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Factors affecting how a pickup sounds

Magnets: It is often said that ceramic magnets are brighter than alnico, but that isn't entirely correct. What makes a magnet "brighter" than another is it's strength. A stronger magnet will be brighter. Because ceramic is so much cheaper than alnico, Alnico in grades above 5 (or8) is rarely ever used. High output pickups often use ceramic magnets. Ceramic magnets are actually weaker for a given grade/size after a certain point. In the sizes used for pickups, Alnico is weaker. A pickup which utilizes alnico polepieces can have different poles made of different strength magnets to accentuate or minimize certain characteristics. Pickups which have a bad sound or string may have a magnet which is not matched to the others; rarely one polepiece will actually be upside down.

Page with Alnico magnet properties (link to other magnet materials are there as well)

Here's a page with "magnetic design considerations" includes info on demagntization factors. some say alnico will demagnitize if ground or filed due to the heat. As shown on this site, the maximum "practical operating temperature for alnico is 540*C (1004*F). I don't think you'll get it that hot with a file or a grinder...

A trick I learned when grinding hardened and temepered steels was to keep the fingers in close proximity. If it gets too hot for the fingers, dip it in water. It's still WAY below any critical temperature (critical temp for some steels and hardness/temper is around 350*F)

Here's a page of FEMM simulations showing magnetic fields for a few different pickup types

Wire: The finer the wire the fewer highs pass through. Finer wire also has a higher resistance for a given length. For this reason a pickup wound to 6k with 43awg wire will have less output than a pickup wound to 6k using 42awg wire. Regardless of what has been said I do no believe there is any difference based upon type of insulation alone. However, wire with a heavier insulation (i.e. "double build") will result in a wider coil at the same resistance/output. See "shape of coil"

There is a characteristic of wire called "skin effect" which is more pronounced in smaller diameter wires due to thier higher restance. "Skin effect" is where the higher frequencies travel along the surface of the wire rather than travel thru the center of the wire. This leads to that "brittle" characteristic of high output pickups which must be wound with the finer wires...

Here's a link to wire guage classification chart that gives diameters etc.


Number of windings: The greater the number of windings the greater the capacitance and inductance of the pickup. Because of this more low end is generated along with an increase in output. Additionally, more windings will make a slightly wider coil, see "shape of coil" below.
Grounding: If a pickup has a metal baseplate or cover, and it is grounded, some of the highest frequencies will pass to ground by a means called "flux line coupling"

Metal base/ cover: if the plate is magnetic, and not grounded it will increase the capacitance and inductance of the pickup much like more windings do. The metal will also add lows/mid lows.

Shape of the coil: A coil which is taller and narrower will be clearer, more focused and slightly brighter than another coil which is shorter and wider if they have the same output. This is because the shorter wider pickup is sensing a wider section of the string, which gives it more variance in the signal it's sensing (due to variance in oscillation size/ pattern of the string along the length of string sensed)

Magnet placement: How the magnet(s) are placed has an effect on the field of the pickup and therefore the signal generated. An example of this is a P-90 type pickup which has the polarity of the magnets repelling each other in comparison to a similar pickup with the polarities attracting each other. The opposing polarity pickup seems to be less focused.

Magnet age: Some say alnico weakens with age, and this relates to magnet strength as previously explained. (Magnet manufacturers claim a loss of strength at a rate of aprox .2-2% / 100yrs) However, some manufacturers are "aging" magnets by heating. I have found through testing that this type of "aging" does NOT weaken the magnet (there is a point at which it will, but it's almost an "all or none" situation) What it does do is "temper" the magnet (alnico) relieving internal stresses. My testing has shown that before tempering there was often an unevenness of strength between magnets of the same "rating", i.e.alnico5, even between the two poles of the same magnet. The tempering almost always equalized the strength of the two poles of the same magnet, and lessend the variance between magnets of the same rating. However, it was not uncommon to still find some variance (I believe significant). For this reason I now temper all alnico magnets and test them for strength. As a side note, information provided by a magnet manufacturer indicated that tempering in this manner will make the magnet less susceptible to outside interference.

Coil Age: Much of the characteristics which are attributed to the aging of the magnets may actually be due to the aging of the coil wire. This makes more sense based upon tests and experience, and what is known about magnet aging. The older insulation (formvar and enamel) will get hard and brittle with age, this would also "stiffen" the coil windings, changing their characteristics slightly. Also note that the older "Lacquer potting" on some pickups tends to break down significantly with age. This will have a definite effect.

Winding pattern: machine wound pickups have a very even wind pattern; custom wound, hand wound and very old pickups generally have a much less regular winding pattern. This is called "scatterwinding"; what happens is every time the wire crosses, the flux line generated also crosses and couples making one larger irregular flux line. I believe this causes the pickup to react as one large "whole" instead of more like many finer flux lines interacting with and reacting to each other. I believe this is why scatterwound pickups almost never have "brittleness" even if they are bright, scatterwinding and the flux line couple helps destroy the "skin effect".

Besides breaking up "skin effect" it also causes something called "distributed capacitance" which is where the capacitance of one winding is spread to other windings within the coil. Scatterwinding causes the capacitance to be "spread" across many more windings. It also minimizes "mutual (self) inductance" which is where each individual winding picks up and amplifies a portion of signal from adjacent windings.

Potting: let me start by saying this is all subjective and I don't fully understand everything here (well, I don't have any hard data to back it up)...First off, a properly wound pickup doesn't need potted(fact). An unpotted pickup is going to be more "musical" than an unpotted one if wound properly; however, it will also be more prone to damage and will wear out more quickly. A pickups windings actually move w/ vibration as the electomagnetic field moves and w/ the body vibration to a small extent. That's why unpotted is more musical, however if the windings are too loose the pickup can be microphonic, even to the point of picking up your voice (I suspect the voice somehow causes the windings to move ever so slightly). Potting prevents the vibration and thus eliminates the risk of microphonics. The harder the potting material the more "high fi" the pickup will sound. Thats why epoxy pottedpickups are often considered sterile, but this lack of overtones helps those same pickups stay defined in very high gain situations. Also, the potting material will effect the pickups "resonant peak" and can actually change the point and frequencies at which the pickup "breaks up" or feeds back.
Now, what is often called microphonic isn't, it's a pickup squeeling or feeding back due to a loose part somewhere, any air gaps between surfaces can vibrate and cuase the squeeling, very often it's the pickup cover. It's also a common problem w/ tele bridge pickups because the copper plate underneath becomes loose. Potting fills the voids and prevents vibration stopping the squeeling. From a production standpoint, it is just too easy to have problems without potting especially if the pickups are going to be used in a very loud/ very high gain environment, so most pickups are potted from the factory (the "good ones" anyways, there are a few exceptions) My solution is a "partial potting" of the coil, only isolating the outer windings and allowing the inner ones to move

Most of these factors are not huge on thier own (in general, magnet strength being one exception, it's pretty significant. Coil shape /size is another). But combining them will have a significant impact on how the pickup sounds. All of these factors must be considered and balanced when trying to achieve a particular "sound". It is easier to start from a known point, and make minor modificatins to that than it is to "start fresh" because there are too many interactions going on to determine "which" factor(s) made the difference.


Also related: Pickup specifications for Fender, Gibson, etc.