Of Polepieces and Magnetic Fields

http://www.harmonycentral.com/servlet/JiveServlet/downloadImage/102–1832–4–13484/343–481/Main.jpgWhen I interviewed Eric Johnson in his Austin-based studio a few years ago, I was struck by something that at the time seemed rather mundane. With his guitar in hand, Eric talked and played, demonstrating some of his approaches to soloing. But as brilliant as that was, what caught my eye was the periodic modifications he made to the his guitar while he played. In between demonstrating the Mixolydian mode and a string-bending lick, Eric casually reached over and grabbed a small flathead screwdriver, gave the polepiece below the B string on the neck pickup of his ES-335 a quarter turn, and then kept playing. He did this as quickly and as effortlessly as you and I would tune up a slightly flat string. Here’s a guy with total control over his sound, I thought.

Be truthful: When’s the last time you looked at the alignment of your pickups to make sure they were still optimally placed from the strings? And do you even know what that distance should be? Your pickups are as critical to your guitar’s tone production as anything else that follows downstream, and as we know from our devotion to all things audio, there’s no place like the source to really fix a problem.

There are several ways to tweak your pickups without causing a permanent change, so there’s no reason not to have it as an option. If your tone has been lacking, or if it’s out of balance with respect to the individual strings’ outputs, consider adjusting the pickups first, before trying other, EQ-based methods. If you’ve never tweaked a pickup before, just think of Eric Johnson. He would adjust a polepiece as readily as he would roll the tone control from 9 to 8 — if it were the right thing to do. Wouldn’t you like to have that kind of confidence over all your guitar’s parameters?

Pickup Types

All pickups can adjusted with respect to their position to the strings through a simple, reversible (if necessary) turn of a screw. Whether you have single-coil, humbuckers, covered pickups or exposed polepieces, or even pickups with non-adjustable polepieces, you can always move your pickup up or down in relation to the strings. Moving a pickup up, or closer to the strings, will increase the output of the pickup (i.e., make it louder), because you’re moving the magnet and the magnetic field closer to the source (the vibrating string). This is similar to moving a microphone closer to your mouth. In a pickup, moving the magnet closer to the string causes the vibrations to increase the amplitude of the disturbance in the magnetic field, which in turn creates a stronger current at the output.

You would think, then, that moving your pickups closer, for more output, would be a no-brainer. Who wouldn’t want maximum output from their pickups? Well, the problem is that two other aspects of the sound change when you move the pickup closer to the strings. For one, the tonal balance of bass and treble shifts, because the frequency ranges don’t produce bass and treble with equal energy. The bass tends to dominate here. This phenomenon gets magnified when you put the pickup closer to the string, where things get boomy fast. The other issue is that the pickup’s magnet increases its magnetic pull on the string itself as you get the two closer together. Putting the pickup closer to the string inhibits the string’s ability to vibrate, causing the string to decay faster than normal. Not the best thing for those sustained string bends on ballads.

In addition to adjusting the overall height of the pickup to the string, consider that you can raise just one side higher than the other. For example, if your neck pickup sounds too boomy or bassy, you have two choices: You can lower the bass side of the pickup (reducing the output), or you raise the treble side (increasing its output). Either move produces the same relative effect: the treble side of the pickup will be closer to the pickup than the bass side, increasing its output relative to the bass side. Because the pickup is now on a slant, the change between the bass and treble strings will be gradual, with a linear, or straight-line, fall-off toward the bass side.

But what if you need even more precise control over the tone? For example, what if just the B string is sounding anemic, with its notes becoming buried when played against its two neighbors, the G and the high E strings? In that case, you can — if your pickups allow — adjust the individual polepieces. For this to be an option, you have to have exposed screw heads facing the strings. This isn’t an option for non-adjustable polepieces (such as those found on a classic Strat), or bar magnet pickup designs, such as many well-known models by EMG.

But if you do have adjustable polepieces (that is, with screw heads), you can try moving them up and down to get your strings in balance. Keep in mind, that as with our side-to-side example earlier, you can increase the presence of the B string in two ways: by raising the B string polepiece or by lowering both the G and high E polepieces. Once the individual strings are in balance, you can raise or lower the entire pickup, or raise or lower either side. This gives you lots of options!

If you do decide to adjust your polepieces, follow these precautions:

• Don’t screw the polepiece to the extremes. If your screw juts out to within a 1/6th of an inch of the string, you should consider another route. Conversely, don’t torque the screw all the way down, as you risk compressing or damaging the pickup bobbin.

• Count the screw turns, and write them down. Whenever making any type of adjustment, always note where you started from, so that you can get back to square one if you really screw things up (no pun intended) or become totally disoriented. Also note the orientation of the screw’s slot when you start, and make adjustment in quarter turns, noting the results and checking your work (with your ears) constantly.

• Have your amp sound together before you start. It’s easier to make polepiece decisions with a clean amp sound. Forget the effects, and get a good workable clean sound before you break out the screwdriver. Then when checking your results, vary the volume of your amp and your guitar to make sure you’re getting consistent results.

• Choose the correct size screwdriver. If you choose a tool that’s too large or too small for the job, you risk scratching the pickup cover or gouging the screw slots, respectively. Also, take care when using any sharp metal tool near your guitar. You can easily slip and scratch the surface of the top. 

To Everything, Turn, Turn, Turn

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Figure 1 shows a humbucker and how you turn the screws to get it to move. Most humbuckers attach to the plastic rings surrounding the pickup itself. The four corner screws hold the ring into the body, and the larger, middle side screws are used to adjust the height of the pickup. Turning the side screws clockwise raises the pickup. Turning the polepieces clockwise lowers them.

Figure 1. On a humbucker with a spring-loaded pickup ring, turning the middle side screw clockwise raises the pickup. Turning the polepiece screws clockwise lowers them.

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Figure 2 shows a single-coil pickup. If the pickup is attached directly into the body, turning the height-adjustment screw clockwise lowers the pickup. Though most single-coils don’t have adjustable polepieces, if yours does, turning the polepieces clockwise lowers them, just as in humbucker pickups.

Figure 2. On a single-coil pickup that screws directly into the body, turning the height-adjusting screw clockwise lowers the pickup.

Even acoustic guitar pickups can have adjustable polepieces, as shown in Figure 3. The Artec Wooden Sound Hole pickup (WSH12) features 12 polepieces, aligned as 6 pairs, for versatile tone control. Figure 4 is the Eric Johnson Signature Strat, and you can see clearly how the polepieces are staggered (that is, not all at equal height, or distance from the strings). Figure 5 shows a set of three single-coils with a humbucker. Note their basic differences: The single-coils are thinner and have non-adjustable polepieces. So it’s not just that single-coils have a single wrap of wire around a bobbin: they are also non-adjustable.

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Figure 3. Some acoustic-guitar pickups have adjustable polepieces, even when they don’t have height adjustment screws. This Artec WSH12 has 12 adjustable polepieces with which to sculpt your sound.

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Figure 4. Eric Johnson’s Fender Signature Strat (note the bound neck). Eric was deeply involved with all aspects of this guitar’s design, including the height of the polepieces. Note how low the B string polepiece is compared to the G string’s.

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Figure 5. Most single-coil pickups have fixed polepieces. Most humbuckers have adjustable polepieces.

If 6 was 9

http://www.harmonycentral.com/servlet/JiveServlet/downloadImage/102–1832–4–13490/450–337/Fig_06.JPGFor those of you who know to describe Jimi Hendrix’s guitar as having the strings reversed (and the modifications required to the nut and bridge), don’t forget that the pickups are also reversed, with respect to the original polepiece setup. Pickup maker Stan Hinesley recognizes that part of the Hendrix sound is this pickup reversal, and so makes an “upside down” pickup for right-handers seeking that sound. Pictured in Figure 6 is Hinesley’s EXP pickup, with hand-beveled, reverse-staggered Alnico 5 magnets. Hinesley also makes single-coils with adjustable polepieces (Figure 7), which is unusual but welcome for its versatility.

Figure 6. Stan Hinesley makes a reversed pickup called the EXP (for Hendrix, get it?), which has the polepiece position opposite—or upside down—from the usual orientation.

http://www.harmonycentral.com/servlet/JiveServlet/downloadImage/102–1832–4–13491/450–337/Fig_07.JPGFigure 7. This single-coil pickup from Stan Hinesley features adjustable polepieces, which is unusual in a single-coil but versatile!

Equal Time for Fixed Polepiece Pickups

http://www.harmonycentral.com/servlet/JiveServlet/downloadImage/102–1832–4–13492/450–369/Fig_08.JPGThose of you who have EMG pickups (Figure 8), or other pickups that eschew adjustable polepieces, might wonder why manufacturers make non-adjustable polepieces at all, if it robs you of an opportunity to tweak you sound. EMG feels that the whole polepiece design has problems, and that bar magnets are superior technology. In the interest of equal time, here are their thoughts on the matter, quoted from their website:

All initial EMG designs use a bar magnet for two reasons – Pole pieces place too much magnetism under the strings and cause the lower ones (primarily low E, A, and D) to go “out of pitch” with a Doppler effect. This is especially true of the Fender Stratocaster where 3 poles under each of the strings push and pull them through a variety of unnatural movements. Poles can also make intonation and tuning difficult. On the other hand, pole pieces have the benefit of a percussive attack giving the pickup much more of a “plucky” sound. Designs featuring a bar magnet have a much more linear (balanced) output from string to string. Its attack is less pronounced than the pole piece design resulting in smoother distortion, and much better sustain. String bending is smoother because the output doesn’t fade when you bend strings. By relying on the internal preamp for gain the bar magnet can also be smaller, further limiting the magnetic “pull” on the strings. And, the continuous magnetic field of the bar allows for any string spacing. Perfect for any multi-stringed instrument, and the less conventional instrument. Most EMG Pickups use a magnetic bar. Single coil pickups are available in both bar and polepiece designs. There are fewer negative attributes to the bar and it’s preferable, but if you like polepieces for your playing style then there is an EMG model for you. [See Figure 9.]

Figure 8. Most EMG pickups feature bar magnets, which don’t have adjustable polepieces. The company feels this is the superior technology, because bar magnets don’t create an undesirable magnetic pull on the strings the way polepieces do.

http://www.harmonycentral.com/servlet/JiveServlet/downloadImage/102–1832–4–13493/450–381/Fig_09.jpgFigure 9. For those who like the traditional design of adjustable polepieces in their humbuckers, EMG offers models in that configuration, too.

Manufacturer Recommendations

Many manufacturers will recommend how to ideally set up their pickups. They typically start from the factory setting, or provide turn-numbers assuming the screw head is flush with the pickup. Here’s one set of instructions using the turn method:

Set all poles when looking at the screw head from the side that only the rounded part rises above the flat part of the pup.

Low E: no change

A: raise 1 full turn

D: raise 1 ½ full turns

G: raise ½ turn

B: lower 1 full turn

High E raise ½ turn

Some guitar manufacturers give measurements from the strings to the pickups, as in this example from a Carvin owner’s manual:

Adjusting Pickup Height:  Each pickup has 2 or 3 height adjusting screws. For maximum power output keep the pickups adjusted as close to the strings as possible while maintaining enough clearance so that the pickup pole pieces will not touch the strings when playing on the upper frets. If you want a mellower sound, then adjust the pickups further away from the strings. For humbucking pickups we recommend 5/32” clearance. For single coil pickups go with 1/8” clearance.

Adjusting individual pickup poles:  We set each magnetic screw head in both pickups for a balanced sound. If you wish to raise or lower the output of a certain string, then lower or raise the adjustable screw heads until you get the desired power output of that string. Press strings down on the 24th fret and make sure that you have at least 1/16” clearance between the strings and the pickup screw heads, otherwise you may get static as a result. Keep the pickup pole pieces clean as any metallic particles on them can cause static.

What’s clear here is that both approaches assume you will be adjusting your pickups. They don’t warn you that it will “void the warranty, ” and they even offer their recommended setups. You should feel encouraged by this to experiment for yourself.

Conclusions

Even the simple act of changing your brand or type of strings (from a light set to light-top/heavy bottom) may require a pickup modification. And if you find your guitar’s tone has been uneven, lackluster, or just wanting in general, try adjusting the pickups first. Your actions are completely reversible, and you can’t hurt anything — except perhaps for the tone if you go too far, but then you can just “hit Undo” in the analog way — by reversing your screw-turning steps!

This article was originally published on Harmony Central.  Reprinted with permission.