Electric noise

Discussion in 'Hardware, Setup & Repair [BG]' started by Btone, May 11, 2001.

  1. Btone


    May 5, 2001
    I'm not shure if this is the right forum, anyway: I've got this terrible electric noise that stops when my fingers come in contact with strings or bridge or knobs. This goes for both my basses, a Jazz 68 and a Marcus Miller Sig.
    Is it the amp? A ground problem? Any solutions?
    Thank you!
  2. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    Well, this has come up many many times on here and on the Fender forum (FDP). What you have most likely got is the famous Jazz Bass hum, which a lot of people on the FDP will tell you is part of the JBass sound and synonymous with single coil, passive pickups - if you don't have the hum, you don't have the classic "vintage" sound.

    If you read about how Roscoe Beck designed his signature bass for Fender he explains about his 64 Jazz and how he loved its sound, but in some rooms the hum was just too bad to be usable, so he designed the unique humbucking pickups for that bass, with switches so that he could go to the humbucker when the hum got too bad.

    Fender are now supposed to be producing "noiseless" pickups and there are many replacements pickups available for Fender Jazz basses, but the purists would say that they just won't get the same sound!
  3. Btone


    May 5, 2001
    Thanks Bruce - I didn't know I was dealing with that famous Fender hum- I thought the Fender hum was a constant noise that you (to a certain degree) could control with pickup balance. My noise is only present when I keep my hands off the bass, and it's not going away no matter witch way I turn the volume knobs. And it's extremely annoying! You can't have it all - is that the clue? I'll look in the archive for more info on this bugger...See ya
  4. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    Well - the way to tell, is if you have both pick-ups on full then its should improve or theoretically cancel out, but in my experience, this isn't always the case. You don't say where this is happening - single-coil passive pickups are very good at picking up noise from lights with dimmer switches, fluorescent lights, computers or other electronic equipment. People also mention shielding the control cavity properly, with foil or similar, but I think the only proven solution is to change the pickups.
  5. Oysterman


    Mar 30, 2000
    But if it's only present when not touching the strings, I would say it's very much a grounding problem, no?
  6. embellisher

    embellisher Holy Ghost filled Bass Player Staff Member Supporting Member

    Sounds like a grounding problem to me, too.

    Take the plate off and look in the cavity for a single wire in a rout going towards the bridge. Pull gently on it. If it pulls out, there's your problem. If it doesnt, you might look at the end in the cavity and make sure that it is secure and doesn't look cold soldered.

    Failing that, you might have to remove the strings and pull the bridge - I have heard stories of bridge grounds that were painted over, or the insulation wasn't stripped back on the wire. Some people with persistent ground problems have soldered the ground to the underside of the bridge.
  7. Btone


    May 5, 2001
    Thank you for your help Bruce, Oysterman and Embellisher.
    The problem is still there, but mainly when I play my small practice-amp. I can live with the problem if I turn of all electric gadgets (like my computer) and balance the pickups.
  8. Oysterman


    Mar 30, 2000
    Sounds like the noise you're experiencing actually is a mix of three different kinds of noise:

    1) The buzz when not touching the strings is likely to be related to a grounding problem.

    2) If some noise goes away when having both pickups at full, you're experiencing hum cancellation, and that kind of hum you just cancelled out is always there with single-coil pickups. If you don't want to change pickups to humbuckers or always run both at the same volume, you have to live with it.

    3) "Electric gadgets" (such as computers, TVs, fluorescent tubes) cause electromagnetic interference (a.k.a. RF interferece?), which will induce buzzing into the electronics in your bass. This buzzing can be reduced (and possibly eliminated) with a proper shielding of your bass, using copper foil, silver paint or whatever.
  9. Btone


    May 5, 2001
    Yes, Oysterman - I came to the same conclution. I didn't check the grounding wire to the bridge, I might do it later - funny though, if both my basses have this defect, one brand new, the other 30+ years old.
  10. Oysterman


    Mar 30, 2000
    Well, what can you expect from Fenders? ;)
  11. I always point to the amp when someone has a "touch the strings and it goes away" buzz. And I always think it's the polarity of the AC outlet. On old tube amps, there is a polarity switch that can be used to get rid of this. On newer amps, they assume the house wiring is correct and leave off the polarity switch.

  12. Oysterman


    Mar 30, 2000
    Throbbin: In such cases, can't you just turn the power plug (correct term?) upside down in the socket? Wouldn't that be a quick fix to "reverse the polarity"?
  13. nowadays, we have the 3 prong plugs. ground, cathode, and anode. They make it this way so you don't f*ck up your amp by having the polarity reversed. :)
  14. Btone


    May 5, 2001
    I just tried Oystermans trick. Didn't work. Thanks anyway.
  15. Yep, same result if the plug is not polarized with one blade wider than the other. On really old stuff, the 2 prongs are identical. Then there's 2-prong polarized where one blade is wider than the other, and then modern 3 prong which kinda prevents the easy flippover unless you cut off the grond prong or use a 3-2 adapter AND the remaining 2 prongs are not polarized. For those who care, the wider prong is the neutral, the narrow blade is hot, and the round prong is earth ground.

    And yeah, this may not work on every AC noise problem. But in the simplest of setup, one way will give you a pop when you touch the strings and the other way will not give you a pop.

    Look at an old Fender Bassman schematic and note the Polarity switch and cap arrangement.

  16. Hi guys.

    I've read this thread with some concern. Having spent quite some years dealing with electrical safety matters I couldn't help wondering whether or not this amp problem should be referred to a qualified amp tech.

    First, I should say that I'm not familiar with this concept of altering the 'polarity' of the power cord nor, especially, reversing the power connector in the socket. Here in UK that latter idea would simply not be possible because our power connectors are designed to prevent that happening. However, in this case it does sound as though there is a lack of earthing. And, possibly, under fault conditions, that might lead to the chassis of the amp becoming live. A fair few musicians have been electrocuted because of such (and similar) things.

    I believe some amps of many years ago were fitted with what were known as AC/DC power supplies. And that such equipment was well known to be potentially lethal under fault conditions.

    Of course, none of the above may apply in this case buth I thought it worthy of a mention.

    And I agree with Oysterman in that it does sound like there may be one or two problems here. Either way, for safety's sake, please get the gear checked over by someone who knows exactly what they're doing.

    Rockin John
  17. Btone


    May 5, 2001
    Thank you for your reply, Rockin John - I am about to do some more digging into this problem. Try different basses with different amps in different rooms and so on...so far I've tried another bass, same amp in the same room: Still there. Another amp in the same room with two different basses: Still there...
    I'll check some more - but I think I will end up with this: There is some kind of electric interference in my room. I've turned off all computers and stuff: No effect. Funny thing is: Once in a while it's OK.....!! No noise! The fridge in the other room going on and off..?
    I'll check things and get back to you.
  18. I forgot to post the "Don't try this at home" warning. Rockin John is right, though. Don't mess with it if you don't know exactly what you are getting into.

    I started talking theory and forgot that some people may have thought that I was giving how-to instructions. You should not alter plugs by filing prongs or cutting off ground prongs. That's a no-no.

    The UK and US are definitely different in there philosophy on electrical safety, though. Most US houses wired before the 70's don't even have an Earth ground, just Hot and Neutral. So it is not uncommon to play in locations with no safety ground. We only use 120V, though, you guys have 220 at every outlet, Yikes! Plus you got fuses in your plugs, switches on your outlets, etc.

    One thing I always point out, is the fact that the true Earth ground connection is there for safety, not noise reduction. It is just as easy to build a noise-free amp without a ground prong on the plug. The ground prong is there so if something shorts to chassis it will blow a fuse or trip a circuit breaker. Under normal conditions, no current should flow in the Ground conductor.

    The old AC/DC sets really apply to old tube radios. If you plugged it in one way, the chassis was connected to Neutral, if you flipped the plug over, the chassis was connected to Hot 120V! That's why these radio's had plastic knobs and were totally enclosed with no metal accessible. Deadly in a bathroom to say the least. I don't know of any guitar or bass amps that use this scheme.

    Definitely better safe than sorry.

  19. Well, Throbbinnut, to the best of my belief (don't hold me to this, anyone) some of the very early Carlsbro amps built over here used AC/DC power supplies. I guess that must have been because there were some domestic DC supplying done in various parts of the UK in the early 60s. Makes you shudder to think of it, eh???

    Just for the info' the UK supply is 230VAC, 50 Hz. 'Used to be 240VAC but what with cutbacks, the Common Market and all that.....we've lost a bit. Even so, 230V is quite sufficient to give one a bit of a tickle....

    And, dead right. The main function - indeed, the sole purpose - of the earth connection is safety. It has nothing to do with reducing noise. The fact that it can do that is a bonus.

    Take care.

  20. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    So, I should NOT cut the cord off the amp and put both ends on my tongue will plugging it in?