Pickups: The 10 Most Frequently Asked Questions [Guitar Player Magazine, December 1975]
Bill Lawrence (or Willi Lorenz Stich) was born March 24, 1931 in Wahn- Heide, Germany. Living a half mile away from the largest artillery shooting range and air force base in Germany, he started building rockets with discarded ammunition when he was six. By the time he was ten, he had shot himself through the leg with a homemade gun. At thirteen, he rigged his bicycle to be propelled by a rocket, lost control of its speed, and woke up in the hospital. A broken left wrist ended his violin studies, though his injuries did not prevent him from mastering the guitar. In 1945, Lawrence worked as an interpreter for U.S. troops and learned about jazz and electric guitars via recordings of the Les Paul trio and Charlie Christian playing with Benny Goodman. Re-channeling his love of electronics into less explosive areas, Bill began consuming books on electro dynamics and making electronic equipment for his guitar. By 1953, he was a consultant for Framus, the largest European guitar factory. His name at this point became Billy Lorento, which was used on Framus' top line guitar. In 1965, he started his own pickup factory and changed his name again, this time to Bill Lawrence, because "Billy Lorento" was owned by Framus. Lawrence has subsequently designed electrical systems for individuals and companies, including Dan Armstrong and Norlin. A few examples of his new product work for Gibson (done in cooperation with Bruce Bolen) are guitars like the SG with super humbuckers, the Ripper Bass, the L6-S, and the Howard Roberts guitar. Most recently Bill generally recognized as one of the foremost authorities on pickups has been doing custom work on string instruments out of his own shop [Lawrence Sound Research, 217 Shady Grove, Donelson, TN 37214]. - Editor
1. What is a guitar pickup?
Nothing more than a coil and a permanent magnet. A vibrating string (with a ferrous base) cuts through the magnet's field, inducing a variable current in the coil that is then fed to an amplifier. The amp in turn causes a speaker to vibrate at this same electrical frequency, and air in front of the speaker transfers this wave to the ear that hears it as sound.
There are two basic designs for a single-coil pickup. One is a coil with a permanent magnet in the center (see Figure 1). The other is a coil with an iron load charged by one or more magnets (see Figure 2).
What today's players call a "hot pickup" is an item that does not exist. Pickups made today are generally matched to standard guitar amplifiers. Therefore, a low impedance amp with an input matched for a pickup with an output of 8 millivolts is easily overpowered by a pickup that puts out 12 millivolts. Used with such an amp, the pickup will sound "hot," but used with a standard guitar amp, it will sound weaker.
Impedance is determined by the number of turns of wire around the coil and the iron load. It should be noted that impedance has no relationship to the resistance of the coil. An air coil with 48-gauge wire and 2000 turns may give you a resistance of 4000 ohms and is still low impedance, while another coil with 40-gauge wire, 6000 turns, and a heavy iron load may give you 1000 ohms resistance but is still high impedance.
2. How do Alnico magnets compare to ceramic?
There are sixteen basic Alnico magnets and eight ceramic magnets. Each has different properties and requirements with regard to the gauge of wire and the number of turns which must be. used with it to carefully match the specific guitar for which it is intended. Alnico magnets (1 to 9, cast or sintered) have about 50% iron with aluminum, nickel, cobalt, and copper (the name comes from the first two letters of each element). The flux is relatively high, but the demagnetizing force on 1 to 6 is low. Ceramic magnets (Oxide 1 to 8) have no iron or other metals. Every manufacturer uses different names for their ceramic materials such as Indox, Diox, Arnox, etc. However, an Indox 5 is the same material as an Arnox 5 or Diox 5.
Ceramic magnets have only one quarter the flux (Gauss) of Alnico magnets, but they have six times the demagnetizing force. The energy product of a magnet relates to the flux and the demagnetizing force and changes with the size of the magnet. The cost of a ceramic magnet is about one third that of an Alnico unit.
3. What is a humbucking pickup?
It is a combination of two pickups in one cover. The coils are wired in series out-of-phase to eliminate hum and are charged magnetically opposite (by turning the magnets around in one pickup), so they are electrically in-phase.
On the old Les Pauls, the pickups were powerful but not humbucking. To make such a unit was not so important at that time. Players were using low volume and usually were some distance from the amps, so there was no trouble with extraneous hum being picked up and amplified. However, as rock and roll became popular volume increased, amps became larger, and the performers began standing right in front of them. The chances of extraneous signals being amplified also increased, so humbuckers were introduced (and are still produced the same way as they were in 1956).
Everything I have said about singlecoil pickups also applies to the humbucker. The most commonly used model has two active coils. When you adjust your pole pieces so they are even with the cover, you pick up the string at two different spots. When the string vibrates up and down above the pickup, you double the fundamental and the lower frequencies (this gives the pickup its beautiful mellowness), but cancel the harmonics when the string moves down on one coil and up on the other. This changes, depending on where you position your pick over the strings and the angle of attack. With a distinguished picking technique you can get some weird and very funky effects out of your axe. This can become an art, especially when you use two pickups out-of-phase.
There are three basic designs of humbuckers: Two active coils (Figure 3); one active and one passive coil (Figure 4); and two active coils focused to one point (Figure 5).
In this case, both coils pick up the string at one spot the way a single-coil does (it is the design used on the Ripper Bass). But even a humbucker will pick up the 60-cycle hum from the input transformer if you get closer than 10" to your amp.
4. What effect does a pickup have on sustain?
There is no unit that can pick up a string that does not vibrate, but a good model must be capable of picking up the minutest vibration of the string. Several factors can stop a string from moving: Tension, air resistance, the attraction of a pickup with a too-powerful magnet, and loose parts on a guitar. If every part of the instrument is free of vibration, and the pickups are mounted solidly (and are sensitive), and you are close to your speaker with the volume loud enough, you can get infinite sustain on every note. The string movement is picked up, the signal is sent to the speaker, the speaker then causes your string to vibrate again, and this frequency is sent back through the amp again and again. This process is called feedback and is desirable. There are two other types of feedback which are undesirable. One is that caused by a guitar's top, which is set in resonance by the speaker (this happens on flat-tops, arch-tops, and some cheap solid bodies with air pockets where they should not be, especially under the bridge). Another unwanted feedback is that which comes from the pickups. This happens when they have parts that vibrate or are mounted poorly on the guitar. If you come close to the speaker and your pickup squeals, this may be the problem. Even the oldest Les Pauls with single-coil pickups did not squeal, because they were solidly mounted. However, if you have one of these instruments and it creates wolf tones, check the mounting screws. After about 25 years, the screws might have become a little bit wobbly (imagine driving a car for 25 years without a checkup). If you have a pickup with loose parts that cause microphonic feedback, dipping it in wax may eliminate the aggravation though I can only recommend this for models that don't have any adjustable parts (like pole pieces, etc).
5. What effect does a metal cover have?
It shields the pickup from outside electrical signals such as those that come from neon transformers, etc. Any pickup shielding thicker than .002" interferes with the electromagnetic field and cancels frequencies in the audible range. Most covers are .040" and destroy beautiful sound of a lot of pickups. But in itself, removing the metal cover does not normally affect the sound. There is a loss of high frequencies, but that is usually way beyond the range of guitar amps. If you remove the cover of a Gibson humbucker, it will not increase unwanted noise like hum or buzz. If a cover has magnetic properties there is also the possibility that it will contribute to a volume loss.
6. What accounts for the different sounds of various pickups?
The sound of a pickup depends on the size of the coil, the number of turns of wire, the load of the coil, and the energy product of the magnet. Each relates to the other. A magnet with less flux and more turns will produce a more mellow sound than a stronger magnet with fewer turns.
Tampering with the number of turns or the power of a magnet to "hot wire" it will not necessarily produce a better sound. For example, recoiling a Fender or Gibson pickup with more turns results only in a muddy sound, self-induction of the coil, and other disadvantages. When somebody uses more than 8000 turns on an iron-loaded, single-coil pickup, the impedance and capacitance are so high as to degrade the guitar signal considerably. If the magnet is too strong and your pickup is too close to the strings, the magnet will attract the strings, cause false harmonics, and lead to a loss of sustain. A pickup made with the correct magnet, 4000 turns, and shielded with aluminum not more than .005" thick produces an unbelievable sound, especially when used with a speaker system having a range up to 15,000 Hertz. With the amplifier set on volume 3, it may not be as loud as a pickup that has too many turns, but set on volume 8, it will outplay.
7. How should pickups be adjusted?
They should be parallel with the strings. If you press the low E string down on the last fret, the fingerboard pickup should be not more than 3/32" away from the string and the bridge pickup not more than 1/16". On the high E string, the distance should be 1/32" less.
To get a sweeter and much cleaner sound with no cancellation of higher frequencies (though you'll lose gain and sensitivity), put your pickup further away from the strings. and adjust your pole pieces so the strings will almost touch them when you play a barre chord on your last fret. By doing other tests, you will discover some more nice sounds. Moreover, if you use a string with less magnetic properties, you can increase the volume of that string when you adjust your pole pieces closer to it.
8. What are some wiring possibilities for more than one pickup?
You can wire them from series to parallel, in- and out-of-phase. With two humbuckers, you have four coils which you can wire with any two coils, series to parallel. As long as you have opposite magnetic poles in the coil, you are in-phase. With like magnetic poles you are out-of-phase. Don't put too many switches on your guitar, or you'll need a driver's license to play it!
Now, a guitar that's fun to rewire is one with three single-coil pickups. The first one I ran into was a Fender Strat. I wired it like a two-pickup guitar and hooked the middle pickup to a three-position switch. Middle position was off, up was in-phase, and down was out-of-phase. I put the switch at the back of the instrument right below the bridge pickup so that I could move it with my body while I was playing. Next, I rewound the pickups with fewer turns, turned the magnet of the middle pickup around, and used a six-position switch that connected them in series, like humbuckers, in- and out-of-phase. The spacing of the pickups created through cancelling midrange and pushing highs and lows the most beautiful sounds imaginable: Sweet, funky, you name it.
9. How do you stereo wire a guitar?
Divide the output of the three-position switch into two separate channels and connect them to a stereo output jack. This is not really what I call stereo; it's more a two-channel system. Channel 1 is the fingerboard pickup, and channel 2 is the bridge pickup. The advantage is that you can use different amplifier inputs or two separate amps, and each input can be preset with totally different sounds. The disadvantage is that your phasing effects will lose their characteristics.
10. What is string grounding?
It is a cheap excuse for bad shielding and can kill the performer. When a guitar's pickups are improperly shielded the strings will act as an antenna for any electrical signal, which will be amplified as unwanted noise. It is common practice to attempt to eliminate this effect by running a wire from the tailpiece to the ground on the instrument's jack. The results can be murderous. In West Germany alone there were twelve deaths in ten years caused by the PA or the guitar amplifier having the wrong polarity. When the player with sweaty hands touched both the strings and microphone at the same time, the effect was fatal. With moist hands, you make a perfect connection for the entire voltage to run through your body. If your heart is not in the best condition, you've had it.
If a guitar is perfectly shielded, you can sit on top of your amp or a neon light transformer, and there will be no buzz. But if your wiring has bad shielding, and you touch your grounded strings, your body is used as a shield. I think your body is too valuable to be used as shielding. As long as you are using a guitar with the strings grounded, check the polarity of all your equipment, or you may get electrocuted. If an automobile had such a dangerous factor, Ralph Nadar would go bananas!
[Ed. Note: Many guitar manufacturers ground their strings in this manner, and the wires may not be visible on the surface of the guitar body. Have a competent repairman disconnect this ground, if you wish to shield your guitar in a safer manner.]
Some of the terms in this article may seem obscure to those unfamiliar with electronic jargon. However, a book such as A Dictionary of Electronics, by S. Handel (published by Penguin Books and available in the library), should help clarify fine points and definitions.
