Help me ground my amp/rack...please.

Discussion in 'Amps and Cabs [BG]' started by Grahams Groove, Feb 24, 2005.

  1. My gear list is in my profiel, but just incase...

    I'm running the following setup:
    Modulus Q5 (Barts) >

    Furman PL-PLUS
    Korg DTR2 Rack Tuner
    BBE Sonic Max 482
    ADA MB-1 Pre-amp
    QSC PLX 2402 Power Amp

    I use mesa cabs, but I noticed teh grounding issue while playing through headphones since I don't have my cabs here at my apt.

    It must be a grounding issue because the hum goes away for the most part when I make contact with the strings, but I would like to htink I can ground it by doing something to the rack or the components....something...

    There's no ground switch on any of my components except for the Direct Out on the pre and that doesn't do anything.

    I should also mention that the humming goes away completely when I touch the metal on the rack...

    Please give me a quick, cheap and/or easy fix for this issue if possible.

    One additional thing...It seems like my body positioning in relation to the Rack directly effects the intensity/prevalence of the hum.


    P.S. - forgot to mention that it's not this particular apt./outlet either, because it did the same thing in my bands practice area where I had never had problems with grounding on any previous amps/setups.
  2. Trevorus


    Oct 18, 2002
    Urbana, IL
    Try getting the electronics cavities of your instruments shielded. It cust the hum out a LOT!
  3. I would think teh shielding job on a modulus would be pretty good...maybe not though.

    What's my easiest way to do this?

    Also, I should add that my body positioning REALLY makes a it seems like the hum is most intense when my body is turned sideways so the face of the amp is facing my side/arm/ear....also, I noticed today that having my computer monitor on will also cause alot of hum/buzz...and I was playing through headphones.

    Does this give any further indication of what the problem may be?
  4. r379


    Jul 28, 2004
    Dallas, Texas
    Had that happen with a Jazz Bass once. Turned out to be a bad connection with the bridge ground wire. Took the bridge off and made the connection solid. Hum went away.
  5. Just opened the back up and the control cavity seems to be very well shielded....

    Is there a quick, easy or harmless way to find out if it's the bridge ground wire?

    Also....the thing that makes me think it's the amp, is that before when I was running the bass straight into my tascam recorder, there was NO noise at all, and when I used my pre-amp (w/ and w/o my BBE sonic max), there was lots of hum and buzz.
  6. Trevorus


    Oct 18, 2002
    Urbana, IL
    Check grounding problems between your pream/amp/instrument. Also, do you have a large amount of gain on?
  7. I don't think it's too hums no matter how I have my pre-amp configured...the only way to get rid of the hum is to turn way down, which isn't going to work out for me...
  8. Also, how do I physically check for a grounding problem in my instrument, amp and pre-amp seperately?
  9. Trevorus


    Oct 18, 2002
    Urbana, IL
    Make sure all your cables are in good shape. Then also make sure all grounding wires are soldered well in the bass. Without getting my hands on the whole setup, it's hard to to tell exactly what it is.
  10. notanaggie

    notanaggie Guest

    Sep 30, 2003
    YOU are the thing that isn't grounded. Everything else seems to be.

    Almost certainly, when you touch the strings, you are then grounded. Maybe not directly, but through some impedance. That indicates that something in the bass is not well shielded, maybe the pickups. In some cases the phase can be flipped and it will fix the problem, by grounding the ouside wires of teh pickup coils.

    That to me confirms that you are the ungrounded item, and the bass isn't well shielded. Touching the rack is a better ground for you than the the hum is less.

    I know, I know, you don't think so......but the evidence all points that way......Probably it is NOT the "cavity" but the pickguard side that isnt well shielded. If there is shielding, it may not be making effective contact....the evidence is that it isn't working if present.

    Cable is only a "maybe", you'd expect that it would hum with you far away if shield was open or even pretty crummy.

    Put bass down on table, plugged in, on, etc. Stand as far away as possible, and move your hand over the outside of the bass, very close, but not actually touching it.

    Wherever your hand is when the hum is loudest, that is where the shield problem probably is.
  11. Thanks for the advice...but (un)fortunately it didn't work as expected.

    The buzzing was as loud as ever and always present when I turned on the amp and ran the bass through it at a high volume. Standing far from teh bass and then hovering my hand over different parts of the body yielded no variation in the seemed perfectly constant.

    And it seems like maybe there was another factor, because I tried touching the rack metal again, and it didn't do anything. The buzz was still there.

    What else can i try to maybe eliminate something?

    My resources are my entire rack, listed above...a small peavey combo amp, headphones, my bass a recorder...

    Any mixing/matching I can do to try and figure this out?

    A weird thing I should mention is this...if I'm not mistaken, when I first got this pre-amp, I plugged it into my drummer's PA for power and ran it through his PA speakers and tried it through my bass cabs as well and I don't remember being it this noisy (I'm not 100% positive as I only had a few minutes to test that setup)....but I seem to recall really noticing how noisy it was the first time I racked everythign together and plugged it all in.

  12. Trevorus


    Oct 18, 2002
    Urbana, IL
    AHAAA! You may want to isolate the individual rack devices from the same ground. They make little plastic inserts that will unhook the rack devices from the metal rails. You have what is called a ground loop going on.
  13. OK, I just took everything out of the rack and plugged in teh devices 1 at a time and each one buzzed in teh same way. (The pre was louder, but that's because it is the only device in the rack that is used to boost volume, so naturally it will be louder)...

    So after going through all of them to elimante something, and having them all buzz, I assumed it was the bass. (What's left at this point? Not the rack, not the components, not the combo amp since it buzzed through a recording device w/ headphones...)

    So I tried my roommates guitar (epiphone LP)....same buzzing (not as loud, his guit. is passive obviously)...

    So the only thing I can think of is that my cables are unshielded.

    Would this make for the buzzing?

    I know one of them is unshielded for sure because my roommate bought it and he is positive it's unshielded. The cables I bought were on sale for like 10 bucks each at mars music when they went out of business. They are mars music brand 20 foot cables...they seem pretty cheap.

    Would this make sense? Is there a way to figure it out now since I can't go buy shielded cables at 2 AM to confirm this?

  14. thing that could throw a wrench into this whole thing. I just plugged directly into the peavey combo and that's buzzing too...

    idk what to think.
  15. Trevorus


    Oct 18, 2002
    Urbana, IL
    Make sure everything is shielded. I would reccomend getting some new cables. Whirlwind, ProCo, something similar. I don't like monster cables personally, for certain reasons, but that's up to you. I sould reccomend good quality cables first.
  16. Rav

    Rav Supporting Member

    Dec 29, 2004
    Aurora, IL
    Lets back up a second here.

    1) Get a multimeter. Go to whatever local electronics shop and just buy one. Should be able to get a decent one for $40 or so. Make sure it reads dc resistance and has a continuity test mode.

    2) Disconnect your bass from everything. Set the meter to continuity check mode ( Or DC resistance mode if you wish ) and check for resistance load/continuity between your strings and the output jack of your bass.

    If there is no continuity then your bridge isn't grounded. If there is continuity but the resistance load is extremely high then you have a bad connection(s) in the sheilding and grounding inside the bass.

    If the bass checks clean and looks good then move up the circuit checking for the weak connection.

    If your meter has AC voltage modes you can check your power source for ground fault while your at it.

  17. Could be a ground fault...I know that most of the outlets in this apt. are 2 prong...the one I plug my powerstrip/bass stuff into is 3 prong, but it may not be grounded.

    Also, I noticed when I cranked the volume a ton and listened to the hum/buzz that there seemed to be a phasing of some sort going on 'beneath' the buzz...

    Anyhow, hopefully I can get this all figured out soon.
  18. Rav

    Rav Supporting Member

    Dec 29, 2004
    Aurora, IL
    If the buzz sounds 60Hz ( 60 cycles per second ) Then it's on the AC side of your setup or interferance from an outside AC source. Sometimes flourescent light ballasts or neon light transformers induce this to DC circuits that are close by.

    You can get a ground fault detector from home depot or lowes hardware for about $5 and plug it into your 3 prong outlet to find out if it is really grounded.

    If its not you can ground the 3rd prong to a grounding strap and hook it to something large in the house that is grounded for certain. Heat registers or vents work pretty well bcause they are hooked to the airconditioner or heating fan at some point and that is grounded for certain to meet code in 99% of the country.

    I might also mention that some houses even though they are wired correctly are not themselves grounded properly. There should be a ground rod driven into the ground near where your power and gas lines come into your house. Some house contractors skimp on this and use rods that are too short for the ground composition.

    Either way should be easy to find and isolate.

  19. Rav

    Rav Supporting Member

    Dec 29, 2004
    Aurora, IL