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How to find a noise that only shows at gigs?

Discussion in 'Amps and Cabs [BG]' started by nsmar4211, Apr 5, 2009.


  1. nsmar4211

    nsmar4211

    Nov 11, 2007
    Many months ago I posted about a humming noise coming from my amp here:
    http://www.talkbass.com/forum/showthread.php?t=479692

    Well, since then most of our gigs have been outdoors so noise hasn't been an issue, not to mention this has never happened at home!

    The last gig the noise was there, but it was within toleraable levels-and I was standing about 10 feet from my amp. But tonights gig, well :ninja:. It was so bad that I ended up turning my amp volume *off* and just running through PA.

    Suituation:
    I'm running an Ampeg B2R head, rack mounted along with a power conditioner, into an Ampeg 410 cabinet. We then take a line out to the board and also run me through the PA (Yorkville tops and subs). I use my amp as a monitor basically.

    The noise is exactly like a 60 cycle hum. There's also a hiss/static noise, but that's been there as long as I can remember. This hum is *horrible*. It varied in intensity. One thing that it seemed to depend on was on how high I put the treble on the bass itself (high treble=worse hum). We tried adjusting gain versus master, the higher my volume the louder and more intense the noise. Now,the noise did come and go, it was not a constant noise. It varied depending on where I was standing, which way I was facing, etc. It also would build in intensity, and then if I moved a touch it'd change how loud. (pitch of it stayed the same). For the show I was about 4 feet from amp, when I was walking around trying to find a noiseless spot I got as far as 10 feet with no steady luck.

    The fun part about this is it has thus far never done the noise at home!! I've tried and tried to replicate it and no go....

    After the show, the guitar player and I tried out a few things to see if we could find the source. We turned off the PA equipment (two tops, two subs, one monitor, and the mixer) one piece at a time with absolutely no effect. Once we were down to just my amp on, we physically unplugged everything in the line, until it was just my amp plugged in. Noise was still there. We switched cables out, three different ones. Mine are custom so just in case we put his planet waves one in -the noise doubled in intensity! I had just changed the basses' battery, wasn't that. I went out and grabbed my backup bass, thinking it was the bass. My main bass is an active Ibanez Soundgear, the backup is a passive Peavey. With the passive bass, as long as the treble was down I could turn the amp up to stage volume, the noise only showed at top level. However, turn up the treble and OW. We then tried plugging an acoustic guitar into the head, there was no noise at all. We check ground (we carry a ground tester), and ground was fine. Power conditioner showed at 116-120 the whole time.


    What would make a head/cabinet do an intermittant 60 cycle hum noise like this? How can I find which part is the culprit if it only does it at gigs? I do have the subwoofers here and was toying of running through them instead of the cabinet until I remember it doesn't do the noise at home :(.

    And if somehow *both* my basses are shielded poorly, how on earth do you check shielding?:bawl:
     
  2. The fact that the acoustic guitar didn't make any noise through your rig, and that you can "control" the noise with your onboard eq is a sign that the noise is coming from/through your basses...right?
     
  3. So, you've potentially isolated the noise to the bass (basses?) itself, and not the amp? Here's some more things to try:

    Replicate the live setting (volumes up, your bass making the noise) and:
    Try another bass - one with humbuckers would be preferable.
    Play your current bass through another rig at live volume and listen for noise.
    Try touching your bridge, strings, etc and letting go and see if that changes the noise.

    Really try to replicate this at home - if you can't, then it will be tough to solve.

    Also, check your speaker cable - maybe try a different one. (you're not using an instrument cable for your cab by mistake, right?)
    If all else fails, you might want to look into a Rocktron Hush noise reduction system. They really quiet down noises like that - but take away some of the upper shimmer in the process.
     
  4. Stumbo

    Stumbo Wherever you go, there you are. Supporting Member Commercial User

    Feb 11, 2008
    Intergalactic Mind Space CA
    Song Surgeon slow downer software- full 4 hour demo
    Play your basses through another rig to check them out.
    What if you plug the basses directly into the PA?
     
  5. MIJ-VI

    MIJ-VI Banned Supporting Member

    Jan 12, 2009
    Hi nsmar4211.

    Man this is perplexing!

    Have you tried your basses through your guitar player's rig at a gig to hear if they still make the same noise as they do through your amp?

    Have you tried temporarily removing your Ampeg from its rack (there may be a ground loop) to hear if the noise is still there?

    If so, have you tried plugging it into a power source which is different from the one that you usually use?

    Does your amp still make the noise when there's no cable plugged into its input?

    Have you taken your basses to a music store and tried them through one (or more) of the store's amps?

    I'm assuming that the acoustic guitar you tried through your amp has a piezo pickup? If so, then it wouldn't pick up the Electro Magnetic Interference which seems to be afflicting your basses (likely induced by the gig's neon signs & dimmer packs etc).

    You can check your basses for excessive noise pick up at home by waving them around near a powered up computer monitor or TV, or a dimmer pack (which is turned down a bit), or a florescent light while they are plugged into your amp turned up to stage volume.

    Have you considered taking your favorite bass to a good tech for a thorough shielding job?

    If the instrument is one that you'll likely keep, then doing so will be money well invested.
     
  6. nsmar4211

    nsmar4211

    Nov 11, 2007
    Wow, you guys bring up some good points and are awesome :).
    This is driving me nuts :( and upsetting.

    I work with copiers are work and know just about how impossible it is to fix a problem you can't replicate :(.

    Stumbo and ashtray:
    I'm pretty sure Speaker cable isn't the culprit.... after the last gig I went out and bought ALL new cables for everything! It was a different cable than last time...and I made sure I labeled the speaker cable as such so no mixups. Plus we've used that exact cable on the PA with no issues.

    I have played the active bass live at stage volume through other rigs with no problems before, as recently as a month ago at a jam. And at the jam I was directly in front of the amp-ok I was leaning on the amp because there was no room. I also played through a friends rig on New Years and not a peep out of my bass no matter where I walked. That's why I didn't think it was my basses fault.

    As for plugging right into the PA, we didn't try that at this gig. Guitarist says we did at last gig, I *swear* we didn't so not sure there.

    MIJ-
    The hum is gone when I unplug the bass from the input (the hiss is a nother story LOL). I don't dare plug a cable in without an instrument attached. I had tried spraying the input jack with contact cleaner, no effect.

    Last gig we blamed the lights, this gig was at a country club and there were no flourescents to blame...or neons or anything :(. The noise does come through the PA so its in the output......

    I didn't think about it, but yes the acoustic was a piezo pickup. Shoots that in the foot :(.

    On the active bass, if I up against my laptop it does hum-but it's a different hum than this is, never gets intense, different pitch, etc. It'll also pick up my nextel phone tickticktcik when a call comes in, but every speaker in the house does that! I don't play the passive much so I don't remember if it does that.

    "Have you tried your basses through your guitar player's rig "
    Well, the guitars go direct into the PA, so how would I go about doing that?? The lead guitarist uses a pedal board between his acoustic and the PA, but he has noise suppression on that so that prob. wouldnt help...

    "Have you tried temporarily removing your Ampeg from its rack (there may be a ground loop) to hear if the noise is still there?"
    Nooooooo that I have not. As I was going to sleep last night I was wondering if the power conditioner just didn't like any other power source besides my house.... That's a really good idea. I used to use the head not in the rack, but it's really awkward to pack that way...

    "If so, have you tried plugging it into a power source which is different from the one that you usually use?" Well, it doesn't do it at home, only at gigs, and not at every gig. I am using the same extension cords in the same order, I made SURE I was because I figured since it'd been quiet at home problem was fixed.

    As for having my bass super shielded, I don't have a local bass tech..... the guy my teacher uses can take *weeks* to get things back because he's so good he's swamped.I'm going to call and see if anyone knows another tech though. But Is this something I can do myself? (I'm thinking sticky backed foil or something to line control cavity with?)

    So tonight after work I'm going to drag everything out. I keep the subs here, I'm going to plop them on either side of my amp and plug em in.... try and replicate gig situation and any interference sources. Volume wise, my volume at practice is pretty close to my volume on stage so that's easy (cause the amp is a monitor and either way I hafta get over the drummer).
    I'll see if I can make it do it at the house......am hoping so! Well, kinda :bawl: If I can, it's a whole new ballgame :).
     
  7. wildhorse

    wildhorse

    Mar 15, 2009
    Every piece of equipment that is in your rack that is connected in anyway to another piece of equipment with any type of cable, guitar cable etc and if they are all plugged into your power conditioner should have a 3 prong to 2 prong adapter hooked up to it. Only one piece of equipment should be grounded with the 3 prong plug, preferably your amp head.
    The reason is that with the connection cables each one is grounded by the other and if they are all plugged in with the 3 prong chord it creates a ground loop thus a 60 cycle hum.

    Also if you are plugging into your pa with the direct out then you are grounded to the pa and perhaps you can resolve your issue just by placing a 3 prong to 2 prong adapter at the end of the conditioners cable. But you said you unplugged everything but your rack so it sounds like the ground loop is in your rack. Some direct outs have a reverse polarity ground switch. Trying to duplicate the problem at home may be a waste of time if you don't have the same p.a. hooked up.

    Ground loops can be a pain to find but those little adapters work wonders. Happy Hunting
     
  8. FFTT

    FFTT

    Mar 15, 2009
    You may want to consider investing in an isolation transformer for use
    in some locations with less than ideal power. Or a good quality voltage limiting
    UPS for your gear.

    My old band always used a volt meter to check the line voltage before we started setting up.

    Some old buildings were barely holding 110 while in some locations you my get between 124-127 volts.

    It also helps to keep one of those wall switch plug in checkers to make sure
    the outlet is properly wired and grounded.
     
  9. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    You may be standing too close to your amp. If your bass is positioned near to your amp (or any other for that matter) your bass will pick up hum from the magnetic field of the power transformer. Even humbuckers will do this. If the noise does not happen at home it may not be a grounding issue.

    Experiment: Take everything out of the rack and place on the ground separately. Connect everything up. Is it humming? This will tell you if it is a ground loop. It could also be induction from one unit to another.

    Paul
     
  10. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    The most likely culprit is the bass itself. Borrow another with humbucking pickups to test.
     
  11. BillyRay

    BillyRay Supporting Member

    Jan 20, 2008
    Quebec
    Any large electrical appliances connected to the same circuit ? Is the problem solely at this venue ? I'm just grasping at straws here, but I've heard fridges that make noise through amps. Dimmers also (no need for fluorescent). I have a dimmer in kitchen that hums *loudly* by itself. If I present it with a bass plugged into an amp, I pick that hiss right away and it does get louder if I don't roll the tone off.

    Make sure all your rack stuff is properly grounded too.
     
  12. Howlin' Hanson

    Howlin' Hanson Lighter cabs, please. Supporting Member

    Sep 3, 2007
    Austin TX
    I think BillyRay may be onto something here. We once played in a school cafeteria that had flourescent lights (and the ballasts associated with them) and my Jazz hummed like a choir that had forgotten the words.

    I had to stand sideways to the audience to minimize the hum, and stood stiller than Entwistle. (Didn't play like him, though. :( )
     
  13. Does this only happen at that one venue? I have a place here in town that I had hum troubles. I switched my placement to the opposite side of the drummer (away from wiring in the walls) and no more hum. Yes your bass maybe to sensitive to hum pickup and shielding will greatly reduce the trouble, but that venue maybe the main problem.
     
  14. georgestrings

    georgestrings Banned

    Nov 5, 2005

    Do not listen to this advice - defeating a device's original power cable ground is a very bad idea, and has resulted in more than a few fatalities over the years...



    - georgestrings
     
  15. Also possible that venue has a miss-wired plug, swapped neutral and hot leads?? :meh:
     
  16. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    +117 (220 for our European and Australian readers)
     
  17. MIJ-VI

    MIJ-VI Banned Supporting Member

    Jan 12, 2009
    Yeah, it's a drag when gear goes wild. :eyebrow: It can be licked though! :)

    I had assumed that since you use an amp on stage, your guitarist does too.

    What I had in mind was temporarily removing your Ampeg from its rack, the next time that you are confronted with the bedeviling noise, just to hear if doing so makes any difference.

    What I meant here (in addition to pulling your amp from its rack the next time that you encounter the noise) was to plug your Ampeg into an AC outlet which is on a different circuit in the same building where your amp is making the noise.

    Unfortunately, troubleshooting intermittent problems is often a matter of trying the 99 things which don't work in order to find the one which does. :-(

    Yes you can shield your basses yourself (if you're handy with a soldering iron and you have all the shielding supplies). If you decide to do so, I would suggest that you start with your backup, passive bass (no pre-amp to potentially complicate things) since your active bass has performed sans 'the noise' when played through other rigs.

    Also, please make a detailed drawing of your bass' wiring before you take it apart.

    Here's a thread on shielding a Jazz Bass: 'Jazz Shielding Pictorial (Big Images Warning)'.

    Unfortunately, the photos which were used at the start of said thread are now missing! :eyebrow: (But they're available as 'Jazz_Shielding_Pictorial.doc' in post #103.)

    However, the discussion is still in place, and there are links to guitar/bass shielding-related web pages.

     
  18. wildhorse

    wildhorse

    Mar 15, 2009
    You apparently are not paying attention. You are not defeating the original power cable ground. The main amplifier is grounded and the rest are grounded to the main amplifier through the connecting cables. This is standard proceedure and not doing so is the cause of ground loops. Do not listen to this persons ill advise. Just be sure that anything in your rack that is not connected to another item via cables is indeed grounded with a 3 pin ground. The disclaimer here is that you are responsible for proper grounding of your own equipment. People are talking about shielding a guitar here that does not have this issue plugged into a different outlet in a different location. Something is obviously creating a ground loop at this gigs particular location and the obvious is it's connection to the pa system. Then again he claims he disconnected everything else except his rack. Thus the problem most likely is a ground loop in the rack itself. Eliminate the ground loop.
     
  19. wildhorse

    wildhorse

    Mar 15, 2009
    Oh and BTW, have you ever noticed your effects pedals don't have a 3 prong ground? That is because they are grounded by the connecting cables to the grounded guitar or bass amp.
    Never a problem because all are grounded. I wouldn't stand in a bathtub grounded or ungrounded as some idiots have done over the years.
     
  20. wildhorse

    wildhorse

    Mar 15, 2009

    Good point... In my recording studio I was having a terrible buzz on my recordings even with proper ground lifts. Turned out to be one of those new low energy light bulbs in the next room. Turn the light off, buzz gone.
     

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