When someone uses the term hot pickup, they are essentially talking about the signal output being stronger than a ‘standard’ one. Some might call a certain pickup “hotter” than the other, so they are pretty much comparing the output strength of a pickup to another. Without getting too deep into the logistics of guitar pickup inductance, your average single coil pickup has less signal output than that of a humbucker, or even that of a single coil bass pickup because in essence it doesn’t really need as much as output as the other two if your goal is simply to play. But let’s say you don’t simply just want to play, but rather want to play with something that requires more power – or more specifically – a style of music that takes advantage of more power.
Hot pickups send out more output signal which in turn gives it a set of advantages and disadvantages to that of your less hot pickups. Some prefer hot pickups because they control distortion better but it turn will sound harsher when played clean, this is why metal guitar players who rarely play clean prefer a hotter pickup set up. If you were to play a Telecaster and a Les Paul with the same amp and distortion effect, you should hear a thicker bite with the Les Paul as its humbucker pickups are hotter than the Telecaster’s single coils.
A higher output signal is also helpful in maintaining signal integrity when playing through a long cable and/or several pedals connected to each other. Critics of hot pickups tend to dislike their compressed sound, claiming they lack the amount of clarity of the standard pickup. This is due to the increased resistance of the output signal which pretty much chokes off the high end tones. Also, too much output signal can cause EQ problems with amplifiers that can’t properly handle the extra power.
And while you can certainly go and buy yourself a pair of these ‘hot’ pickups from a manufacturer, you can actually heat up those stock pickups of yours as well – with a little mod of course, known as the overwound pickup. This mod essentially falls into the category of a hot pickup in that the features of its build give it more signal output than that of your standard single coil; ergo, hotter.
Overwound pickups are wrapped with more coil than that of a standard pickup which in turn strengthens the impendence of the magnet, increasing the voltage which then increases the output signal, making them hotter than a normal pickup.
The advantages and disadvantages of this are what you would expect from a hotter pickup; stronger mid range attack but less clarity of the highs. When a pickup is overwound, the “position” of the resonant peak of the signal is significantly lowered, creating less treble, while the peak at the midrange is increased, meaning a stronger mid.
And just in case you don’t know what a resonant peak is, it is the frequency of the signal with the highest output level. The output frequencies of almost all magnetic pickups are never level, but have peaks and valleys in frequency, giving each pickup its own character, in other words, some have better highs, better mids, better lows, etc, and hotter pickups just happen to have their peak much lower than your standard pickup.