“What is a pickup”
A pickup is a transducer that adheres to the laws of electromagnetic inductance. As your steel (ferrous) strings move and vibrate within the magnetic field of the pickups static magnet it causes a fluctuation in the field inducing an alternating current in the wire (coil) that is wrapped around the magnet (pickup).
Well that’s all great to know but what the f**k does that really mean?
Thanks to laws set out by Mr Faraday way back when, as you strike a string its vibration pattern encourages a similar fluctuating pattern in electrical current within the wire that is wrapped around your pickups magnet. This small alternating current can then be amplified and we hear that current as sweet, sweet guitar licks!
So lets start looking at the makeup of your pickups. There are hundreds of different types of pickup on the market with each type constructed in a different way. These differences have a direct impact on tone. Winding size, bobbin size and material, magnet type and wire gauge are just a few variables.
For simplicity we will be mainly focusing on the humble yet classic single coil pickup as found on the Fender Stratocaster.
To look at the principle parts of a pickup we first need to remove the plastic cover. These covers are there purely to proteect the pickup’s fragile windings and to make it visually pleasing. With the cover removed the first thing we see is the main “body” of the pickup, this part is called the bobbin and it is what the very thin copper wire is wrapped around.
When you read “stats” on pickups the manufacturer will often refer to “windings”…these are the windings! The stats will also mention DC resistance when referring to the output of the pickup….the more windings you have, the more material there is in the circuit and therefore the higher the resistance, the higher the resistance the higher the output. This, however, is a way too simplified way of looking at things. In reality you simply cant judge a pickups output by it’s measured DC resistance. For one thing the actual resistance of the coil needs to be measured in units of impedance or Ohms as we are dealing with alternating current and resistance changes with the frequency of this current. Also the DC resistance is one of many different variables which will ultimately affect the pickups output. It is best to say that if all parts of the pickup were equal and the ONLY variable was the coils DC resistance then the coil measuring a higher DC resistance would have a greater appreciable output.
One thing to remember when thinking about a pickup’s output is the trade-ofF between DC resistance and treble loss. The higher the DC resistance, the higher the output of the pickup, however, as the DC resistance increases the pickup’s treble response decreases. Underwound pickups can sound thin and weak but have sparkling clean treble response, overwound pickups sound big and beefy but at the cost some sparkle and snap. Like a lot of things in the world of guitars, it’s a balancing act. The two extreme ends of the coil are connected, directly or by tag terminal,to the rest of the guitar circuit, this is where the current exists and can be manipulated by your guitars tone/volume pots and broken/made with the introduction of your guitar lead.
The next parts of your pickup to look at are the poles or magnets. Within the pickup’s bobbin you will (in the case of a strat pup) see metallic parts. In the case of a single coil pickup, for simplicity, you will see either a strip of metal (bar/blade) magnet or six individual magnets or slugs. It gets a little bit complicated here as there are differences in magnet layout between single coil and double coil pickups. Again, for simplicity, we shall look at a single coil system. The six individual pole pieces in this pickup are magnets and can be set at different heights, in relation to the pickup body, to interact with the strings in different ways so we can balance output between strings…hence the “staggered” pole pieces of a classic Stratocaster pickup. The slug type pole pieces in vintage Strat pickups are set from factory.
The entire body of the pickup can be raised and lowered to increase/decrease pickup output. The “staples” seen on classic Gibson “dog-ear” P90 pickups act in much the same way. When the “soap bar” P90 pickup was developed the pole pieces were actually magnetized screws that could be adjusted on their individual threads to balance out the varying magnetic interference of individual strings. So here is a good time to look at different layouts of pickups having an effect on tone. The classic Fender Stratocaster pickup and the classic Gibson P90 soapbar pickup are very similar. They are both single coil pickups with a row of six magnetized elements, however, these pickups could not sound any different, why? Because they are constructed in different ways. The most notable difference between the two is their magnetic layout. As i said before the strat pickup has slug magnets which sit proud of the bobbin body and interact with the strings. The P90 has six threaded screws that are magnetized by a bar magnet at its base.
So this is probably a good time to talk magnet materials. When you read stats regarding pickup construction you will generally see the magnetic materials being described as Alnico or Ceramic. Although there are different types within both of these material categories (ie Alnico II and Alnico V) we will just look at these two common and different materials.
Alnico, imaginatively titled through being an alloy of Aluminium, Nickel and Cobalt was one of the first types of magnet used in electric guitar pickups (save for the steel types used in the original Charlie Christian pup). Alnico has a comparatively low magnetic pull but sounds very smooth and articulate.
Ceramic magnets are formed of ferrous iron and materials such as barium which are fused using high pressure/heat to form solid bar type magnet slabs. The ceramic magnet has much greater “pull” than Alnico and, as a result, is far more aggressive and is more powerful all round. It is also worth mentioning here that the Ceramic type magnets have a greater shelf life than the Alnico type and is more resistant to magnetism loss through mechanical shock.
So where does this all leave us? Well, in the case of an electric guitar it is the pickup’s job to translate your guitars resonance pattern into electrical energy so it is a link in a very important tonal chain. No matter how good your guitars wood and construction is, if your pickups suck or are incorrectly adjusted then your tone will suck! So we can see that pickup choice and/or adjustment forms a very important part of a setup. There are literally thousands of types of pickups on the market offering different outputs and tone signatures and we should choose our pickups to best suit our tonal needs and playing styles. As i mentioned earlier pickups also need to be adjusted correctly for optimum performance. These adjustments can range from seating the pickups correctly as to not introduce any extraneous vibrations that the pickup will re-amplify to setting the hight of the pickup body and/or pole pieces to balance output and tone. This last part is critical to any electric guitar setup…set your pups too low and they can sound thin and distant…..set them too high and the magnetic field of the pup can actually pull on the strings themselves interrupting their natural vibration pattern causing dissonant “wolf” tones and pulling intonation sharp.