Subwoofer hum.....receiver causing it!

Discussion in 'General Audio Discussion' started by krimney, Nov 14, 2017.

  1. krimney

    krimney Super Member

    Messages:
    2,969
    Location:
    Calgary, Alberta
    I hooked up a sub yesterday. Nice little energy e xl-s8. I am happy with the sound but annoyed at the hum it makes when I shut off my receiver, a Cambridge Topaz SR10. I have owned the Topaz since new and it has given me no problems.

    If I shut the Receiver off, the hum starts. I thought it might be the sub so I gave it some time as I understand the sub should shut off after a bit if time with no signal. I gave it an hour and still a hum. I decided to unplug the Cambridge and the hum stopped. So even with the receiver off, it seems like there is still some signal going through the sub out??
    When the receiver is on and playing, even at very low volume I can hear no hum, it is only when the receiver is plugged in and off that it is there.

    Any suggestions? Or is this just an issues with receiver design. Maybe just plug them both into a power bar.
     
  2. JoeESP9

    JoeESP9 ESL's & tubes since 83

    Messages:
    14,695
    Location:
    Philadelphia PA
    "Sounds" like a ground loop problem.
     
  3. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,799
    Location:
    uk.. the middle bit
    is there a ground lift switch on any of it ?
     
  4. Oerets

    Oerets AK Subscriber Subscriber

    Messages:
    9,764
    Location:
    Derby City U.S.A.
    Bad RCA cable?


    Barney
     
  5. Powertech

    Powertech New Member

    Messages:
    25
    Location:
    South Wales, U.K.
    You have an earth loop. This is probably created when the CA is switched off because the pre out signal is grounded by the disconnection relay within the unit until it's power up sequence has completed. The problem is caused by there being more than 1 route to ground which forms a ring circuit which generates a potential difference between each end of the connecting cable ground wire - this generates the hum, and this 'signal' level is sufficient to keep the auto run sensing in the sub unit energised. To avoid opening up the units, break the connecting lead and connect a 10ohm resistor in series with each ground wire. Solder a 0.1uF film bypass capacitor across each resistor. Not absolutely guaranteed, but this should break the hum loop without doing anything electrically dangerous.
     
  6. krimney

    krimney Super Member

    Messages:
    2,969
    Location:
    Calgary, Alberta
    So after determining that I was not on the same circuit as the fridge, and making sure that I had the sub and receiver plugged into different circuits, I swapped out the RCA cable and the hum is gone!! Sub is acting like it should. The new RCA I am using fits a lot tighter than the previous one and is of a heavier gauge wire. Glad it was a simple fix.
     
    woodj likes this.
  7. sanford12

    sanford12 Old Stuff New Stuff As long as it's Good Stuff Subscriber

    Messages:
    3,627
    Location:
    Blue grass country
    You gotta love a simple fix.
     

Share This Page