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Help With A Strange Cab Distortion Issue

Discussion in 'Amps and Cabs [BG]' started by Bryan R. Tyler, Sep 14, 2005.


  1. Bryan R. Tyler

    Bryan R. Tyler TalkBass: Usurping My Practice Time Since 2002 Staff Member Administrator Gold Supporting Member

    May 3, 2002
    Connecticut
    Okay, so I normally have my setup hooked up this way: Sansamp RBI into QSC PLX1602, whch is set with Bridged Mono off and Parallel Inputs on. From there it has one channel going to my Avatar 112 and the other going to my Avatar 410.

    I've been playing with volume only turned on on my 1x12 for a while now. I'd occasionally turn the volume up on the 4x10 and play through both, but I haven't tried that in a while. Today I tried it, and the 4x10 is completely distorting. The Clip light is coming on when playing with the QSC put at only two notches of volume turned on. I don't think I've changed anything at all on my setup, but something's definitely wrong now. Why would it distort and clip at such low volume?

    Any ideas? Thanks.
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Did you recheck the little dip switches on the back to make sure that you're still in the stereo mode with parallel inputs?

    Does changing the state of the limiter switches make any difference? How about the filters?

    How about if you swap the cabinets (run the 410 off of channel 1 and the 1x12 from Channel 2)?

    Are both speaker cables wired to 1+ and 1-? (btw, they should be).

    Did you PM Bob Lee (QSC)?

    Good luck! Please keep us posted.
     
  3. Bryan R. Tyler

    Bryan R. Tyler TalkBass: Usurping My Practice Time Since 2002 Staff Member Administrator Gold Supporting Member

    May 3, 2002
    Connecticut
    I've done most of that, but I'll double check everything a little later when my daughter takes a nap. I'll let you know if anything changes.
     
  4. Dkerwood

    Dkerwood

    Aug 5, 2005
    Midwest
    Very interesting. If your amp is clipping, you know that at least it's not in the speaker ... yet...

    If your QSC is like mine, you'd have to plug two inputs in if you aren't running in bridged mono. So do you have two inputs coming off of your preamp? If not, I have no clue what could be causing the distortion. If you do, maybe the problem lies in your preamp... sounds like the signal going to the channel that's driving your 4x10 is too hot.

    Follow BillyB's advice first. Here's a step by step to pinpoint the problem's source.

    1. Plug in the 410 with the 112's cord and vise versa. The problem should switch to the 112. If not, the problem is in the 410 cab.

    2. Go to the amp. Swap channel 1 and 2 out. The problem should now be back in the 410. If not, the problem is in the speaker cable.

    3. Now swap your inputs 1 and 2 on the amp. The issue should now be in the 112. If not, then the problem is in the QSC.

    4. Finally swap the outputs 1 and 2 on your preamp. If the issue was switched back to the 410, the problem is in your preamp. If the problem is still in the 112, then the problem is in your cable running to the QSC.

    If you have any other stereo components, you'll have to check those. Just remember to check every cable. I can't tell you how many times I've cussed out my amp, my mixer, my microphones, my axe........ just because I had a bad cable.
     
  5. Bryan R. Tyler

    Bryan R. Tyler TalkBass: Usurping My Practice Time Since 2002 Staff Member Administrator Gold Supporting Member

    May 3, 2002
    Connecticut
    Okay, it looks like I figured out the issue, but it's a bit odd.

    The Avatar B410 has two 1/4" inputs. One of them causes the distortion (it didn't use to) and other works fine. They're supposed to be wired in the exact same way. Any idea why it would distort or make the clip light come on on my poweramp?

    At least I can use the cab without worries again.
     
  6. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    my guess is a short that's presenting the amp with a very very very low impedance.
     
  7. Dkerwood

    Dkerwood

    Aug 5, 2005
    Midwest
    Ahhhh! I wouldn't have thought of that...

    But does that explain the clip light on the amp itself??
     
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    It would probably be a good idea to pop the input cup out of the Avatar and take a look for debris that could cause an intermittant/partial short.

    Here's a picture of the backside of a non-Speakon equipped Avatar crossover/input cup...not much to go wrong...