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Feedback on bassguitar/amp

Discussion in 'Live Sound [BG]' started by Herm-Jan, Jun 22, 2018.


  1. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    Hello!

    I am playing in Church as drummer and helping technician aswell.
    Now we are expierencing problems with the Bass players. Everytime we've got a bass player in the band we get alot of feedback on that channel on our mixing station.

    Our setup:
    Mixing desk: Allen & Heath GL2200.
    A snake from the desk to the stage.
    The mid/high frequency sound goes to a 100 volt system. The low ends goes to a turbosound IP15b.

    One of our bass players is using a hartke 115c amplifier with a DI output. This doesn't work for some reason.
    If we go from the Bass guitar into a DI and return the signal to his amp and the main DI out to our FoH we get feedback aswell.

    Maybe you guys have some tips for us or feel free to ask us questions about what we've tried etc.

    - Herm-Jan
     
  2. Wasnex

    Wasnex

    Dec 25, 2011
    Is this your setup?

    upload_2018-6-22_17-30-4.png

    Check the aux sends on the mixing board to make sure they are not routed in a loop. If the auxes are setup post fader and routed back to the channel, you will get feedback as you push the fader up.
     
    Last edited: Jun 23, 2018
  3. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    This is one of the ways we tried it. On the hartke 115c there is a DI build in where you can choose between pre EQ and post EQ (of the sub) That is just a normal XLR out. And he just plugs his Bass guitar into the AMP. I would like to think that we are correct on the aux sends. Because when we plug it into a different channel (which works with a different instrument or mic), we still get the same problem.
     
  4. Wasnex

    Wasnex

    Dec 25, 2011
    Draw a picture to show how you are hooking it up. The image I provided was drawn and copied from MS Paint.

    What speaker is the feedback coming from? Is the feedback high or low frequency? Does the feedback occur when the channel fader is moved or when the bassist plays a note? Does it feedback if all other mics are muted?
     
  5. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    Uhh the feedback come's out of every speaker. FoH and monitors. High frequency. Hmmm when it's moved up. Sometimes it works but than occur again later in the evening. Like we had no problems in rehearsal tuesday but on thursday we played a bit before going on stage and it gave a ton of feedback. We didn't do anything to our setup. It does feedback when all other mics are muted yes.

    We tried the picture you drew and we tried this: XLR out is pre or post EQ on AMP we tried both.
    Also ground lift etc. We tried new cables. We tried different channels on mixer/stagebox. We tried only bass and disconnected everything else. upload_2018-6-23_1-53-14.png
     
  6. Wasnex

    Wasnex

    Dec 25, 2011
    You have swapped 1/4" instrument cables, mic cables, DIs, snake channels, mixer channels.

    Do players always use the same bass, or does the problem occur with different basses? If only one bass and it is active, try a fresh battery.
     
  7. juancaminos

    juancaminos Supporting Member

    Is there a "PAD" button for the channel your using on the mixer? Or do you have pre-padded channel (Generally a channel with 1/4" jack inputs or combined stereo inputs). Or a channel with a way to attenuate the incoming feed (trim/gain knob)?
     
  8. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    We tried 4 basses, 3 different amp's, also fresh battery's.

    It does have a PAD button. And a gain knob. But the gain knob does not work if you select ''line level'' input with the PAD button. With the DI we use the ''mic?'' level input on the PAD button.
     
  9. Wasnex

    Wasnex

    Dec 25, 2011
    At this point it appears you have swapped out just about everything except the mixing board, power supply, snake, and associated outboard gear.

    Is anything being inserted in the bass channel, like a compressor or EQ?

    Is the channel direct out routed back into the board connected in any way?

    When the feedback occurs, if you mute the speakers and solo the channel in headphones, is the feedback still there? We need to determine if the feedback is acoustic or electrical.

    Is the feedback always the same pitch or does it vary with gain and stop completely when the fader level is lowered. Does the audio tech have to run the gain on the input trimmer really high with the bass to get enough signal. Does the channel continue to feedback if the bass is not connected. Leave the snake connected and run the channel trimmer and fader up to increase gain. Is it possible that the snake is split and has mics connected on the bass channel at a another location?
     
  10. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    Yep agreed. I think we tried swapping everything except the mixing board, snake, speakers. We tried swapping out the power. We tried clean power. (a different power source in the church 360 volt or something. that's for big bands etc.)

    Nothing is inserted. We dont use compressors/eq yet.

    No it's not.

    We will have to test that. We have to play tomorrow so ill ask the technician to check this if it occurs tomorrow.

    ''Is the feedback always the same pitch or does it vary with gain and stop completely when the fader level is lowered. ''
    It vary's. When the gain or fader is moved down it stops. I think i even saw the gain was on 0 and when we moved the fader up a towards the 0 it started to give feedback.

    ''Does the audio tech have to run the gain on the input trimmer really high with the bass to get enough signal.'' I think i heard him say this yes. The signal is comming in really low or something. ill ask him tomorrow aswell.

    ''Is it possible that the snake is split and has mics connected on the bass channel at a another location?''
    no, not possible.

    ''Does the channel continue to feedback if the bass is not connected.''
    no it does not. But i will check tomorrow.

    Sorry if it looks like i give a curt response. I really aprieciate your guys help :D
     
  11. Wasnex

    Wasnex

    Dec 25, 2011
    Your answers are fine...this is a pretty perplexing problem.


    Wasnex said:

    When the feedback occurs, if you mute the speakers and solo the channel in headphones, is the feedback still there? We need to determine if the feedback is acoustic or electrical.


    We will have to test that. We have to play tomorrow so ill ask the technician to check this if it occurs tomorrow.

    Try muting or lowering the fader of each speaker system, one at a time.

    If the gain is being run really high in the bass channel, I wonder if the problem could be cross talk in the snake...I.E. The send wires are being picked up and amplified through the mic channel wires. We are talking a wire snake rather than digital right?


    Try a DI that puts out a stronger signal so less gain is required on the bass channel. If you don't have such a DI, try close mic'ing the Hartke.
     
  12. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    Yeah we are talking a wire snake.

    We don't have such a DI. And we did twice close mic the Hartke or another sub amp because the ''normal'' signal was giving feedback. The close micing worked fine.

    Could it be something related to the ''loop?'' i dont know the english word. Ringleiding is the dutch word.
    ringleiding: induction loop ; ring line ; collecting pipe ; common main ; inductance loop ; induction loop system ; closed circuit.
    It's a system that the older people in the church can listen in for hearing aid.?
     
  13. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    We have these: Fame Studio DI Dual 2-kanaal DI-Box, passief

    we can only have a knob to put out negative dB on the signal. And we tried putting the signal down and gaining it up on the mixing desk. That doesn't work haha
     
  14. Wasnex

    Wasnex

    Dec 25, 2011
    I am assuming from your description that Ringleiding is an assisted listening system. I don't know how these systems work, but you certainly don't want feedback hitting anyone's hearing aid. My assumption is the Ringleiding basically broadcasts a radio signal to that is taken from the main signal buss. Does this sound right? Unless a receiver is routed back into the mixing console I don't think this is the likely problem...but weird things can happen with radio frequencies. The audio system could somehow be decoding the Ringleiding signal. You can test by simply turning the Ringleiding off.

    If the mic works reliably I suggest using it. Perhaps you can barrow a DI with more output to test before money is spent, or just use a mic indefinitely if the results are satisfactory.

    I would try to determine if the problem is crosstalk in the snake and which channels specifically are interacting. If this is the problem, the audio tech should be able to produce the problem at will by increasing the gain on the bass channel until feedback occurs.
     
  15. Wasnex

    Wasnex

    Dec 25, 2011
    I suspect using the pad on the DI might make the problem worse. I suggest setting the pad to 0dB to provide the hottest output possible.
     
    Last edited: Jun 23, 2018
  16. Wasnex

    Wasnex

    Dec 25, 2011
    I Googled induction loop assisted listening system. Yes, I think that could possible be the source of the cross talk. Does the snake run near the induction loop area?
     
  17. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    I am not sure what it does either. I did not install the system. And i'm not sure if the induction area is near the snake. I will have to ask the person who build the system in the church. But isn't it weird it's only reacting on the Bass? And not on any other instrument? Like my electric drums or a saxaphone.
     
  18. Wasnex

    Wasnex

    Dec 25, 2011

    I don't think it's weird if the bass channel requires more gain. Here's a short article that may be relevant Do Induction Hearing Loops Cause Interference to Nearby Electronic Equipment?

    To test, it should be possible to run up the gain on the bass channel until feedback occurs. Then, turn off the Ringleiding and see if the problem goes away. As I mentioned earlier, cross talk could also be occurring in the snake.
     
  19. Wasnex

    Wasnex

    Dec 25, 2011

    I think we have found the problem and if you look at the last post on the thread below.... a possible solution may be to delay the feed to the induction loop a bit. I suspect the use of an active DI with a hotter signal may also solve the problem, but I could be wrong.

    http://www.hometheatershack.com/forums/pro-audio/38938-hearing-aid-loop-causing-problem-our-pa.html
     
  20. Herm-Jan

    Herm-Jan

    Jun 14, 2018
    Hmmm it isn't the hearing aid acording to the technician. They shut it off already. But isn't a active di with a active instrument wrong? We've got two active di's. So we could check this. How can we check for crosstalk? Run another cable all the way from the bass to the mixing desk? (I didn't understand what you meant earlier how we could check).
     
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