The Jazz Guitar Chord Dictionary
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  1. #1

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    Hi, i have a little puzzling problem here. I would really appreciate if someone could help a bit.

    The context:

    Archtop with a Floating PAF pickup, with volume knob on the ebony pickguard.
    The wires from the pickup to the volume know are high quality vintage style push-back wires.

    Absolutely no noise whatsoever in a room that's properly grounded to earth.

    Very bearable noise in a room that's not connected to earth so i guess the pickup is properly wired and connected to the metal tailpiece,

    BUT,

    if i rest my fingers on the pickguard a buzz comes in. And if i touch the tailpiece with the other hand the buzz stops.

    Touching the strings or pickup itself does not generate any noise so i guess the signal and ground wires are not inverted.
    And again, i does seem like a grounding issue but if i don't bring my hand closer to the pickguard, or rather, to the pickup wires under the pickguard, i have almost no noise, even in a not grounded room. And of course, the problem stops as soon as i connect the electricity to earth.

    So is it :

    -Just normal, can't have miracles if an electric installation is not properly connected to an earth.

    OR

    -Just have to replace the vintage pickup wires going to the volume pot with shielded wire.
    Well, of course it never harms to put shielded wire, but if this is not the cause, i'd rather be lazy and keep it as it is.
    BTW, if indeed it's some shielded wire that i need, would it be enough to wrap the two pickup wires with some alumi foil or shielding tape ?


    OR

    Both ...

    Thanks for any help !

  2.  

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  3. #2

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    When there is a great deal of ambient electrical noise, any guitar will be more susceptible to hum.

    In your case though, the unshielded length of "hot" signal wire from the PU to the pot makes it particularly problematic. When you rest your ungrounded hand near the wire (on the pickguard), you are a sort of AC hum antenna bringing the evil buzz as close as possible to the unshielded wire.

    When you touch the tailpiece, you ground yourself, and are a far worse hum antenna.

    EDIT: I mean that when you ground yourself you are no longer an effective antenna for the hum. Also you are now somewhat a shield for the guitars electronics.

    Things you can do:

    1. Use shielded wire from the PU to the pot.

    2. Twist the existing wires together for partial shielding.

    3. Add a layer of grounded copper foil to the back of the ebony PG. I use copper foil on the back of Tele pickguards to get rid of static electricity sounds from fingers rubbing on the plastic PG in dry weather.

    I am sure your situation can be improved.

    Chris
    Last edited by PTChristopher2; 06-13-2014 at 07:21 AM.

  4. #3

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    >>> if indeed it's some shielded wire that i need, would it be enough to wrap the two pickup wires with some alumi foil or shielding tape ?

    You can do this, but reliably grounding an aluminum foil wrap is not all that easy.

  5. #4

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    Thanks a lot PTChristopher2 !

    Today i tried a bit with some leftover shielding tape i had and i was not even thinking i had to ground it also

    That idea of twisting the existing wire is great ! Gonna try this first.

    Really appreciate the help !

  6. #5
    Chris, your input here is most interesting.

    Can I add a Q: I have a 60s Hofner with a new floater, pot in the pickguard, as above. She does absolutely fine with the vol fully turned up. However, if I turn the vol down, certain amps start to hum (strongly), but not all. I talked to my tech and he was not sure what to do. In his workshop, the guitar makes no hum, vol up or down. Would be great to know your thoughts, understanding the limitations of a remote diagnosis.

  7. #6

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    Regardless of the cause, the Electroharmonix Hum Debugger gets rid of a lot of ground loop hum problems. Worth a try if you can get your hands on one.

  8. #7

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    Quote Originally Posted by Doctor Jeff
    Regardless of the cause, the Electroharmonix Hum Debugger gets rid of a lot of ground Loop hum problems. Worth a try if you can get your hands on one.
    I bought one of these after recommendations here and, contrary to what had been said, found it to alter the sound quite a bit more than I cared for.

    Which, of course, only goes to show how different people hear things differently.

    This specific gadget is a workaround rather than a causal solution. Does get rid of the hum, though.

  9. #8

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    >>> I have a 60s Hofner with a new floater, pot in the pickguard, as above. She does absolutely fine with the vol fully turned up. However, if I turn the vol down, certain amps start to hum (strongly), but not all.

    This can be due to two things. As counter-intuitive as it may seem, some amps can be very susceptible to hum even though the hum becomes apparent when you turn down the volume control on the guitar. I have seen this when the amp input jack was in a very noisy location (like near the amp's power supply).

    For fun, run the guitar through a buffer of any sort. This can be a volume pedal or a mild effect box (like a compressor with the compression turned way down or an EQ pedal). Now you are feeding a low impedance signal to the amp. Turn the guitar volume down and see of the hum is still there. If so, then it is primarily from the guitar. If the hum is gone or greatly reduced, then it will be very difficult to solve at the guitar alone.

    Assuming the hum is still there, I suggest first checking for a grounded pot housing. Typically this is done by having the ground end of the pot soldered to the metal case.

    Next would be to add a shield to the backside of the pickguard. I use adhesive backed copper foil. Then make sure this shield and the pot case is grounded.

    >>> In his workshop, the guitar makes no hum, vol up or down.

    This can be due to the input configuration of his amp, or a generally low ambient electrical noise in his shop.

    >>> Would be great to know your thoughts, understanding the limitations of a remote diagnosis.

    Well let us know what you find out based on my suggestions above and maybe we can get somewhere despite the nature of a web forum "fix".
    Last edited by PTChristopher2; 06-10-2014 at 10:54 PM. Reason: spelling

  10. #9

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    I would avoid broadly using the term ground loop in this context. Ground loops can give you a hum, but it usually comes from running your guitar into two amps via a patch cord from one amp input to the other.

    The ground loop is then formed by the patch cord shield being one ground path, and the amps power cords also both being grounded. In such a case, you would lift the ground on one of the power cords to break the ground loop.

    BUT, this carries some notable danger. Far better would be to make a special patch cord with the cord shield attached to ground at only one end of the cord.

    Better still would be to buffer the whole mess. And what jazz player runs parallel into two amps anyway?

    In any case, I would avoid casually throwing "ground loop" out as a term when discussing guitar hum. It is not a very common source of trouble - in my opinion.

    Chris

  11. #10
    Quote Originally Posted by PTChristopher2
    >>> I have a 60s Hofner with a new floater, pot in the pickguard, as above. She does absolutely fine with the vol fully turned up. However, if I turn the vol down, certain amps start to hum (strongly), but not all.

    This can be due to two things. As counter-intuitive as it may seem, some amps can be very susceptible to hum even though the hum becomes apparent when you turn down the volume control on the guitar. I have seen this when the amp input jack was in a very noisy location (like near the amp's power supply).

    For fun, run the guitar through a buffer of any sort. This can be a volume pedal or a mild effect box (like a compressor with the compression turned way down or an EQ pedal). Now you are feeding a low impedance signal to the amp. Turn the guitar volume down and see of the hum is still there. If so, then it is primarily from the guitar. If the hum is gone or greatly reduced, then it will be very difficult to solve at the guitar alone.

    Assuming the hum is still there, I suggest first checking for a grounded pot housing. Typically this is done by having the ground end of the pot soldered to the metal case.

    Next would be to add a shield to the backside of the pickguard. I use adhesive backed copper foil. Then make sure this shield and the pot case is grounded.

    >>> In his workshop, the guitar makes no hum, vol up or down.

    This can be due to the input configuration of his amp, or a generally low ambient electrical noise in his shop.

    >>> Would be great to know your thoughts, understanding the limitations of a remote diagnosis.

    Well let us know what you find out based on my suggestions above and maybe we can get somewhere despite the nature of a web forum "fix".
    hi Chris, thanks, this is very helpful. I tried the pedal route - hum still there. Next step will be to see is the pot is grounded to its base. I will also try the copper foil shielding.

    Highly appreciated, danke vielmals.

  12. #11

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    Quote Originally Posted by palindrome
    I bought one of these after recommendations here and, contrary to what had been said, found it to alter the sound quite a bit more than I cared for.

    Which, of course, only goes to show how different people hear things differently.

    This specific gadget is a workaround rather than a causal solution. Does get rid of the hum, though.
    I agree YMMV. There are 2 settings on the EHX HD, a high and low. To my ears the low setting had no discernible effect on the P90 tone with the treble rolled off a bit, but the high setting did affect it. I bought it from a store with the understanding I could return it if it didn't work for my situation.

    Re' ground loop hum, this is a common problem with single coil pickups. (The GFS floater I recently installed can be wired as either single coil or humbucker, so maybe you have a single coil configuration?) My last 2 houses have had old tube and post wiring, which is not easily fixable without spending thousands of dollars. So a workaround? Maybe, but it solved the problem.

  13. #12

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    Hi Doctor Jeff,

    Not to be annoyingly questioning, but can you specify the actual ground loop you describe? What are the dual paths to ground that are "causing" the hum?

    Is it remotely possible that we are actually talking about something other than an actual ground loop here?

    A dual path to ground (often described as a ground loop) is not specifically associated with the hum from single coil PU that is thwarted by a humbucking PU design.

    Just semi keeping it almost real here.

    I understand the issues you had with old "knob and tube" (as they say in these here parts,...) home wiring. But there is no particular condition of a ground loop associated with this wiring in a home unless you are describing some specific retro-fitted ground system that formed a loop??? Such a condition could present some notable personal danger.

    Ground loops in power distribution can be a very exciting and profoundly unfortunate thing. I would not casually associate this term with some ambient "un-bucked" hum from a single coil PU. But that's just me.

    Chris

  14. #13

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    And what the heck:

    If you live or play in a location with knob and tube wiring, there is often a greater amount of ambient hum than in a modern wiring location.

    This (along with everything else in the thread) has nothing to do with a ground loop.

    With knob and tube wiring, a single conductor can often be a significant distance away from its complementary conductor. This is much different from modern wiring where the hot and neutral lines always run in parallel and in close proximity inside the insulating jacket of the wire assembly as supplied by the manufacturer.

    Anyway, the potential distance between hot and neutral in knob and tube wiring makes for a potentially far stronger (and farther reaching) magnetic field in a room. This magnetic field is of course humming along at 60 Hz in the US.

    So yeah, you can have more hum in a building with old wiring if it is of the knob and tube variety.

    In my opinion.

  15. #14

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    Quote Originally Posted by PTChristopher2
    In my opinion.
    Most interesting opinions. I find myself instinctively agreeing with what you’ve said in this thread, although I would be using hopelessly incorrect words and trains of thought trying to express these things myself.

    BTW, precisely for what reason should the noise level on most of my guitars increase on rolling off the volume control from 10? (Sorry if you explained it already and I didn’t notice or understand it…)

  16. #15

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    Quote Originally Posted by Doctor Jeff
    I agree YMMV. There are 2 settings on the EHX HD, a high and low. To my ears the low setting had no discernible effect on the P90 tone with the treble rolled off a bit, but the high setting did affect it. I bought it from a store with the understanding I could return it if it didn't work for my situation.

    Re' ground loop hum, this is a common problem with single coil pickups. (The GFS floater I recently installed can be wired as either single coil or humbucker, so maybe you have a single coil configuration?) My last 2 houses have had old tube and post wiring, which is not easily fixable without spending thousands of dollars. So a workaround? Maybe, but it solved the problem.
    I guess there are several potential explanations for our different experiences, and I am certainly not trying to suggest that I have bigger ears than you. I bought an EH Hum Debugger after getting tired with the noise from various guitars, which I gather today was definitely due to no/poor shielding and/or grounding due to poor wiring and/or inadequate body temperature or body-mass index (I hope I'm expressing this correctly, PTPhristopher2).

    The Hum Debugger suggestion came up here after I had bought my Peerless Sunset and found it too noisy for quiet playing. So my judgments on the gadget are mostly based on the Sunset experience. To me, it made for a noticeably thinner tone even in the low setting. More importantly, the sound obtained a somewhat “cheesy” quality, for lack of a better word. That said, I was strictly playing through good-quality studio headphones (H&K Tubeman I > Boss JS-10 > phones) at the time, so I guess YMMV particularly if your experience is based on full-blown amps and speakers. Meanwhile, the wiring in the Sunset has been changed (along with the pickups), and the noise is now down to an acceptable level. Doesn’t your Sunset have an annoying noise floor?

    Also, I remember thinking that the tones from the Hum Debugger were more acceptable with some grit involved.

  17. #16

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    Hi Palindrome,emordnilaP iH

    I have been doing rather poorly of late with what is likely excessive opinion detail, and impatience with more spiritual approaches to the tech side of thngs. But if I mention unicorns and pixie dust, that can be equally annoying. It seems tricky to me unless 3/4 of a post is geared toward sensitivity to the variety of reader.

    Anyway, onward in insensitivity,...

    >>> BTW, precisely for what reason should the noise level on most of my guitars increase on rolling off the volume control from 10?

    In my view, you will have the maximum opportunity to pick up ambient low frequency electromagnetic noise (60 Hz hum) when the low frequency (nearly DC) output impedance of the guitar is at its maximum.

    (This sentence probably raises an excess of questions, but I think I am burning out on the forum to some extent.)

    If your volume pot is wired in the normal way, and not backwards as some are, then the maximum DC (and very low frequency) output impedance of your guitar will be when the wiper (center contact) of the pot is slightly above the mid-point of the resistance range of the pot. With an audio taper pot this will be only a short distance down from "10".

    So if you hear relatively less hum at "10", then maximum hum as you get toward maybe "8.5" or something, then gradually less hum down to none at "0" - all is working as one would expect.

    Careful shielding of as much of the guitars electronics as possible will reduce the overall hum and the severity of the notable peak as the volume is set at the mid-point of the resistance in the pot (not "5" on an audio taper).

    Even when the hum on a guitar is imperceptibly low, it will still in principle be at its maximum in the situation described above.

    I am being a little loose with the definition of impedance here, and leaving out some of the interactions that occur in the circuit. I am also excessively implying causality in one area and ignoring it in another. This is my idea of keeping it short, but it also means I am being somewhat incomplete - but more sensitive.

    (Imagine GIF of kittens here,...)

    Chris
    Last edited by PTChristopher2; 06-12-2014 at 12:04 AM. Reason: spelling

  18. #17

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    Thanks, Chris, for the explanations. They will take some time to sink in (it's 6 a.m. where I am).

    Thanks also for the loose unicorns, spiritual pixie dust, and insensitive kittens.

    (I'll try to sort out what all of this means tomorrow.)

  19. #18

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    Chris the hum I was referring to is caused by old wiring. I have often heard that referred to as ground loop hum. Maybe it's more of a magnetic field problem?

    In any event, it was an issue when I lived in a previous house and got a single-coil P90 guitar, to the point that the guitar was intolerable plugged in. In my case it was virtually eliminated with the EHX HD.

    Please expand on this if you want. I have no engineering background, just a dumb guitar guy.
    Last edited by Doctor Jeff; 06-12-2014 at 11:00 PM.

  20. #19

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    >>> Chris the hum I was referring to is caused by old wiring. I have often heard that referred to as ground loop hum. Maybe it's more of a magnetic field problem?

    As I understand the knob and tube wiring situation, I think you are right that it is more an issue of the unbalanced electromagnetic field from the likely distance between wires.

    >>> In my case it is virtually eliminated with the EHX HD.

    As I understand this pedal, I can imagine it doing a very good job. I can also imagine some notable artifacts to some based on how it appears to cancel/reduce the hum.

    Like many things in guitardom, one player can report no sound change and another can report a notable sound change.

    In my opinion, both players could be objectively accurate depending on the way they play and the low end emphasis of their overall setup.

    Thanks for the feedback on whatever thumb tack I had metaphorically sat on in this thread.

    Chris

  21. #20

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    I've always wondered, where does hum come from? This has helped. Thanks!

  22. #21

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    >>> I've always wondered, where does hum come from?

    I suppose it can be summarized that hum comes from the AC power in the building.

    In most cases it is primarily from electromagnetic radiation from wires and lamps.

    The extremely weak and high impedance signals from a passive guitar make it particularly susceptible to picking up the ambient electromagnetic hum.

    There are certainly far more thorough and better explanations of the complete phenomenon than in a forum thread.

    In my opinion.

  23. #22
    follow up: I cleaned up the space around my amp (there were lots of computer cables etc), and that almost eliminated the issue. The remaining hum was killed by installing a grounding wire from pot to tailpiece, which had been omitted so far. All good - thanks Chris. :-)