not have an answer to your question but I have some healthy advice for you. I worked in electricity transmission and distribution for the last 15 years, got within the limits of approach at voltage level going from 120V to
750kV on two continents. My main specialty is work safety so what I'm telling you is mostly from this perspective. Remember that the ONLY protection you have, as a living creature is the ground (what you call "earthing"). If that fails you're virtually dead - meaning that you're not breathing, seeing, talking, eating, f..., etc - the fact that didn't happen yet doesn't mean it cannot happen, just that it didn't happen yet. If you have any doubt, even the smallest one, that your house grounding is not 100% safe have it checked ASAP before what I just said happens. As a rule of thumb, for normal people like you and me (and probably 99% of the guys writing here) everything above 24V is lethal and should be treated accordingly. There's only one thing that makes the difference between life and death: your skin resistance. As long as that holds you're ok, as soon as it fails you're gone. What's underneath your skin is mostly salted water which guarantees a massive failure due to the electrical current passing through. Examples of how your skin resistance can decrease are: moisture (sweat, hands recently washed, hand lotion, etc), cuts, burns, scratches, etc. In other words, there is one thing that works for you, one million things against you. Household grounding failure is a main cause for many accidents, some lethal, some not, some with long term consequences. Remember that copper oxidizes, the oxide increases the contact resistance which diminishes the efficiency of the ground connection. Also contact pressure has a tendency of decreasing in time with the same effect. Also bending the solid copper wires can reduce the copper section increasing the resistance thou reducing the overall grounding efficiency. In this scenario, one hand on the metal case of your PC and the other hand on the floor establishes a current path dangerously close to your heart, you had no problem when you first tested it because your hands are dry, next time you'll try it after eating an orange, you'll have some juice still on your finger and the next person entering your room will find you immobilized there and if this happens after more than 4 minutes your brain already suffered irreversible damage... Even if they manage to re-start your heart they'll never manage to fully re-load your operating system... Again: if you have the smallest suspicion that your house grounding may be faulty or not necessarily faulty, just if you thing it lost some of it's efficiency, have it checked. If you know exactly what you're doing you can do it yourself.... which I believe you would've done already... if you knew what you're doing... remember that money are of no value if you're not around to spend them, hire a certified electrician to have your grounding checked and eventually brought back within proper operating parameters before something unwanted happens. This may also fix your problem... but again, it may not. The switching power supplies used in computers are converting the household AC voltage into DC, converts it back to AC but this time with a high frequency that allows use of a little high efficiency step down transformer to reduce the voltage. Once reduced it's converted to DC that's used by all components. To eliminate - as much as possible - interferences between the household AC frequency and whatever goes out of the power supply they use all sorts of filters (capacitors, inductors, etc). As you know, all filters have a certain range where their efficiency is high, outside of that range the efficiency decreases so it may allow some system frequency components or harmonics to enter your PC. If the ground is ok it may be that you, acting as a capacitor, change the filter range a little, sufficiently to reduce the hum to more acceptable levels. In which case you may want to try a different power supply, one that may better filter the primary components.
..sm
"andy12345" wrote in message news:42952024$1 snipped-for-privacy@alt.athenanews.com...
Could be light dimmers or other equipment causing the problem..... try shutting off lights, television, etc ...... also move the microphone several feet away from it's present location, and definately away from your computer and monitor. You can purchase an inexpensive plug-in wiring checker at most hardware or electrical supply stores that will verify if your outlet is wired and grounded properly. electricitym . .
Thank you very much for all of your replies. I believe maplin electronics sells a checker for such things. The points you make are just like walking down the street without any body armour. You never know if body armour is going to save your life one day until it happens. Unfortunately, at that point, the knife blade will penetrate and kill you because you did not have the body armour on...... Correct? It is easy to electrocute yourself when you are not thinking correctly or fail to understand whats going on. I do understand such things of course, but, i never thought of the implications of doing what i did, as i havent thought to actually be aware of a potential earthing failure. You know what its like.... No one expects to suddenly be potentially electrocuted. So, thanks again and I will get onto the matter at hand. By the way, the microphone is a combo headphones/microphone set which I do not hold at any point, except for on my head. Maybe the wire screening is crap. thanks
Hello again, After reading my initial post, I was shocked (ahem) to notice that I said 'I have bypassed the psu earth.........' Let me elaborate on that. What I meant was that the pc was connected to the mains in the totally normal way. All I did was attach an additional cable to the earth contact of the extension lead socket to the internal pc case chassis. I know that I could still be dead of course. andy
OKay, its me again. This time I thought hmmmmm. Use a multimeter. I set it from 0-600vac and 0-600v dc and nothing showed all on the case, inside or outside. I can stop the microphone hum just by touched painted, non conductive pc case surfaces therefore I diagnose that there is not an earth problem. I trust that I am correct however, I dont want to be wrong in anyway so if you can just give your verdicts when you have a chance, I believe that the matter can be closed and put down to something else other than earthing problem. bye
Hello Again, I just remembered that i have one of those screwdriver tester devices which has a led that lights up when touched or hovered near wires and plug sockets. I touched the case with it and nothing lit up at all. Does that give new ideas? bye
using a straight wire to ground is shorting the two points out. however they are already shorted by chassis grounds internally. so, the only difference between the 2 points is distance and that allows noise to get on the line.
your body acts like a filter ( a capacitor). if you want to try installing a more permanent filter, try installing a 0.1 micro farand,200vac cap between the pc case and earth ground....about 50 cents at radio shack.
the 58vac hot to ground and neutral to grd are because when you unplug the input power cord you lose your reference ground. during an outage, with input and load power cord present, your safety ground reference would still be present....the voltage would be close to 0 neutral to ground.
the voltage change:
when input utility is present the apc just passes that through to the load with some isolation. when the input is lost, the dc to ac conversion is not perfect and the load does not really care. you would see this change with an o-scope.
Just another theremin fan:- Thanks for the water pipe idea. I will try that when having a bad hair day. The screwdriver power tester led works fine just by hovering it near cables as I checked beforehand.
main account/sm:- Thanks for your highly detailed post. I will chew that over for some time. Mark:- I am in england and therefore on a 50 hz system and could potentially be coupling that into the microphone. I am not holding it, but, it is on my headphones set isolated by some headphone padding. Can it couple under such circumstances?
Stu_e. I do not see the 58vac that you refer to anywhere in this thread. Am I missing something? Okay, so the 0.1uF capacitor stores charge, but why is that relevant? Is it to just remove some interference at a quicker pace than it builds up or something like that (I am a noob in some aspects) o.0 ?
I should definitely buy a quality headset or quality standalone microphone before I post anything else I suppose. Do ferrite filters work on microphones leads? bye
Is the comms unit self powered? Ie by a wall wart? If so it's likely to be double insulated so no *safety* earth required. So what you're dealing with is an audio ground. Is the casing of the mic connected to the screen of the output cable? The mic *might* be a balanced type with the screen floating.
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*I don't suffer from insanity, I enjoy every minute of it *
Dave Plowman dave@davenoise.co.uk London SW
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