Blog Forums Consumer Electronics Repairing Thomann Box – bad hum

last updated by Chedwin 1 year ago
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    • #14653
      filbert
      Participant

      Hi folks,

      I have a Thomann the box 350w powered cabinet https://www.thomann.de/gb/the_box_pa502a_aktives_fullrangesystem.htm that has recently developed a very nasty hum (after having returned from a repair shop that cannot fix it).

      The hum is so loud that if I turn the volume to even the first notch it feels like the speaker might blow!

      If no XLR cable is plugged in then the hum disappears, and if I plug-in an XLR to minijack cable (which probably has no grounding), there is also no hum. But if I use other XLR cables, the hum returns immediately, even if they are not plugged in.

      Any ideas what this is and how to fix it?

      Many thanks!

      Matt

    • #14654
      Chedwin
      Participant

      @filbert Sounds like this could be a shell grounding issue

      XLR connectors have a normal ground connection on pin 1 but they also have optional grounding of the outer shell. this due to the variety of signal types xlr (and other d series panel mount connectors) are used for as some use cases and signal types require shell grounding whilst others dont

      to help diagnose this better can you tell me what audio source is connected to the other end of the xlr and can you open the XLR connector at each end of the XLR and share photos of how the wiring has been terminated


      Josh Evans, Professional Live Sound Engineer, High End Commercial AV Install Technician

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