Re: Coil-tap vs parallel coils vs single coil
Coil Tap usually refers to a an asymetric tap in the winding of a pickup and that gives you "two modes": by example hot and vintage.
By example, you get an standard fender single pickup and you add some extra turns to achieve a texas-hot pickup.
If you put a tap between the turns of the "standard" pickup and rest of turns, you can have two virtual pickups in one.
Those extra turns usually are just a few more, not exactly double the first ones.
Therefore, Coil Tap will give you a hotter or softer version of the same pickup and, will preserve most of pickup's natural sound.
Coil split it's a term used to just select one of the coils of a humbucker (double-coil) pickup.
This isn't a tap inside one of the coils, even that both coils can be asymetric.
Some pickup makers, instead of having a separate wire for finish coil wire of each pickup, are providing just a single wire that corresponds to the link spot of both coils and, name that the tap wire.
Anyway, a coil split never sounds the same as a true single coil. Magnetic field is arranged horizontally in a humbucker or P90, while vertically for fender-alike pickups.
Usually, a coil split sounds weaker than a true single (it doesn't matter if we talk about P90 or fender, or whatever) and, it lacks some punch and body. But, vintage-hot, medium-hot or hot humbuckers can achieve better split sounds (because of extra turns).
An Split coil can sound to you at around 60% of the loudness of the full humbucker (depending on each particular pickup).
A humbucker with each coils wired in parallel will sound to you at about 70% of the loudness of the in series mode (always, depending on each pickup), maybe due to the fact that most of the bass frequencies seem to be cancelled, what opens the sound and removes any muddiness or box-alike sound in that pickup. It's very useful to clear the voice of a dark or high-output pickup and, specially good for neck humbuckers, with the benefit of still cancelling the hum.
In weak humbuckers, going to parallel can mean to achieve a very thin and trebbly tone.
True single coils have also some difference.
We have the Gibson-trend (P90, Phat-Cat, etc.) and Fender-Trend (strato, tele, etc).
Gibson ones have their coils laying over one or more magnets and, therefore, magnetic field is horizontal (projected vertically with the help of screw or bars).
They are oftern hotter than Fender ones and have great punch and strength.
Fender ones have no magnet bars below, they have 6 bar magnets, placed vertically, what completely changes the magnetic field.
They have punchy and ice-picked highs (when pushed hard), a very vocal and growling basses but, less sustain and body than Gibson's.
For sure, there are different versions of all them, just to get rid of some of the issues (creating new ones, ha ha).
Then, you have also stacked pickups, having a couple of coils vertically stacked, that work similarly (but not equal, because of the vertical magnetic field) to humbuckers and, also as true singles when split.
But, there are also stacked pickups with a dummy coil (that's there just to cancell the hum), they sound close to true single but, not the same.
You can even change the character of those pickups with some "accessories", like a bottom plate for singles, that gives them more body and punch; or removing or changing the material of humbucker covers, etc.
There is also another way to "split" a humbucker, called "half-out-of-phase" that, suposely gives you a closer single coil sound than a "standard" split. Still not experienced by myself.