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A few problems with amp/cabs and noise...

Discussion in 'Amps and Cabs [BG]' started by Westy, Jun 30, 2005.


  1. Westy

    Westy

    Jun 9, 2005
    Ireland
    I have recently built some custom cabs with the help of a friend who knows a bit about the science behind the sound.

    Basically, I've now two rather large cabs for a Boogie Walkabout head I have, but the other night during a gig I was pushing the amp pretty hard and I was getting a bit of a distorted noise. I wasn't sure if this is due to the amp (valves might need replaced, but not sure how to know this, one does seem to be glowing more than the other, I assume this is not normal, and ideas, as valves are new to me), or maybe some of the joints in the cabs aren't the best, any ideas on how I can be sure?

    Also (long winded for a first post I know!!), but when I plug into the DI from the amp, I sometimes get a buzz that carries through the whole PA system. Sometimes this doesn't happen and sometimes it does, deoending on the venue. Initially I thought it was the earth in my bass, but I've earthed it and also put some foil over the back of the backplate to try and reduce anything getting in, but sometimes the noises are still there, I think I pick up a lot of lights and stuff.

    I play a Warwick Corvette Standard Fretless bass if that's of any use to you.

    Hope someone can help. I'll give all the info I can if you need more.

    Cheers
     
  2. DaveMcLain

    DaveMcLain

    Jun 19, 2005
    Cuba MO
    It sounds like you have a ground loop setup between your bass amp and the mixer board/pa to me. Try using a direct box with a ground lift connection and see if that cures your hum problem. What happens is that the ground connection on the stage where your amp is plugged in has a slightly different potential than the ground where they have the mixer plugged in. Your amp chassis, the shield of the cable, the direct box, the snake cable shielding, the case of the mixer all conduct current under these conditions causing the hum. If you break the connection anywhere along this path the hum stops because current is no longer flowing and thus inducing a signal(hum) into your signal. Depending on where you break the ground circuit you will have different levels of sucess, try it at your direct box connection first..
     
  3. Westy

    Westy

    Jun 9, 2005
    Ireland
    Cheers Dave.

    There is a DI built into the Amp, but I will try using an external box to see if that helps.

    I'll let oyu know.

    Cheers again
     
  4. DaveMcLain

    DaveMcLain

    Jun 19, 2005
    Cuba MO
    That's what I would try first and then you might try making up an XLR cable with the ground lifted that you only use for your amp connection at gigs where you have a problem.
     
  5. Westy

    Westy

    Jun 9, 2005
    Ireland
    The only thing is, that I still get this buzz through the amp and bass on it's own, even without DI-ing, so I think there might be something wrong with the guitar itself, although this is acceptable when I'm not going through the PA.

    But I'll take all suggestions on board and give them a lash.
     
  6. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Distorted sound from speakers can be from an air leak. The noise from even a 1/4" jack is surprisingly loud. Any leak on the front side, around a speaker, for instance is even louder.

    Doesn't matter if the cab is vented, there is still pressure in it at low frequencies.

    The walkabout has preamp tubes, and yes they may not glow equally, not necessarily a problem.

    For buzzes, I agree, a DI.

    Not all built-in DIs are good DIs, although I thought the Boogie ones were decent transformer isolated ones, which should avoid a buzz. Maybe the problem is in the PA, or the cables.
     
  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You'll get noise direct from the pickups if the electricity in the club is messed up with bad grounds, refrigeration equipment, dimmers, flourescent lights. If the noise goes away when you turn off the volume control on the bass it's RFI and EMI that you can't do anything about.
     
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Except humbucking pickups, shielding the control cavity, making sure the pickup wiring is shielded and connections are good, etc, etc, etc. I would assume the Warwick would have that done already, but......

    Sometimes, though, if its bad enough, nothing seems to work.