XLR cable pin 1 variations

Discussion in 'Pickups & Electronics [BG]' started by Happy Camper, May 13, 2019.

  1. Happy Camper

    Happy Camper

    Feb 11, 2019
    I've seen ostensibly high quality XLR cables that connect the cable shield to pin one only versus some that connect the shield to pin 1 and the connector body (which is typically earth as opposed to signal ground). I've also seen cables arranged with each end treated differently.

    I've read that the best practice is for the shield to be considered part of the equipment housing and be connected to the connector body on both ends but that seems like a excellent to way to increase ground loop sensitivity. I have seen cases where not connecting the shield to the connector body as well as pin 1 seems to increase the susceptibility of hum being induced (e.g. cable near to pedal PS picking up hum).

    Any opinion/experience on a best practice/method for handling pin 1 and connector body most likely to give good general results?
     
  2. Warpeg

    Warpeg

    Jun 20, 2005
    Ohio
    I was a CTS-certified technician for an AV integrator for many years; we NEVER landed a ground to the tab on an XLR. Ground ONLY went to pin 1. Landing ground to both locations opens up the possibility of ground loops. The input device should be managing ground.

    Also, those tabs are usually much less reliable than the pins in terms of durability.
     
    Bob_Ross likes this.
  3. Doc Blue

    Doc Blue

    Mar 29, 2019
    St Augustine
    Short answer for good general results. Don't connect pin 1 to the body.

    Long answer for best results. Depends. If the connector body connects to an isolated chassis that is designed to serve as a shield, it's beneficial to tie the cable shield to the connector shell. But the box must be designed for this. I don't know how often this happens with music gear. My grounding and shielding experience comes from aerospace instrumentation ground test and flight systems. Another example is connecting 2 XLR cables together. Tieing the shield to the shell shields the entire connection.

    The flip side is using an XLR cable with a shielded shell to connect to a box that ties power ground to the chassis. This can result in a real mess.

    Ground and shield are not the same thing. And ground is power ground or signal ground, and they aren't the same thing either. So you have shield, signal ground, and power ground all to contend with. At some point they all get tied together, and how and where that happens matters too.
     
    Bob_Ross likes this.
  4. Happy Camper

    Happy Camper

    Feb 11, 2019
    Thanks for the responses, not connecting the tab seems a good plan. A related question is that I have an amp module with an XLR input, it seems reasonable to not connect pin 1 to the chassis ground nor to the tab. If the tab is not connected on the cable, it seems reasonable to the tab unconnected on the amp connector? Out of curiosity I'll have to check the devices I have for pin 1 connectivity to chassis ground.
     
  5. Doc Blue

    Doc Blue

    Mar 29, 2019
    St Augustine
    The amp input falls under the "depends" answer. The circuit designer will use pin 1 as a ground reference or "signal common" for the amplifier input. This may or may not be chassis ground. I expect the input is a board connector, so you'll need to follow the traces.