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PA pyrotechnics on power dropout-help please

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  • #16
    "If the connection from the board to the amps is properly balanced you'll never get a ground loop. I've worked with hundreds of systems in major concert venues with the FOH a hundred feet or more from the stage, using both FOH and separate backstage monitor consoles, and never had a problem. However, not all devices, especially signal processors, are properly balanced. Another reason for having all signal processors next to the board is that allows everything to use the same breakout box, and if there are improperly balanced devices or even some that are unbalanced the interconnects are short enough to keep ground loops from arising."

    Generally in large production systems there is a common power distro that all but takes care of power grounding issues between equipment.
    In Marvin's church that's probably not the case.





    Mike Caldwell
    http://www.mikecaldwellaudioproductions.com

    Comment


    • #17
      Mike & Bill,

      My memory failed me again There was a time when we lifted the ground at the mixing booth, but that must have been with a prior system. I looked today at the booth and amp rack and found everything to be in order respecting power cord ground pins. Now we all feel better.

      Back to the original power failure plosive problem.
      How would you recommend proving a UPS could solve the problem? When we lose all power we get that horrible BANG through the main speakers. I suppose I could simply power everything on and then switch off the culprit amp or unplug it while maintaining power to all upstream devices. However, I hate to even do that for testing purposes because I am afraid it might damage a driver. What do you think? Is it safe to test this way?

      Comment


      • #18
        BTW, here is a line diagram of our PA system.

        Church PA line dwg08112022.pdf

        The SEQ1, 2, or 3 denote which step of the Furman power sequencer the device is plugged into.
        Attached Files

        Comment


        • #19
          The switch box is interesting, is that used to turn on and off the speakers in the different sections of the church? Is it maintaining a balanced line connection through the switching?

          It maybe be hard to tell when it happens but do all the speaker zones, stage monitors, nursery, overflow and the main speakers all make the the loud pop or is it just
          certain speaker zones?

          If possible try to set up a test to see if you can narrow down if there is a single piece of equipment causing the pop.
          Maybe turn the levels on the amps very low and pull the power that is feeding all the amps and the processing to see if you hear any noise at that point.

          To check the input side of things turn the amps off, plug a pair of headphone into the mixer and pull the power feeding the mixer, wireless equipment and anything
          connected to mixer inputs and see what you hear in the headphones.

          If it's something connected to a mixer input from the stage that is the biggest noise pop issue a UPS on the mixer and processing would not really solve the problem.
          Mike Caldwell
          http://www.mikecaldwellaudioproductions.com

          Comment


          • #20
            Originally posted by Mike C View Post
            The switch box is interesting, is that used to turn on and off the speakers in the different sections of the church? Is it maintaining a balanced line connection through the switching?

            The switch only opens the tip (#2 pin) circuit. The 1 and 3 lead continuity is maintained. There may be a small capacitor across pins 2 and three but I would have to confirm that. Is this a valid way to switch outputs? It works perfectly well.


            It maybe be hard to tell when it happens but do all the speaker zones, stage monitors, nursery, overflow and the main speakers all make the the loud pop or is it just
            certain speaker zones?

            Unknown. When it happens I, and most people, are in the sanctuary and it is so loud there is no way to hear anything else. The ancillary rooms are mostly unoccupied at that point of the service. I do know that during normal shut down sequence, I can hear a small pop from another room which indicates one of the amps is not shutting off before the upstream devices. However that pop doesn't sound destructive.



            If possible try to set up a test to see if you can narrow down if there is a single piece of equipment causing the pop.
            Maybe turn the levels on the amps very low and pull the power that is feeding all the amps and the processing to see if you hear any noise at that point.

            That sounds like a good test. I will try it and let you know.



            To check the input side of things turn the amps off, plug a pair of headphone into the mixer and pull the power feeding the mixer, wireless equipment and anything
            connected to mixer inputs and see what you hear in the headphones.

            Connect headphones to the mixer headphone jack? Or the main output of the mixer?



            If it's something connected to a mixer input from the stage that is the biggest noise pop issue a UPS on the mixer and processing would not really solve the problem.


            Thanks, Mike

            Comment


            • #21
              "
              The switch only opens the tip (#2 pin) circuit. The 1 and 3 lead continuity is maintained. There may be a small capacitor across pins 2 and three but I would have to confirm that. Is this a valid way to switch outputs? It works perfectly well"

              That is not correct to switch a balanced line audio circuit on and off.
              Pin 1 is ground, pin 2 is positive and pin 3 in negative. Pins 2 and 3 both carry audio they are just opposite polarity/phase, disconnecting just pin 2 would still
              pass audio on pin 3 to the connected equipment the resulting level would be lower but still there.
              Maybe the switch box is not actually wired for balanced line switching.

              Could you post a picture of the box showing the internal switches and connections?
              Mike Caldwell
              http://www.mikecaldwellaudioproductions.com

              Comment


              • marvin
                marvin commented
                Editing a comment
                I will open it and inspect it. Will let you know.

            • #22
              The switches have no capacitors in the circuits (An old drawing showed caps, but there are none).

              Interestingly, the SPDT switch closes the pin 2 circuit in the on position, and shunts the downstream 2 & 3 leads going to the amp when switched off. Is this a good way to switch balanced lines? Should we use a DPDT to interrupt both circuits 2 & 3?

              See this wiring sketch:
              Church PA switch wrg08132022.pdf


              Comment


              • #23
                Both in the drawing and looking at the switch I can't see how shutting the south wing is not also shorting / shutting off the mains.
                That switch is a hack job and not helping things,

                Yes double pole double throw switches would be the correct switches to use. The input feed + & - would go to one pole set on each
                switch, the common / middle switch connections would go the zone output jacks and the other pole would be shorted together, shorting an input pins 2 and 3 together is a way to mute the input on a piece of equipment,

                Actually I would use the mixers group outputs to feed the zone and do away with the switch.....unless you are using the groups for your mixing operation.

                Looking closer now at the one picture I can see you channel group assignments and it looks like your only using the main LR .
                Mike Caldwell
                http://www.mikecaldwellaudioproductions.com

                Comment


                • #24
                  Originally posted by Mike C View Post
                  Both in the drawing and looking at the switch I can't see how shutting the south wing is not also shorting / shutting off the mains.
                  That switch is a hack job and not helping things,

                  I thought the same thing at 1st look, but they are independent. Each switch shunts it's common terminal (signal lead 2) to the switch off position terminal (signal lead 3) only on the load (amp) side of the switch. That state leaves the line side (mixer output pin 2 common feed to both switches) isolated from the shunted side of the off switch, with an intact path to feed the other switch. It works!



                  Yes double pole double throw switches would be the correct switches to use. The input feed + & - would go to one pole set on each
                  switch, the common / middle switch connections would go the zone output jacks and the other pole would be shorted together, shorting an input pins 2 and 3 together is a way to mute the input on a piece of equipment,

                  I will try to rebuild that switch box.. Is it necessary to short the amp input when unused, or good practice? Couldn't we just open pins 2&3 with DPDT switch without shunting 2 to 3, or does that risk a pop when the switch is thrown?

                  Does the DPDT need to be break before make or make before break?




                  Actually I would use the mixers group outputs to feed the zone and do away with the switch.....unless you are using the groups for your mixing operation.

                  Looking closer now at the one picture I can see you channel group assignments and it looks like your only using the main LR .

                  We coulD do that, however, all operators are amateur volunteers. We are maxed out on post fade buses in the mixer so the two switches on the main output are needed to turn off the South wing zone when needed.

                  The four post fade sub outs are used for recording, streaming, and two separate monitors. We could eliminate the other switches, but they are convenient.


                  Thanks a bunch,, Mike, for your time and expertise!

                  Comment


                  • #25
                    "I will try to rebuild that switch box.. Is it necessary to short the amp input when unused, or good practice? Couldn't we just open pins 2&3 with DPDT switch without shunting 2 to 3, or does that risk a pop when the switch is thrown?

                    Does the DPDT need to be break before make or make before break?


                    Shorting the input cable will take care of any stray noise the unterminated cable run could pick up acting as it is antenna.

                    A standard DPDT switch will be fine.
                    Mike Caldwell
                    http://www.mikecaldwellaudioproductions.com

                    Comment


                    • #26
                      Hi Marvin.

                      Did you ever get this fixed/figured out?

                      Craig
                      Craig

                      I drive way too fast to worry about cholesterol.

                      Comment


                      • marvin
                        marvin commented
                        Editing a comment
                        Hi Craig,
                        Not yet...getting sidetracked by other things, including assembling a little speaker before the Meniscus GTG.

                        I ordered and have the DPDT switches from PE and intend to replace the SPDT switches per Mike's suggestions. Later, I will try to trace down the big bang problem. It isn't at the top of my list right now, but I do plan to take advantage of all the input kindly offered here.

                        I will update when there is some progress.

                        Marv
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