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How can I prevent this from happening again.....

Discussion in 'Amps and Cabs [BG]' started by g4string, Apr 28, 2003.


  1. g4string

    g4string Supporting Member

    Sep 19, 2002
    Melissa, TX
    I played my gig on Saturday at a place I have played about five or six times prior. I set up my amp, turned it on, and this horrible hum/crackle potruded from my speaker cabs. I am using a Demeter HBP-1, QSC PLX-1602 (bridged @ 4 ohms), 2ea Aggie GS112's, and a Lakland 55-94.

    I do not know what could make my amp hum/crackle so bad. I set my preamp volume at full open and adjust my master volume through my power amp. All of my cables are good. There were no neon signs lit. Out of the five or six times I have played there, this has only happened to me once.

    The funny thing is that we rehearsed for four hours prior to the gig and no weird sounds. I get to the gig and all this noise. After the gig I try my amp at home and no buzz. Help me! What was going on and how can I prevent this.
     
  2. Thor

    Thor Moderator Staff Member Gold Supporting Member

    It is very difficult to rectify electrical or electronic problems that are not reproducible.

    Because the equipment checked out elswhere as ok
    ( with the same rig, right? ) there are 2 areas I would suspect.

    AC power supply from wall.
    Were you or the band using more power
    than at the rehearsal. Lights, board, etc, that might have been plugged into the same outlets
    leading to a voltage drop.

    Were there other appliances turned on in the venue
    that may have added voltage spikes or 60 HZ hum
    to the line. Line filters are available, but usually not needed. Ice machine, radio in the kitchen, walkie talkie transmission.

    I would be looking at the power available to you at the venue at this point as the potential culprit.
    ----------
    There was one venue we used to get a spanish language radio station who had a transmitter nearby
    - bummer

    :mad:
     
  3. g4string

    g4string Supporting Member

    Sep 19, 2002
    Melissa, TX
    I was suspecting power. But know one else had this problem. All of our amps were plugged into the strip. I even went as far as to set my bass up seperately in another corner of the bar pulgged into a seperate power source. I still had noise. Do you think that it is time that I broke down and bought a power filter/conditioner. They are quite expensive, around a couple hundred bucks.
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I don't think a power conditioner is the answer. I'd certainly look at one of it had been buzzing at the rehearsal as well, but if it didn't start till later in the day........... hang on

    Lights. Chances are you rehearsed during the day without lights and without noise. The lights come on after dark and suddenly you're buzzing........ coincidence?
     
  5. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    What the hum/crackle louder when you had the preamp volume up full than when you had it turned down?
     
  6. g4string

    g4string Supporting Member

    Sep 19, 2002
    Melissa, TX
    Pete,

    Good idea about the lights, but that does not explain why it has never happened when I have played there before.



    Bob,

    Yes, with the preamp volume louder the noise would get louder. I tried everything. I hooked up the amp in bridged mono, mono, stereo. It did not matter.
     
  7. Did you dis-connect the pre-amp completely leaving the power amp on through the speakers. If so did the noise go away or stay?
    If the noise stayed, then it probably is in the power-amp. If it went away then it probably is in the pre-amp or cable between pre-amp/power-amp.
    Did you try plugging the bass directly into the amp and by-passing the pre-amp all together?
    If you get a clean sound then the problem is definately in the pre-amp or cable between pre-amp/power. If the noise is still there then problem is problably in the power-amp or cable between bass and power-amp.
    Did you try coming out of the pre-amp into another power-amp of some type?
    If you get a clean sound than the problem is definaltely in the power-amp or cable between pre-amp/power-amp.

    Problem is that when the sh!t happens it is at a time when it is hard to be mithodical and structured about your testing proceedure. If you're anything like me, you were probably plugging and unplugging everything you could get your hands on. Try and isolate each link in the chain starting with the Bass guitar it's self. The electronics themself craped out in my Lakland 5502. Just the other night it started making this thumping sound with no tone. I had to take the battery out and put it back in to get it to work properly. Work your way to the speakers from the guitar to the cable to the pre-amp to the cable between pre-amp/ power-amp then the power-amp and speaker cable. I'll bet it was a cable.

    If this happens again (Let's hope not) try these proceedures to isolate the each link in the chain and identify the problem. Good luck!
     
  8. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    Even if the room had been fine before, it could still be the power. Maybe they rewired something, maybe they installed some new appliances, etc.

    I had that exact problem where one gig in a room I play often resulting in much amp weirdness (distortion, low output) and the next gig there all was fine.
     
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    That would certainly indicate that the noise is getting into your system either in the preamp or before it--i.e., in the bass or instrument cable. That would also explain why doing different things with the power amp didn't affect it.

    Did the intensity or tone of the noise change when you changed the position of the bass? For example, you face the bass one way and you get more or less noise than when you face it in another direction? If so, that would indicate that your pickups are picking up the noise and it would explain why you had the noise in one location and not another.
     
  10. g4string

    g4string Supporting Member

    Sep 19, 2002
    Melissa, TX
    Yes, the intensity changed (got louder) if I faced the amp. The funny thing is that when the **** hits the fan, it hits the fan when you should have already started playing. If the power at the club, was at fault, do you guys think a power conditioner/filter would prevent this. I do not think that it is my rig, cables, or bass. The reason why is because when I got home I gave my rig a test run and had no problems at home. And not to mention that I rehearsed at my house prior to the gig and had no problems.


    Greybeard,

    I agree that it is difficult to troubleshoot when your under the wire. But you had a lot of good ideas. Hopefully this does not happen again. But if it does, I will use some your pointers.
     
  11. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    That would seem to indicate that your pickups were picking up the noise. A power conditioner will not make your pickups quieter and it won't do anything for a power amp, but it might help the preamp if it doesn't already have good rejection of power line noise designed into it.

    Did the place have a lot of fluorescent lighting?
     
  12. g4string

    g4string Supporting Member

    Sep 19, 2002
    Melissa, TX
    Do not know about flouresect lights. I do know that the neon lights were off and unplugged.
     
  13. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I've got an old Ibanez Bass that I don't use much any more bacause it does exactly this. What's the fix? New pickups? Maybe some shielding?
     
  14. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Hi Pete,

    Shielding will help against electrostatic noise but it won't help against magnetic hum and noise fields unless you use a highly permeable metal like iron, steel, mu metal, or nickel.

    The hum that varies when you change the orientation of the instrument is of magnetic origin, and it's picked up by the pickups. This is usually a characteristic of single-coil pups. Humbuckers will help. Also, many basses use two single-coil pups, but one has its polepieces and coil winding direction reversed, so that together they cancel far-field hum if you set both pickups to the same volume.

    Shielding is still worthwhile to do, though, and it's really easy if you use conductive paint.
     
  15. It has been my experience that PU noise is usually a directional thing. Meaning you can turn a certain way or move to a different location and the noise will change. Did it? I also had an Ibanez SR805 that had really noisy PUPS. I had the cavity re-shielded with copper tape. Didn't change a thing.
     
  16. jad

    jad

    Aug 29, 2002
    Pittsburgh, PA
    I'll be looking at a MIM Jazz tomorrow night and might be in the market for shielding material by Friday morning! Is conductive paint available at, say, Home Depot? Is there a particular brand name that anyone can suggest?