This is the fourth in a series of blog posts on guitar pickups. The intent is to present the info in a way that's informative to someone who might not know anything about pickups, but is still interesting to those more familiar with them.
If you're knowledgeable about pickup design you might say "aren't P-90's a single coil pickup?" And the short answer to your question is, yes! That said they're also unique enough in their size, design and tone from typical single coils (Strat or Tele styles) that they warrant their own blog post.
P-90's originally were used by Gibson for around a decade before the invention of the humbucker. They've remained a popular option through the decades due to their unique tone.
Some notable differences between a single coil and a P-90 are as follows:
Magnets: Single coils use rod magnets (ie the pole pieces are the magnets) while P-90's use bar magnets (ie magnets that run the width of the pickup on the underside with pole pieces transferring the magnetism up through the pickup).
Components: While the basic components more or less overlap in both models, the P-90 has more parts involved in their build which inevitably change the tone.
Size: P-90's are roughly double the physical size of most single coil pickups. Again - this impacts the variety in tonal differences.
(images courtesy of Seymour Duncan)
So what does the P-90 sound like compared to single coil (or even a humbucker)? The P-90 falls somewhere in the middle of the two tonally. Generally louder and full than the single coil and quieter and a bit brighter than the humbucker. It provides great punch and clarity compared to a humbucker and a nice gritty edge to it that simply can't be found with a single coil.
Now that we've covered the differences between single coils and P-90's, let's look at the three main sizes of P-90's.
As its name implies, this is the shape of a...wait for it...bar of soap! This is the most widely used size of P-90. The mounting screws and springs go through the body of the pickup.
These have the same base shape as a soapbar model, but with dogear shaped mounting ears which allow for a different mounting option.
Humbucker sized P-90
In recent years many pickup manufacturers have released P-90's in a humbucker sized housing which allows guitarists to swap out their humbucker equipped guitars with a P-90 without any modification to their guitar. These retain the essential design structure of a traditional P-90. Models such as the Tonerider Rebel 90, Seymour Duncan Phat Cat and Lindy Fralin P-92 are all great examples of these at different price points.
It's worth mentioning that there are some hum-cancelling P-90 models on the market. These essentially stack two single coil P-90's under one housing with one being reverse wound/reverse polarity for hum cancelling operation.