Are TCI pickups tuned on the guitar?

Julian

It's a '59 with 4 knobs
Joined
May 3, 2021
Messages
149
The pot resistance in a guitar circuit does not actually make a pickup brighter or darker. What it does is affect the q-factor of the circuit. The q-factor defines the sharpness of the resonant peak. Q-factor is the ratio of inductive reactance (XL) to resistance (R).

Q = XL / R

As R goes up, Q goes down, resulting in a more even frequency response.

Most guitarists confuse a pickup's output with its DC resistance, but that is not how a pickup works. In fact, DC resistance is a poor measure of a pickup's output. What matters is the inductance and self-capacitance of the coil(s) as well as the strength and shape of the magnetic field. Inductance is a factor of the number of turns of wire on a pickup bobbin. Self-capacitance is a function of the number of turns and how the wire is laid down on the bobbin. There are two ways to increase the output of a pickup. The first way to increase output is to use a permanent magnet with a stronger magnetic field (i.e., a magnet with a higher gauss rating). That is why pickup manufacturers eventually switch over to using ceramic instead of alnico when attempting to boost pickup output. Ceramic magnets are available with higher gauss ratings than alinico magnets and unlike alnico magnets, ceramic magnets do not lose strength over time. The second way to increase output is to put more turns of wire on the bobbin. In order to do that with a stock bobbin, the pickup designer has to resort to using thinner wire. Thinner wire has a higher per foot DC resistance rating than thicker wire. That is the only clue DC resistance gives one when attempting to determine the output of a pickup. Higher DC resistance usually means more turns of wire, but more turns of wire also means more resistance per foot of wire due to the physical limitations of stock pickup bobbins.

Now, you have probably heard about wire with magical insulation. There is nothing magical about a wire's insulation other than its thickness. A wire's overall thickness is important when attempting to wind a higher output pickup with lower self-capacitance. A buzzword in the pickup industry is "scatter winding." Scatter winding is little more than imprecisely wound coils. A scatter-wound pickup bobbin usually has a lower self-capacitance than a perfectly wound bobbin. That is due to the fact that individual turns on the bobbin are farther apart (i.e., there is more air in a scatter-wound bobbin). A pickup with a lower self-capacitance usually has a higher resonant peak than a pickup with the same number of turns, but higher self-capacitance. The resonant peak is the frequency at which a pickup is loudest. It is easier to get more wire on bobbin that is perfectly wound by a machine than one that is scatter wound by hand or pseudo-scatter wound by a machine. However, perfect winding equals more self-capacitance, which equals lower resonant frequency (i.e., a darker sounding pickup).

Where the value of the volume pot comes into play is by lowering the q-factor of the circuit. As mentioned earlier, q-factor goes down as resistance with respect to inductance goes up. What happens is the frequency response of a pickup flattens out as the size of the volume pot is increased. In essence, the pickup does not get brighter, it gets less bassy because the resonant peak has been lowered, which widens the frequency response, making it sound brighter.

With that said, has anyone ever wondered why a Strat quacks in positions two and four? It is due to the fact that Strat pickups have a high resonant peak and inductances add in parallel while resistances divide, which means that the q-factor increases, resulting in an sharper resonant peak around which the frequency response drops off at an even faster rate.

In a nutshell, that is why TCI is called TCI, which stands for Tuned Capacitance and Inductance. The only time that resistance comes into play when tuning a pickup is adjusting the q-factor of the circuit.
This is absolutely incredible. Good to know those RLC courses came in handy for the tone heads:p.
 

Simon Says

A Dentist for the Lawyers
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Dec 21, 2012
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1,114
Location
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This is just an theory but here is what I think TCI might me.

It's started with development of pickups to JM Silver Sky, right?

All 3 pickups has same resistance - not sure the capacitance or inductance...

It's safe to assume they are 3 fairly close pickups specwise.

JM likes in between sounds, especially neck and middle pickups together.

So - In question of position 2 and 4 quacky sound theory is - if the 3 pickups have the same spec (resistances, inductance, capacidance), the effect will be more prominent. But If you put different resistance/inductance pickups or compensate the volume because of the position of the pickups, the desired inbetween effect will be diminished.

So I think the TCI thing is tuning the coils to certain wound count, resistace, capacidence and inductance. In 3xSC by keeping all 3 pickups the same spec. For HB by doing multitap coil splits to aim for even coil spec in two given pickups.

I Can't proove it and its just a theory. I may be totally wrong
 
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