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High voltage measured on amplifier case to earth

Discussion in 'AV Receivers & Amplifiers' started by gihana, Apr 6, 2005.

  1. gihana

    gihana
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    Dear users,

    I recently set up my Denon AVR1802 amp with a REL Strata ii subwoofer. I have had this set up running before previously in another house.

    This time round, I noticed a background hum from the sub when the amplifier was in standby or on mode.

    After disconnecting everything, I turned the amp on and measured the case to earth voltage (The AVR1802 is double insulated and earth free).

    I measured a voltage of about 117V ac to earth.

    I've opened the amp and dis a visual to see if something had fallen in and was shorting anything to the case but I could not find anything.

    Since then I have bought a Marantx SR4400 which is performing well.

    However, I can still measure a standing voltage of about 80Vac to earrth when nothng is connected.

    When I connect the REL to the amp, the system gets an earth path from the REL via the subwoofer coax cable.

    My concern is, should there be such a high voltage in the first place on the amplifier case?
     
  2. Cliff

    Cliff
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    It is a fact that if you measure case to earth most equipment these days will set the case at about mid point between live and neutral. It's not dangerous and that is the way it is designed.
    The current is very small and your meter is very sensitive!.

    Think of it this way- if there is no earth wire where would you set the potential of the case (let it float?)




    When you connect your REL it will earth everything and there will be no loop.
     
  3. gihana

    gihana
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    Cliff,

    Thanks for the response.

    It is comforting to know that it is a design intent to have that level of voltage on the case.

    From what you have said, is it fair to assume that once an earth path is available (in this case via the REL) the voltage source impedance is so high at the amplifier that the voltage is dropped within the amplifier as the small leakage current flows to earth?

    The thing I haven't resolved is the standing hum on the REL when I use the Denon AVR1802 (my old amp). This is not present with the Marantz SR4400.

    Any pointers??
     
  4. Cliff

    Cliff
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    Yes, on connecting the REL the amplifier case will be go down to earth potential.

    If you get a hum that does suggest an earth loop.. Is there any other earthed equipment connected to your Denon?

    Is the subwoofer cable long and running near any large transformers?

    When you turn the subwoofer volume down does the hum reduce to zero- if so probably not an earthing - could be pick up.

    If the amplifier is off then output impedence (sub woofer out) may go high and it will be more susceptable to hum pickup.

    These things can be tricky to track down :)
     
  5. gihana

    gihana
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    Cliff,

    Thanks for the reply.

    I'll do a bit of chasing with the Denon and REL setup.

    Regards

    Gihan
     

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