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Potential diffrences question

Discussion in 'Electronic Basics' started by Anders N. Vinje, Apr 28, 2004.

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  1. Hey.

    I have this thing that puzzels me.
    I have a question about electrical potential. Well this is the case.
    I my bathroom i have wall outlets, they are of course groundet.. Everywhere
    else in the house
    there i no neutrual pin in the outlets. So i took a piece of wire and
    connected to the neutrual
    in the bathroom and brought in to my room. The i measured Dc and Ac voltages
    between the neutrual
    and the ground on my MIXER. At DC it said +- 1,5 v At AC it said 81,5
    Volts!! Ok. So here there
    is a big potential between the ground on my equipment and the
    ground(neutrual) in the wall
    outlets. Is this dangerous?? I also measured the same values between the
    neutrual and my pc

    I am also into music and i have three synths . I have one problem with one
    of my synths.
    Its a Korg Wavestation EX (digital). Sometimes the sound gets extremly
    distorted and loud.
    Then sometimes it just goes bact to normal. But sometimes it can go weeks
    before that happens.
    In my guess there is something wrong with the DAC becuse the sound is really
    clipped and the
    envelope of the sound is clipped. By that i mean when you play a sound, the
    duration of time
    before the sound decays is just cut suddenly. This is just a guess. I am
    not a Electrical
    enginner.I do fiddle around making preamps with opamps and making oscilators
    as a hobby. I am
    going to school this year to study to be bachelour in electronics. But now i
    The point to all this is that i allso mesured the voltages between this
    synths ground and the
    neutrual. AC was 65 volts when the power was turned of and 115V!!! when it
    was on. This is
    really diffrent from all the other equipment i have. Then there was no
    diffrence when the equipment was on or off. And lay at a stable 81,5 Volts
    I measured this several times. Does this indicate a potential problem??
    Is this what makes the DAC goes ditstorted(in my guess)??? Maybe there is
    connection inside the
    synth between one of the hot wires and ground. Everything else works fine ex
    cept the sound. Like menus and knobs etc. You can actually hear the orginal
    sound in the back of the exstremly heavy distortion.

    I really dont expect any to answer the problem with my synth but what is
    this about potentials
    floating around. I guess everything electrical should have be groundet to
    the neutrual in the
    building. I think its alot when there is 113 V AC diffrence or even 81,5 V.

    Any thoughts??

    Anders N. Vinje

    Ps. You have to excuse my english i am only norwegian :)
  2. Soeren

    Soeren Guest

    Hi Anders,

    Inside the power supply of many switch mode supplies is two capacitors.
    One from phase to ground and one from neutral to ground. They create a
    capacitive potential divider giving you half of 230V on the box if it is
    not properly grounded (through an earth connection).

    The reason for the lower readings is probably that smaller capacitors is
    loaded down by your volt-meter.

    Yes, if you connect (sound) equipment with such a capacitor-filter, to
    other equipment which is referencing its input ground to the box, you
    might put 115VAC into an input - many a stereo has blown when people
    connects their PC to their HiFi.

    Don't think so, other possibilities seems more likely (dried out caps,
    partly bad semiconductors etc.), try fault finding with a spray can of

    You could try to feed the equipment with a multi-connector *with* an
    earth-line (from the bathroom, if it is not isolated with a transformer
    rated for just a shaver.
    If that helps, call an electrician and get your mains outlets properly

    And you will have to excuse mine, I am only _human_ ;)
  3. Rich Grise

    Rich Grise Guest

    Sounds like an intermittent volume control pot. Or, it could just be
    dirty. That'd be the first thing I'd check.

    As far as the wiring issue, if you're not in the US, I really can't help
    you, other than to say that neutral and ground are really two different
    things - neutral is the return path for the load current, and ground
    is for safety ONLY. The case should be grounded, so that if there's a
    fault, it will blow the fuse, but the case should NEVER be connected
    to EITHER side of the mains, no matter what country you're in.

    Hope This Helps!
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