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Leo Fender's Tone Secret - Paramagnetism

Leo Fender discovered that using metal shielding, i.e; metal control covers and pickguards, reduced the hum associated with his single coil pickups.

Lap steels and Guitars - Leo was using chrome steel covers and brass shielding on his lap steel instruments as early as 1947. Did you know Leo started making lap steels in his radio repair shop in Fullerton, CA? Who was his first partner and what was the company called? *Answer Below, at the Bottom of this Page.

When Leo started Fender Musical Instruments, he was using the single coil pickups he developed for the lap steels, but now he was putting it in a new guitar called the Telecaster. Later he developed new versions of the single coil pickup for the Stratocaster, P-Bass and Jazzmaster guitars, to name a few.

In 1957-58, Leo used an aluminum pick guard on the Stratocaster, Precision Bass, Jazzmaster, Mando-caster (Mandolin), and Duo-Sonic guitars. The tone that those guitars could generate is legendary! Today builders and players are seeking the Holy Grail of the tone that those guitars could produce, the womanly bluesy tone as some call it.

Here's the secret to that tone - Even if you buy reproduction perfect parts and have a master Luthier build it. You will not reach that soulful tone without using an aluminum pick guard. Why? Paramagnetism effects the high notes, by "rounding out" the ice picky highs found in many pickups.

We use what Leo used; .0625 (metric) or what we also know as aircraft grade 14 gauge aluminum, in the USA. The aluminum he used was 6061-T6. We use the same material and thickness. We think Leo had the correct thickness as well. Who could argue with the results?

Actually, it was likely happenstance, as material's were limited after WWII. Hence we have the tonal results of the chaos of that time and the good and diligent efforts by Leo to produce a sound that players wanted, besides easily replaced necks and components for road worthy instruments, the players needed.

The effect that the aluminum guard has is based on the principle of Paramagnetism. Leo did not know this was the scientific reasoning. Neither do most of the pickup and guitar makers out there. I even discussed this with a former JPL/NASA physics expert, working as a consultant to a famous pickup maker. He did not know the answer. He actually had no answer as to how an aluminum pickguard could effect a pickup? I found out by researching something a machinist / guitar player mentioned to me about magnetism and tooling. I read a lot of info on magnetic principles, found many useful sites on the internet, and distilled it down to what we guitar folks wanted to know.

Answer: Paramagnetism - Where the nonferrous aluminum is temporarily slightly magnetized in the immediate magnetic field of the pickup. See the Pickguard Specs page link in the sidebar for charts on materials and effect measured.

Almost imperceptible to some ears, and immediately noticed by others, it can effect the high end ice picky highs, rounding or softening them slightly. Not to be confused with microphonic issues. I hear some guys say the aluminum guards induce or cause the pickups to be microphonic. This is flat out wrong. They confuse the cause of the issue. It's your pickups, not the guard!

Though, the first thing you'll notice is that with most single coil pickups, the dreaded 60 cycle hum is greatly reduced or eliminated. This can make a Squire Strat sound as good as an American Strat! No kidding, we have A/B'd and demoed it.

This effect is in addition to the shielding from common sources of interference (RFI/EMI), static reduction, and the added resonance that using an aluminum guard can bring to your palette of tone "colors" in your search for your tone.

What Bill was talking about was the bridge plate, but the same answers hold true. A bridge plate is much thicker than a guard or cover. Also, steel for a bridge surrounding a pickup is going to effect the tone because steel is a ferrous metal that can be magnetized, hence altering the magnetic field of the pickup.

This begs the question: Why did Leo Fender stop using aluminum guards? I'll be sharing some information I got from Leo's longtime friend and business associate George Fullerton. I had the good fortune to meet Mr. Fullerton, many years ago, before his passing; and we spent some time talking about this subject To be continued……

Q: A builder recently asked the following question about using aluminum:

"I was reading an article by Bill Lawrence the pickup guru on aluminum bridge plates for Telecasters.  He was saying that aluminum is a great shield for electronic signals but if the aluminum is too thick it would blanket some of the high end of the guitar. I was curious if you chose your aluminum thickness by studying the acoustic properties, cosmetics or both.  From reading your website and talking to you in person I know you picked up your research where Leo Fender left off but I’m curious as to what you have learned." 

A: The short answer for you is; yes, thickness can have a differing effect. Depends on how hot the pups are wound and the strength of the magnets used.

A little info about HyperPhysics and magnetics: 

Magnetic Properties of Solids

Materials may be classified by their response to externally applied magnetic fields as diamagneticparamagnetic, or ferromagnetic. These magnetic responses differ greatly in strength. Diamagnetism is a property of all materials and opposes applied magnetic fields, but is very weak. Paramagnetism, when present, is stronger than diamagnetism and produces magnetization in the direction of the applied field, and proportional to the applied field. Ferromagnetic effects are very large, producing magnetizations sometimes orders of magnitude greater than the applied field and as such are much larger than either diamagnetic or paramagnetic effects.

Check out these links to read more scientific data on the subject.

Check out the right side table of contents of the Hyperphysics page. Scroll down to Paramagnetism. Also check out the Overtones and Harmonics section. Fascinating reading if you like knowing why and how stuff works. I know, I do.

* Answer to the question above: Doc Kaufman, K&F. What did they make? Lap steels.

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More info:

Magnetic Field Characteristics

Magnetic Field In and Around a Bar Magnet: As discussed previously, a magnetic field is a change in energy within a volume of space. The magnetic field surrounding a bar magnet can be seen in the magnetograph below. A magnetograph can be created by placing a piece of paper over a magnet and sprinkling the paper with iron filings. The particles align themselves with the lines of magnetic force produced by the magnet. The magnetic lines of force show where the magnetic field exits the material at one pole and reenters the material at another pole along the length of the magnet. It should be noted that the magnetic lines of force exist in three dimensions but are only seen in two dimensions in the image.


It can be seen in the magnetograph that there are poles all along the length of the magnet but that the poles are concentrated at the ends of the magnet. The area where the exit poles are concentrated is called the magnet's north pole and the area where the entrance poles are concentrated is called the magnet's south pole.

Diamagnetic, Paramagnetic, and Ferromagnetic Materials

When a material is placed within a magnetic field, the magnetic forces of the material's electrons will be affected. This effect is known as Faraday's Law of Magnetic Induction. However, materials can react quite differently to the presence of an external magnetic field. This reaction is dependent on a number of factors, such as the atomic and molecular structure of the material, and the net magnetic field associated with the atoms. The magnetic moments associated with atoms have three origins. These are the electron motion, the change in motion caused by an external magnetic field, and the spin of the electrons.
In most atoms, electrons occur in pairs. Electrons in a pair spin in opposite directions. So, when electrons are paired together, their opposite spins cause their magnetic fields to cancel each other. Therefore, no net magnetic field exists. Alternately, materials with some unpaired electrons will have a net magnetic field and will react more to an external field. Most materials can be classified as diamagnetic, paramagnetic or ferromagnetic.

Diamagnetic materials have a weak, negative susceptibility to magnetic fields. Diamagnetic materials are slightly repelled by a magnetic field and the material does not retain the magnetic properties when the external field is removed. In diamagnetic materials all the electron are paired so there is no permanent net magnetic moment per atom. Diamagnetic properties arise from the realignment of the electron paths under the influence of an external magnetic field. Most elements in the periodic table, including copper, silver, and gold, are diamagnetic.

 materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed. Paramagnetic properties are due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field. Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum.

 materials have a large, positive susceptibility to an external magnetic field. They exhibit a strong attraction to magnetic fields and are able to retain their magnetic properties after the external field has been removed. Ferromagnetic materials have some unpaired electrons so their atoms have a net magnetic moment. They get their strong magnetic properties due to the presence of magnetic domains. In these domains, large numbers of atom's moments (1012 to 1015) are aligned parallel so that the magnetic force within the domain is strong. When a ferromagnetic material is in the unmagnitized state, the domains are nearly randomly organized and the net magnetic field for the part as a whole is zero. When a magnetizing force is applied, the domains become aligned to produce a strong magnetic field within the part. Iron, nickel, and cobalt are examples of ferromagnetic materials. Components with these materials are commonly inspected using the magnetic particle method.

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