Winding an S-90 pickup

 

The S-90 is my version of a strat pickup like a P-90. This essay covers the conversion of an inexpensive pickup (in this case a mexican fender singlecoil)

First thing that must be done is to strip the pickup down to it's components. The windings are cut off with an xacto knife. The pole pieces are pushed out with a screwdriver, and the magnets are carefully pried off. All glue is scraped from the magnets and the bobbin. The eyelets are cleared of solder, and checked for rough spots which might catch the wire durring winding (especially the mounting holes!) The bobbins are then boiled in an attempt to remove the wax (a little dish soap helps). The bobbins now look like this.

These bobbins are ideal for this conversion as they already have the ceramic magnets preferred (alnico is generally too big or too weak), and the solid bobbin makes the conversion to screw polepieces easier.

Next step is to adapt the bobbin to take screw polepieces. To do this I use nylon bushings (3/16"x 1") which can be found at many large hardware stores. Rough the sides of the bushings with 150 grit paper, and cut them in half. They are then coated w/ thin superglue and inserted so they are flush with the bobbin bottom. The bobbin should now look like this.

By cutting the bushings in half it leaves them low enough in the openings that the screw heads can be seated fully.

The bobbin is now attached to the winder with heavy duty double sided tape, and the wire attached. The wire(42 guage w/ poly nylon solderable single build insulation is preferred) is wrapped half way around the bobbin and taped to the top of the winder plate. The end on top of the plate is sanded with 600 grit paper (lightly!) and is used to check the resistance later.

note the tape on top of the faceplate

I manually wrap several wraps to confirm the table height and depth stop are properly adjusted so the wire stops just shy of the bobbin plates (aprox 1/16")at the ends of it's travel. The first several wraps must run right against the bottom plate (guided with fingers) to prevent future wraps from cutting it. It is ok to run the wire across the bobbin at an angle as long as it's not too great. The bobbin in the picture above has aproximately twenty windings on it, the adjustments have been confirmed and it's ready to be wound under power.

To begin winding I confirm that the tensioner is slightly loose (see previous page if unfamiliar with the setup I'm using) and turn on the drill press. Now that it is running under power I increase the tension to the correct level by tightening the tensioner knob (I can actually hear a noise change in my setup when the tension is slightly over) It actually requires more tension than you would expect. Too much tension can stretch the wire, increasing the resistance of the coil even if it doesn't break the wire. Every once in a while I will use my fingers to guide the wire closer to the bobbin plates to fill any gap due to setting the travel short. This isn't always required as the coil will spread as it builds up under tension. Simply use the drill "press" function to spread the coil evenly yet randomly. Care needs to be taken to not change direction of travel too quickly as it will result in loose windings at the edges. Once the bobbin is almost full the winder is stopped. With 42 guage wire the bobbin will look like this when it's about 6 k ohms resistance (a counter can be used for reference, but coils should be wound to resistance)this one actually tests at 5.75 k ohms

To test the resistance the wire is sanded with the 600 grit paper with the wire held against the "tensioner shelf". This bare spot is then sprayed with laquer to reinsulate it (just in case it should happen to contact a weak spot in the wires insulation on the coil) The bobbin is then wound and retested until the desired resistance is reached. For the best hum cancellation, the coils should read within 5% of each other. For a strat I typically wind the bridge pickup to 6.5, the middle to 6.25, and the neck to 6; 5% of 6.25 is aproximately .30; I'm using .25 for both the hum cancellation and an even change in output from each position to account for the (relatively even) change in string volume in each position. If a resistance above 7k is required 43 guage wire must be used. Changing the wire diameter affects the tone......

The wire tail is taped to the bobbin, and the bobbin is now removed (remember to remove the tape holding the wire to the winder faceplate first!). The ends of the wire are sanded and then wrapped through the eyelets. I tie a half hitch each wrap for added security. It is then soldered. For this I use a 15watt pencil and melt a drop of solder onto the tip (pointed tip) this way as soon as the metal eyelet gets hot enough the solder flows into place and I can see that it's done without applying excess heat.

The screw polepieces (allparts is a ready source of good ones) are now screwed in fully. these screws are typically self tapping, cutting threads as they go. I once tried to use the pole pieces from a cheap Epiphone humbucker, but the shafts were too skinny to engage the bushings.

The magnets are now glued back on. Gel superglue or epoxy work well for this. In a p-90 configuration the magnets are placed so the same poles face the inside and rest against the polepieces. I use a very cheap compass to check the polarity. The result looks like this.

Note that the polarity for the middle pickup (or second pickup in a 2 pickup guitar) needs to be reversed for hum cancellation when combined with the others.

I now attach the metal plate typical of humbuckers. I will use the metal bar with holes in it if I have one availiable which fits, In this case I didn't have one, so I used bar stock. It doesn't really matter as the screws do not engage the drilled bars either. It now looks like this.

Next step is to attach the lead wires. I use shielded wires in 22-24 guage. I use the same method as before to attach the wires to the bobbin Having tinned the wires already I do not need to add any additional solder. The ground wire is attached to the baseplate using a 40 watt soldering iron, and the plate is checked to ensure the glue didn't come loose from the heat (it could be soldered first). If this is a reverse polarity pickup I switch the locations of the wires on the bobbin. resulting in a "reverse wind" The reverse wind keeps the pickup in phase when combined. This picture shows one normal and one "reverse wound reverse polarity" pickup

The last step is to pot the pickup. I've found that vinyl sanding sealer works well, looks very clean, puts a shine on fiber bobbins, and allows future repairs. It also has none of the risks or requirements of wax potting. The drawback is it isn't suitable for potting metal covers to prevent vibration, and it takes longer to dry. I use the lead wires to suspend the pickup in the can of sealer, and lightly pinch them in a drawer to hold it in place.

It is left there until no more bubbles appear. I use a soft bristle paintbrush to wipe off excess sealer when the pickup is removed and set the pickup on a paper towel to dry. In it's normal use the sealer dries in under 1 hr. I leave it overnight.

The finished S-90 pickup! Everyone LOVES these S-90's, why not make one for yourself?