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Purple_String

Grounding issue...

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So I redid electronics in an Epi LP. Put Duncans in, swapped electrical components and shielded every cavity. However, when I plug the guitar into a small tube amp, the hum is quite noticeable. I checked everything, all wiring seems fine, shielding is connected to ground also. Then if I use my finger to touch a string, any hardware on the guitar, metal part on the cable connector, or even metal tip of the amp's power switch, the hum is practically gone. I tried different cables and another solid state bass amp, same situation. Really don't know what to do next.

 

Had anybody have the same issue before, or have any idea on this? Thanks!

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Thanks guys! But on that post it was a loose bridge ground wire that caused problem. In my case, it seems the bridge ground wire is good. If I touch with my finger strings or tuning posts, PU covers (both), bridge / tailpiece, pots, switch, jack, metal part of cable connector, or even any part of shielding foil I used , the hum goes away.

 

Is it possible that the amp is not properly grounded through the house circuit? The power outlet I'm using has a GROUND indicator and it says grounded...

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So I took of both PU covers to see if there's any improvement since I suspected the posts on bridge PU touched the cover. I can't really tell if it really helps...

 

I also notice that, if I turn volume pot the max the hum is gone, and otherwise not. When the volume is turned to minimum, the hum is at its greatest. Does this suggest that the volume pots are not properly grounded? Could it be ground wire jumpers I put between pots or the problem lies at the ground lug on volume pots?

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Too wierd - just went thru this! However, by touching the metal

parts you described, you are "completing" the ground circuit by

becoming the missing leg.

 

What are you basing the fact that the bridge ground is good on?

 

1. Sometimes the clip in the plug in jack doesn't have enough

"oomph" to press the cable jack against the inside wall of the

plug on the guitar, completing the circuit. Plug up, wrap a small cloth

around the cable where it goes into the guitar (to insulate yourself from

completing the circuit again), the gently press to one side to "help" make

contact inside the guitar jack. did it work? If not....

2. Remove screws of plug-in plate on side of git, gently pull back to

verify both wires are definitely connected, not almost loose or broken.

3. If not broken, are the cavity shields also grounded?

4. Good ground at toggle switch?

5. Do you have a multimeter?

 

Just have to find the "missing leg" of the ground circuit..........

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Soldering ground wires to the back of the pots is

sufficient, as long as ALL grounds are interconnected.

You mention "grounding lugs" on pots -

what wiring diagram did you use?

 

Hello, GL! Whatcha thinkin' here?

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It IS a bad or weak ground. If it doesn't happen with a differnent guitar, its the ground system in the guitar you just worked on. You just have to find it because we can't test long distance.

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So I took of both PU covers to see if there's any improvement since I suspected the posts on bridge PU touched the cover. I can't really tell if it really helps...

 

I also notice that' date=' if I turn volume pot the max the hum is gone, and otherwise not. When the volume is turned to minimum, the hum is at its greatest. Does this suggest that the volume pots are not properly grounded? Could it be ground wire jumpers I put between pots or the problem lies at the ground lug on volume pots?[/quote']

 

The part about turning the volume up all the way makes it go away is a strange one, and could be related to the problem

but

What you described in your original post is something that all guitars do. If the hum goes away when you touch the strings then the ground is working correctly. It's really a pain in the *** 'cause it means that you have to keep your hand somehow in contact with the metal of the guitar or humming may become noticeable, especially when recording direct. Try plugging the amp into a different outlet (on a different circuit). Also, deflepfan stated in the other topic that a power strip helped with the hum. I would say it's an issue caused by home wiring, fluorescent lights, monitors,etc.. and there isn't much that can be done...besides moving and that's not a guarantee fix either.

I'd try different outlets first before rewiring.

 

They do sell powerstrips designed to filter out electrical interference but I never really looked into them.

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I used to get a bit of a hum on some guitars when I

would practice sitting only a couple of feet away facing

the amp (amp and me on floor) unless I had hand on

strings. Eventually discovered cable tip connector inside

cable cover had become loose - had to re-secure it with a

bit of solder...

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DSC_3748.jpg

I tried to experiment wiring with connectors. I put little pieces of electric tape on the shielding where I suspect the solder lugs on pots would touch shielding material (the cavity routing at factory was not very smooth). The green wires are common ground I used except from switch, bridge and output jack (they are black). I didn't put wire in shielding because it is my understanding that as long as switch and pots are tightly installed, shielding material is connected tothe groudn through component housing. Is this theory wrong?

 

Switch and pots were ordered from Guitar Fetish, others from Newark. I don't think there's severe quality problem with these components. Although I'm no electrical technician, I'm getting better at soldering now.

 

wd2hh3t22_02.jpg

This is the wiring diagram I used, except I wire pickup and switch at the volume pot using this formula:

1217_0133_2.gif

 

DSC_3750.jpg

I think the switch is properly grounded as I did the switch part before and there was no problem. I used shielding shrink tubing to group the wires from switch to control cavity that going through the body.

 

And yes, I have a small simple multi-meter. Although I know how it functions, I don't know where to start...

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I forgot a very important question. Did the guitar do this with the old wiring' date='etc..?[/quote']

 

I don't quite remember that but I doubt it. (This guitar I put away for quite a while...)

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looks to me like you did a very good job. I bet it's just normal electrical interference. A good noise gate will help out if it bothers you too much.

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looks to me like you did a very good job. I bet it's just normal electrical interference. A good noise gate will help out if it bothers you too much.

 

Well, thanks GL. But if that is the case, what does those "dead silence" comments on the internet mean? And also, I'm not sure if there is really no issue when I turn down the volume pot and the hum gains.

 

I have no access to high-end gear; I really wonder how "dead silence" is in reallity... The VOX AC4TV I use is a little noisy itself in fact, but I don't think the Acoustic B20 solid state bass amp sounds that noisy.

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Is it possible that you have a ground loop issue caused by using copper foil and having all of the pot casings grounded together with wire as well?

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Is it possible that you have a ground loop issue caused by using copper foil and having all of the pot casings grounded together with wire as well?

 

Thanks, dchale!

 

Frankly, I never fully understand how "ground loop" really works. But I don't see any bad reason get all pots and switch on a common ground bus. I guess isolating shielding material from pot housing could help. Let me try this next.

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Purple String - excellent attention to detail, an exceptional

job. Nothing wrong with keeping the stock Epi connectors as

long as the point-to-point connections thru the connectors go

where they are supposed to.

I've been asking myself what would I do, looking at your pics and

reference schematic, plus other schematics on the Guitarelectronics

website, then it occured to me -

 

I see only ONE push-pull switch, it appears to be for the bridge

pickup only (based on the pot lay-out in your pic). Are you planning

on using the single push-pull switch as a MASTER coil tap switch for

BOTH pickups, or just for a SINGLE pickup, with the other pup wired

as normal? (I'm guessing you're tapping the Bridge, but leaving the

Neck wired normally).

 

I'm also not sure why you used the "independent volume control"

option that you added to bottom of schematic.

The schematic you posted is for TWO push-pull switches, vice ONE.

I did find a schematic for a Single P/P switch, using the switch as a

MASTER control, this can be used for just bridge only by simply not

connecting the Neck pup (top left pup in diagram) to the P/P switch,

wiring the Neck North/South Finish wires together as would be if installing

as regular "untapped" pick up (as per standard Les Paul schematic).

 

I'm thinking it's an inadvertant mis-wire, would definitely recheck EVERY

point-to-point connection (including thru the Epi connectors). I'm posting

links to 2 schematics - first one with single P/P switch as MASTER for both

pups, second one showing standard LP wiring (I'm sure you've probably

already seen 'em).

 

Push/Pull as MASTER:

 

http://www.guitarelectronics.com/product/WD2HH3T22_01/Guitar_Wiring_Diagram_2_Humbuckers3Way_Toggle_Switch2_Volumes2_TonesCoil_Tap.html

 

Standard LP Wiring:

 

http://www.guitarelectronics.com/product/WD2HH3T22_00/Guitar_Wiring_Diagam_w_2_Humbuckers3Way_Toggle_Switch2_Volumes2_Tones.html

 

Hope this doesn't just ADD to to confusion!!!

Others with more experience will hopefully add input, for me, I

wouldn't deviate from the schematic...

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A few things I'd do. And good job on the shielding!

 

1. Get those crappy connectors out of there and hardwire everything. post haste!

2. Do you zero the pots before soldering on them? Those pots aren't too robust, you'll fry them quite easily.

3. Rewire the whole thing. IMO you have way too many splices in there, and plastic connectors. You need to be running one solid lead from point to point. Not component, a lead, a splice, a lead, a plastic connector, a lead, to the other component. Way too much can go wrong. Do all this and your troubles will go away.

 

P>S> use shielded wire for the longer runs as well.

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Thanks animalfarm!

 

The neck pickup I have in there is a two-conductor one and the bridge is four-conductor (5 counting the bare ground wire). So I'm only using push/pull for tapping the bridge pickup. I'm using "individual volume control" setup so that I can easily blend sounds from individual pickups when the switch is at middle position. After all, I'm experimenting stuff here.

 

I didn't keep Epi connectors. I've had experience making cables and connectors for occasional design work at work and I have easy access to cable making tools. So I ordered contact pins and connector housings directly through Newark. (By the way, they sell Orange Drop 715P caps for $0.882 each (P/N: 89F3470) and SwitchCraft jacks for $1.98 (P/N:39F782). They don't carry pots used in these guitars though; otherwise think of all the money that could have been saved...)

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Thanks Musikron!

 

Yes, I zero the pots before soldering on them.

 

Well, all the wires and connectors don't bother me that much. (I work with industrial instruments at work, plus I always keep records on paper for tracing each wire I run besides color-code them.) The connectors are all industry standard (Molex and Tyco); we use these on our ten-thousand-dollar dedicated instruments. Although when I measure ground-to-ground resistance between components, ground terminal on switch to ground terminal on jack (when connectors are plugged in) is almost 6 times the resistance of that from pot to pot (connected through short green 22 AWG wires in the picture), (thinking all the wires from shoulder to butt, male and female contact pins). It seems in theory that eliminating connectors would increase conductivity. But I don't consider it a big issue comparing the ease in swapping pickups later on. Like I mentioned before, I'm doing experiments on this particular guitar. But still thanks for pointing out!

 

The reason I don't use shielded wires is that I so far haven't figure out a convenient way working with those shielding braids. I mean, they really entangle together! So I keep using insulated hook-up wires, although I'm thinking using 24 AWG bare braids for ground bus next time. But I did use almost a foot long shielding heat shrink tubing to enclose the longest wiring that runs more than half way across the guitar body.

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I checked again relating chapters in Dan Erlewine's "Guitar Player Repair Guide" and the "Practical Electronics For Inventors" book I have, I stand on my theory that connecting shielding with ground bus (ie. pot housings) is okay. Plus there's no point ground-lifting within the source (the guitar).

 

So I did comparison test again with other instruments I have. I turned of computer monitor, most of the lights in the room, plugged in alternatively all-stock Squier Classic Vibe Tele and Epi Viola to my VOX AC4TV amp and turned amp volume up - humming (at different levels). And it's not the hum that Tele pickups produce, I can tell the difference. Then I used my finger to touch metal parts on Tele, Viola, cable connector, as well as power switch on amp, and they all stopped the humming. Then I plugged the LP in Vox headphone amp, there was no hum at all (although I'm not convinced that it proves anything).

 

I measured between grounds on each two parts within the guitar circuit including shielding, and it indicates every ground is connected. And it is reasonable, since touching the metal toggle switch on the amp stops the humming also proves the fact that it is a closed circuit. My impression, then, is the amp is not properly grounded. Which is weird because both Belkin and Philips power strips I'm using have "grounded" indicators and they say grounding okay... Conclusively, it is either the input on the amp has grounding issue or the housing does; either way, the guitar itself is fine.

 

But I'm still not 100% certain about my conclusion. My major was not electrical engineering nor knowing how to comprehensively test a circuit [thumbup] So feel free to follow on ideas folks!

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OK, you know that YOU complete the ground circuit when done properly right? Take your hands off the guitar and it will buzz, this is normal. When you touch your hand to something metal, you close the ground and the buzz goes away. This is also normal.

 

If you touch the strings and it still buzzes, then you touch a pup or switch or pot and it goes away, then your string ground is the culprit.

 

You should be able to touch the strings and complete the circuit, eliminating ground hum.

^^^ What happens during these tests?^^^

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There was no humming when you used the headphone amp because I'm guessing the headphone amp takes batteries. Which leads me to believe even more that it is electrical interference. I've heard that using a wireless transmitter will eliminate this, because you are no longer part of the ground. and also, that active electronic guitar and basses don't really have the problem either.

Work on the interference instead of the guitar imo.

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OK' date=' you know that YOU complete the ground circuit when done properly right? Take your hands off the guitar and it will buzz, this is normal. When you touch your hand to something metal, you close the ground and the buzz goes away. This is also normal.

 

If you touch the strings and it still buzzes, then you touch a pup or switch or pot and it goes away, then your string ground is the culprit.

 

You should be able to touch the strings and complete the circuit, eliminating ground hum.

^^^ What happens during these tests?^^^[/quote']

 

Yes, the hum stops also when I touch the strings or even tuner posts. That being said, the hum stops when I touch any metal / conductive part that connects to the circuit. So I'm safe to say the guitar is done?

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Yes, done, you complete the ground circuit. It didn't happen on your headphone amp cause you are not connect to ground in any way when using that.

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