Bumble bee subwoofer !

Discussion in 'Subwoofers' started by torimusic, Jul 16, 2002.

  1. torimusic

    torimusic
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    Anyone have any ideas on how to silence a humming subwoofer. I have a Velodyne CT-120 and it hums regardless of whether it's connected to the rest of my system or not. There is no earth pin in the IEC power plug and so I can't earth it.
    I've tried swopping over the neutral and live wire in the power plug but still no joy.

    Any useful suggestions would be appreciated.
     
  2. Guest

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    Is the hum from the cone or the electronics behind it ?

    Mike.
     
  3. torimusic

    torimusic
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    It appears to be coming from the cone. If I turn the sub's volume down to zero, the hum is still there but much fainter. As I raise the volume, the hum increases proportionately. It's possible that the cone and the transformer could be humming. I bought the sub when I was still in South Africa and the only difference between South Africa's voltage and UK is that South Africa's mains outputs about 15 to 20 volts AC less than UK. The mains frequency is the same.
    I recall the hum problem in South Africa as well but it was not as bad. It's possible that the house we are renting here has a lot of 'dirt' on it's mains because about 100 yards across the road from the house, is an electricity pylon that carries kilovolts I would imagine.
    I don't know if this is the culprit.

    The rest of my speakers also have a faint hum but I can live with it because it's not really noticable unless you put your ear up to the speaker.

    Hope this helps.

    Thanks for replying. Hope you can provide advice with the info above.
     
  4. Guest

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    Try a much shorter signal cable, along with resiting things away from all runs of mains cable (even the hidden ones).

    Set the sub up in another room to see if any difference ?

    Mike.
     
  5. MikeK

    MikeK
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    Firstly, all tranformers hum - the bigger the transformer, the bigger the hum, but not all transformers of equivalent size will hum the same amount - it can also depend on the load.
    Whether you can hear it outside the box is another matter though.

    If the sound is coming through the cone, and the sub is not connected to anything else, then it's usually the power supply design - not enough smoothing, insufficient regulation, etc etc) - this causes a slight ripple on the DC power supply to the amplifier, which, depending on the amps' design, may be picked up by the amplifier, gets amplified and driven into the bass speaker. If that's the case, there's little you can really do about it, save for redesigning the power supply/amplifier.

    With yours, it could be exacerbated by the fact that the unit may never have been designed to work from 240V, rather 220.
    It may well function, but the ripple will be bigger due to the higher input voltage - again, there's little you can really do about it.
     
  6. torimusic

    torimusic
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    Hi Guys

    Thanks for your input. I think I have isolated my problem. I have a Rotel RB991 amplifier and I connect the speaker outputs to the sub's high speaker level inputs on a separate cable run. The Rotel amp was supplied at the time with a cable that had the 2-pin American type plug on it and I changed it to a 3-pin UK plug and I SHOULD NOT HAVE CONNECTED THE EARTH WIRE!!!!

    I only found that out when I went through the instruction manual again. It's strange that the Rotel amp has an IEC power connector with an earth pin though if it's not meant to be earthed.

    Anyway, after disconnecting the earth wire, the sub's hum dropped to a level which is acceptable now although it is still there if you listen carefully. The hum does not increase anymore when I raise the sub's volume, which is a great improvement. My entire system seems to have benefitted from disconnecting the earth wire on the Rotel power amp's mains power input.

    I used to have quite a bad hum on my main speakers (which the RB991 drives) as well which has now disappeared. Thanks again for your help and I hope that others will benefit from my findings.
     

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