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Strange issue with Mic and PA ?

Discussion in 'Live Sound [BG]' started by Doley50, Dec 22, 2013.

  1. Doley50


    Sep 4, 2005

    I run sound for my band and last night the guitar was only coming out of the left FOH monitor for the life of me I could not find the problem.
    The guitar amp is mic'ed with an SM 57 with 2 XLR cables connected together to extend the length .
    I checked through the routing of the channel , gain , sub groups, mute, faders, pan. I tried a different channel same results.
    I disconnected and reconnect the XLR cables same results.
    The only thing I can think of is that some of our cables are cheep bulk cables purchased online and some are starting to fail. Could a faulty XLR cause this ?
    I was going to change the cables out, but we needed to start playing, so I decided to let it ride .
    Any insight would be greatly appreciated.

  2. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Okay, let's go through the system one step at a time. It would help to know a few things:

    *Mixer brand / model.

    *How many monitor channels? What power amp(s) are you using to power the monitors?

    First thing I would do is grab the guitar mic and yell into it. Are vocals present in both monitors? Have you, in some way configured a dual channel monitor system and assigned the guitar to one side only? Don't worry about answering the last question...it will be disclosed as the investigation continues.

    Do us both a favor and don't change a bunch of stuff at the same time. We may fix the problem in this manner but won't have a clue as to what the culprit was to start with. This is particularly problematic if the anomaly appears again in a critical, time-constrained situation...like during a gig!

    BTW, while you're at it: grab a vocal mic and yell into it, as well. Are vocals present in both monitors? This little exercise will help immensely.


  3. NO.

    And if there wasn't any sound in the left FOH speaker at all (no vocals, nothing at all), check the speaker cable, amp feed, amp, etc.
  4. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Spot-on, Joe! Brevity is a virtue.

    I'm thinking along the lines that we're seeing a dual-channel monitor configuration (i.e Aux 1 and Aux 2 like I run) or mis-configured power amps (dual mono vs bridged, Y'd, whatever). Some of these possibilities, however, would demo complete loss of vocals on the same side as the guitar.

  5. Doley50


    Sep 4, 2005
    Let me start by saying, I do not have the PA set up or even at my house, so I can not do any real time troubleshooting at the moment.
    with that being said I can still answer most of your questions.
    Here is the set up:

    Mackie ProFX 16

    Monitors ( all powered )
    QSC k-12 ( mains )
    Yorkville NX 720 s ( subs )
    Mackie TH-12A ( floor monitors )

    Two Monitor channels using Aux Mon 1 and 2 on mixer

    While I don't have the system set up to test, all the other channels on the board were coming out of both speakers.

    I did check the Pan knob, a few times !

    I just asked my drummer ( who has the board ) to take a picture of the board, and while faders and some knobs get moved in transport.
    It looks like I may have had the right channel selected to a sub mix and the sub fader was down.

    I going to have to grab the PA this week and test it out to be sure.
  6. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Not sure how you've rigged your monitor signal path. May want to check both Aux 1 and Aux 2 levels on your guitar mic channel but that be more relevant to how I run my monitors. Sounds as if you've narrowed the search, though.

  7. Doley50


    Sep 4, 2005
    The floor monitors are not really an issue, We only use two, one for the lead Vox ( Aux 1 ) and one for the drummer ( Aux 2 ) , we put a little B Vox into then and sometimes a little guitar in the lead Vox monitor ( depending on the venue )

    Hopefully the issue was the sub mix sends. I'll get back and let you know .

    Thanks for your help

  8. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    I'm following you now. You're assigning either desired mic channels or the whole shebang to a sub-mix and routing to FOH monitors. I'm a little slow on the uptake as we're using only floor monitors with vox...no FOH monitors, no sidefills.

  9. JohnMCA72


    Feb 4, 2009
    1. Guitar is in the left only to FOH.

    2. All other instruments & vocals are present in both FOH channels (L & R).

    3. Does the guitar work in any other channel? I'd check that first.

    4. Attached is from your mixer's block diagram, typical mic. channel at the top. From the information we know, your guitar signal is present all the way from the input (upper left), through the pan pot. where it gets routed proportionally to the L & R Main Busses. From the Main Busses on, everything is OK (i.e. all other channels are present). The only things between where the signal is known to be good (input of the channel pan pot.) & the Main L & R Busses are that pan pot. & the L & R Assign switches (buttons).

    I'm guessing you're due for a factory authorized service call. It may be as simple as a stuck contact in the R Assign button or an open connection to the R terminal of the pan pot. Could be a switch or pot. gone bad. Definitely check out all of your channels thoroughly.

    Attached Files: