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AC Hum: What can be done?

Discussion in 'Amps, Mics & Pickups [DB]' started by Chris Fitzgerald, Jan 31, 2004.


  1. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Last night I played a gig at a club in which I've never had any amplifier noise problems. Previously at this club, I had always used my EA iamp800, but last night I thought I'd try my beloved Clarus on the gig, since I felt that the 800 was a bit of overkill (it sounds great, but is a huge schelp). Anyway, the Clarus ended up sounding great but was subject to an annoying buzzing or humming that wouldn't go away, even when the master volume was turned all the way down. The sound man said that the sound was "AC hum", and the drummer said it was a "60-cycle hum". If that is correct, what is the nature of the problem? Is it necessarily a function of the amp, or could it also be patch/speaker cables or preamp? If it's the amp, is there some sort of filter I could stick under the seat of my car for instances like this? It was very frustrating. Tonight I plan on bringing the iamp back in and seeing what happens, but I love my Clarus and would like to find out the nature of the problem, which I've never had before with this amp.
     
  2. JonB

    JonB

    May 27, 2003
    Indianapolis
    Chris,
    Were you using a seperate preamp, or running straight into the Clarus?
    Was there a direct out to the board? If so, where was it connected to your gear?
    My reason for asking, is this week, after a soundman plugged into my preamp, I had the same situation as you, and flipping the "ground lift" switch on my preamp cured it.
    Another time, I had a long cable (15') from my bass to preamp that induced hum, and a shorter cable was the fix.
    Someone told me once that a ground problem is usually the cause for AC hum.
    Hope you get it fixed - that's an annoying sound!
     
  3. Hey Chris,
    I played at a Church a few years back that went a little overboard with the lighting. They instaled "christmas like" lightstrips along the stage. They were on a variable knob switch that controled brightness. These lights threw my Eden Rig into fits. Turn them off the hum went away. I tried the ground switch and it wouldent help. Just a heads up if they have those things... :meh:

    Dave
     
  4. sean p

    sean p

    Mar 7, 2002
    eugene, oregon
    chris - i had a similar problem when running bg and db into separate channels of a raven labs pmb-1, then into the effects return of a gk. the buzz was in the signal out of the preamp (affecting both the line signal at the board and the signal to my amp) and was caused by a 'ground loop.' contacted the raven folks and they suggested using a 3-to-2-prong adaptor on the amp power cord at the socket (to bypass the ground prong). tried it, problem gone.

    i understand very little about this type of thing, but i thought i'd share just in case you have a 3-2 prong adaptor laying around and could try it easily on the off chance it would help...

    sean p
     
  5. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Just played the same venue tonight using the iamp, and everything was perfect. I used the same preamp, plugged into the same direct feed, and played under the same lights, which were plugged into the same dimmer. The only wild card was the small monitor I used - tonight I used an EA VL108, wheres last night I used a Falk 1x8. I don't think the speaker could have caused the hum, but I noticed last night that the Speakon to 1/4" cable running from the Falk to the Clarus was a bit "wonky" - when I would turn it on the back of the monitor, it cut in and out a couple of times. Could that have caused the hum?
     
  6. Uhh,
    I`m a hick from the South also but.....that`s a new one on me Bro. :smug:

    Dave
     
  7. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    The fact that the 60 cycle hum was still there with the volume down makes it sound like a ground loop.

    That's why the Ground Lift switch is on the Clarus and so many other amps - I'm surprised the sound guy didn't ask if you had one and could throw it.
     
  8. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    I'm actually quite embarrassed to admit it, but I didn't realize the Clarus had a ground lift switch. Where is it? The only switch that I remember is the little red one which adjusts voltage for US/Europe.
     
  9. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Yeah, me too. Must be all the Canadian grad students I've been hanging around with, eh?
     
  10. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    It's a pushbutton on the front panel adjacent to the XLR out on the Series II models. I forget which one you have; I don't think the original had a ground lift switch.

    It's easy to sort of "make one" if necessary, just with a short female-male XLR cable with the ground wire disconnected at the female end. In most cases the DI boxes have a ground lift or the sound guy can pull it off.
     
  11. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    I think I have the original - it's the one I bought from you that used to be your personal DB amp. I'm actually a bit relieved to discover that it doesn't have a ground lift, as I would have felt pretty stupid not noticing it on an amp with as few buttons as that one has. :)
     
  12. I get the 60 cycle hum in the worst possible place, my schools recording studio. I have the original clarus, so if you could go a little bit more in-depth on how to "make" a ground lift I would definitely appreciate it. I understand the part about the xlr cables ground being disconnected at the female end, but do you do this by cutting in to the wire and disconnecting the ground wire? and also, If I am not recording my bass, or going in to the board, will this get rid of the hum (ie, im just running my Golden Trinity preamp into the AI Clarus, and out to the speaker cab.)? I've had the problem be the fault of a cable before, but I'm using the monster bass cable, so I'm pretty sure thats not to blame..

    Thanks for the help in advance..
     
  13. brooklynbassguy

    brooklynbassguy Supporting Member

    Feb 8, 2004
    maplewood, nj, usa
    I recently had the same problem as you with the hum on a clarus. It was caused by a voltage brownout. My line voltage dropped to about 100 volts. The nature of switching amplifiers causes the amps to hum loudly, regardless of volume levels or input signal. I talked to Rick Jones about and he confirmed my suspicions. It will only go away when line voltage returns to normal (110-126) If you want to carry a computer voltage regulator, like the APC Line-R 600, you'll never have this problem. They cost about $100, and weigh around 10 pounds. Fortunately this doesn't happen often, but ConEd was having some problems during the really cold days with supply voltage, and we had the brownout for 3 days, affecting computers and DSL service. I hope this helps.
     
  14. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Played another gig with the small Clarus rig, and the signal was completely clean. I guess the best thing would be to keep a "ground lifting device" under the seat of the car just in case.
     
  15. QTraXQ

    QTraXQ Guest

    Aug 16, 2002
    San Antonio, TX
    Definitely keep a "Ground Lifting" Device or adaptor with you at all Gigs..Don't pull the Ground piece off your Electrical Plug, but get the "Ground Lift" adaptor instead

    Mixing chassis-grounded with Signal-Grounded will definitly cause this problem..
     
  16. I have had this problem with the Raven Labs blender running into an AI Coda. Everything is fine until the XLR feed to the house is plugged into the preamp's direct out. Then the problem with the buzz. I wonder if the buzz would still occur if I powered the preamp with the 2 9-volt batteries instead of the AC adapter. Oh, well, there's one way to find out...

    The strange thing is that the buzz went away when they took the feed from the direct out of the Coda. I say strange, since the power cord to the Coda is 3-pronged and the adapter for the preamp is 2-pronged and not even polarized. Taking the feed from the Coda is not practical, since I can't control stage volume without affecting the signal to the board.