AR2412, hum over thin cables

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This topic contains 8 replies, has 3 voices, and was last updated by Profile photo of NZdave NZdave 2 years, 5 months ago.

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  • #82057
    Profile photo of Barryjam
    Barryjam
    Participant

    Don’t know where to put this. I’m creating a splitter rack, where 24 XLR patch cables have to run underneath of an ar2412. I got a bunch of 4 channel 2ft snakes, but after connecting, I hear a gradual hum build-up that seems to increase with every channel. Since these are little snakes with thin gauge wires, I’m currently blaming the cables. I’ve read that the cable characteristic that defeats hum is double twisted wires and/or double twisting shielding. I’d hate to have to buy 24 separate 2ft mic cables that are double twisted, but I will if I have to. Have others run into hum with the ar2412 with patch cables, and what worked?

    #82064
    Profile photo of NZdave
    NZdave
    Participant

    Can you supply some pics of what you are doing?
    Are you building a rack for a seperate mic split for a balanced feed to a FOH or recording scenario?
    With the cables that you have bought, 4 way… are they XLR to XLR?
    Or XLR to TRS = tip ring sleeve) ?
    Do the cable have seperate insulation sleeving on all cables right through?
    Some evern small sub snakes and looms share common ground.
    And yes the common terminology for cable is twisted pair with earth and some also have a drain wire. There is a whole lot of variables like foil sheilded andthe type of sheilding for all measures in the old analogue world which is still relevant today.
    But if its in a rack with what you are biulding just simple XLR to XLR cables should work fine UNLESS there is something wrong with your rack mount splitters.
    As far as I’m aware the AR2412 is switch mode power so no transformer hum from there?

    Some pics would help

    #82068
    Profile photo of Barryjam
    Barryjam
    Participant

    The rack is being built so that QU-SB or SQ5 is IEM monitor desk. The splitter is three ART S8s, with the monitor desk receiving transformer output from the splitters, the 24 transformer outs feeding 24 inputs on the AR2412. The 12 outputs on AR2412 feed 6 stereo IEM units.

    The first photo shows a few AR2412 inputs being fed from the ART S8s. Imagine all 24 inputs occurring the same way.
    The 2nd photo shows a few ART S8 transformer outputs headed toward the AR2412.
    The 3rd photo shows the location of my power conditioner in the back of the rack, in case this could be a problem.
    The 4th photo shows the 4 channel 2 ft. XLRM to XLRF snake, which I suspect just don’t provide enough hum prevention.

    So, I’m thinking I need to ditch the thin snake concept and get 24 individual mic cables that are twisted pair.

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    #82073
    Profile photo of Barryjam
    Barryjam
    Participant

    Here is the photo of the back, again just showing a few channels connected to the splitters.

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    #82076
    Profile photo of NZdave
    NZdave
    Participant

    hmmm Really
    ok
    And the hum increases per channel ?
    Have you tried using just mic cables you may have.. It dosn’t matter if the 5 10 or even 20 meters!?
    Its just to try to eliminate that hum.
    And if you unplug everything else including those 3 power supplies dose that help?

    #82077
    Profile photo of Barryjam
    Barryjam
    Participant

    I’ve tried a few mic cables, but not 24 of them. I probably should try a bunch more cables.

    Yes, I have unplugged the power supplies, made sure the QU-SB or SQ5 is plugged into same circuit.

    Maybe I will turn off the power conditioner and power just ar2412 and mixer from the wall power.

    I’ll report back. Thanks for the help.

    #82080
    Profile photo of airickess
    airickess
    Participant

    Barry, does the hum persist if you have something patched into the input of each channel of the ART S8 units?
    Have you tried putting the snakes into the Direct Out outputs of the S8s to see if the hum persists?
    Have you tried engaging the ground lifts on the inputs of the S8s?
    What are you using to hear the hum buildup – headphones or a pair of speakers tied to L/R of the console?
    Does the hum persist with all of the faders down and the gain pots down?

    #82083
    Profile photo of Barryjam
    Barryjam
    Participant

    Thanks for all the problem solving.

    It turns out that the power supply of my Shure Wireless Mic creates a huge hum when close to the ar2412. I have to move that PS to the farthest point in the rack and/or get a new PS (Shure uses a different model number now). Just draping the PS power cable differently makes a difference. I am also considering moving my power conditioning unit further away from the ar2412.

    The cables are fine. My bad.

    I will experiment with suggestions from airickess as well. I do know that the ground lifts on S8s didn’t help. I am aware that S8s want something plugged into the first input of each S8.

    Thanks again for the great problem solving ideas. I’ll remember them for future mishaps!

    Barry

    #82084
    Profile photo of NZdave
    NZdave
    Participant

    I have connected many QUs through racks of splitters [Proel] similar to yours with transformer split and never had any ground issues and never had to lift an earth using digital desks.
    Remember that to get phantom supply to work you need direct connection & not through a transformer.
    Also I have had issues where those little external power supplies inducing AC hum into equipment and used to have them wired on longer looms and hang them out side of racks away from any insert looms.
    You might try wrapping the external power supplies into foil and grounding or earthing to shield,
    But that’s a lot of mucking around.
    Glad you sorted it before a gig and not at the gig in the heat of the night as they say.
    Thanks Barry & airickess :}

    Regards
    NZDave

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