Basically, a magnetic pickup is a magnet with wire wrapped around it. The two ends of the wire connect to an output jack. Real simple. Any kind of magnet and any kind of thin copper wire will work. Just make sure you sand off any insulation on the ends of the wire, so you get a good connection with the output jack.
The voodoo comes in when you want to get a certain sound, or reproduce a certain sound of a certain vintage pickup. Then there are all kinds of variations on magnet alloys, thickness of wire and number of wraps that will change the sound. You will also need to consider a method of mounting the pickup in your guitar.
Here is a picture of the first experimental pickup I made with parts from Radio Shack. It is simply a ceramic magnet with copper wire wrapped around it and attached to an output jack. If you plug in the jack to an amplifier, hold the pickup close to some metal strings, and pluck the strings, it will amplify them.
Here is another experimental pickup I made from Radio Shack parts. This one has three small button magnets superglued between two pieces of styrene that I had laying around. This made a simple bobbin which would hold more wire than just wrapping it around a magnet. The more wire wraps you have, the louder the pickup. The bobbin should be made from non-conductive material like plastic, fiberboard, or even thin wood or possibly cardboard. You could possibly take a pickup like this and glue it to the inside of the box underneath the strings, and have it work, though I haven’t actually tested this out. It might be weak if it’s too far from the strings.
Then I decided to go all out and make a P-90 style pickup for my 3 string CBG. Jason Lollar’s book on pickup winding was extremely helpful for this project. I basically took his design for a regular 6 string pickup and cut it in half.
The magnets are 3 pairs of Alnico 5 magnets from Dura Magnetics. The wire is 42 gauge copper wire covered with a Formvar coating from Wirenetics. Amazing stuff – it’s about the thickness of a hair. The top bobbin and spacer are made from sheet plexiglas which I got from McMaster-Carr. The bottom bobbin is made from PC board from Radio Shack. The polepieces are iron-containing screws (if the screw sticks to a magnet, it contains iron). The whole thing is super-glued together. I use a professional quality superglue such as UFO.
After the bobbin was made, then it was time to wind the wire onto it to make a coil. The Lollar pickup winder looked pretty complicated, so I made a simple pickup winder from a record player, vs. trying to wind 8000 or so wraps by hand. Here is a picture of my pickup winder. I have also heard of people using a drill press as a winder, and may try that for a future project as it would be faster than the record player.
I drew the wire in heavier so you can actually see the path it runs. The record player had a tall spindle, so I found a quart paint can that fit over it, and mounted it to a board with a hole in it, so it would fit over the spindle. Then on the side, I mounted a dowel in a wooden block, and set the spool of copper wire on that. The wire then goes straight up through a smooth hole in a piece of plexiglas so it unwounds off the spool evenly and without breaking (like a fishing reel).
From there it goes through a tensioner, which is a machine screw with a guitar knob on it, tightened down over a piece of felt. There has to be a certain amount of tension on the wire so the coil is not too loose, but not so much that the wire breaks. Some people screw or tape their bobbins down to a board, but in this case, since I had already glued the magnets onto it, I just magnetically stuck it to the paint can.
Then came the hard part, which was about three hours of winding the wire onto the bobbin. I ended up doing it in half hour sessions over a couple of days, because you have to hand-guide the wire onto the bobbin, so it goes on evenly. When the bobbin is about filled up, you are done. The two wire ends are tied down to two little holes drilled in the bottom bobbin, then soldered to an insulated lead wire, then connected to an output jack.
The pickup was fairly microphonic (makes noise if you tap on it while plugged into the amp), so I ended up soaking it in melted wax. This is called “potting the pickup”. This makes the coil more solid, so it doesn’t vibrate. I used the wax formula from Jason Lollar’s book and melted it in a double boiler on the stove, watching the temperature very carefully with a thermometer. I let the pickup soak for about a half hour, then wiped off the excess wax and let it cool. Then I wrapped the coil in tape to protect it.
Then I had to figure out how to mount the pickup in the cigar box guitar. I had built a neck-through-the-body model, so I ended adding two little “wings” onto the neck in the area where the pickup was supposed to go, then routed a cavity in the whole thing. I made a plate out of brass the same size as the pickup, but with two little tabs sticking out. The pickup was superglued to the plate. I drilled a hole in each tab, and screwed the whole thing down into the cavity.
Here is a picture of the pickup mounted in the guitar. You can see the copper coil through the plexiglass bobbin, and the two brass tabs extending past the pickup. I covered the pickup with a cover plate (laying on the side), to keep gunk out of the cavity and to protect the pickup.
If the pickup is humming a lot through the amp, you may want to shield your guitar. Shielding is another topic that seems to have a alot of voodoo associated with it, but it is not really that hard either. Basically you will need to surround the electronics in your guitar on all sides with a barrier of copper tape, aluminum foil or shielding paint, then run a ground wire to it. You can anchor the ground wire with a screw right in the shielding vs. trying to solder on the ground wire.
Heavy duty aluminum foil would be a poor man’s shielding material – you’re supposed to be able to spray it with spray glue, then line the box with it, but it wasn’t working for me. Shielding paint would be the easiest, but I didn’t want to deal with the fumes. I ended up using copper tape and covering the entire inside of the box and lid with it. You can get shielding paint and copper tape from Stewart MacDonald’s.
Here is a picture of the shielding, taken before I glued the box shut.
Here are some examples of various pickup designs. They are all variations on the same theme, of wire wrapped around a magnet. Some have polepieces, some don’t. Some have one long magnet, some have several smaller magnets. I had a few old pickups laying around, which I took apart to see how they were made. This was a very helpful exercise. There are also pictures and diagrams of various pickups in Donald Brosnac’s “Guitar Electronics for Musicians.”
1. single coil pickup from a cheap Japanese guitar
2. double coil “humbucking” pickup
3. lipstick tube pickup
4. blade polepiece pickup (just guessing here, I’ve never actually seen the guts of one).
“Basic Pickup Winding and Complete Guide to Making Your Own Pickup Winder” – Jason Lollar – A really great book – diagrams for various kinds of pickups, what kind of magnets and wire to buy, how to build the bobbin and pot the pickup, how to build a professional pickup winder.
“Guitar Electronics for Musicians” – Donald Brosnac – lots of pictures and diagrams of different kinds of pickups, plus great info on wiring your guitar.