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Electric Guitar Pickups The job of a pickup is to convert the vibration of a string into an electrical signal. The basic design consisting of a magnet and coil arrangement where the strings interact with the magnetic field to induce a voltage in the coil. Even with this simple concept, there are quite a few variables and trade-offs. A common misunderstanding is that the pickups on your guitar sound different because they are made differently. Maybe they are different, but there is also a huge difference in sound caused by the pickup's position on the guitar. Most electric guitars up to around the 70's (including Fender and Gibson) generally used the same pickups in all positions, so it was the pickup's position alone that caused different sounds. These days, it is more common to combine different pickup types, and use hotter pickups in the bridge position. Stronger magnets (or placing pickups closer to the strings) gives a higher output but also damps string vibration by pulling the strings towards the pickup. In severe cases, this can cause "false harmonics" or "double notes". Providing additional windings on the coil increases the output, particularly midrange. Manufacturers can only take this so far, because eventually the loss of highs gives a very muddy sound. Also the high output can overload the input of some preamps, making a "clean" sound impossible without reducing the guitar volume setting (this may be desirable by some players). Additional coil windings produce a higher impedance which pose problems with treble loss when used with long cables. There are similar options and compromises with coil wire gauge. "Active" pickups typically have a lower number of coil windings, giving a low output, low impedance, and very clean and clear, uncoloured sound. The low output is boosted by an onboard active preamp which maintains the low impedance. Low impedance pickups (on their own, or with a preamp) can drive long cables without noticeable treble loss. Probably the most obvious difference in pickup designs is the single pickup versus humbuckingpickup. A humbuckingpickup contains two single coils placed side by side, with a common magnet 24 arrangement. The sound is typically "fatter" (more midrange) due partly to the larger number of coil windings and partly because the sound of the string is "read" over a longer portion of the string. The shape of the magnetic field af fects how much of the string is read. The pole-pieces you see on strat single coil pickup s are individual magnets and give a very focused magnetic field, reading a small section of the string vibration. On the other hand, screws in a humbucking pickup are just screws, but conduct the magnetic field from a magnet placed underneath the pickup. There is another set of magnetically conductive slugs in the other coil, so the combined humbucker reads a larger length of string vibration. Magnetic material also affects tone. Popular opinion is that Alnico II produces a sweet, vintage sound, while Alnico V is a little stronger, and gives a brighter, more attacking tone (ideal for rock). Ceramic magnets have a slightly harder edge, and are favoured by met al players. With so many variables it's easy to see why there are many different choices. There are a few established standards, notably the original Fender Stratocaster, Gibson PAF, along with some popular models from retrofit manufacturers like DiMarzio, EMG and Seymour Duncan. Even before you plug your guitar in, its character is determined greatly by the type of guit ar woods used, construction methods, string gauges, etc. It is this basic character that the pickup picks up, adding its own colouration. Other Pickup Types All of the above desribe magnetic pickup s which are by far the most common pickup s used on electric guitars. They are designed to work with strings that interact with a magnetic field, so they are not normally subject to acoustic feedback (you can't talk into one!). These magnetic pickups CAN be microphonic if anything metallic in or around them is loose and vibrates with the sound. This is common in old and cheap pickups that have loose coil windings or fittings. It is rarely a problem with modern pickups that are wax potted to make sure everything is secure. Magnetic pickups are not suitable for nylon acoustic guitars, because nylon strings connot interact with a magnetic field. Even for steelstring acoustic guitars, magnetic pickups are raraely favoured, because of their limited frequency range, and the fact that they read only a small portion of the string length. For acoustic guitars, it is essential to capture the vibration of the top, and this is most commonly done with a piezo pickup mounted underneath Piezo the bridge saddle. Piezo pickups use crytals to detect pressure changes, and provide a very wide frequency response. They also have a very high impedance (typically over 5 Meg), and therefore need to be buffered with a preamp. This is usually provided in the acoustic guitar itself, often with extra tone control options, such as bass, middle and treble. Opinions vary, but these piezo pickups convey about half of the sound of an acoustic guit ar. Acoustic guitars are just about always recorded with one or more very high quality microphones, but this is difficult to do effectifely in a live environment. Many guitar makers, such as Parker (with their revolutionary Fly series), Godin, and others have added piezo bridges to solid body electric guitars. These guitars offer standard electric sounds, acoustic sounds, and even the ability to mix both! Their acoustic sounds can be quite convincing in a band setting, mainly because of the wide frequency response, and partly by the conditioning we listeners have had from piezo equipped acoustic guitars. Fishman, L R Baggs and other manufacturers offer bridge piezo pickups that can be added to many guitars. Fishman offer an interesting pickup for acoustic guitars presently, called the Rare Earth pickup. It is a slim magnetic pickup that clamps into the soundhole Apparently, the rare earth magnetic material provides a wider frequency response than typical electric guitar magnets. Also, a "deluxe" model includes a microphone that you can bend underneath inside the guitar, providing you with a blended acoustic and magnetic sound. MUSIC MAKER
Guitar Pickups - Variety Most guitarists have at least some idea of their ultimate sound. Even though the effects, amplifier, overdrive level and speakers all have a large impact on the final sound, it all st arts with the pickup, and like wines, players usually acquire an appreciation of the subtleties in pickup sounds over time. Also, as you upgrade your amplifiers and speakers, you will hear more clearly the special sound of your own guitar and its pickups. For example, pickups which sound characterless (clear but un-coloured) with clean settings generally maintain their clarity at very high overdrive levels, while pickups with their own unique sound maintain a strong character at low to medium levels of overdrive, but lose some clarity at high overdrive levels. It has to be said that if you use a lot of overdrive, you will miss the subtleties of dif ferent pickups. Instead, you're more likely to notice other factors in different guitars such as pick attack, sustain, even-ness of response, and so on. Probably one of the main traps to avoid is going for too much variety on the same instrument, particularly if you play live. I've heard many times of respected players who have problems with the difference in sounds between the neck and bridge pickups. If you set your amplifier for the ultimate sound on one pickup, it can make the other sound very ordinary, so you either accept it, or go with a compromise where both pickups sound reasonable. One option on two pickup guitars is to go with a stereo set-up, so you can optimise the sound of each pickup. There have been many other attempts to match the tone between pickup s more evenly, while still retaining the timbre (that's the sound unique to the pickup, and it's position on the guitar). A popular option with companies like Seymour Duncan is to of fer a neck/bridge set of pickups, where the bridge pickup has a few extra coil windings to give it a slightly hotter output (to compensate for less string vibration over the bridge pickup) and a little more middle (to more evenly match the tone of the neck pickup). The only downside is that the combined pickup sound is marginally compromised (explanation later!). Another common solution along similar lines, and even more extreme, is to use a single coil in the neck position and a humbucker in the bridge position. There can be good reasons for doing this, such as using the pickup s, and associated controls for switching between good rhythm and lead sounds. This approach has the advantage of simplicity, but deprives you of worthwhile variety in a combined pickup sound. The answer is to use the pickup s alone and in combination to provide a palette of useful sounds, and find another means to change between rhythm and lead settings. Channel switching amplifiers are ideal, of course, but other possibilities are volume pedals, equaliser stomp boxes, a master guitar volume control, overdrive pedals, and so on. Guitar Pickups - Different Positions how to work out which pickups go in which position. It is a reasonable question, because everyone knows they each sound different. The answer though is that it doesn't matter , because the (original) strat pickups are identical. Even recent single-coil pickups are "reverse-wound & reverse-polarity" in the middle position to cancel hum, but this doesn't affect the tone at all. Guitar Pickups and Harmonic Content The three sets of pickups shown for an electric guit ar such as the Fender Stratocaster allow the player to adjust the quality of the sound by choosing the amount s of signal used from each pickup. The knobs shown are volume controls for the three set s. Of the string modes shown, the fundament al will actually be much larger than the others, and the others diminish progressively. Using the pickup set to the right gives much more fundament al and a mellower sound. MUSIC MAKER The sound of identical pickups vary in different positions on the guitar because the sound of the string changes along its length. There are variations in tone (the ratio of higher harmonics compared to low), the timbre (the relative strength of different harmonics caused by the position of the nodes of each harmonic) and in the overall level. The closer the pickup is to the bridge, the sharper the tone (stronger higher harmonics), and the overall level is lower (because there is less string vibration closer to the bridge). The timbre is simply different, and depends upon all the things mentioned in the previous topics. It is also important to realise that this change of sound along the string is exponential. That is, changes near the bridge are far more dramatic than those near the neck position. You can verify this for yourself by picking the string at different positions. This is best done acoustically, so you can hear the whole string sound rather than the small portion heard by a pickup. First, pick a string right next to the bridge and notice how bright and "twangy" it sounds, then pick the string at 1 centimetre intervals towards the neck. You will find that the changes at first are quite dramatic, but become less noticeable as you pick closer to the neck. This illustrates why on a strat, there is less change in tone between the middle and neck pickups compared to the sharp sound of the bridge pickup. Granted, the pickup is angled back on the lower string side to partly offset this effect, but it still remains difficult to get a great sound out of identical pickups with the same EQ settings. That's not to say that there's anything wrong with the design, it is useful for various music and playing styles. A common modification is to simply replace the bridge pickup with a hotter and warmer sounding pickup. There's one other point to note about the changing timbre of a string along its length. When fretting notes right at the top of the fretboard, next to the neck pickup, it effectively makes the neck pickup sound brighter because it is closer to one end of the string's vibrations. There are compensating factors here also, such as reduced brightness and sustain due to the shorter vibrating string length. To be continued................. 25
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