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Thread: Breaking earth loops

  1. #11
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    Fitting a resistor on the signal ground “lifts” it from the chassis earth. If you can insert a 10-100 ohm resistor between your signal ground and safety/chassis ground, this will stop the hum if it’s that causing the earth loop.
    “Music has always been a matter of energy to me, a question of fuel. Sentimental people call it inspiration, but what they really mean is fuel. I have always needed fuel. I am a serious consumer. On some nights I still believe that a car with the gas needle on empty can run about fifty more miles if you have the right music very loud on the radio”

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  2. #12
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    Quote Originally Posted by Ali Tait View Post
    Fitting a resistor on the signal ground “lifts” it from the chassis earth. If you can insert a 10-100 ohm resistor between your signal ground and safety/chassis ground, this will stop the hum if it’s that causing the earth loop.
    Thanks Ali
    I like the idea of putting the earth lift in my passive pre, but it obviously is not plugged in the mains so the case is not earthed.
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  3. #13
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    Will still do the same job though, you just need that bit of resistance in the signal ground, doesn’t matter which end of the cable it’s at.

    Yes it would be the same with my pre- a wooden box with Tribute AVC’s inside.
    “Music has always been a matter of energy to me, a question of fuel. Sentimental people call it inspiration, but what they really mean is fuel. I have always needed fuel. I am a serious consumer. On some nights I still believe that a car with the gas needle on empty can run about fifty more miles if you have the right music very loud on the radio”

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  4. #14
    Join Date: Jun 2015

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    Quote Originally Posted by Ali Tait View Post
    Will still do the same job though, you just need that bit of resistance in the signal ground, doesn’t matter which end of the cable it’s at.

    Yes it would be the same with my pre- a wooden box with Tribute AVC’s inside.
    I'm no expert but I don't understand, as the passive chassis is isolated don't you need the earth lift resistor to be on a component which is earthed to mains. What does lifting it to a small piece of metal achieve?

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  5. #15
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    The interconnect is a cable between two components, in this case preamp and amp. It has two wires, one signal, one ground. The point of this earth lift is to add between 10 to 100 ohms to the ground cable to stop the hum. Think about it, it doesn’t matter which end of the wire you put the resistor, if you measure the cable with a multimeter you will get the same ohms reading whichever end you’ve put the resistor in.

    Make sense?
    “Music has always been a matter of energy to me, a question of fuel. Sentimental people call it inspiration, but what they really mean is fuel. I have always needed fuel. I am a serious consumer. On some nights I still believe that a car with the gas needle on empty can run about fifty more miles if you have the right music very loud on the radio”

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  6. #16
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    'Fraid not, I agree it changes the resistance between the ground at one end and the passive case at the other (which is not earthed), but is the important measure not the resistance between the grounds in each joined component which is still equal to the resistance of the cable?

    In fact I don't understand how changing the resistance between grounds eliminates hum anyway, might have to go back to first principles on this...

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  7. #17
    Join Date: Apr 2016

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    Quote Originally Posted by Ali Tait View Post
    The interconnect is a cable between two components, in this case preamp and amp. It has two wires, one signal, one ground. The point of this earth lift is to add between 10 to 100 ohms to the ground cable to stop the hum. Think about it, it doesn’t matter which end of the wire you put the resistor, if you measure the cable with a multimeter you will get the same ohms reading whichever end you’ve put the resistor in.

    Make sense?
    I'm struggling too. If you put a resistor between the ground of the cable and a case that is not connected to earth, then its seems no better than inserting a resistor and dangling the other end in fresh air.
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  8. #18
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    A ground loop is just that: a circular conducting loop, which when threaded by an external magnetic field (due perhaps by leakage from a transformer, or from being in close proximity to mains cables) will cause a 50Hz current to flow in it. Increasing the resistance of the loop by inserting a 10R resistor (so called earth 'lift'), will greatly reduce the size of this induced current and hence the effect it will have on the audio circuitry.
    Barry

  9. #19
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    Also, using a passive with transformers will also break the earth loop.

    I had a passive once which did just that.

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  10. #20
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    Quote Originally Posted by bumpy View Post
    I'm struggling too. If you put a resistor between the ground of the cable and a case that is not connected to earth, then its seems no better than inserting a resistor and dangling the other end in fresh air.
    I agree, I think Ali is suggesting that the resistor is inserted in the 'ground' connection out to the output sockets.

    As far as an earth lift goes in an earthed case system, the extra resistance between the signal ground loop and the earth loop forces any current that is flowing to flow in the earth connections between cases, rather than the signal connections, thus reducing the 50Hz currents to virtually zero.

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