Building some P 90's. Is the metal bar between the 2 magnets really necessary?

[John Fisher]

Building some P 90's. Is the metal bar between the 2 magnets really necessary? Isn't it good enough for the magnets to just butt up against the screws? Also is the bottom metal plate no magnetic? Thanks!

[Jim Darr]

John,

I've built them both ways with great results. The traditional P90 does have the keeper bar, so if you are going for a vintage reproduction, include the keeper bar.

Try it both ways and see what sounds best to you.

[jack briggs]

Lollar doesn't use one. It will change the tone somewhat - brighter and punchier without; more vintage with.

[John Fisher]

Thanks for the reply! Just another question or 2: Because we are living in an imperfect world what if because of slight inaccuracies with the hole drilling, 1 or 2 of the pole pieces are not touching the magnets perfectly? Also does it matter if the base plate is non magnetic or not or do we even technically need a base plate if the magnets and pole pieces are grounded?

[Jim Darr]

Because we are living in an imperfect world what if because of slight inaccuracies with the hole drilling, 1 or 2 of the pole pieces are not touching the magnets perfectly? Also does it matter if the base plate is non magnetic or not or do we even technically need a base plate if the magnets and pole pieces are grounded?

I'd say it depends on how far off the holes are from center-line. A great deal of space (or gap) will lower the Gauss level for those affected pole pieces. They really all should be in a straight line.

As for the base-plate, traditionally it is usually used for shielding/grounding and holding the bobbin & magnets in place.

[John Fisher]

Thanks for the very helpful reply. You guys are confirming what I feel and also filling in some of the blanks. Please let me pick your brains hopefully just one more time
So far I have made a bobbin out of 2 pieces of circuit board material with a wooden maple core that is glued onto the 2 circuit boards using super glue. I have the bottom surface of the bottom circuit board with the copper surface facing down against the magnets. I burned off all the copper surface of the circuit board that is on the top part of the bobbin. I figured that the bottom will help shield the coil even if I don't use a base plate. If I want I can even just glue the magnets in a bit using a glue gun to avoid having to make a base plate. I have seen some pickups like that. One question is.... would it be convenient to leave a copper coating on the top circuit board facing the strings for better shielding? I will be using a plastic soap bar cover. Does shielding the top plate of the bobbin effect the sound?
One more thing... I noticed in a drawing of the P 90 that the 2 south sides of the 2 magnets are pointing towards the pole pieces. It just made me wonder if the 2 south sides of the magnet will repel each other. Is that the way it should go.
Thanks so much for answering my many questions. You guys are great!

[Jim Darr]

I noticed in a drawing of the P 90 that the 2 south sides of the 2 magnets are pointing towards the pole pieces. It just made me wonder if the 2 south sides of the magnet will repel each other. Is that the way it should go

South facing South, or North facing North are the only ways the pickup will work properly. Think about it...you need to transfer the polarity to the pole pieces and if you had North facing South it just wouldn't work correctly magnetically. I purchased several vintage guitars with "Bad P90s" on the cheap and all I had to do was flip one magnet around and they worked perfectly.

[big_teee]

I do N/N.
Then if you ever need to hook one with a humbucker, most of them do North on the + output.
They will be in phase.

[Peter Naglitsch]

Also does it matter if the base plate is non magnetic or not or do we even technically need a base plate if the magnets and pole pieces are grounded?

You should not use a ferrous base plate. That will "short" the magnetic circuit and make a very bad pickup.

[David Schwab]

You should not use a ferrous base plate. That will "short" the magnetic circuit and make a very bad pickup.

Right, and you don't really need a metal baseplate. But it helps shield the pickup.