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slight buzz with board muted

wrgflyfishwrgflyfish Posts: 9
edited April 2010 in 200 Series Connectivity
Brand new driverack 260. My board has both trs and xlr balanced outputs. When I first set it up I got a little buzz and then have spent several hours trying to eliminate things that could cause it. I'm now thinking it is the DR because...

First...this is a new snake and new cables everywhere.

I set up the mixing board using the xlr out (bal) to a 3 foot xlr cable. I plugged that into another 3 foot xlr cable. I plugged that into a xlr to trs adapter (not a transformer). I plugged my 1/4 trs snake return into that. Using that configuration everything is fine. When I put the DR between the 2 3 foot cables...I immediately get a slight buzz. Pressing the ground lift button doesn't help. The only difference is the DR. The DR is plugged into the same power strip as the mixing board. Did I manage to get a bad DR? This is very frustrating.

I can post info about board, amps, speakers, etc but considering my problem I don't think it is relevant. If I'm wrong let me know.

Any ideas would be appreciated.

Comments

  • DennisDennis Posts: 801
    Did you test all of your new snakes, adapters and cables with a cable tester? Pin1-sleeve, Pin2-tip, Pin3-ring. The ground switch lifts ground only between the board and the 260. If the issue is between the 260 and the amp(s), you will have to lift pin 1 on the cable(s) between the 260 and the amp(s). I assume for this test, the only thing connected to the board is the 260. You should probably post info about all of your gear before Gadget sees your relevance comment.

    Dennis
  • DraDra Posts: 3,844
    Does it buzz on both inputs and all outputs?

    DRA
  • wrgflyfishwrgflyfish Posts: 9
    I don't know Gadget but you are right. When trying to figure out a problem everything is relevant until it has been determined that it isn't. I should know that I work on computer problems all day. So...

    Behringer 24 channel board SX2442FX Eurodesk (I think this is the right model)
    Behringer EP2500 amps (1 for 2 aux fed monitors, 1 for stereo mains)
    Veris 28 main speakers
    Rapco 20 channel (16 xlr - 4 trs)

    I didn't test all the components. I'll test all the cables tonight but I would hope brand name cables wouldn't be a problem especially since everything works fine before I put the 260 in the loop. I soldered the snake at the stage myself so the returns should be correct. I had disconnected all the xlr sends from both ends to eliminate that as a possibility. I did have to solder pin 1 at the snake or I got a TERRIBLE hum. I ALSO had to use a ground lift plug on the amps or I got a terrible hum. The snake is connected to the mains with a trs cable. The test included the board, 260, amps, and speakers. I don't notice any transformer hum from anything until I switch the amps on.

    A little electrical information too. The amps are on a switch at the sound booth. That puts the switch near several other switches including dimmers and ceiling fan speed controls. Can that be part of the problem?

    Thinking out loud here...Is it possible the ground lift plug on the amps is masking something and lifting pin 1 at the snake (with the 260 in the loop) will fix it?
  • GadgetGadget Posts: 4,915
    Man... there's a LOT going on here...and yes as Dennis say's it's all relevant...I'm confused here...The amps are UNGROUNDED? I don't like that at all...

    Ok so what happens with just the amps hooked up to the speakers and properly grounded? Do you have this terrible humm? Then if you eliminate EVERYTHING other than the driverack and the short cables do you have the problem? Trouble shooting is a tough thing unless you start at the beginning with a known good and work from there...I like to \"divide and conquer\" as well... in this case I would consider that removing the snake and seeing what gives...then one cable at a time...If as Dra says the problem is on only one channel that needs to be considered.

    Gadget..chief DRUG guy...
  • DraDra Posts: 3,844
    Just curious. Why did you buy a TRS return snake? If you are at all handy, I'd recommend replacing the channels going to the DR260's outputs with XLR.

    DRA
  • DennisDennis Posts: 801
    I'm with Dra on the snake. 1/4\" connectors were probably cutting edge technology during WW II.

    Dennis
  • wrgflyfishwrgflyfish Posts: 9
    >>> Does it buzz on both inputs and all outputs?

    I've only tried both inputs and channel 1 & 2 outputs all at the same time. I'll do more testing tonight.


    >>> The amps are UNGROUNDED? I don't like that at all...

    I don't either but I had a ground loop hum with them grounded. I'm planning on a humx (or equivalent) but haven't gotten it yet.



    >>> Ok so what happens with just the amps hooked up to the speakers and properly grounded? Do you have this terrible humm?

    I'm even getting confused looking at my notes but...if I interpret what I wrote down correctly..if the snake is NOT connected to the amps and they are grounded I get NO hum (which should eliminate the amps and speakers as suspects). My notes indicate the hum signal was coming from the snake and ungrounding the amps fixed it; lifting pin 1 on the snake return didn't (which implicates either the snake or the board).


    >>> Then if you eliminate EVERYTHING other than the driverack and the short cables do you have the problem?

    No problem when I eliminate EVERYTHING else but I'll confirm my previous statements about the grounded amps tonight.



    >>> Trouble shooting is a tough thing unless you start at the beginning with a known good and work from there...I like to \"divide and conquer\" as well... in this case I would consider that removing the snake and seeing what gives...then one cable at a time...If as Dra says the problem is on only one channel that needs to be considered.

    As I read my notes trying to answer these questions I see that at one point I had a slight buzz in the monitors and I'm not currently using the 260 for those. I think I need to open up the snake and check some things. I think I'll work on just 1 channel at a time too.



    >>> Just curious. Why did you buy a TRS return snake? If you are at all handy, I'd recommend replacing the channels going to the DR260's outputs with XLR.

    Because that's what we had before we built our building. :-) Probably not a bad idea. I'll have to schedule that around everyone using it. This is a church set up and it is used frequently during the week. Using the adapter shouldn't be a problem though, should it? It seems to work fine when the 260 isn't in the loop.


    The 260 is FOH and the amps are on stage. Can I test the 260 by taking the 260 to the amp and plugging a mic directly into the input and the 260 directly into the amp? (Of course turn down the amps first to make sure the signal isn't too hot since it is an untested configuration.)
  • DraDra Posts: 3,844
    [quote="wrgflyfish
    Can I test the 260 by taking the 260 to the amp and plugging a mic directly into the input and the 260 directly into the amp? [/quote]

    I hope you meant a mic cable. :shock:

    DRA
  • GadgetGadget Posts: 4,915
    I doubt if there is enough output from the mic to get a good test but it wouldn't hurt anything to try...

    Is the phantom power on the mixer on by any chance?

    Adapters are a recipe for failure...

    You have a ground loop somewhere...you say with the system all hooked up and NO driverack (everything normally grounded and hooked up ) you have NO buzz... (monitor system disconnected) what about WITH the monitors connected...

    Then with the driverack without the monitors....
    and with the driverack AND the monitors...(by monitors I mean disconnecting the monitor feed at the board AND other end of the snake as well...totally eliminated...

    Are you running your power to the mixer back along the snake and from the amps rack? Or how are you doing it? You said it was on the same feed... explain please...

    Have you used a tester to determine if the wall outlet power is done properly?

    So many questions...

    G
  • wrgflyfishwrgflyfish Posts: 9
    I only had 90 minutes to work on the problem but made good progress.

    It happens with all inputs and all outputs.

    It happens with 1 and only 1 channel.

    The BAD hum did NOT happen when I removed the ground lift plug on the amps. Don't know why we thought we needed that now but I know when we did it that it solved a problem we were having then.

    The good news is that when I took the 260 to the stage I didn't have any problems whether I used a stage power source or an extension cord from the FOH.

    I think that that isolates the problem to the snake. I have more evidence for the snake causing a problem because it seems like I might have short in one of the channels (getting a monitor signal someplace it shouldn't be).

    I wish I could say it was fixed but at least I have a better idea where to look.

    Thanks!
  • kpippenkpippen Posts: 551
    wrgflyfish wrote:
    The good news is that when I took the 260 to the stage I didn't have any problems whether I used a stage power source or an extension cord from the FOH.

    The ground loop is most likely coming from using two different 120VAC circuits that have a difference in ground potential. When using the stage outlet or extension cord you are most likely either putting the 260 on the same circuit as your amps (same potential), or you might be making the grounding conductor on two different circuits the same length which makes the potential the same. To verify if your hum (60Hz) is coming from using two different AC sources try one of those two-to-three prong AC adapters on your 260. If the hum is eliminated then you may want to get a couple of these http://www.ebtechaudio.com/humxdes.html

    Kev
  • kpippenkpippen Posts: 551
    I did it again...:roll: This post is almost a year old...:lol::lol::lol::lol::lol::lol::lol:
  • GadgetGadget Posts: 4,915
    I know I know... you and the dog right... :mrgreen:
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