Preamps picking up noise from cables

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This topic contains 8 replies, has 5 voices, and was last updated by Profile photo of Mike C Mike C 2 months, 2 weeks ago.

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  • #90248
    Profile photo of Steve
    Steve
    Participant

    CDM32 with DX168 on DX1, C1500 via GigAce connection.

    Noticed that I could hear noise through regular XLR cables when using PAFL. Extra loud if the cables are wrapped in TechFlex braiding. Here’s how I recreate the issue:

    1) Plug in a XLR cable to any preamp on the CDM32 or DX168. Example: Channel 2 on the CDM32.
    2) Go to surface and PAFL CH2 from CDM32
    3) Set input gain to 27dB
    4) Tap/thump the XLR cable (no mic on other end); if I step on the cable, I can hear noise as well.

    I can hear the tapping/thumping/stepping in the PAFL. If I turn off the PAFL, I can hear it through the PA, even at moderate volumes.

    No other cables/inputs active or connected to the CDM32 or DX168, so it’s not another mic picking up noise.

    The DX168 seems more sensitive to picking up the “handling” noise of the cable. And again, there isn’t a mic on the other end of the cable, nor are there any other mics/cables plugged-in to the system.

    Anyone else experiencing this? I contacted my local rep; waiting for info.

    #90250
    Profile photo of Underscore
    Underscore
    Participant

    I guess my 1st question would be, how old and what quality are your cables…

    #90252
    Profile photo of Steve
    Steve
    Participant

    I have tried it with brand new (straight out of the package) cables, as well as numerous “known good” cables that don’t exhibit the same behavior on our M32.

    Definitely not a cable issue.

    #90256
    Profile photo of Steffen R
    Steffen R
    Participant

    Definitely not a cable issue.

    you stressing an unterminated input cable, what is your use case for this?
    academic b…it

    what happens with a nicrophone connected? it works?

    #90260
    Profile photo of volounteer
    volounteer
    Participant

    @steve

    Terminate the cable.

    Not sure why but we had problems with cables still attached to stage ins when the devices had been removed after being used.
    Sounds like you have the same issue.

    We used Qu so it seems to be a generic electrical phenomenon not an AH device problem nor specific cable problem.

    #90265
    Profile photo of Steve
    Steve
    Participant

    Thanks, and yep I understand it’s not normal behavior to look for/listen for noise in unterminated cables. With a mic attached, I can still hear the noise in the cables, and it doesn’t happen with our M32 consoles. Just struck me as odd that the dLive is somehow picking-up noise via the cable when other systems don’t.

    It may not seem like a big deal, until someone steps on them during a show and the noise is potentially transmitted to the PA. @volounteer – thanks for confirming your system had a similar issue!

    #90267
    Profile photo of volounteer
    volounteer
    Participant

    @steve

    Similar but not after they were coiled up instead of left lying straight to where the guitarist had been that night.

    Makes me wonder if they are picking up something like an antenna if you are still hearing them after terminating them.
    We had no problems that I have heard when they are used with devices connected.
    [Or after they were rolled up not lying long and straight on the stage]

    #90327
    Profile photo of Steve
    Steve
    Participant

    Update – Problem is SOLVED.

    It was suggested to me that I make a dummy microphone by soldering a 150-ohm resistor across the male pins 2&3 of an old XLR cable end and then test for the noise.

    Sure enough, the noise disappears completely when the dummy mic is plugged in. The resistor simulates the load of a normal non-condenser mic. As soon as I unplugged the dummy mic, the noise returned.

    So, apparently it’s normal behavior for an unterminated XLR cable. I’m guessing the contact noise that I could hear with real mics plugged in was being picked-up by the mics (even though they were 20+ feet from where I was trying to induce the noise on the cable.

    Thanks to all – hopefully this post saves someone from future headaches.

    #90330
    Profile photo of Mike C
    Mike C
    Participant

    I also followed you post over at PSW.

    What brand and model mic cables do you use?
    More importantly what is make and model of the wire itself.

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