System developed Hum and hiss......pls help !

Discussion in 'AV Receivers & Amplifiers' started by Hungseto, Mar 16, 2006.

  1. Hungseto

    Hungseto
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    Hi everyone.

    Here is my set up :

    CDP to Pre amp -> VDH d102 mkIII speical (very old cable in white color)
    pre to power -> Ecosse MA2 (resonablely new)
    Power to speaker -> QED Silver sipiral (resonablely new)
    pre and power amps - cambridge C75 and A75 (about 20 years old)

    The system was running perfetly okay with just a very small amount of hum ie. have to put my head within 1/2 meter of the speaker to hear any hum.

    Last night I swapped the VDH cable which was used between the pre and power with the Ecosse cable which was between CDP and Pre around.

    (this chage improved the sound quality of my system so I would like to make it permenant)

    then i noticed a much lounder hum and hisss. the hum is just about listenable at listening distance (only when no souce is playing) and i can feel the bass cone virbrating if i touch it with my hand (softly of coz).

    I selected different source on the pre-amp, hum level and hum sound unchanged, turned volume up and down, nothing changed, I have even swtiched off the CD player. its the same.

    I did some reseach on Internet and guessed the problem may be 'ground looping' . As far as I can remeber both of my old age cambridge pre and power amp (about 20 years old by now) has no earth connection to the socket (but I am not sure, I remeber chaging it from a 2 pin plug to one of those 13A british starndard plug about 10 years ago myself and I remeber there was no earth wiring to it)

    I am planning to earth my pre-amps's casing to the earth on my wall socket.

    can anyone advise how can it be done , SAFELY?

    Is my problem is ground looping? (I have doubt about it becuase it only shows up after swapped cable around)

    or could it be the VDH which seems to be famous for picking up noises?
     
  2. chrisgeary

    chrisgeary
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    it sounds to me like your new interconnect has a poor or broken shield. if you put your old interconnect back, does the hum go away?
     
  3. Hungseto

    Hungseto
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    All I did was swapped around two interconnect which have been using in my system without causing this hum. did not add new interconnect or nor taken away any.

    lower level of hum:
    CDP to Pre amp = Ecosse MA2
    Pre to Power amp = VDH D102 MkIII speical(not the hybird one, Old version white in color)

    Hum problem:

    CDP to pre amp = VDH D102 MkIII speical(not the hybird one, Old version white in color)
    Pre to Power amp = Ecosse MA2
     
  4. chrisgeary

    chrisgeary
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    do you have another interconnect spare (even if its a cheapo one)? i would set up your system so it hums. power down. remove the pre to power interconnect and change it for your spare cheapo interconnect. power up. what happens?
     
  5. Hungseto

    Hungseto
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    Been lazy and did not test it last night after went home because after I powered up the system I just keep enojoying the music.

    I looked into (listened to) the hum problem again just before going to bed. It is in fact not noticeable while sitting in listening position (you could) but you have to pay very very close attention. but surely within one meter distance in front of the speaker one can hear it.

    and I noticed that the speaker on the left side has a slightly lounder hum and at a lower frequency.

    I suppose the hum was always there even before I played around with the cabling (I noticed the hum long long ago) but somehow it is now more noticeable I think I will try to find out the reason but even with this little hum the sound is still very good to my ears.

    Will this background hum decrease the sound quality by a lot? I understand hum is unavoidable in any hi fi system but I think mine is quite bad but I am glad that its not so bad that make it unlistenable.
     

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