Technical specs of a pickup
After final assembly, each pickup will be controlled for its overall performance, the main part of which is the frequency response. But what are the main electronic values that describe a pickup’s performance? And how are these measured and confirmed? Does the widely mentioned DC resistance (the kOhms value) really tell anything about the pickup’s final frequency response and output level?
At first glance, a magnetic guitar pickup is a very simple, primitive device. It consists mainly of one or more coils, permanent magnetic, non-permanent magnetic, and paramagnetic (non-magnetic) parts, such as the magnet bar (or rod), the pole screws, and the plastic bobbin (as respective examples). The pickup is a mechanic-electric transducer since it "translates" the string vibration into an electrical signal which changes through time by following a similar frequency pattern. This audio signal has the same root frequency of the string note that is being played (example an A at 220Hz), but a different harmonic content (frequencies that are mulitples of the root frequency, and cause the overall tonal characteristics of an instrument - the so called "timbre"). However, this is a very complex process. In the case of deep scientific analysis, this function cannot be easily described with a certain, generally used mathematical equation, a fact that certainly incommodes the proper design of a pickup. There are many reasons for that (such as imperfections in string vibration, inhomogeneity of the pickup’s magnetic material, and boundary conditions in the pickup’s surrounding areas, just to name a few), so we won’t go deeper here.
A way to describe the pickup functionality is to separate the whole process into a magnetic and an electrical part.
The magnetic part takes place right between the string and the pickup’s neighborhood and assigns the string vibration, which is a periodic (regularly changing in time) effect, to a respective periodic change of a magnetic value called the magnetic flux density.
This periodic change of the magnetic flux density induces an electrical current (the audio signal that is described above) through the pickup coil(s), and that's where the electric part of the pickup takes over. This current represents the sound of the string vibration and, hence, of the guitar itself. However, the pickup coil (as well as other metal parts on the pickup) acts as a filter for this primary signal, and it shapes the overall frequency spectrum. That's why it was mentioned before that the harmonic content of the electric audio signal is different than the harmonic content of the vibrating string. In a way, the guitar pickup is a microphone and a filter at the same time. And probably to great disappointment for those who believe it, a pickup is certainly not a sound generator; that’s why the same pickup will result in a totally different sound when put on a different guitar.
The overall frequency spectrum of the pickup is therefore a crucial characteristic because it will describe the expected effect of the pickup on the overall guitar tone. The spectrum is visually described by an x-y plot curve, which is called the frequency response (fr) curve. This curve shows how each pickup affects the whole frequency spectrum: Some frequencies are boosted, some are cut, others remain unaffected.
In order to better understand this, a typical such curve for a single coil pickup is shown above. The fr curve shows the enhancement or decrement of the pickup’s primary signal at each frequency inside a specific range. This range is usually set between 50 Hz and 12–13 kHz, which more or less corresponds to the audible range of the human ear.
Looking at the curve above, in the very low and low midrange frequencies, nothing happens; we have a more or less 1:1 signal transition. Depending on the pickup’s design, the midrange-high midrange range is where it starts to become interesting. There is always a bell-like curve formed (boost range), after which the signal level falls rapidly to non-audible levels (cut range). The highest point is the resonance frequency of the pickup, fres. The width of the bell curve (pointed at the 3 dB bandwidth) indicates the harmonic content of the resulted tone. The height of the resonance curve (resonance peak) also indicates how much the sound will be colored
The resonance frequency (Hz–kHz), the 3 dB bandwidth (Hz), and the resonance peak height (dB) are mainly dependent on the form of the pickup coil(s) and further metal parts found on a pickup (mostly on humbuckers and P90s), and less on the DC resistance (kOhms). Tone-wise, these values are the most important characteristic of a pickup since they tell us a lot about the range where the frequencies of the guitar signal are colored mostly. The assumption that "the higher the Rdc, the higher the output" is only valid if ALL other specs of the pickups to compare are identical (wire diameter, wire insulation, coil size, metal part alloy, magnet material, hookup wire, etc.), a fact that for regular users is very difficult to verify. As an example, we have the GAStation and the GAShopper, with 10 kOhms and 12 kOhms Rdc, respectively. The GAStation definitely has a higher output than the GAShopper. The reason here is the difference in the diameter (AWG) of the wire used on each model.
Therefore, from the facts that are described above, please keep the following in mind: When comparing pickup data, we strongly recommend not judging a guitar pickup by its DC resistance. Furthermore, it's the frequency response curve (frequency vs. level) and especially the resonance frequency of each pickup model that better describe the frequency response and harmonic content, which will determine the overall sound. You may find the resonance frequency in the specs section of each of our pickups.
Apart from this, there are other important factors that will further degrade the pickup’s frequency spectrum by lowering the peak and the value of the resonance frequency. These are:
Metal parts (as mentioned, found mostly in humbuckers and P90s): if you like more detail on this, please read here
The connection wire (a.k.a. "hook-up cable") of a humbucker and a P90-style pickup. GAS buckers and G models are fine-tuned during final quality control by the length of their connection wire (single braided or 4-conductor). Therefore, we recommend not shortening the wire in any way when installing a GAS humbucker or G model on a guitar.
The guitar electrics (volume and tone pots, tone caps, and the internal guitar wiring) The pots are used to mainly reduce the resonance peak and result in a more flat curve. That’s why singles, who show a higher (10dB range) peak, usually match with 250k pots, whereas humbuckers, who show a lower peak (5dB range) due to material-caused losses, usually match with 500k pots. However, this is not a rule. The user decides on the final sound
The guitar cable that is used. The part that connects the guitar to the next rig stage (pedalboard or amp) will drift the resonance frequency to lower values due to its considerable length (a few meters at least). Therefore, this cable must be considered a permanent part of the guitar (like the strings, pickups, etc.). We strongly recommend using the same cable for the same guitar.
Last but not least, a typical 12" guitar loudspeaker carries frequencies up to 7-8 kHz, a fact that also must be considered.
The resonance frequency as given for every GAS pickup model is measured on the same device, the Lemme Pickup Analyzer, with no additional load of any volume or tone pot, except an 1 MegOhm resistance load (which represents a typical value for an input of a guitar amp) and no further added cable, just the hookup wire of the pickup itself. This allows an easy, valid comparison between different models, but ensures also the consistency of our pickup models.