Reverse wind/reverse polarity question...

[Possum]

...

Uh we're talking about different things here, I'm talking about shorts to the poles, not adding a copper strip and grounding it. Shorts to the poles probably involve some closed loops. I see no point in taking the extra time to ground strat magnets. Yes bucker magnets are grounded, trying isolating them and you will hear a little bit more clarity not much and you should see a very small change in LCR readings. Gibson actually used to tape their magnets and/or varnish them to insulate them. I've seen these in P13's and P90s. I think eventually they figured it wasn't worth the extra effort to do that, same conclusion I had as I tried both. Some of their magnets are so burned they don't conduct electricity at all and are completely insulated by carbonized alnico, I have one in my early Patent.

[David Schwab]

Uh we're talking about different things here, I'm talking about shorts to the poles, not adding a copper strip and grounding it.

You said:

Grounding magnets adds metal to the circuit so you are adding inductance which changes the tone

I said add a switch and see. You wont hear a change in tone when you ground the magnets. The metal is there already, and has nothing to do with it being grounded, as Mike pointed out.

Gibson actually used to tape their magnets and/or varnish them to insulate them. I've seen these in P13's and P90s. I think eventually they figured it wasn't worth the extra effort to do that, same conclusion I had as I tried both. Some of their magnets are so burned they don't conduct electricity at all and are completely insulated by carbonized alnico, I have one in my early Patent.

Your baseplate is grounded, as are the poles. Not grounding the magnet wont change a thing. They probably put varnish on the magnet to stop it from rusting.

[David King]

Emg states that ceramic magnets have a lower inductance than Alnico. I guess that's what I was wondering about.
Ceramic also have lower eddy current losses which is probably part of why it sounds brighter too.
I stand corrected.

The reason I got to thinking about this is that ceramics mags are hard ferrites similar to inductor cores of transformers etc which are soft ferrites (won't hold a magnetic charge.) All this goes to show that you can't judge an alloy's properties by it's contents.

[Mike Sulzer]

It doesn't make a huge inductance change but there is a definite measurable effect most noticeable in the AC resistance. This is actually one way to spot a short to the poles. Alnico after all is mostly iron and is metal, replace it with ceramic and the inductance drops way back.

When you short to a pole, you make a path for current to flow. This is like a shorted turn in a transformer. You can think of it as a one turn secondary that is shorted out, although in the pickup case it might involve a number of turns, but the idea is the same. Or you can think of it as an ideal secondary with no resistance connected to a load resistor equal to the resistance of the actual secondary.

So what does the Extech see? The Extech is in the series loss position so that it can measure the inductance of the coil and its resistance. The "shorted turn" is a secondary which appears as a resistor in parallel with the coil. The Extech measures two numbers, which could be thought of as a magnitude and phase, but are actually the corresponding real and imaginary part. In the series position, the real part is interpreted as resistance, and the imaginary part as the magnitude of the inductive reactance. This is because the impedance of a resistor and and inductor in series is R + j(2*pi*f*L), where 2*pi*f*L is the inductive reactance. The meter then uses it to compute L.

If we put a resistor across the coil (and to figure out the value of the resistor, you need the turns ratio of the "transformer"), as we are doing with the short, the meter still measures the real and imaginary part, but now the circuit is more complicated. But the meter does not know that so it still interprets the measurement in the same way. The apparent inductance goes down, and the apparent resistance goes up. But actually the inductance has not changed and the increase in the apparent resistance can be interpreted to mean that losses in the circuit have increased.

For example, if the resistance of the parallel resistor is equal to the inductive reactance, the apparent inductance drops to one half the actual inductance. In most cases, the parallel resistance is higher, and so the decrease in inductance is smaller.

[Possum]

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Dave no offense but I sometimes wonder what you are hearing, when I comment on anything it is guitar pickups only not bass pickups. Thats a whole different range of frequencies; I am very sensitive to what is happening in the high treble ranges that probably you don't really even care about in bass pickups maybe. You CAN hear a difference in an ungrounded alnico magnet in a humbucker and you can measure it with the Extech. I really don't care exactly what it is measuring, I mostly look at AC resistance when I use the meter, thats the most useful measurement. Why would Gibson wrap tape around a magnet? To keep it from rusting? That makes no sense. Varnishing a magnet insulates it. Those old magnets don't rust anymore than new ones do which is practically nonexistant over the course of 50 years. P13's are horribly dark pickups and it makes sense that they tried to kill some dullness by isolating the magnet. I had this idea myself even before seeing the guts of a P13. I've also tried increasing treble loss in the magnet and didn't like how that sounded. Both technique work but very little, not enough to warrant doing it in a production scenario.

With ceramic magnets vs alnico you're talking about basically a chunk of iron vs. a piece of oxidized iron clay, big difference and why ceramics have a reputation of being shrill in some uses. I do use ceramics but only with blade pickups because alnico makes them way too dark.

[Zhangliqun]

The second can be achieved by interchanging the two coil wires. It is not necessary to rewind the pickup.

Exactly. All you have to do to "reverse wind" is just reverse the leads. What was hot is now the ground lead and vice versa. Your only problem is flipping the polarity of the magnets which is pretty easy with A2 and A3, but a bit harder with A5.

[Possum]

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Yeah you can do that but its a hobbyist solution, bad idea to be selling pickups made that way, eventually you'll get that phone call from a customer, "HEY! WTF..."
Also, customers don't like it when they get a loud buzz when touching the poles of a pickup made that way because your coil start is now hot lead.

[Possum]

...

Also, tearing apart a fiber strat pickup just to flip the magnets, isn't going to be fun or easy. If the bobbin is plastic with magnets inserted then you can push them out and flip. With a fiber strat bobbin you probably won't be equipped to take it apart and successfully put it back together. It would be much easier to buy a neodymium magnet off Ebay of sufficient power to just remagnetize it to opposite polarity in 2 seconds.

[David Schwab]

Dave no offense but I sometimes wonder what you are hearing, when I comment on anything it is guitar pickups only not bass pickups.

Dave, basses these days tend to be much brighter than guitars. Besides often using very bright sounding strings, the fundamental is lower, and the scale length is much greater, so you have a wider harmonic spread. With guitars the higher notes push the upper harmonics out of hearing range. That's why the upper register sounds smoother, and the lower end twangier.

Since I make "modern" sounding bass pickups, these are expected to be bright and hi-fi. I keep the pickup's ground separate from the coils. The ground includes the magnets and blades, as well as the shielding. So I can disconnect the magnet's ground and do an A/B comparison. The only difference is a little bit of buzzing from the shield being lifted, but no loss in high end.

It would be very simple to isolate the magnet from the rest of the metal parts on a humbucker, and then attach a wire to it with some copper foil, and switch that to ground. Then you can strum some chords and hit the switch and see what you hear.

[David Schwab]

Also, customers don't like it when they get a loud buzz when touching the poles of a pickup made that way because your coil start is now hot lead.

The solution is to ground your magnets!

You shouldn't have to worry that a customer might have to, or want to, reverse the polarity of a pickup and then get humming if they touch the magnets. Some people like to wire in phase switches you know!

[Joe Gwinn]

I do not see how the electric potential of the magnets affects the inductance. It should change the capacitance a little bit.

I don't know if this is the cause, but one effect of self-capacitance is to change the apparent inductance.

[Possum]

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Why ground the magnets, just wind it reverse with reverse polarity then you don't have buzzing magnet poles. Players who pay for vintage strat pickups don't want to see a copper strip on the bottom of the pickups.

I didn't know modern basses are bright, but now I think of it those vintage tele type basses I guess didn't have dark pickups in them I guess. I know zip about bass, I got asked to play bass at the jam one nite and I ran screaming out the front door, I know one bass pattern and my hands die trying to bend those giant strings :-)

[Mike Sulzer]

Why ground the magnets, just wind it reverse with reverse polarity then you don't have buzzing magnet poles. Players who pay for vintage strat pickups don't want to see a copper strip on the bottom of the pickups.

But that does not work for a humbucker that has the coils in series. One of the coils has one lead grounded, but the other coil has neither lead grounded.

[Possum]

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His pickup is a strat pickup, not a bucker.

[David Schwab]

Why ground the magnets, just wind it reverse with reverse polarity then you don't have buzzing magnet poles.

Because the magnets pick up hum, as any non grounded metal part on a pickup can.