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Thread: Speaker hum problem

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    Speaker hum problem

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    Hello,
    I have two PCs for recording, one with an E-mu 1820m sound card linked to a pair of Fostex active 5" speakers and another one with a Roland Quad-Capture sound card linked to a pair of Fostex active 4" speakers. Both setups work perfectly well. However, I recently tried to link the Quad-Capture to the Fostex 5" speakers and they hum like crazy. What could be causing this ?
    Lend me your ears

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    Are they plugged into same electric circuit with grounded plugs? Hum usually comes from a ground loop problem.
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    In addition to power ground problems I find that connecting an unbalanced output to a balanced input can cause pretty bad hum.

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    Quote Originally Posted by mjbphotos View Post
    Are they plugged into same electric circuit with grounded plugs? Hum usually comes from a ground loop problem.

    Well, the Quad-Capture is USB powered- although its PC is powered by the same circuit as the 5 " speakers. However, the Quad-Capture's previous machine was plugged into the same circuit as the 4 " speakers- and they didn't hum. All the circuits are well grounded, yes.
    Lend me your ears

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    Quote Originally Posted by bouldersoundguy View Post
    In addition to power ground problems I find that connecting an unbalanced output to a balanced input can cause pretty bad hum.
    I'll look into that, thanks, - although I'm pretty sure that none of my gear is ' balanced '.
    Lend me your ears

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    Monitors are susceptible to hum if they're connected with unbalanced leads. I had the same problem with my KRK Rokit 8 monitors until I switched them to balanced. Now they're dead quiet and sound great.

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    I will obtain a pair of balanced leads- but that does not explain to me why the 5" should hum with the Quad-Capture and not with the 1820m- using the self-same leads.
    Lend me your ears

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    Quote Originally Posted by wuzzo View Post
    I will obtain a pair of balanced leads- but that does not explain to me why the 5" should hum with the Quad-Capture and not with the 1820m- using the self-same leads.
    I just looked them up and both of your interfaces have balanced output. It may be that different ways of doing the balancing interact differently with your unbalanced connection.

    Interestingly, the E-mu manual specifically says to use unbalanced cables to connect to unbalanced devices to avoid noise problems.

    I looked up "Fostex 5"" and there were several models so I couldn't determine if the inputs are balanced. What is the exact model number?

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    Quote Originally Posted by bouldersoundguy View Post
    I just looked them up and both of your interfaces have balanced output. It may be that different ways of doing the balancing interact differently with your unbalanced connection.

    Interestingly, the E-mu manual specifically says to use unbalanced cables to connect to unbalanced devices to avoid noise problems.

    I looked up "Fostex 5"" and there were several models so I couldn't determine if the inputs are balanced. What is the exact model number?
    They are PMO.5n . I tried the Quad-Capture and the Fostex 5" with very good quality Lynx 2,5mm speaker leads- but they still hummed. They are silent when connected to the 1820m. It would be easy to write off the Quad-Capture as cheapo kit- but there's no hum when it's used with the Fostex 4" .

    Thanks for your time, incidentally. Appreciated. I've reverted to using the 1820m but it's showing its age, I think.
    Lend me your ears

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    Quote Originally Posted by wuzzo View Post
    I tried the Quad-Capture and the Fostex 5" with very good quality Lynx 2,5mm speaker leads- but they still hummed.
    Speaker leads? Like this?That cable is for connecting an amplifier to a passive speaker. Your active speakers have the amps in them and so you need to use shielded line cables, preferably balanced. That could be the cause of the problem.

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