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turntable hum and reduction of output

Discussion in 'Troubleshooting and Repair' started by brabock, Jun 30, 2013.

  1. brabock

    brabock

    1
    0
    Jun 29, 2013
    I have an Optonica rp-7100h turntable that has developed a couple of issues.It has what appears to be an earth hum which is present with each of these settings earth wire from deck connected or disconnected.Cartridge connected or disconnected.Using amplifier with built in phono pre amp. Using av receiver with phono pre amp.I have also changed rca cables and checked continuity of rca's and earth wire to turntable chassis. I have checked wiring in tone arm for continuity and that there are not earthing to tone arm.
    The other issue is that the output sound is extremely low even though it sounds correct with both channels present. Any opinions and suggestions would be appreciated.
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,264
    Nov 28, 2011
    Is the hum the same in both channels?
    Are both channels low in volume?
    Have you checked continuity of the phono cables from the plug tip through to the cartridge connection? And the earths as well?
    Is the sound normal, apart from being very quiet? For example, are the low frequencies missing?

    The normal best wiring arrangement is:
    Cartridge left channel hot and return connected through to hot (core) and return (screen) of left phono plug, with no other connection
    Ditto for cartridge right channel
    Turntable chassis earthed to earth terminal on back of amp/preamp
    Tonearm metal earthed to turntable chassis.

    You can also measure the resistance across the cartridge outputs, separately for left and right, and tell us the make and model of the cartridge. The cartridge's DC resistance, for each channel, should be only a few ohms if it's a moving coil cartridge, and probably less than 1k for a moving magnet cartridge (I'm not sure).
     
  3. Emilytronics

    Emilytronics

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    Nov 23, 2018
    Sounds like the earth connection has become damaged even if it looks ok (. The (usually) very thin earth wire may have a break in it, or could have been pulled loose from the PCB inside, perhaps if the cable has been pulled/yanked or trod on. Time to get out your continuity meter.

    If it walks like an earth cable problem, and it talks like an earth cable problem...
     
  4. Tha fios agaibh

    Tha fios agaibh

    1,872
    592
    Aug 11, 2014
    Thanks but note that this post is over 5 years old.
     
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