Pickup designs : simple slugs and magnet at the back

[jnohlic]

Hello,

I have often seen very cheap SC pickups that had simple slugs and a magnet at the back.
I guess they do this because it is cheap ?
Are there good pickups that are designed this way ?
If not, why ?
What is the consequence of such a design ?

In the p90 design, why are there two magnets and why are the same polarity of the magnets facing each other ?
Thanks for your answers,
Julien

[big_teee]

On the two magnets same polarity, on a P90?
It increases the magnetic field with two magnets.

A lot of the SC pickups with the magnet on the bottom, are glued together, and can't be rewound.
The traditional fender type rod magnet pickup, have a Alnico sound, that most players like!
Also They are made to be repaired & rewound.
T

[copperheadroads]

In the p90 design, why are there two magnets and why are the same polarity of the magnets facing each other ?
Thanks for your answers,
Julien

in the 2 magnet p-90 style pickup ,if you have 2 magnets oriented any other way than facing each other ,What polarity would you have at the poles ?

[jnohlic]

Makes sense !

[Steve A.]

In the p90 design, why are there two magnets and why are the same polarity of the magnets facing each other ?

The flux patterns of a P-90 are very unique (I'll see if I can dig some up pix.) The two magnets of the same polarity force the screws and optional keeper bar to be the opposite polarity... and very strong at that!

Funny how those P-90's can do mellow jazz and hard rock equally well (the distance from the strings to the pickup can make a big difference.)

Definitely my favorite pickups!

Steve A.

[big_teee]

I think everything in the middle of a P90 would either be all north or all south.
You can see it on a gauss meter.
Like this picture, but with a screw and keeper in the middle.
All the south flux pattern would be coming from each south edge of each bar magnet.
Your magnet strength on the screws at the top middle, gauss will more than double, compared to just one magnet.
I've seen cheap import P90s with just one ceramic magnet on one side of the keeper bar, and a plastic spacer on the other side.
They work fine that way, but sound better with 2- A2, or A5s.
It works similar on a sidewinder also, but the coils are rotated 90 degrees.

[copperheadroads]

"In the p90 design, why are there two magnets and why are the same polarity of the magnets facing each other ?"

The OP ask why 2 magnets have the same polarity -great question ,if think about it ,if you flip one of these magnets you will then you have a pickup with little to no gauss from your magnets ,basically like a pickup with 2 uncharged magnets .

[SonnyW]

1. You're right, they do it because it's cheap. No other reason IMO.

2. Are there good pickups that are designed this way? - Not really. I have seen a few that were actually halfway passable though. Depends on the definition of "good".

3. If not, why? and 4. What is the consequence of such a design? - For one thing, designing this way often alters the mechanical dimensions of the coil and also geometry relative to the magnetic field. Usually in those cheap pickups the slugs are installed in a molded bobbin that keeps them significantly further from the coil, and the number of magnetic flux lines that cross the coil windings is less. Traditional strat type designs have the coil essentially touching the magnets. At the risk of inviting criticism from much more educated forum participants, I understand that a permanent magnet's field strength decreases as approximately the cube of the distance (1/r^3) or in other words the inverse cube of the distance from the poles. It's more than the inverse square law that many other fields decrease by. It's actually a little more complicated than that, it's given by an equation: B=(μ0AI√1+cos2(θ))/4πr3 - see this link:
https://www.physicsforums.com/threads/magnetic-field-strength-dependent-on-distance-from-source.522223/

Reference https://www.physicsforums.com/thread...source.522223/

So at any rate, a very little bit of separation between the coil and the source of the permanent magnetic field can have a relatively large effect. We are all accustomed to the sounds of the traditional designs and at the risk of stating the obvious, the different design sounds different because it has a much different magnetic field. This is much more complicated than I have described, but hopefully it touches on the causes.

5. Why 2 magnets in the P-90 facing each other? Copper has already covered this one and I agree.