Bass Guitar Pickup Impedance

Impedance refers to resistance for alternating current signals (or signals). Mismatching of impedance will prevent maximum power transfer and may lead to noise, distortion or other unwanted side effects.

The humble guitar cable introduces capacitance; this increases with length as well as pot type (linear versus log taper), altering pickup impedance as a result.

Inductance

Impedance and guitar pickups both depend heavily on inductance for proper functioning. Inductance measures how much current can be generated by the pickup, which is vital given that voltage is dependent upon current, as is evidenced in physics by any sudden spikes or dips in voltage without an equally rapid change in current. A pickup with high inductance will produce substantial current flow resulting in significant voltage shifts as a result.

Inductance measures the magnetic flux surrounding coils inside of a magnet, with different magnets, pole pieces and coil windings having differing inductance values. More magnetic flux around coils typically means higher inductance due to current passing through them creating another magnetic field that pushes back against it via Lenz’s Law and produces resistance (technically known as reactance in this context).

Pickups with higher inductance tend to produce more resistive voltage, leading them to sound louder and have greater gain than pickups with lower inductance. Furthermore, their inductance affects frequency response – as we will discuss later.

Capacitance is also crucial when it comes to pickup tone, but less so than inductance. This is due to how capacitance only accounts for about one fifth of its overall capacitance when used – your guitar cable adds additional capacitance that typically increases three or four times larger than what the actual pickup offers.

Capacitance plays an important role in how much of a signal from your pickups reaches your amplifier. A 1-kOhm amplifier input impedance will transfer 99.9 percent of pickup signals (assuming all other factors remain constant); with higher impedance amps only transmitting 50%. As much of your pickup’s signal should reach your amp as possible!

Capacitance

A capacitor consists of two electrodes connected by an electrolytic dielectric material and separated by an air gap, or dielectric layer. They are constructed by layering ceramic and silver alloy electrodes until reaching their specified capacitance value based on voltage, current, and frequency requirements.

Most guitarists don’t realize it, but the capacitor connected to their tone pots (or between volume and tone in active guitars) has a significant effect on the bass tone. By altering its value, guitarists can access new sounds not previously achievable with previous settings of their tone control.

A capacitor is usually connected in parallel with the pickup, increasing its impedance. As impedance increases, more frequencies that you don’t want to hear may enter through interference; this can result in harsh or shrill tones depending on its construction and type of pickup used.

One factor that can alter the capacitor value is temperature of its coil. Copper wire ions vibrate more when exposed to higher temperatures, and this results in different ohm readings. However, it should be remembered that an ohm reading only represents DC resistance against pushing electric current through a pickup coil.

Factors influencing capacitance include voltage rating, dielectric constant and how close together its plates are. A thicker dielectric allows more electricity to pass between its plates of the capacitor but this usually causes it to expand further; to counter this effect electrodes must often be brought closer together in order to decrease space taken up by their capacitance.

An often-held misconception about capacitors is that their value can be altered simply by heating or cooling down their circuit, but this is simply untrue! Although temperature does have some bearing on its DC reading, this has nothing to do with how well it performs compared to similar-rated and dielectric constant capacitors like Electrocube AM or PM series models. To maximize performance it is therefore vital to select high quality models such as these for best performance results.

Resistance

A guitar pickup consists of magnets, wire coils and some plastic and metal components; how those elements are configured has an immense effect on tone. For instance, high output pickups tend to feature thousands of turns (windings) of wire for coil resistance-increasing purposes that contribute significantly to its impedance rating.

Single coil pickups typically feature much lower resistance due to having only a single or very few coil windings, thus producing much lower ohm readings with a multimeter than that of a humbucker pickup.

Low resistance contributes to a pickup’s ability to transfer current efficiently, as well as its sensitivity to feedback. But other factors also come into play here — for instance how tightly packed together coils are packed together and whether they have any magnets installed (along with whether or not vacuum impregnation occurs).

If you’re using a bass amp designed for magnetic-based guitar pickups, it is ideal that they all possess similar impedance values to ensure optimally loaded input (as opposed to overloaded input, which could negatively alter your tone).

Impedance matching is critical in order to maximize pickup performance without overstraining your amplifier or overheating it due to excessive loading. Furthermore, matching helps safeguard amps by decreasing their chances of overheating due to excessive strain.

Resistors provide another level of tonal shaping options beyond what pickups, capacitors and pots can. As an example, here’s an illustration.

To improve their compatibility with single coil pickups, add a 1Meg resistor in parallel with your volume pot to lower its value from 500K to 333K and thus increase current transmission capabilities. This trick can work for both linear and logarithmic pots.

Frequency Response

Ohm readings from pickups provide us with an idea of their inductance and resistance; however, that doesn’t tell us much about its tone; that depends on its construction – how big/many turns, coil size or even number can influence its inductance (more turns = more inductance), but other factors also impact its tone such as tuning or cable length can all have an effect.

Changing the number of windings around a coil can alter its magnetic field strength and alter inductance and frequency response, altering inductance as a result and thus sound. Furthermore, material used for winding as well as any ferrous materials attached will have a dramatic impact on inductance – including metal baseplates on Telecaster pickups or even screws that alter its inductance by up to one Henry (which can make an audible difference).

Many people assume that more windings on a pickup will translate to higher output, but this is not always true. Windings increase coil resistance, necessitating additional power from higher frequencies in order to push through it. Low-impedance pickups present less of a load on signals passing through them and allow higher frequencies more easily pass through.

Preamp choice also plays a large part in frequency response. Some valve preamps with higher input voltage can produce distortion when driving low output impedance pickups too hard for their design; other preamps may alter tonality by offering different forms of gain or feedback loops and presence/tone pot adjustments which have significant impacts on frequency response of guitar pickups.

Finalize your bass rig by adding a filter that rolls off high frequencies. Most bass instruments don’t rely on upper harmonics to cut through a mix, and by filtering these off it removes a potential problem and helps your bass stand out more. It is an efficient yet simple solution to making your bass instrument shine in any mix environment.