DIY XLR Attenuation (In-Built into XLR Cable)

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  • tane0019
    Junior Member
    • May 2012
    • 6

    DIY XLR Attenuation (In-Built into XLR Cable)

    Hi all,

    Would appreciate all the experts help here to verify if my understanding is correct before I start building. Many thanks in advance.

    As per mentioned (don't know if this had been discussed before, if so pardon me) - would like to DIY a pair of XLR inter-connect between the pre-amp to power amp with in-built attenuation (~12dB) at the power amp plug side.

    I reference the article/formula at this site: http://wiki.slimdevices.com/index.ph...ve_attenuation.

    The connection circuit I think should be something like this (in which I think both R1 & R2 values used have to be halve w.r.t. if it was unbalance), right ?
    Click image for larger version

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    The formulas from the site are:-
    Attenuation [dB] = 20 * Log( R1 / ( 1 / ( 1/R2 + 1/IMPload )))
    New Source Impedance = 1 / ( 1 / (IMPsource + R1) + 1/R2 )
    New Load Impedance = R1 + 1 / ( 1/R2 + 1/IMPload)

    The values I gathered from my pre and power amp are:-
    Power amp input impedance = IMPload = 104K-Ohms
    Pre-amp output impedance = IMPsource = 500 Ohms

    Using the following values:-
    R1 = 82.4 K-Ohms - Or for Balance Line = 0.5*R1 = 41.2K-Ohms
    R2 = 27.4 K-Ohms - Or for Balance Line = 0.5*R2 = 13.7 K-Ohms

    The resulted values are:-
    Overall attenuation ~ 11.6 dB
    New Source Impedance ~ 20.6 K-Ohms
    New Load Impedance ~ 104.1 K-Ohms

    Are all my above assumptions + calculation/result correct ?

    Regards, EH.
  • tane0019
    Junior Member
    • May 2012
    • 6

    #2
    any experts advises please .....

    Comment

    • paulster
      Senior Member
      • Jan 2009
      • 841

      #3
      You only need 3 resistors, and you don't have to connect anything to pin 1 at all.

      See http://www.uneeda-audio.com/pads/

      I just made some -10dB attenuators using this method and they sound and measure perfectly.

      Comment

      • blackbear
        Senior Member
        • Aug 2006
        • 101

        #4
        An alternative would be to use Rothwell in-line XLR attenuators.

        Comment

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