Shielding/Star Grounding Troubleshooting Help Needed

[bongomania]

When you say "swap pickup direction around" do you just mean a 180 deg rotation with the pole-face (outward-pointing) top still "on top"? Because N and S polarity do not change in that case.

 

[SGD Lutherie]

I'd like to get some more commentary on this subject before I go buying more pickups or sending mine off for re-polarizing, etc. It seems as though "polarity" and "phase" are being used interchangeably in this thread, at least enough to where I'm confused. Of course they have different meanings, but the mechanical function of pickups has me in doubt.

The correct terminology is actually "polarity". Phase is time domain related. So you really can't have two pickups out-of-phase, but you can have them revered polarity. Delaying a signal and mixing it back in causes phase shifts, and is how a flanger works. Phase shifters are similar but use all-pass filters.

But "phase" has become so common for the polarity of wave forms that everyone uses it. You can think of the signal of two opposite polarity coils as out-of-phase with each other, but technically phase is one of them delayed in time.

On a technical level, what is the exact relationship between the magnetic polarity of the pickup poles and the directionality of the two wires from the pickup?

If both coils are wound in the same direction, and wired up with the same polarity, reversing the polarity of the magnets on one coil will render them "out-of-phase" with one another, because as one is going positive, the other is going negative. Then by reversing the electrical polarity of one coil, or winding it in reverse, you now have them back in phase.

The reason this cancels noise is because the noise does not rely on the magnets to get induced into the pickup (some noise does however, but for this example we can ignore that). So when the two reverse polarity noise signals are summed together, they cancel out.

Since the strings are being sensed by the coils using the disturbance of the flux lines from the magnets (variable reluctance), and the two magnets are opposite polarity, the signals from the two coils sum in phase.

So the reversed magnets puts them out-of-phase and the reverse wiring (or winding) puts them back in. But the noise enters both coils the same, regardless of the magnet polarity. Same direction hum-canceling coils are always wired out-of-phase, while reverse wound coils are wired in. Most humbucking pickups have both coils wound in the same direction.

 

[greenboy]

When you say "swap pickup direction around" do you just mean a 180 deg rotation with the pole-face (outward-pointing) top still "on top"? Because N and S polarity do not change in that case.

Oops. Brainfart from not reading thread there, Bongo. With some pickup configs this works, but not sure about ones with each slug being a separate magnet.

Are we talking your SCN by any chance? I'd give Bill Lawrence a call or email.

 

[SGD Lutherie]

SCN's are stacked humbuckers. They will have the same magnet polarity on each pickup. There's no reason for them to have opposite polarity .... that only works for single coils. Humbuckers present a composite signal regardless of the magnetic polarity.

In the case of the SCN's, the magnets (one of each side) are between the top and bottom coil, with the same pole facing in to the pole pieces. So both the top and bottom coil will have N or S facing out. (I'll have to look at the patent again, but that's the way I remember it)

 

[bongomania]

Ah. So hmmm... Yes it's the SCN's I'm wrestling with here... So you're saying they are supposed to have the same N/S directional polarity. So that wasn't my problem after all.

Right now I have them wired like so:

pup 1 hot --> pup 2 gnd
pup 1 gnd --> output jack sleeve --> shielding
pup 2 hot --> output jack tip

Before I reverse the wiring of one of the pups, does it really make sense that that would be a good thing to try?

 

[SGD Lutherie]

You have them wired in series?

The problem is likely that the common on pickup 2 is also the shielding (the metal parts of the pickup), so that must go to ground. So now you have pickup 2's metal parts in the signal chain, so you are getting noise.

To run them in series you need to separate the ground from the common on pickup 2. Some pickups have three wires, hot, common and ground. It's possible that they wont work in series correctly.

 

[bongomania]

Hm, OK. I'll do some experimenting. These have only two wires per pup, so perhaps series is out.

 

[Angus]

Either way, I spent 50 cents on it, so I hardly consider it a "big waste of money."

And further, there's just something philosophically satisfying about using high quality components, even if they don't make that big a difference.

The reason why I mention the orange drops is because they are way, WAY overrated for a passive guitar application. They were initially use (I suspect) because someone wanted to modify a tone control in a guitar and took it to an amp repair shop where they had these caps laying around. They're originally used (at least where I've seen them) in the power circuit (and the bias circuit in one amp I've seen) for the tubes in a tube amp. The original orange drop is a 600V-rated cap used in a circuit that will see 0.5V if it's lucky.

It's like taking your Hummer H1 to go buy a carton of milk. It works, and you know that the carton will fit, but omg is it excess.

I just rail against what I've heard from a lot of guitar players, which is that it sounds better because it's rated higher...which has absolutely zero to do with it's functionality. Sigh.

Anyway, the point about using high quality components is perfectly fair and I would never disagree with that. In fact I agree really strongly.

 

[samuelzero]

The reason why I mention the orange drops is because they are way, WAY overrated for a passive guitar application. They were initially use (I suspect) because someone wanted to modify a tone control in a guitar and took it to an amp repair shop where they had these caps laying around. They're originally used (at least where I've seen them) in the power circuit (and the bias circuit in one amp I've seen) for the tubes in a tube amp. The original orange drop is a 600V-rated cap used in a circuit that will see 0.5V if it's lucky.

It's like taking your Hummer H1 to go buy a carton of milk. It works, and you know that the carton will fit, but omg is it excess.

I just rail against what I've heard from a lot of guitar players, which is that it sounds better because it's rated higher...which has absolutely zero to do with it's functionality. Sigh.

Anyway, the point about using high quality components is perfectly fair and I would never disagree with that. In fact I agree really strongly.

I hear you man. I know alot of folks become obsessed with the mystique of Orange drops and bumblebees and what not when they probably couldn't tell one from the other in a blind listening test. It sounds like you know more about electronics than the average guitarist, and I can understand the frustration of listening to people argue about things they know little about... (all too common on message boards unfortunately)

Myself, I'm just starting to get into electronics, and finding it all very exciting. I'm still very intrigued at the discovery that a guitar's tone control is nothing more than a pot and a capacitor. I always imagined the tone control to be something more sophisticated.

Now that I'm thinking of it, I'm new to actually USING my tone controls too. I played for years with them all the way up without a second thought.

Very fun stuff.

 

[SGD Lutherie]

The reason why I mention the orange drops is because they are way, WAY overrated for a passive guitar application. They were initially use (I suspect) because someone wanted to modify a tone control in a guitar and took it to an amp repair shop where they had these caps laying around.

I think these types of caps are used because on the old Gibson guitars they did indeed use caps that they already had available from their amp manufacturing.. plus those were the available caps at the time.

For passive tone controls, any mylar film cap will sound good, and maybe better than a cheap ceramic cap. But we are talking about a very small change. What a good quality cap will do is be closer to it's rated value.

The whole pseudo vintage craze going on is more based on looks than substance, so those spending big bucks on NOS or repro oil and paper caps are just wasting their money, just like hi-end audiophiles who spend $600 on a wooden knob to make their stereo amp sound better!