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Discussion Starter · #1 ·
This is a weird one.

I have a powerful source of EMI somewhere near my music area. I have no idea what the source is, but it makes my single coil pickups buzz like crazy.

I'm not trying to solve the EMI problem right now, but rather I'm using it as a diagnostic tool for what I believe is maybe a wiring problem.

My Tokai strat has HSS pickups - a humbucker in the bridge position and single coils in the middle and neck spots.

The humbucker is a custom-made pickup. The coils are asymmetrical (on purpose) and it's a 4-wire model, so I can split the coils as desired. I've swapped out my old stock tone pot for one that has a push pull switch, so I can do just that.

I believe my middle pickup is reverse wound. I'm not entirely sure. I do know that the wire polarity is opposite to the neck pickup (i.e. white wire is on the left for one of them and on the right for the other).

Here's the problem - the ONLY position on the 5-way switch that is relatively silent is pos 4, where the neck and middle pickup are both on.

Here are my observations and measurements:

pos 5 (neck) - 5.9K, buzz
pos 4 (neck+middle) - 2.99K, QUIET
pos 3 (middle) - 5.9K, buzz

pos 2 (mid + bridge) - 3.99K, buzz
pos 2 (mid + bridge) - 3.42K, buzz < coil tap engaged here to split the bridge humbucker

pos 1 (bridge) - 11.78K, buzz
pos 1 (bridge) - 7.89K, buzz < coil tap engaged here to split the bridge humbucker

It seems to me that pos 2 (mid + bridge) and pos 1 (bridge humbucker) really should be QUIET, but they are not.

I did some quick 1/R = 1/R1+1/R2 calculations, and the values I'm getting when engaging 2 pickups at a time are in the right ballparks.

I THINK that means I have the right windings engaged at the right times, but I'm not getting much of a hum-cancelling effect.

The notes I received with the Humbucker indicate the two coils are wired like this:

adjustable coil - start black, finish white
slugs coil - start green, finish red

His recommendation (the guy who made the pickup) was that I wire as follows:

Connect white and the bare ground wire to ground (always).
Connect black to the output for single coil
Connect black to green and then connect red to the output for humbucker

I checked my switch, and that's how it's setup.

Any idea what might be going wrong here? And how to fix it?

Could it be something about polarity?

I should probably mention that this is NOT a standard strat wiring. I don't think it affects this problem, but maybe it's relevant in some way.

Pickups go to the pickup selector first, then to the single volume and single tone pots and out from there. Schematic in the thumbnail if you're interested.

Text Handwriting Line Font Diagram
 

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I've got two thoughts...(caveat...I'm no wiring guru,nor did I stay at a holiday inn last night..and I've got a scotch or two into me.)

#1) EMI should probably not be used as a diagnostic tool,it just muddies the whole situation.

#2 )The fact that position 4 is pretty much silent suggests to me that your middle pu s indeed RW at least as far as the neck p-up is concerned..
seems like the mid isn't RW to the bridge.
had that issue when a I replaced a middle p-up and it didn't play nice with a 'lil59 I had in the bridge position.
I fixed it by putting another SC in the bridge.:D
 

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Discussion Starter · #3 ·
Yeah I had come to much the same conclusion.

Seems like I ought to be able to resolve this by reversing the polarity on the white-black coil of the humbucker?

Right now I'm warming up the soldering iron to fix a loose connection to the shield of the output jack that I just discovered - that might be contributing too.
 

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Discussion Starter · #4 ·
Yeah that did NOT fix it.

Another guitar on exactly the same rig is just fine, no significant buzz, so it's got to be something about the strat wiring.

I just noticed that I get exactly the same buzz when I touch the tip (the hot wire) of the guitar cable with my toe.

Would this mean I've got some sort of rogue ground connection on the hot wire?

Or just that my body is an antenna, and my strat is an antenna?
 

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I've swapped out my old stock tone pot for one that has a push pull switch, so I can do just that.
Did these issues start after this swap?

I just noticed that I get exactly the same buzz when I touch the tip (the hot wire) of the guitar cable with my toe.
One end of the cable is plugged into your guitar and you touching the tip of the other end with with your toe...and getting a buzzing sound!!!
 

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Discussion Starter · #6 ·
Did these issues start after this swap?
No, swapping the polarity of the black-white coil in the humbucker didn't change anything, so I put it back the way it was.

One end of the cable is plugged into your guitar and you touching the tip of the other end with with your toe...and getting a buzzing sound!!!
LOL, also no.

One end of the cable is plugged into my pedals and amp, and it's quiet if I don't touch it, but it buzzes when I touch the tip. And it buzzes in exactly the same way that my strat buzzes.
 

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One end of the cable is plugged into my pedals and amp, and it's quiet if I don't touch it, but it buzzes when I touch the tip.
That is what I thought...I was just pulling your leg...or toe... in this case

That buzzing is normal. The hot is going to a ground source somewhere.
I would check all of your wiring to see if there is any connection between hot and ground occurring somewhere.
 

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Discussion Starter · #8 ·
I checked for continuity between each of the pickup hot wires and the shield on the output jack and I'm not finding any connections.

On a hunch I tried swapping the polarity of the green-red coil, thinking maybe that would help.

Originally it was like this:

ground - white wire - adjustable coil - black wire - (tap here to hot output for single coil) - green wire - slugs coil - red - hot output (humbucker)

Tried it like this:

ground - white wire - adjustable coil - black wire - (tap here to hot output for single coil) - RED wire - slugs coil - GREEN - hot output (humbucker)

That DID change things, but not at all in an expected way.

With this wiring change in place, the one silent position has MOVED to the middle pickup spot. WTH?

I tried adding an extra ground strap from the pickup switch body to the tone/vol pot backs and that didn't help either.

Seriously puzzled by all this.
 

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Discussion Starter · #9 ·
Further troubleshooting:

Disconnected the tone pot from the circuit - no change

Disconnected all of the humbucker wires and measured across them to confirm that black-white is one coil (~8K), green-red is the other (~4K) and there is no short between any of these leads and the bare shield wire; everything seems to check out

Checked the output jack to verified polarity on the leads - cable shield is continuous with the back of the pots inside the guitar, cable tip is continuous with the hot path inside the guitar

Disconnected the volume control from the hot path and wired the pickup directly to the hot wire on the output jack - in both single coil and humbucking mode there is still major buzz

Checked my SG on the same cable, same amp - the same buzz is there (as it is when there is no guitar at all) but it's vastly quieter, barely noticeable. Even when I coil-split the SG, the buzz is not really appreciably louder than the cable by itself

Wandered around the room with a guitar cable plugged into my amp, bringing the other end of that cable close to various things in the room to try to identify the sources of this 60 cycle hum:
- overhead flourescent fixture is bad
- cheap power bar on my soldering desk
- desk lamp with an LED bulb
- desk lamp with a compact flourescent
- turning all of those off reduces the hum considerably, but...

Checking those same sources with the strat plugged into the end of the cable - same buzz, but dramatically louder. I mean massively louder.

So... what the heck is turning my guitar into a giant antenna? What am I missing here?
 

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So... what the heck is turning my guitar into a giant antenna?
Are you using any significant amounts or lengths of unshielded wire in your guitar's wiring harness?

EDIT...I just reread your 1st post that says this is a Strat style guitar. Doubtful that my question applies. This can be more of an issue with semi and fully hollow style guitar harnesses.
 

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Did the guitar hum before doing the work you're doing now?

Can you throw another humbucker in it to see if the hum is still there?

Does the hum disappear when you touch the strings?

For reasons beyond my electrical knowledge, some guitars just pick up more interference than others.

I have a 70s LP that hummed even with a new harness. The only thing that solved the problem was shielding the pot and toggle cavities with shielding paint from Stew Mac.
 

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Discussion Starter · #12 ·
Thanks guys.

I don't honestly know when this started.

I really only play electric for a few months of the year, while working up to an annual reunion jam.

The strat has always been a lot noisier than the SG, but I would expect the humbucker to deal with a lot of that, and it doesn't.

I do remember replacing the output jack a few years back, to fix a very similar problem. Maybe it's the output jack again, even though everything checks out electrically.

It's damn frustrating, lemme tell ya.
 

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1) For greatest hum cancellation, the pickups involved should sense the identical amount of hum, such that when they are out of phase the two hum signals are of equal amplitude. When the bridge pickup is a humbucker, it already cancels hum, but in tandem with the middle pickup, there will now be two coils of one "orientation", vs one coil of the other. In other words there is more hum of one polarity than of the other, yielding imperfect hum-cancellation. In theory, cutting one of the HB coils would yield better hum-rejection when middle and bridge are used, but you would have to know which of the two coils in the bridge PU is the one to keep in circuit.

2) Asymmetrical pickups can sound great. Keep in mind that the degree of asymmetry is not perfectly reflected in the DC resistance. If I use a thicker-gauge wire for one coil than the other, if may read as having a significantly lower DC resistance but have almost as many, or maybe even more turns than the other. In general, the number of turns is a stronger predictor of output than the DC resistance, although clearly more turns = greater resistance (so DCR is correlated with output, if imperfectly). What you don't seem to know here, is which of the two coils in your HB is the optimal one to cut for achieving hum-free "cluck". It may be the builder of the pickup made some assumptions about the magnet orientation and polarity of your other pickups that was inaccurate. There is a possibility that the cure to your woes is to flip the bar magnet around in the bridge pickup such that the magnetic polarity of the coil you tap is the optimal one.

3) There is a brilliant trick, devised by the late Bill Lawrence (which is pretty much where you go for briliant pickup ideas), described in this recent Premier Guitar column from Dirk Wacker. It describes how to maximize hum-rejection when using coil-cutting. Mod Garage: The Sound of Silence | Premier Guitar
 

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Discussion Starter · #15 ·
Thanks, that's some interesting stuff.

These pickups are a custom set, they all came together from the same guy. I presume he knew what he was doing, but it's possible that they are not optimal.

I use the hotter coil (black-white) in the bridge as a single - 8K vs. the 5.9K of the neck and middle pickups gives it enough bite for a screeching treble lead tone.

The 4K coil in the humbucker is much quieter and more mellow, not really useful on its own, but engaging it along with the 8K coil changes the sound of the pickup quite significantly, shifting EQ towards the mids and boosting output to give me a driving rock tone.

I'm not really worried about the tone of any of the pickups or their combinations. Middle + bridge actually SOUNDS great and has the expected sort of tone.

BUT... overlaid on these wonderful sounds is a boatload of noise. Way more than I would ever expect. When I plug a different guitar into exactly the same rig, even in a single coil setup, it is vastly quieter.

Zero'ing the vol control on the strat (or shorting hot to ground, basically the same thing) makes it dead quiet.

I just realized that the ouput jack is a TRS, and I've got the ring and the sleeve strapped together as ground, with the hot wire just on the tip.

There's a possibility that the way the jack fits into the body is pushing that ring connector (ground) very close to the hot tip. I could clip it off, but maybe an easier step is just to disconnect it from the ground wire. Trying that now.
 

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If the hotter coil on the HB senses more hum than the middle pickup, your degree of hum-rejection will be limited, even if their respective polarities and phase are exactly as they should be. I find it useful to think of pickup coils as having a "radio antenna" as well as string-sensing function. Their ability to pick up radio station CBUZ 60hz to the same degree depends on their orientation, spacing and sensitivity. Remember that the "dead quiet" HBs we grew up with had matched coils sitting right beside each other. Hard to get more equal hum-sensing than that.

Your hot coil on the HB is 8k and your middle PU is 5.9k. As I noted earlier, the output level and DC resistance are not perfectly correlated. But that big discrepancy in DCR, and your preference to use the 8k coil because it is the hotter of the two bridge coils, suggests that they might not be sensing 60hz hum to the same extent, providing less hum than one alone, but not as much as matched coils.

I suggest taking a gander at that PG article. It might be just the ticket. The punch line is that the mod keeps both coils in circuit when the "coil-tap" is used. However, frequency content from the "unused" coil is shunted to ground. In this way, the hum from both coils is preserved, and cancelled out, but only the string content from one coil is heard. Damn clever.
 

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I just realized that the ouput jack is a TRS, and I've got the ring and the sleeve strapped together as ground, with the hot wire just on the tip.

There's a possibility that the way the jack fits into the body is pushing that ring connector (ground) very close to the hot tip. I could clip it off, but maybe an easier step is just to disconnect it from the ground wire. Trying that now.
Good Luck....I hope changing this solves your problem!
 

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Discussion Starter · #18 ·
Monkeying with the output jack didn't change anything.

I hear what you're saying Mike, but the thing that's bothering me most here is how noisy the guitar is REGARDLESS of the pickup config.

With a different guitar, even coil tapped to give me a single coil config, it's a LOT quieter, barely noticeable, in exactly the same room, same cable, same amp, etc.

I do have a regular (symmetrical) humbucker kicking around. I'll try wiring that in (just that one pickup) as an experiment and see if it still buzzes.
 

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Pickups vary in their sensitivity to EMI. On my Coronet, I have a Mighty Mite P90 in the bridge position, and a narrow-scale SC I wound myself, using polepieces from a busted late-60's grey-bottom Strat PU. The homewound pickup is a whole lot quieter than the P90.
 

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Discussion Starter · #20 ·
Understood.

I just did another experiment.

I found a 2-wire humbucker in my parts bin that's about 8.5k or so - I connected it directly to the guitar cable and noted the volume of the buzz.

Then I did the same thing with the asymmetric humbucker from the strat - connected it directly to the guitar cable and listened - the buzz was a LOT louder.

Then I remembered there is a bare braided ground wire on the asymmetric humbucker. I connected THAT ground to guitar cable too, and tada! much quieter and much closer in volume to the noise level of the spare humbucker I just tested.

So... I think perhaps what I've been fighting this whole time is a bad connection on that braided ground wire.

I'm going to have to re-do a bunch of the strat wiring anyway, since it's pretty much torn apart at this point from all the troubleshooting, so I'll do my best to clean all that up and use fresh wire, plus I'll try to make the grounds more robust all around.

Hopefully this will do the trick.
 
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