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TD12 Hum and Cabling Question

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  • TD12 Hum and Cabling Question

    Hello,

    Been reading this forum for months now, and finally got around to posting.

    I've recently treated myself to a Peavey PR-15P PA powered speaker, to use as a monitor for my TD-12 and one day something to practise/gig with.
    Very impressed, very low-level hiss, and terrific punchy bass, unfortunately due to the neighbours, I can't turn the volume past 2, let alone up to 11!

    The problem I've got is that when running the TD-12 though the amp, I'm getting an audible hum. I only get this hum when running the TD-12 in, so it's obviously not a problem with the Active Speaker. This just leaves the TD-12.
    The amp is wired up via the master out, left into one input and right into the other input, each input is mixed and fed into the active speaker amp.
    I get no hum (from my headphones) if I plug my headphones into the master out. I do get hum if I plug the patch lead into line in (just investigating..).
    Measuring the AC voltage between the ground on the speaker and the ground on the TD-12 brings up ~8V, which is not enough to be audible, I believe.

    The cables are standard "good quality" mono shielded cables, and I've played around with some others, no change..
    I can obviously live with this hum (but why should I?), since the speakers are turned way down, but if I wanted to crank them up, this hum would be quite noticeable!
    Any ideas what my next check is?

    How do people connect their TD-12 to their active speakers? I've only got one speaker, so I only need one input, but I like the stereo separation in my headphones and rapidly switch between the two. So don't really want to compromise here.
    Is running left and right into 2 of the active speakers three inputs correct, or will there be some phasing/distortion problems?

    Cheers

    Jonathan

  • #2
    Hello and welcome. Try searching for 'ground loop' in the search, or on google. It might also be worth using just 1 output. If you run a single cable from the L/Mono output on the module, it'll automatically send a summed mono signal to the speaker. Whether this would help in your situation or not is another matter.

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    • #3
      Hello,

      I've measured the AC voltage between the ground points again, it was actually ~6V not ~8V.

      Earth pin socket on mains outlet -> Earth on speaker cabinet = ~6V
      Earth pin socket on mains outlet -> Earth on TD-12 = ~0V
      Earth on speaker cabinet -> Earth on TD-12 = ~6V

      Huge resistance between Earth on speaker cabinet and Earth on TD-12, means minimal current flowing between the two.

      I don't have any other mains powered audio equipment to run to the active speaker, apart from hifi, so stuck.

      Cheers

      Jonathan

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      • #4
        I also get a hum sometimes when using the master outputs of my TD-12 or my TD-20. I bought a direct (DI) box with a ground lift input and that has solved the problem for me.
        TD-20, SPD-S, TAMA '82 Superstars
        http://www.outawhack.net/drumming ___ http://www.zendaddyband.com ___ http://www.myspace.com/353238983

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        • #5
          The hum is probably indicating a poor ground connection

          - try balanced cables from your master out to the powered speaker
          - try taking an output from your headphones to your powered speaker and see if the hum is still there
          - you could try putting one of those magnetic collars on the power cables (I doubt this will do anything but it's worth a test)

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          • #6

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            • #7
              Hello,

              The DI box fixed my mains hum problem.
              It has a button labelled "Ground Lift", when this was pushed in, the hum stopped.

              Cheers

              Jonathan

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