How Important is Guitar Pickup DC Resistance?

[OBX351]

Very interesting article about PU output based on DC resistance. I am a long time guitar player but novice when it comes to the technical side of guitar wiring/pots/caps and pickups. Anyway I asked the folks at Lollar about hotter vintage pickups and they pointed me to the following article.

Lollar Pickups Blog » Blog Archive » How Important is Guitar Pickup DC Resistance?
How Important is Guitar Pickup DC Resistance?

There is quite a bit of misunderstanding about the use of DC resistance as a measurement of a guitar pickup’s output. DC resistance (kΩ) is a handy but rough measure of a pickup’s output. It is most useful for making general comparisons, but not taken much beyond that.
We say this because there are a number of variables that can affect DC resistance. In fact, two of these factors can actually change the DC resistance reading on the SAME guitar pickup.
Temperature, specifically, will do this. The very same pickup will have a higher DC resistance reading when the pickup is warmer, and a lower DC resistance reading when the pickup is cooler. For example, if the pickup has been sitting in a sunny window, the dc resistance will read higher. If you took that same pickup and stored it in your basement / practice room and it was cooler in temp, the DC resistance would read lower.
The dc resistance will also read lower once the pickup has been installed into your guitar.
Another factor is variation of copper wire. Although it’s manufactured to rigorous specs, variation exists between spools of copper wire—including spools made by the same manufacturer and from the same lot number. A microscopic size variance that’s still within specs can affect DC resistance.
Equipment calibration can vary between ohm meters and can also change if your battery is low.
We get phone calls from customers who have questions about the DC resistance their new guitar pickup is showing - at that moment - and the DC resistance values that we publish on our web site. They want to know if there is something ”wrong” with the new pickup.
We tell them that unless they are taking that reading at exactly the same temperature as we did here in the shop, their pickup will read slightly differently. More often than not, they will have just received the pickup, pulled it out of the box, and tested it moments after it has just been sitting in either a very cold or a very hot delivery truck.
Another thing to keep in mind is that the DC resistance values we publish are midpoints. The testing was done on average size production runs. Each of the pickups in those runs had a different reading. The values we publish are the midpoints of those groups of readings.
Follow this link to see a full listing of Lollar Pickups DC resistance.

[Dave@Martin6String]

DC resistance is only one part of the equation. Often, a novice will see a high DC resistance and get the impression that a pickup is as hot as a matchstick, this is not always the truth. If the pickup has a high resistance with a weak magnet, or, something in between the magnet and the poles (dimarzio air buckers), it will calm down the output of the high resistance pickup.

[Dave@Martin6String]

That Lollar article is spot on BTW!

[VintageGuitarGuy]

Also, many people get resistance confused with impedance...


Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent.

Resistance is due to electrons in a conductor colliding with the ionic lattice of the conductor meaning that electrical energy is converted into heat. Different materials have different resistivities (a property defining how resistive a material of given dimensions will be).

However, when considering AC you must remember that it oscillates as a sine wave so the sign is always changing. This means that other effects need to be considered - namely inductance and capacitance.

Inductance is most obvious in coiled wire. When a current flows through a wire a circular magnetic field is created around it. If you coil the wire into a solenoid the fields around the wire sum up and you get a magnetic field similar to that of a bar magnet on the outside but you get a uniform magnetic field on the inside. With AC since the sign is always changing the direction of the field in the wires is always changing - so the magnetic field of the solenoid is also changing all the time. Now when field lines cut across a conductor an emf is generated in such a way to reduce the effects that created it (this is a combination of Lenz's and Faraday's laws which state mathematically that E=N*d(thi)/dt , where thi is the magnetic flux linkage). This means that when an AC current flows through a conductor a small back emf or back current is induced reducing the overall current.

Capacitance is a property best illustrated by two metal plates separated by an insulator (which we call a capacitor). When current flows electrons build up on the negative plate. An electric field propagates and repels electrons on the opposite plate making it positively charged. Due to the build up of electrons on the negative plate incoming electrons are also repelled so the total current eventually falls to zero in an exponential decay. The capacitance is defined as the charge stored/displaced across a capacitor divided by the potential difference across it and can also be calculated by the size of the plates and the primitivity of the insulator.

So simply resistance and impedance have different fundamental origins even though the calculation for their value is the same:

R=V/I

What is the difference between resistance and impedance?