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Yet another Grounding question...

Discussion in 'Pickups & Electronics [BG]' started by C-5KO, Jul 30, 2005.


  1. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    After reading many posts on "grounding" I've yet to come to one that explains how to check for bad grounding?

    Besides hearing the obvious hum, what are the physical steps to take to check for bad grounding?
     
  2. Put your ohmmeter on the lowest ohm scale.
    Touch your meter leads together and note the reading (i.e. .2 ohms etc).
    Now put one meter lead on the nut holding the output jack and the other on the bridge. Subtract the reading you got from touching the leads together (that was the leads internal resistance) from your reading. It should be as near zero ohms as possible (0.4 or less).
     
  3. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Awesome. So I continue through the different parts of the bass? ie: shielded walls, the back of the pots... basically anywhere there's a ground wire soldered? This would insure that there wouldn't be any discrepancies between different grounding points? Of course, star grounding would presumably take care of all of this.

    I just wanted to make sure it wasn't a bad connection somewhere, before I tear all the shielding out and redo it.
     
  4. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    So I took a trip down to my local Radio Shack and bought a multimeter.

    Please take into consideration the last time I soldered anything was 15 yrs ago in high school:

    1. Connected leads together to measure multimeters resistance. There's a little wheel on the side to correct it to zero, which I did.

    2. I connected the multimeter to the areas circled in red then to the connection on the jack.

    3. I also check the connections between each individual solder (circled in red) to each other.

    4. I checked from the bridge to the jack.



    All of these readings came to "0". Does this mean my grounding has continuity? Can I have grounding that has continuity but still buzzes?


    Of course this still doesn't solve my problem of the buzzing.


    Next, I would like to test each pot, then then passive/active switch, and the mid selector switch.

    Is there a way of going about testing pots, WITHOUT having to solder? I would prefer not to change any of wiring or setup with the electronics. So, I guess I'm asking how to check the pots with the multimeter.


    How will I know if the pot is the cause of the buzzing without removing from the signal chain?
     

    Attached Files:

  5. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    I guess I should have explained the wiring:

    It looks as if there is a ground wire coming from each of the pots.

    Each of these wires connect to a single wire that connects to the jack. You can sort of make out the single wire running parallel to the orange one.

    A ground wire from the bridge also connects to the single wire.



    All suggestions are greatly appreciated. I have a 5 string with the same wiring inside, and it is completely silent. Unless I'm holding it 8" from my computer monitor. The 6 string picks up buzz within 6' or so, depending on the angle.

    Also, I notice that the sides of the cavity aren't shielded (in both basses). I'm sure this would help, but it still doesn't explain why the 5 doesn't buzz, and the 6 does.

    I've tested the 5 with the same method as the 6, and the readings were identical.
     
  6. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    bump...

    still looking for some help
     
  7. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    bumpage.

    mr wilson where are you??? ;) lurknfur??? ;)
     
  8. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    you don't say when you're getting the hum. At all times? When not touching the strings?

    nothing obvious springs to mind, but I do recognize an Elrick cavity when I see one ;)
     
  9. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    It's all the time.... wait now.... hmm.... yes. it's all the time. i've recorded clips of both the 5 and the 6. and the 5 is dead quiet. while the 6 hums/buzzes while i'm playing and not playing as well. it seems to be interference from my monitor or tv. (it gets worse depending on the angle the bass is facing)

    the 5 string will buzz, but only when it's almost against the monitor. the 6 will buzz when i'm sitting in my chair a few feet from the monitor.

    it's actually quite annoying. i just strung the 6 with dr fatbeams, and really love it. I'm aching to record some bass parts into the computer, but the buzzing is too loud. i've resorted to turning off the monitor during recording, but that's not really a long term solution.

    thanks for the help david.

    oh there was one other thing. i noticed that the blend pot doesn't have a back cover to it? while on the 5 it does. and the blend pot seems to be wired a bit different on the 5 as well. the 6 has 2 white wires wrapped around the pot and soldered to the connections. the 5 doesn't.

    i've talked to bryan tyler who is a big elrick fan, and he said that he doesn't get any buzzing in his basses. so i find this quite odd. he did mention the level for the preamp may be set too high, but in both the 5 and 6, the level is the same.

    my repair guy said over the phone, that it may be the preamp itself. But I just wanted to rule out as much as I can on my own (with a pinch of TB help).

    so i'm hoping it's a bad solder somewhere, or a bad pot? otherwise i'd have to replace the preamp. maybe a ground loop?
     
  10. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    oh,

    also, i still get the noise, to a lesser degree, whether the bass is active or passive. would this mean that since i still get the noise in passive mode, that the pre has nothing to do with the problem?
     
  11. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    possibly. How do you have the gain pot set on the bart preamp? If you have it set to flat (i.e. zero gain) and the noise is the same regardless of whether you're in passive/active modes then chances are it's not the preamp IMO.

    As to your earlier comments re the blend pots, Bart started using newer blend pots in the last year or two so I'd surmise that's the difference.
     
  12. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    The 6 is from 2000, and I think the 5 is newer. So, I'm guessing that the 5 has a newer pot, especially since it's wired differently.

    The gain pot in the 6 (and the 5) is set to 2. I just set it to zero now, and it's still there, to a lesser degree. But I can still hear it, which means so can protools. ARGH! The 6 seems to be picking up more of a hi-pitched wine/hum. almost like my ear was ringing after a loud show. the 5 doesn't pick that up at all. the 6 picks up a lower sounding buzz also, which the 5 will only get when i put it less than 6" from my computer monitor, and then the hi-pitched wine will also start to be heard.

    So, since the gain was set to 0, and it still was present, we can conclude that the pre is not the culprit?
     
  13. you haven't said (or I missed it) which pickups the two basses have. Do they both have the same pickups?
     
  14. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Both basses have Barts. The thin soapbars (shaped like J's). X5's and X6's if I remember correctly.

    :help:
     
  15. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    bump... david? lurknfur? niftydog?

    any ideas? I'm going to try to locate the NEW bart blend pot. Maybe that will make a difference. Is there a way I can test the 5 blend pot, against the 6 blend pot with a multimeter?
     
  16. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    for starters I'm no guru with this stuff. David, Dharmabass (engineer) and others have a lot more grip on component function, how and the whys, etc. I'm just an isolate the component, common sense, trial and error guy.

    The first thing to do is isolate the problem to the bass for a fact - which sounds like it's been done, but that's paramount. You need to know your trying to fix somethng that's broke and not breaking something that's fixed. That includes location. Does the bass make the racket no matter where or what it's played through or is it just in that room? Electronics do very wierd things. Are you using the same cord all the time or one for the 6 and another for the 5? Cords are a problem more often than a bass. Definetly make sure the cord's not a source.

    In the bass itself moving components are by far the most common problem areas - the jack in particular but also the battery clip, switches, and pots on occassion. I would definetly wiggle each terminal on the jack and see if there's any slop there. Also, that's one funky looking battery. Do you know for a fact the battery is up to snuff? Most passive by-passes only cut the hot leg to the preamp so you're still connected to the electronics/battery through grounding which means the passive mode could still be affected.

    The bass of that bay is shielded so anything metal is automatically grounded (including hot leads) and any grounds between the pots are redundant and unnecessary. Probably the reason they didn't shield the sides is they feared the pot lugs close to the wall would short out. I always throw a strip of electrical tape beneath the lugs of each pot and on the wall anywhere near a hot lug. Which brings to mind that some switches aren't to be grounded for whatever reason but that switch is probably grounded by the shielding. Make sure none of the leads going to the switch are hitting the metal casing.

    When I check for continuity I just set the meter on 1k ohms, cross the leads to check for the reading to make sure it's working and to know what the most I can expect is. I guess ideally the reading should be 0 (no resistance) but I ususually have some for whatever reason.

    If you get zip between the bridge and jack, then the bridge wire should be fine. A properly grounded bass should result in touching the strings decreasing the hum to the point of killing it altogether. If hum increases when the strings are touched that's a red flag of improper grounding somewhere. Some active electronics (primarily EMG) don't connect a bridge wire cause it's unnecessary for quiet operation and it's a shock hazard.

    I touch the meter pot to pot and pot to shield, jack to bridge, switch to shield and switch to pot. They should all give me the same reading I got crossing the meter leads (if the switch is grounded). To check bare pots out of the bass or to determine how a switch works, I use the same setting and connect the leads to each possible combination of terminal connections with the switch in each position. For pots, I connect the postive lead to the center lug via alligator clips leads and the negative to the outside lugs one at a time. Each time rotating the pot from off to max and observing the meter arm for travel. There should be a smooth, responsive, and appropriate transition as the pot stem is turned back and forth. I prefer the cheap meters with arms that I can see move to the more expensive digital meters that just give you a number.

    Does a 0 reading mean all grounds are fine? In my experience to date - yes, if the meters fine and checks were done properly. But it's very easy to think you're touching one place with the meter probes when you may not or you may be touching that AND something adjacent to it (which is properly grounded).

    I doubt the blend is the problem. Usually their wired similarly but not always. Typically the 4 perimeter lugs have tiny wires attached in an X patter but I've seen them wrapped around the pot cause it's easier to do. Blend backs are typically open in the center unless they're ganged pots and from what I can tell from your pic the second pot from the left is the blend.

    Looking at that control bay is one reason I've gone straight to jacks with no onboard controls but that is a very well done wiring job for all the junk it contains.

    My approach for onboard electronic trouble shooting is to first run the pups straight to the jack. If the problem is present then it's in the pups or jack (or battery/clip if active pups). If the problem is not present then you know it's somewhere in the harness or something in the way the harness interacts with the pickups. Next I remove the active components from the harness and run the pups through the passive harness. If the problem is present it's in the pots/switch/connections. If not, the pups and harness are fine - that leaves the active components. The only way I know to check active modules is to remove them or replace one with a known working unit or equivalent.

    I had a Tobias harness with buffer, pre, and mid that was distorting and when I removed the buffer, it was fine. It seems like a hassle to gut and start from scratch but it's a lot faster, easier, and more effective in the long run than a hit or miss approach with the components in the bass.

    Does decreasing the gain to 0 with the problem still present indicate the pre is fine. I wouldn't rule out the pre till it's in the circuit and there's no problem. A better indication to me the pre is ok is you get the same problem in passive mode which it implies it's something common to both circuits. Short of abuse and design error, pre's a pretty fault free till they get about 10 years old it seems.

    I always remove the entire harness from the bass and mount it to a piece of cardboard to do any trouble shooting. Trying to work in the bass is asking for grief, poor connections, and inadvertantly melting wires with the iron. Even so, if the bass uses a flush mount jack (like yours), you still have to wire the jack connections in the bass (which I will usually do first while laying the harness on the back of the bass then drop the harness in after the jack is complete). Wire lengths should be no longer than necessary but I leave slop for flush mount jacks so the harness is completely out of the way so I have an unobstructed approach to soldering the jack.
     
  17. C-5KO

    C-5KO

    Mar 9, 2005
    Toronto, Canada
    Fantastic!

    Thanks Luknfur:

    My A - B testing of the 5 and 6 string basses were identical. I used the same patch cord, same settings on my computer, even tried to sit at the same angle/position in my chair.

    I could tell right away when I plugged in the 6 string that it was much noisier.

    I'll try testing the battery. What exactly is "slop on the terminal"?

    I'll make sure none of the leads going to the switches are touching the casing (you mean shielding and pots?).

    The noise is still there whether I touch the strings or not. It is also there in passive mode, but to a lesser degree. Maybe it is the battery. I didn't know that even in passive mode, it may have an affect on the bass.

    Thanks for your help. If this doesn't work out, it looks as if I/somebody will have to go in there with an iron, and start isolating the parts. I didn't really want to have to do this, because as you said, "it's a well done job for all the junk it contains", and I didn't want to go and break something that doesn't need fixing by accident.
     
  18. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    I'll try testing the battery. What exactly is "slop on the terminal"?

    Sorry, that was just a reference to the wires that attatch to the jack terminials being longer than required. The main reason your electronics look so clean is that all wires are only as long as they need to be to make their connections. Otherwise it would look like a plate of spaghetti in there. That takes time and attention and so is very intentional as apposed to haphazard, "sloppy" work.

    I'll make sure none of the leads going to the switches are touching the casing (you mean shielding and pots?).

    By casing I was referring to that metal external surround on a mini-toggle that is usually on all sides except the bottom where the terminals are. Mini-switches are also one of the more challenging soldering tasks.

    The noise is still there whether I touch the strings or not. It is also there in passive mode, but to a lesser degree. Maybe it is the battery. I didn't know that even in passive mode, it may have an affect on the bass.

    I have no idea either, that's why I personally wouldn't rule it out.

    Thanks for your help. If this doesn't work out, it looks as if I/somebody will have to go in there with an iron, and start isolating the parts....

    Understand. Just keep in mind that it may not necessarily be any easier for a tech to resolve than you

    You never did say whether the bass makes this noise no matter where it's played or what it's played through?