Custom Pickup for 7-String

[jdicebassist]

Hey Guys,

I am planning on building a seven string bass in the new year, and to cut costs I want to attempt to build the bridge, pickups, and preamp myself.

I have already built a 3-band active EQ preamp based on a schematic found in one of my Electronics textbooks. I have tested is with my four string and the response it pretty good.

The bridge seems simple enough, and I have an idea how to do this based on looking at many of your guys wonderful ideas.

Now for the pickups. I was planning on doing two J style pickups with a wooden cover for them. I have calculated the positioning of the magnets based on the planned bridge spacing and width at the nut. The number of turns I will decide on later, when I make up my mind as to what output I want the pickups to be. My question is do I need to reverse the polarity of the magnets for a J-style pickup (see attached diagram)? Will this cancel out the 60 cycle noise if I do this, or am I way out in left field.

I was planning on buying a 1/8" alnico V bar and cutting it into about 3/4" size pieces and using that for the poles. Do I have to worry about charging these magnets after I cut them? If so can anyone elaborate on how this is done.

Also when I was going through some threads on the net about building pickups I saw one builder but copper shielding tape on the poles at the bottom of the pickup and attach a ground wire to it. Will this help reduce noise?


Thanks,
Paul

[Phil Mailloux]

Don't reverse the magnets on a coil. You have to keep the same orientation magnets on a coil. I did the mistake of doing what your picture shows on one of my first pickups and it truly sounded like sh*t. Absolutely horrible. You end up cutting out a lot of frequencies you don't want to cut.

Stewmac sells alnico 5 rods in the size you need. Don't bother with bars. Alnico is a very brittle alloy, not easy to cut cleanly. Stewmac has "free information" sheets on their site about building pickups/charging them and such. Go and read up a bit on the subject.

[jdicebassist]

Thanks for the response Phil. Ok so I think I have a better direction with regards to the magnets (especially after reading Stew Mac's instructions).

Woud you recommend using the 0.195" Dia X 0.710" long alnico V magnets for a J-Style pickup?

[jdicebassist]

Once I get my camera back from the repair shop I will post photos of the progress of the Pickups, along with photos of the preamp I have made.