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Help solving my noise issue: bass guitar into a TRS snake into my amp

Discussion in 'Live Sound [BG]' started by johnbegone, Mar 27, 2013.


  1. johnbegone

    johnbegone Supporting Member

    Sep 16, 2004
    Chicago, IL
    Looking to the community to help solve an issue I've been having with my new live setup.

    Here's the deal, my amp sits in a rack in our backline. Also in this rack are two vocal processors. Instead of running 5 cables (4 XLR for send/return from the vocal processors + one 1/4" for my bass input from my pedalboard) I bought a Hosa 6x2 snake. 6 XLR and 2 1/4". I changed the gender of two of the XLR's to use as returns, and I have a patchbay in my rack for the gender correction on that end. We drop the snake box up at the front of the stage and then run the single snake back to the rack.

    All is fine with the XLR's, everything works and sounds great, no complaints from sound guys or anything.

    Again, I want to be able to plug my 1/4" bass line (from the pedalboard) into the snake box and run it to the amp rack in the same way. It works, but it's noisy. The 1/4" returns on the snake are both TRS. It's only a 30FT snake so it doesn't seem like I should be having this much noise. I bought a 1/4" "hum debugger" device that's supposed to help isolate the grounds so I don't get 60 cycle hum and help in the transition from TS to TRS -but to no avail. It's like a high hissing sound.

    Can't get rid of it. No idea. This would help me greatly in not having to run another cable back to the rack every night (we are a touring rock band and we take our quickness of setup/teardown very seriously so we don't hold up the show).

    Any ideas on making this work? Would love for this solution to work but I'm pretty much out of ideas. Thanks in advance!
     
  2. TimmyP

    TimmyP

    Nov 4, 2003
    Indianapolis, IN
    Sounds like you are running an instrument level signal into a line level input. I'd expect that to be noisy. Change the TRS to XLR and get a passive DI to take the pedalboard out to a mic in.
     
  3. Hi.

    Just short the R&S.
    Especially active basses and jacks that use R&S as a switch don't like TRS plugs one bit.

    Regards
    Sam
     
  4. johnbegone

    johnbegone Supporting Member

    Sep 16, 2004
    Chicago, IL
    TimmyP - I'm still going into the instrument input on my amp, so it's not that I don't think.

    T-Bird, that's kind of what I'm thinking. Would I need to do this on both sides of the snake or just one? I can easily open up the box and the male cable on the other end and short both sides, or couldn't I just build a shorted adapter to test the theory first?

    Really appreciate the advice, thanks guys.
     
  5. funnyfingers

    funnyfingers

    Nov 27, 2005
    I may be way off, but will just pose a question. Does a TRS cable shield if used with a mono input? Have you tried a standard (TS) shielded 1/4" cable?
     
  6. Marley's Ghost

    Marley's Ghost Gold Supporting Member

    Feb 9, 2002
    Tampa, FL
    ^^^^ this.
     
  7. Hi.

    For a short run like that it shouldn't matter either way even though the live (T) wire may pick up some interference that the shield picks up and carries on the S wire, but do test it with an adapter first. Making two isn't that much of a task.

    I personally would replace the TRS plugs with TS plugs in order to avoid any confusion.

    BTW, I run TRS cables with my passive basses all the time and without any problems what so ever. I go straight from a TS jack of the bass to the TS jack of the amp though, no effects or pedalboards in between.
    SVTDI doesn't mind a TRS cable either.

    Regards
    Sam
     
  8. johnbegone

    johnbegone Supporting Member

    Sep 16, 2004
    Chicago, IL
    Yeah I'll build an adapter first with RS shorted.

    I have no issues running a regular TRS cable either, it's just once it goes through the snake that I have noise.... so maybe the TRS isn't the issue after all. I thought maybe something was shorted inside the snake but it's brand new and the XLR lines are all clean. I guess I could go to a DI on my pedalboard and use some type of transformer to bring the level back up to intsrument level on my amp side, but that sounds like a recipe for disasters (not to mention more points of failure on any given night)....
     
  9. Plugging a TS connector into a TRS jack will automatically short the RS, provided you're doing the same thing at both ends, it should all be good. I would check the 1/4" jacks in the snake and see if it was accidentally wired out of polarity. Wouldn't be the first time I've seen it happen with a new Hosa, Rapco, etc.
     
  10. johnbegone

    johnbegone Supporting Member

    Sep 16, 2004
    Chicago, IL
    Good point, thanks. I am using a short TS cable to go into the snake, but as of right now it's still going into the amp as a TRS off of the male end of the snake. If all I have to do is short that end of the cable (or just flip it out for a regular TS) then that seems like the best case scenario. Super easy for me to test that with a 1/4" TS extension cable I have as well.
     
  11. Yep, depending on the amp, if it "feels" a TRS in its input, it may expect a balanced signal. Whack off the TRS and solder on a TS.
     
  12. funnyfingers

    funnyfingers

    Nov 27, 2005
    My point in saying use a shielded TS was because the TRS might not be providing shielding, like the XLR line would.
     
  13. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    The only difference between TRS and XLR cables is the plug on the end. Those terms tell you NOTHING about the cable between the plugs, other than it is three wires.
     
  14. Hi.

    That's very strange, in that case I'd say it's not a TRS related problem.



    Nope, ther's no way of knowing how the ring is connected in the jack, or if it's connected at all.
    Or if it is connected, what its function is.

    Possible, even though I have never witnessed such a mistake. But, I have for the most part rolled my own ever since I started all those years ago ;).

    In that case it'd be the first one I've encountered in these 20+ years I've been in the hobby/business.

    All small signal audio cables are shielded by default.
    Clueless DIY ones excluded of course :).

    Regards
    Sam
     
  15. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    Sorry in advance if someone's already suggested this, but I'd attack this by incrementally shortening the BG signal path, checking for hiss after each change you make.

    Lower the amp volume temporarily before you make each change, and then return it to where it was. But you already knew that . . . ;-)

    Your baseline (sorry) will be amp on, up at normal volume, everything connected as usual, instrument cable plugged into the snake, but instrument cable NOT plugged into your BG. The plug for your BG should just hang in free air. That'll be the worst-case condition.

    Next, pull the instrument cable out of the snake head.

    Next, pull the snake cable running to your amp out of your amp.

    Next, and one by one, shut off the other devices in the same rack.

    One of those steps should drop your noise significantly.

    More of a shotgun/intuitive approach, versus orderly/logical: You can also try shutting off the vocal processors while your BG run is intact but with the plug for your BG hanging in free air (3rd paragraph above).

    If the vocal processors use digital technology, it's possible the clocks are leaking into the snake. In other words, the snake conductors -- all of them as an aggregate -- could be acting as a broadcast antenna for leaking clock noise. The balanced cables won't care because the noise is injected into both (+) and (-) conductors, so there's no difference in potential created between them, so there's no voltage created on the lines that use those runs. (Common-mode rejection.) But a single-ended run *is* susceptible to clock leak because clock noise injection will create a difference in potential between the center conductor and the shield, thus creating a signal source that your amp will amplify.

    The double-whammy is that this -- being a run between BG and bass amp input -- is probably at least 10x the impedance of your typical single-ended line feed, which is typically around 10 Kohms. A given noise level injected into a high-impedance run will generate far more noise than one injected into an impedance that's only a tenth of it, and its treble content will be greater, too, because it will be preserved (or, left unattenuated) by the higher impedance.

    Also, don't forget a high-impedance, single-ended run that long is going to act as a receiving antenna for pretty much anything in the immediate vicinity. Light dimmers. Other people's effects boxes. Cell phones. Laptops. Ipads. On and on . . .
     
  16. Bingo. If you have a shielding problem, or ground loop issues, you get hum, not hiss.

    Hiss results from poor signal/noise ratio. Either you're sending little signals into an input that expects big signals (as TimmyP suggests) or your gain stages at the amp are all wrong and you are sending the PA a signal that's already loaded with hiss. Maybe you just can't hear the hiss from your amp because you don't have a cab with tweeters, so it's being muffled by your cabinet.

    You should have a clip light on your amp input, and the gain should be set high enough that it flickers once in a while. If you have that initial gain way down, or the volume on the bass way down (especially if you have a preamp on your bass), and the master volume on the amp set very high to compensate, you're going to get a lot of hiss. Reverse that, turn up the input volume as high as you can without the input clip light flashing a lot, then bring up the master volume to get the levels you want.

    Randy
     

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