Question BUZZING sansui 7500 AMP (earthing?)

Discussion in 'Hi-Fi Stereo Systems & Separates' started by Sings Ohia, Mar 9, 2018.

  1. Sings Ohia

    Sings Ohia
    Novice Member

    Joined:
    Mar 9, 2018
    Messages:
    4
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Location:
    UK
    Ratings:
    +0
    HELLO GUYS, GIRLS

    I HAVE A PROBLEM!

    I have connected a newish Thorens TD 240_2 turntable to my sansui amp
    all works fine
    But it hums, not when i use the sansui tuner but when i turn it to phono for the turntable

    There is a screwable nut at the back where the earthing wire goes to and that is connected fine

    if i put my fingers on the screwnut the buzzing ends

    if i put my fingers on or near the cables at the back connecting the turntable to the amp it buzzes louder!

    any ideas anyone

    thanks for listening

    Sings Ohia
     
  2. dannnielll

    dannnielll
    Well-known Member

    Joined:
    Sep 16, 2017
    Messages:
    1,788
    Products Owned:
    1
    Products Wanted:
    0
    Trophy Points:
    113
    Location:
    ireland
    Ratings:
    +752
    See the comments i wrote today on earthing and grounding.... A 50 Hz buzz is usually induced current in a conductive loop. If you have a braided cable covering the cartridge leads, it needs to be earthed at on side only not both ends of the braid.
     
  3. Sings Ohia

    Sings Ohia
    Novice Member

    Joined:
    Mar 9, 2018
    Messages:
    4
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Location:
    UK
    Ratings:
    +0
    hey danniell,
    thanks mate, but i dont quite understand, are you talking about the turntable headshell ground blue, ground green output red output white cables or?
     
  4. Sings Ohia

    Sings Ohia
    Novice Member

    Joined:
    Mar 9, 2018
    Messages:
    4
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Location:
    UK
    Ratings:
    +0
    do you mean disconnect a red or blue cable?
     
  5. dannnielll

    dannnielll
    Well-known Member

    Joined:
    Sep 16, 2017
    Messages:
    1,788
    Products Owned:
    1
    Products Wanted:
    0
    Trophy Points:
    113
    Location:
    ireland
    Ratings:
    +752
    I don't know what colours are being used but there should be 4 wires coming from a cartridge. These 4 wires carry the tiny stereo signal 2 wires per channel. They probably pass through the metal tube of the tone arm, which provides some interference protection. Don't do anything to these wires. After the tone arm they may well go to a connection strip and be connected inside a wider cable with a braided shield or copper woven layer. The purpose of which is to continue the protection that the tone arm provided. If there is a braid, it should make electrical contact at one end only. Once the signal wires have got into a pre amp or amplifier, they are not as susceptible to noise interference.
    The hum you are hearing is the magnetic field of the electrical wiring in your house being picked up by a loop of wire . Even your body acts as a detector and with the amount of voltage amplification in the preamp, you are injecting noise at the turntable end.
     
    Last edited: Mar 10, 2018
  6. Sings Ohia

    Sings Ohia
    Novice Member

    Joined:
    Mar 9, 2018
    Messages:
    4
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Location:
    UK
    Ratings:
    +0
    Thanks for the note Daniel but I have no idea from that what I should do, no cables come out the end of the tone arm so there is nothing to be done is there? It sounds too technical for me I am afraid. Two cables come out the back to go to amp one red plug one white plug and one thin earthing cable that goes into a nut on the back of the amp. So I am stuck but thanks anyway best Darren
     
  7. dannnielll

    dannnielll
    Well-known Member

    Joined:
    Sep 16, 2017
    Messages:
    1,788
    Products Owned:
    1
    Products Wanted:
    0
    Trophy Points:
    113
    Location:
    ireland
    Ratings:
    +752
    Right what i was describing was the internal wiring within the turntable. The white and red plugged cables are almost certainly RCA plugs and have a single wire inside each with a braided outside which serves as both a signal return line and an earth connection. Both cables should be run close and parallel to each other and then into the amplifier. You can also make a connection between the turntable and the amplifier using that external earth connection again arranging that that wire also is parallel and close to the two signal cables.
     
  8. Mark.Yudkin

    Mark.Yudkin
    Well-known Member

    Joined:
    Sep 19, 2007
    Messages:
    9,990
    Products Owned:
    0
    Products Wanted:
    1
    Trophy Points:
    136
    Location:
    Zurich, CH
    Ratings:
    +1,527
    Since putting your finger on the AU-7500's ground nut removes the hum, I suspect an issue with the amp's electrical grounding, so first off, check the wiring in the plug and that all cables for the TT are fully seated (press hard).

    You can find a manual for the Sansui at SANSUI AU-7500 OPERATING INSTRUCTIONS & SERVICE MANUAL Pdf Download.. Check through all of the items on page 17 for your problem.
     
  9. dannnielll

    dannnielll
    Well-known Member

    Joined:
    Sep 16, 2017
    Messages:
    1,788
    Products Owned:
    1
    Products Wanted:
    0
    Trophy Points:
    113
    Location:
    ireland
    Ratings:
    +752
    An earth wiring in the mains plugs can create the problem, rather than solve it. Fundementally there should be a single signal grounding point, linking all the elements . There should ( at most) be a single earth connection from your system to electrical power earth . That signal and electrical power earthing points should make a single connection .. again preferably at the lug provided. The lug provided on the amplifier chassis is such a point. Check whether the amplifier sansui was expected to use three core cable including an earth. Check whether the turntable has three cored mains cable. If so disconnect one of them and use the lug to make the connection between the frame of the amplifier and the frame of the turntable.
     

Share This Page

Loading...
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice