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The front of my Sony 930 is (a)live?

Discussion in 'AV Receivers & Amplifiers' started by king2001, Aug 15, 2002.

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  1. king2001

    king2001
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    Having experienced buzzing from all 5 connected speakers (Tannoy 2.5/1/mc) for the last couple of weeks I have noticed something strange with the amp itself.

    If I run my finger lightly across any part of the front (including the drop down panel) there appears to be a buzzing or vibrating sensation. I honestly can't say I've noticed this before but it seems a bit of a coincidence that the speakers are buzzing as well.

    Could this be down to faulty grounding inside the amp or is this one of Sony's special hidden features?!

    TIA
     
  2. Reiner

    Reiner
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    It's not a special feature I recon, my Yammy does the same but there is no buzzing.

    Try using a different AC outlet and keep speaker wires away from AC wires (do not run them in parallel as this induces noise).
     
  3. dfield2000

    dfield2000
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    I think there might be a connection on the back for external grounding. If memory serves I think its mentioned in the Troubleshooting part of the manual as a solution to this type of problem.
     
  4. MattB

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    Here's why;

    "
    The worst offenders for having 'live' chassis are things like TVs VCRs and $ky boxes. They all have switch-mode power supplies instead of the traditional linear PSUs.

    A switch mode PSU first rectifies the mains to a (very lethal) 340VDC which is then rapidly switched onto a transformer which provides the safety isolation. This technique is popular because it is more efficient and fits into a smaller space than the alternatives.

    Assuming a two wire mains lead, everything on the isolated side of the transformer will 'float' unless it is grounded by being plugged into another piece of equipment with an earth e.g. most AV amplifiers.

    In order to reduce radiated interference to acceptable levels (to gain a CE mark) it is common practice to capacitively couple the isolated side of the transformer (= the bits you can touch) to the negative side of the mains rectifier which will tend to sit at around half mains or 120VAC! Leakage through the capacitor and transformer will weakly place this half mains on any exposed conductive surfaces connected to the isolated circuits (mainly connectors)

    I first became aware of this issue when I picked up my new Sony VCR and got a 'tingle' from the metal baseplate. It DOES NOT represent a fault. The equipment is double insulated (the little double square symbol) and if it carries a CE mark will have complied with the requirements of the Low Voltage Directive which sets strict limits on insulation breakdown voltage and leakage currents.

    If you are still concerned consult a qualified electronics technician who should be able to test the offending equipment and set your mind at rest.
    __________________
    Matt.
    "

    From this thread: Strange Voltage readings from TV and other AV equipment. Jan 2002
     
  5. king2001

    king2001
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    Many thanks to everyone for getting back to me on this.

    I have tried a couple of power outlets and also moving the speaker cables away from the power cord but there is no improvement.

    I did notice the grounding connection but to be honest I am not sure what I should be grounding it to (apologies for my lack of electrical knowledge).

    Once again thanks everyone!:)
     
  6. Reiner

    Reiner
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    The grounding at the back is for phono (turntables) or FM/AM antennas (in case of a receiver) but not for grounding the amplifier itself.
    If the amp needs to be grounded (based on the design) it has to come with a 3pin plug instead of 2 pins.
     
  7. king2001

    king2001
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    I have finally got around to connecting a wire to the earth terminal and the grounding connection on the back of the 930 and, yes, the buzzing or vibration from the front has now gone!

    However I am still getting buzzing from all the speakers and it's starting to drive me mad as I know it has never made this noise before:mad:

    Any suggestions on this problem or will it have to go in for a service?

    TIA
     
  8. dfield2000

    dfield2000
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    My 930 came with a two prong plug which is inside some sort of 'adaptor' plug which enables you to put it into a three prong socket.
     
  9. bigmacx

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    Try disabling the display output by sitting the dimmer to 100%. I get this buzzing whenever the display is active, some poorly shielded circuit is my best guess as to why this happens.

    Hope this helps,

    Mac.
     
  10. king2001

    king2001
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    bigmacx you are a genius:D

    Thank you for pointing out this rather obscure solution to my problem, but it does indeed work! I still don't understand how it suddenly started doing it but you've sorted it out so I just leave it well alone.

    Thanks again to everyone that replied.
     

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