Tony Iommi humbuckers

[David Schwab]

Re: Pickup parts

In reference to Possum's observations, I don't think GIBSON knows exactly what's going on there. Its just a jumble of parts stuck together that they decided to patent. My guess is that all those magnets crammed on make for a complex bunch of flux lines that end up partially cancelling some frequencies. Maybe this design produces lots of oddly positioned eddy currents that are killing selective frequency response. If you have a good idea of why this pickup sounds the way it does, you're probably way ahead of the people who built it!

Yeah I said way back when we first talked about this pickup, that I'm sure John Riboloff just tried some stuff out to imitate the original pickup. John Diggins didn't remember how it was made except it used multiple magnets.

This meant that J.T. would have to examine the pick-up at his lab in Nashville. To send the guitar or the pick-up over to the US unaccompanied was far too risky an option, so I was lucky enough to be flown, courtesy of Gibson Strings and Accessories, over to Nashville for a few days in June 1996 with the Jay Dee SG. What followed was the most determined electrical detective work I have ever seen! J.T. just lives guitars. With his encyclopaedic knowledge up pick-ups, he started taking measurements, listened and quickly worked out that there were very unusual goings-on within the Jay Dee that gave it the smooth power with a hint of phase cancellation. I have just enough electrical knowledge to understand what J.T. talks about (e.g. “well Mike, the inductance is the motor of the pick-up, and the resistance is its brake”), so to watch and listen to him at work was a great pleasure. Once he had worked out the way to go, which is a radical break from traditional pick-up design, it was a question of experimenting. He worked constantly, pausing only for the occasional cigarette break, to eat or to take me back to the hotel.

He set up the coil winding machines to wind different numbers of turns of different gauges of wire, tried different magnets, milled the pole pieces to different sizes. Coil winders are not like computers, doubling their speed every 3 months, so all this took a lot of time! At the end of the week we had about a half dozen pick-ups to take back to the UK for Tony to try out.

That's full of hyperboles, such as "smooth power" and "with a hint of phase cancellation." There is no phase cancelation going on. All the magnets are "in phase" and the coils are wired as expected.

Eddy currents are produced on conductive surfaces in the presence of a magnetic field. There wont be "oddly positioned" eddy currents, and they will only be on the conductive surfaces of things like the blades and alnico magnets. Eddy currents tend to kill the high frequencies.

I was under the impression that the strings don't need to be magnetized per se. ...That the string is disturbing the magnetic field and those disturbances are what induces the signal in the coil windings. They also induce eddy currents, which can be looked at as though they are magnetic phase cancellation. Call it what you want. The effect is real and you can hear it.

Soft magnetic materials, such as the strings, becomes magnetized in the presence of a magnet.

Eddy currents don't cause phase cancelation. You are hearing something else going on. You notice the pickup doesn't have a metal baseplate? I'm sure that's to reduce eddy currents.

Magnetic polarity has NOTHING to do with the humbucking effect. Pull the magnets out, or shove 'em back in however you like. Doesn't affect the humbucking quality in the slightest.

It does matter if both coils are sensing the same strings. To cancel hum the coils must be out-of-phase. Right? So what stops the strings from sounding out-of-phase? The reverse polarity magnets.

Sure, remove the magnet and put a fresh set of strings on the guitar. Do you hear anything? Flipping the magnet over doesn't matter because each coil on the pickup is still opposite magnetically. If they were not you would hear that thin out-of-phase tone.

A humbucking pickup (last time I checked) looks suspiciously like "two single coils next to each other". OF COURSE a humbucker with both coils having the same magnetic polarity will sound thin- I never said it wouldn't- but it IS a humbucker.

You didn't?

The idea is that there are elements within the pickup (magnetic field orientation) that produce a SLIGHT phase cancellation. We're not talking about the ol' "I wired my Duncan wrong" sound.

You did

....And it is possible to construct a humbucker that is out of phase i.e. no hum. You just have to have the same magnetic polarity on both coils.

No you can't. Not without the two coils sounding out-of-phase. Just get a humbucker and try it out.

[fieldwrangler]

David Schwab wrote:

Soft magnetic materials, such as the strings, becomes magnetized in the presence of a magnet.

David (et al...)



Y'know, although the above statement is beyond question this issue of whether the strings become magnetized or simply cause fluctuations in the surrounding field by providing a varying "low impedance" path for the flux lines continues to be debated among some folks I know.

So, although I'm certainly inclined to trust you & Mike on the issue, is there an experiment that we can concoct to prove this principle?

Bob Palmieri

[Steve Conner]

David Schwab wrote:
this issue of whether the strings become magnetized or simply cause fluctuations in the surrounding field by providing a varying "low impedance" path for the flux lines continues to be debated among some folks I know.

What is there to debate? It's the same thing. If flux lines are in the string, then it's magnetized, by definition.

[David Schwab]

...by providing a varying "low impedance" path for the flux lines...

For magnetism it's known as "magnetic reluctance." So pickups are by nature variable reluctance devices.

[fieldwrangler]

Steve Conner wrote:

What is there to debate? It's the same thing. If flux lines are in the string, then it's magnetized, by definition.

Steve -

In fact, this is why I posed the question, since I can't figure out any way to separate the two models.

Bob Palmieri

[Steve Conner]

There aren't two models to be separated.

Maybe the confusion stems from the difference between soft and hard magnetic materials.

Soft materials just act as a low-reluctance (or "high permeability") path that a magnetic field will take in preference to air. They become magnetized in the presence of an external field, and the magnetization disappears as soon as that field does, because it is just a part of that field that "took a shortcut" if you like.

Hard materials act as magnets in their own right. They get magnetized, but by a different physical mechanism that makes them stay magnetized, producing a field of their own even once the external field has gone. If guitar strings were made of this stuff, then you would still get output even after you removed the magnets from your pickups.

Engineers casually use the word "magnetize" to describe both of these cases, even though they are two different things. A transformer core doesn't "magnetize" in the same way that a pickup magnet does when you charge it.

I believe guitar strings are probably soft, so they "magnetize" in the first sense, and the guitar pickup is a variable reluctance transducer.

Hard materials don't necessarily have high permeability either: a neo magnet has about the same permeability as air.

[fieldwrangler]

There aren't two models to be separated.

Maybe the confusion stems from the difference between soft and hard magnetic materials.

Soft materials just act as a low-reluctance (or "high permeability") path that a magnetic field will take in preference to air. They become magnetized in the presence of an external field, and the magnetization disappears as soon as that field does, because it is just a part of that field that "took a shortcut" if you like.

Hard materials act as magnets in their own right. They get magnetized, but by a different physical mechanism that makes them stay magnetized, producing a field of their own even once the external field has gone. If guitar strings were made of this stuff, then you would still get output even after you removed the magnets from your pickups.

Engineers casually use the word "magnetize" to describe both of these cases, even though they are two different things. A transformer core doesn't "magnetize" in the same way that a pickup magnet does when you charge it.

I believe guitar strings are probably soft, so they "magnetize" in the first sense, and the guitar pickup is a variable reluctance transducer.

Hard materials don't necessarily have high permeability either: a neo magnet has about the same permeability as air.

Steve -

This stuff I understand.

In fact, I think you've identified an interesting factor in this whole business, which is the fact that guitar strings (at least the ones on my test axe) are not as soft as one might think - they retain significant amounts of magnetism even after the permanent magnet is removed from the pickup, and therefore there's still a quite audible signal generated.

Bob Palmieri

[David Schwab]

In fact, I think you've identified an interesting factor in this whole business, which is the fact that guitar strings (at least the ones on my test axe) are not as soft as one might think - they retain significant amounts of magnetism even after the permanent magnet is removed from the pickup, and therefore there's still a quite audible signal generated.

This is true. I have removed magnets from pickups when I first started messing around with guitars back in the 70's. There is an early patent for a guitar pickup in which the pickup has no magnet and doubled as an electromagnet coil. So before you would play, you would charge the coil and magnetize the strings. It's not as efficient as having the magnet in the pickups though. The output is pretty low.

This is I went from thinking about the strings moving through lines of flux (which they do) to the strings being magnetized by that field. After Mike S. kept saying that I thought about how the strings do indeed hold a magnetic charge. But I also think both aspects are true. You can't have one without the other (kind of like electrical fields and magnetic fields).