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How can I safely disconnect from PA

Discussion in 'Live Sound [BG]' started by ktedrow, Jun 12, 2018.


  1. ktedrow

    ktedrow Supporting Member

    Feb 18, 2015
    Folsom, CA
    Our band plays at a venue that provides a high quality PA that is always on (bar staff doesn’t know how to power it off). Connection is made through line-level XLR to our mixer. When I disconnect I first power down the mixer and get a super loud whump sound out of the PA, which I suspect is not good for the speakers. Is there a way to prevent this? Maybe disconnect XLR cable before powering down the mixer?
     
  2. Stumbo

    Stumbo Wherever you go, there you are. Supporting Member Commercial User

    Feb 11, 2008
    Intergalactic Mind Space
    Song Surgeon sofware
    Maybe find out what mix the club has and check out the manual.
     
  3. gumtown

    gumtown

    May 7, 2007
    New Zealand
    Unplug the XLR,s first. Or ask the bar staff to turn down the PA level, or just dont give a damn, not your problem.
     
    ktedrow likes this.
  4. guy n. cognito

    guy n. cognito Secret Agent Member Gold Supporting Member

    Dec 28, 2005
    Nashville, TN
    Doesn’t know how to turn off their PA??? That’s a new one. In that case, just have them mute it.
     
  5. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    If they don't know how to turn it off, I'm not holding my breath on them knowing how to mute it !! And muting it may not stop the thump.

    To the OP.. PULL the XLR feeds from the back of your mixer BEFORE you power it down.. should solve the "thump" problem.
     
    bucephylus and ktedrow like this.
  6. ktedrow

    ktedrow Supporting Member

    Feb 18, 2015
    Folsom, CA
    Thanks all. I’ll try pulling the xlr. We have a gig this Friday. Will report back.
     
    s0c9 likes this.
  7. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    There's a number of ways pulling the XLR could also make a really nasty noise, possibly even worse than the thump you're getting.

    Someone at the venue must know how the system works. Call ahead, connect with that person, find out how to mute your input before you connect or disconnect. They'll probably be glad you asked.
     
  8. guy n. cognito

    guy n. cognito Secret Agent Member Gold Supporting Member

    Dec 28, 2005
    Nashville, TN
    This.....
     
  9. gumtown

    gumtown

    May 7, 2007
    New Zealand
    What does every other band that plays there do?
     
  10. If you have a mute or cut switch of some variety from your end, that might help a little. But from what I can tell, what's going on here is a larger scale example of what happens when you ''hot plug" your amp. The fact that they don't know how to turn off their equipment is gravely concerning though o_O
     
  11. Paulabass

    Paulabass

    Sep 18, 2017
    Huh! You can't turn off a mixer or any outboard gear with the power amps on!!!!!
    Mute your channel.
     
  12. Sounds like it won't be a great system for long...
     
    Spidey2112 and Chris Doherty like this.
  13. Blaze Barlow

    Blaze Barlow

    Mar 8, 2018
    Nashville
    lots of stuff can be muted..or volumes turned all the way down..right at the mixing board..or at the crossover..or at the amps..
     
  14. ktedrow

    ktedrow Supporting Member

    Feb 18, 2015
    Folsom, CA
    Good idea. I'll see if I can find someone.
     
  15. ktedrow

    ktedrow Supporting Member

    Feb 18, 2015
    Folsom, CA
    Our mixer board doesn't have the ability to mute the main out bus, only the input channels can be muted - and I do mute them.

    I bring the faders down before I power down the mixer. I think that's all I can do from the mixer side.
     
  16. TomB

    TomB Supporting Member

    Aug 24, 2007
    Vermont
    Make sure no phantom power is on in either system when you connect / disconnect. Pull your XLR send out of their input. Tell us what happens.
     
  17. ktedrow

    ktedrow Supporting Member

    Feb 18, 2015
    Folsom, CA
    I am worried about this. But thinking about it some more, I realized that I already have been connecting/disconnecting the XLR input to the PA while the PA is powered, I can't avoid it, and I haven't been getting a thump. But maybe I've been lucky. I can imagine how connecting/disconnecting a cable introduces random behaviors as the three pins make/break at different times.

    So here's my plan: first try to find someone at the venue who can show me how to power down or mute the PA. If that goes nowhere (which I suspect it will, this place has new management that seems really clueless) then disconnect before powering down the mixer. And cross my fingers.
     
  18. ktedrow

    ktedrow Supporting Member

    Feb 18, 2015
    Folsom, CA
    After studying the schematics of our mixer (it's an old crest audio mixer, schematics can be found online), I am convincing myself that it's safe to disconnect the XLR input to the PA while the mixer is powered up. That this is in fact, the way I should have been doing it all along.

    Here's the schematic section for the right channel output. The way I see it, with faders down, the right-out input to the op-amp will be static, so the XLR signal lines will be grounded through R167 and R168 (no signal through C45 and C46), so disconnecting should be safe.

    FYI: R73 and switches SW3A and SW3B implement an option to change output level from line-level to mic-level.

    upload_2018-6-13_1-9-5.
     
    TomB likes this.
  19. gumtown

    gumtown

    May 7, 2007
    New Zealand
    The proper thing to do is turn all the volume levels of the PA power amplifiers down to "0", and then preferably power 'off' the PA amplifiers, firstly, before unplugging anything from the desk output.
    I am assuming the house PA system has 2 level control knobs behind the bar, one for the house music, and another for the live bands.
    And do the bands bring their own desk, mics, and monitors, and plug the desk output into a pair of house system XLR leads on the stage side?
    The amps probably get left on 24/7.
     
  20. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    True, but the OP said the venue staff don't know how to do that.. and that may be perfectly valid.. so we've been looking at alternatives.
    Pulling the L/R feeds off the back of the mixer (with master volume down) should work in most cases like this.
     
    TomB likes this.