How to adjust the distance of a
humbucking pickup from guitar strings.
In this article you will find instructions and tips about pickup height setting on electric guitars, with special regard to humbucking models. Another article of this blog deals with single-coil pickups. This is part of the general setup of the guitar, that involves topics covered on the Soundsation blog as neck truss-rod and action adjustments.
Before continuing you should have:
All that verified, we can talk about how to self-adjust humbucking pickups working on their mounting screws on frame or guitar body.
Magnets and coils
An electric guitar pickup is an electro-magnetic transducer that converts string vibration into an electric signal. Easier said, it is a set consisting in coils of isolated electric wire, magnets (permanent magnets made of magnetizable materials as Iron, Nickel and Cobalt), pole pieces and an enclosure.
An electro-magnetic field surrounds the pickup magnet and electrical particles move from the North pole to the South pole of it. When this field is disturbed by string movements (strings must be made of metal to interact), an electrical voltage is induced and it varies as the string vibrations change. This variable electric signal reaches the guitar jack output through the coil, volume and tone potentiometers, and then it is send to the amplifier to be amplified and converted into sound waves.
It can therefore be understood that string-pickup
interaction has a lot to do with their distance, in addition to
the electro-magnetic field strength and shape.
Common pickup magnets are made of Alnico
(Aluminium, Nickel, Cobalt and Iron) in its different classifications (2, 3, 4,
5) or ceramic (Iron oxide powder and Barium or Strontium carbonate ceramic),
also called ferrite, more fragile but cheaper. Ceramic magnets can be
recognised at sight thanks to their dark colour, whereas Alnico is shiny. Some
magnets are produced with the contribution of alternative materials, as Rare
Earth elements Neodymium and Samarium.
How is a humbucking pickup made?
In our blog article about single-coil pickups, I explain they are based on a single coil of isolated electrical wire and one or more magnets. They are easily liable to picking up noise, particularly hum from household electrical wiring (230V 50Hz or 120V 60Hz according to countries).
This problem was solved by means of the humbucking pickup in the '50s, though it had been already studied since the '30s (Electro-Voice, Baldwin, Rickenbacker, Vega). In 1954 technician Seth Lover – who had found a solution to hum in amplifiers – started working on a hum-bucking pickup for Gibson electric guitars. The result was the renowned P.A.F. (initially featuring fixed poles and named PU 490), for which Gibson requested a patent in 1955 – as it is well known, the “P.A.F.” writing on the label means “Patent Applied For”. However sales proposal started only in 1957. At the same time technician and accordionist Ray Butts was working at the Filter'Tron humbucking pickup for Gretsch. A patent was also requested for this pickup in 1957, so this was a “Patent Applied For” too.
The solution offered by the new Gibson humbucking pickup consists in using two wire coils – rather than one – connected in series, in electric and magnetic phase opposition (opposed poles and coils). Interference caused by lights and transformers is virtually cancelled by coil combination. In this process some frequencies are lost, causing the typical less brilliant and warmer sound of humbuckers as compared to single-coils. Using two coils also provide a higher output level.
Humbucking pickup types
Humbucking pickups can be of the following kinds:
Starting from these general categories, through the decades we have seen any kind of attempts, mixing coils, magnets, poles and so on. CNC machinery is capable of making very compact windings with extremely thin wire for productions that were unworkable in the '50s and '60s. For more reference, there are excellent books about pickups and their evolution (*).
Adjusting humbucking pickups
It can seem strange to many, but humbucker setting –
it doesn't matter if they are large or narrow – is mainly an ear guided
operation! Manufacturers have their specifications about pickup pole
distance from strings, usually referring to the 1st and 6th
strings. For example, in the case of a Gibson pickup, leave each screw pole in
the factory position, press the 6th string at the last fret and start
distancing the bridge pickup at about 1,5 mm from strings and the neck one at
about 2,5 mm, roughly builder's current indications.
Don't worry about precision and start listening to open string sounds. Leave the string, lower the bridge pickup just a bit – a quarter or a half of turn normally produce perceivable changes – and consider the sound: is it thicker or thinner? Has it more or less harmonics? Is it more brilliant or deeper? Is it airy or compressed? Clear or hazy?
Stay on the bridge pickup and carry on by attempts, generally lowering just a little the pickup and listening to the result. At some point you'll feel the sound is becoming too acoustic or subtle or undefined; then go back and raise it until you reach a point the sound seems right. Some experts use to say in focus sound, because you are in fact adjusting the interaction between the electro-magnetic field and the string vibrations as you were focusing a subject in an optical lens.
This way of setting a pickup height only
applies to your specific instrument with that pickup, those strings, based on
your essential taste and well trained ear.
Let's go to the neck pickup
Sometimes, even on pros' guitars, it happens to see humbuckers that are almost sticked to the strings, searching for a more powerful and deeper sound. Actually a fundamental pushed sound with little sustain is obtained, since string vibration is limited by the pickup magnetic pull.
Once you have set the toughest pickup, the bridge one, you can handle the neck pickup, that always gives a louder and fatter sound, because of its position where string vibration is broader. You have to lower the pickup just enough to get a sound that matches the bridge pickup in volume. Moving the switch from a pickup to the other, you should not hear big level differences. It doesn't matter if the neck pickup seems very far from strings as compared to the bridge one.
Once you have finished this process, it is time for a more specialized adjustment, searching for the optimal focus of the neck pickup too.
What about if pickups were three, as in SG Custom style guitars? The method is the same. Personally, I always start with the bridge pickup, then go on to the neck one and complete with the middle pickup.
The described adjusting method is good for those with a certain experience. If you feel you are not able to follow it, manufacturer's specs can be taken for granted. Turning to a luthier or a skilled technician is always advisable.
Sometimes you can get unexpected reactions. If you want more bass, do not raise the pickup at the wound string side, instead lower it at the treble side; and vice versa.
A proof of successful setting comes from listening to the switch middle positions: if the sound is not typical and pleasant, you'll have to review something at least for one of the pickups.
If the pickups are very different from each other, by example if the bridge pickup is a lot more powerful than the neck and middle ones, you'll have to turn to splittable pickups or accept some compromise solutions: an audible difference of volume or some drive sacrifice in the most powerful.
Setting very powerful humbuckers can require a little less care, because the pickup sound often prevails on the guitar character, though some designs allow a reasonable magnetic flux restraint. If the coils are mighty indeed (resistance of windings over 12-13 kOhm), it will be difficult to get more highs than those the pickup make permits. It is recommended not to get so close to strings.
Once a coarse humbucker adjustment has been done, there are few things to be considered: alignment to strings and screw pole pieces.
Large humbucker and soap-bar style pickups should
maintain a parallel alignment to strings. That's OK, but parallel to what? To
open or fretted strings? And at which fret? Here is the approximation inherent
to guitar again. Let's take as prevalent an open string parallel alignment.
If the pickup has just two frame screws, we may have to remove it and put some
filling material in the hole. Usually little foam pieces are used,
arranging them to favour the desired placement.
I think that three screw frames are perfect for this setting and should be adopted universally, except for vintage replicas.
pickup a little tilted towards one of the coils. Which one? It depends on coil kinds: let your ear be the judge!
It is possible that something changes when you switch from clean sounds to saturated sounds; there is nothing wrong with retouching pickup setting while an overdrive pedal is turned on.
Poles and pole pieces
Humbuckers mostly have six fixed pole pieces and six
adjustable screw pole pieces, that can be slotted or Allen type. Adjustable
screws help to balance string to string sound level if volume
differences are accentuated.
Play, listen, evaluate and screw or unscrew pole pieces till the strings produce the same volume. Start from screw factory setting and try to follow the fretboard and bridge radius; this normally works.
If magnets or poles are exposed blades, there is no problem: usually they are so powerful that certain nuances became negligible.
And what if the adjustable screws are six per coil, so twelve in all? Well, start working and good luck!
(*) M.Milan, Pickups - Centerstream Publishing, 2007
M.Milan/J.Finnerty, The Gibson “P.A.F.” Humbucking Pickup - Centerstream Publishing, 2018.