Noise between N and G causing guitar amp hum?

Discussion in 'General Electronics Chat' started by danbruski, Dec 21, 2012.

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  1. danbruski

    Thread Starter New Member

    Dec 21, 2012
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    I saw an old thread from 2010 on this forum, but the bot told me it was too old to reply to...

    I have a considerable amount of audible noise (60cyc likely) being picked up by my electric guitar. The noise (hum) is very directional and location specific. The noise is not on the amp when the guitar is not plugged in. This tells me the noise is environmental and being picked up by my pickups... so i'm on a mission to find the source(s) of this environmental noise. I tested my outlets with one of those tester things and they look OK, but on a scope, I see a significant waveform between earth ground and Neutral. Could this cause the EMI/RFI I'm picking up?

    Please see the video of my scope trace here, it's short:
    http://youtu.be/KixlSFGLGjw
    http://youtu.be/X2L2M7vTreM

    from another circuit in the house and effects of a light dimmer
    http://youtu.be/3IDNUrFukVg

    And if you are super bored, but want to see a Electrical PSA from my 4 yr old about tamper proof outlets...
    http://youtu.be/7R2DGFU_iNs

    I know this is a Guitar issue, but the guitar people don't know that much about house AC ... maybe someone recognizes the wave?
     
    ian field likes this.
  2. MrChips

    Moderator

    Oct 2, 2009
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    Locate the mains transformer on your amp.
    Now move your guitar pickups towards the transformer and then away from the transformer.
    Tell me what happens.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    If you recently made any repairs to your guitar or amp you may have cris-crossed the connections to one of the jacks for your cables. Connecting ground to the tip (and signal to the sleeve) of a cable plug will definately cause some hum.
     
  4. danbruski

    Thread Starter New Member

    Dec 21, 2012
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    MrChips, I've done that, and if I get real close, I pick up an additional hum. GopherT, i have made mods, but not to guitar input jack. also, noise is directional, if it were a wiring issue, i think it would Be noisy all the time and not based on location.

    It's something in the studio room. I can relocate the guitar and amp to another room, still on the same circuit and noise greatly drops. Changing amp orientation doesn't change noise. Leaving amp in studio and taking the guitar out with a 25' cord greatly reduces noise.


    I super appreciate the comments and thoughts...any more?
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    Tell us more about the mods you made.
     
  6. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Do you have fluorescent lights in that room?
     
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Do you get hum when you short out the lead on the guitar, inner to outer?
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    If any of your mods could possibly change the "direction" of your guitar's signal, you will have a big problem picking up noise. Changing the direction of the signal can include, wiring a Pick-up backwards, criss-crossing the wires going to a potentiometer for tone control or volume in the guitar. Also, any mis-wired stomp boxes can cause a problem.

    Crossing wires causes your neutral wire to travel down the shielded core of your cable and the signal to be in the shielding. With that situation, the shielding cannot do its job of sheilding the signal and, instead, picks up any interference you can hear like 60Hz AC and motor controllers. It also picks up signals you cannot hear. Instead of shorting to "ground", these interference signals are passed along to the amplifier and you get buzz.
     
  9. tubeguy

    Well-Known Member

    Nov 3, 2012
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    You will pickup AC induced hum through your guitar pickups because they are high impedance coils of wire.

    Does the hum lessen when you touch the strings and increase when you take your hands off the strings. It should. If not make sure your guitars' bridge is grounded to the output jack ground.

    What amplifier and guitar are you using?
    Some guitars have hum-bucking pickups, to help with this issue some do not.

    Does your amp have a ground position switch ?

    Does turning off the lights in studio room make a difference. Are they fluorescent or on dimmers??
     
    Last edited: Dec 22, 2012
  10. danbruski

    Thread Starter New Member

    Dec 21, 2012
    5
    1
    Thanks for taking an interest @tubeguy, @gopherT, @DodgyDave, PotatoPUdding, and MrChips.

    All answer each question you had below. In general though, I don't think it's an equipment problem as I get the really loud directional based hum on any of 4 guitars, 2 different amps (one completely stock) and when using a Presonus input into my PC (amp modeling and recording) A while back, I even brought my Vox AD50VT into a guitar shop that had a similar un-modded one to do A-B tests and they sounded identical. I really think the equipment is doing what it's supposed to do, it's just picking up more than I want.

    Does anyone have ideas on the waveform between Neutral and Ground that I posed on youtube ?

    Now to your questions, which I appreciate:

    "Does the hum lessen when you touch the strings and increase when you take your hands off the strings. It should. If not make sure your guitars' bridge is grounded to the output jack ground."

    No, there's no change, or at least less than the other noise being picked up. This is consistent across all 4 electric guitars, 3 of which I know have grounded bridges (I haven't yet opened up my Tele).

    "What amplifier and guitar are you using?
    Some guitars have hum-bucking pickups, to help with this issue some do not."

    I have a VOX AD50VT and a ROland Jazz Chorus 120, both do the same noise, but more noticable on the Vox when in high gain settings - the JC doesn't really go into high gain.

    I have a guitar with humbuckers, and it's better, but still too much noise. It's about the noise level i'd expect on a single coil. I can pull a pot and split the coil as well and that get's terribly noisy. If I run my single coil guitars in the middle position with both bridge and neck pups on (and most likely wired out of phase), the noise lessens significantly. Again pointing to canceling out noise picked up in the environment.

    "Does your amp have a ground position switch ?"

    The JC120 does, and it makes no difference in the hum the guitar picks up.

    "Does turning off the lights in studio room make a difference. Are they fluorescent or on dimmers??"

    In the studio there are only incandescent lights, not on a dimmer. There are may other incandescent lights on dimmers in the house. I've turned all of the lights off and even turned off all but one circuit (the one powering the amp) at my panel with little change. The character (tone/ modulation) of the noise i'm talking about changes a bit when dimmers are on and adjusted, but will all circuits off but the one, the loud noise is still there.

    "Mods created a situation where the shield was turned into the signal wire possibility"

    I understand this would be an issue - grounding the inner signal wire and using the shield as the signal, but this is unlikely given the switch would have to happen on the signal side (guitar) and the amp side to even get guitar sound. The problem exists on 3 amps and 4 guitars, so not likely a mis-wiring. However, when i pop it open, i'll meter out the path to be sure the sheild is just a shield and well grounded on one side.

    "Do you get hum when you short out the lead on the guitar, inner to outer?"


    No

    "Do you have fluorescent lights in that room?"

    No, see above.

    "Tell us more about the mods you made."
    The VOX was modded to add an effects loop, an external speaker in parallel, a new headphone/line out location and jack. I'll check to see if something happened to the signal path and the ground/shield integrity, but given the situation described above, I don't think that's the cause.

    Thanks again everyone for taking the time and trying to trouble shoot.
     
  11. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    This sounds like the live and neutral are possibly crosswired in the outlet where you are plugging in the amp.

    AC Voltmeter should tell the story.
     
  12. tubeguy

    Well-Known Member

    Nov 3, 2012
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    I'm with potato pudding as far as checking for reversed live/neutral.

    If you don't know, the long slot-silver screw on the outlet is neutral, short-gold is hot.

    Many electronic items are not actually off, but in idle mode as long as they are plugged in
    Have you tried putting the guitar in the room with everything in the room unplugged??

    Anything nearby with motors, transformers ?

    I have an adjustable voltage soldering station from W. which induces bad noise in guitar amps when its on.
     
  13. danbruski

    Thread Starter New Member

    Dec 21, 2012
    5
    1
    Ok, I'll check into the Wiring. I did check some when I was scoping, but not all outlets. Thanks. I sure hope I figure out something...
     
  14. danbruski

    Thread Starter New Member

    Dec 21, 2012
    5
    1
    ...I tested all the outlets in the vicinity of the studio and they all test fine, no G N swaps or G Hot swaps or any anomalies. I picked up a high quality George L cable yesterday to ensure my shielding was as good as possible and there was no improvement in noise (i do think i noticed a tone change though, which is cool).

    I haven't checked wiring on the lights yet. There's just one light switch to an overhead incandescent light fixture, and turining it on or off doesn't change anything. I've had the noise when all circuits in the whole house other than the one powering the studio was off and the noise still there. I'm kinda stuck.
     
  15. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Have you tried turning off all the outlets and/or unplugging everything in the studio and powering your guitar/amp from another circuit with the guitar in the studio room ?
     
  16. mr86

    New Member

    May 1, 2014
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    First post!!! I need your help yall!!! I notice this thread died, but Im having almost the same problem.. Kinda wonder if it ever got sorted out for ol chap? Anyhow, moved into a 1970s house. Almost all wall sockets have 3 prong plug but are 2 wires on the inside. I know little about home wiring and none of the lingo btw... All 3 of my guitar amps hum. They never did before. I have done everything Im capable of to find the problem, but cant. here is a list of things tried.
    3 separate amps= hum
    3 different guitars= hum
    5 different cables
    hums no matter where the amp is ie tried all rooms, garage and outside= still hums
    hum changes slightly when moving guitar around, the cable hums when placed near light switch and sockets
    no cable plugged into the amp= no hum
    volume up and down the hum goes up and down
    hum is worse accompanied with squeal when using ebtechhum eliminator in front of amp tested two eliminators= wtf??
    outlets are not grounded 3 prong holes 2 wires in the wall
    all lights off and everything unplugged= still hums
    no cell tower near by
    tested all sockets (little tester) and most say open ground some say correct
    if i hold the cable balled up and near my chest the hum sort of stops
    no earth ground that I can find
    5 different wires going to metal water pipe outside covered in paint
    panel out side has no ground on the outside
    ran a wire from guitar bridge to ground on the water pipe and heard pops and clicks in my amp. still hummed.
    when hum eliminator was plugged
    in and the squealing was present touching the wire from guitar to water pipe made the squeal leave but the hum was still
    there.
    no dimmers
    turned all power off except one of the only grounded plugs and amp still hummed
    ran the wire from guitar to the panel ground tab. still hummed
    wire from pole going to house looks intact
    phone wires on the side of the house are a mess
    bedroom light switch is not hooked up to any outlets in room ie doesnt work for any plugs on/off but there is power to the switch.
    peavey jsx hum with ground switch set to zero +/- on plus it hums the least.
    there is a open wall socket with wires exposed
    garage light intermittently turns on and off
    the range will not boil water if more than 2 burners are being used
    oven gets a strange hum and stops when you wiggle the front mount.
    guitar shielded with a frying pan. still hums

    I have 3 tests left that I can think of,

    run a generator with the house power on like normal. If it hums it has to be emi from the wires in the walls right?

    run the generator with the house power off and see

    and politely ask a next door neighbor if i can use one of there outlets for a min and see if its just mine.

    Any ideas guys? I am at a loss and am pulling my hair out. Any info would be great, look forward to hearing something
     
  17. Doug Tisdlae

    New Member

    Jan 2, 2015
    1
    0
    I have had the same issues and went through a lot of the troubleshooting with no success in figuring out where the humming is coming form. Did you get it figured out?
     
  18. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    Welcome to AAC.

    Congratulations, you have practiced the arcane art of necromancy, the revival of a long dead thread. Likely the OP (Original Poster) has solved his problem in the years that has passed, or thrown it away, or something.

    If you want to pursue this topic then you will need to start your own thread.
     
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