Humbucking Pickup Rebuild
The Gibson-style Humbucking Pickup is one of the two most popular and widely recognized coil-magnet pickup designs in use, the other being the Fender Single-Coil design. As produced by Gibson it is a well-conceived design, although originally the coils were not waxed nor were the assembled pickups wax-potted resulting in undesirable microphonic response in some, particularly in the presence of loose parts. Gibson appears to have started waxing these pickups sometime in the late 80s.
More detailed, interesting and unique information about modification of pickups in general, including coil winding Theory and practice, appears elsewhere in this section.
Here is the procedure for coil winding, wiring and assembly of the Humbucker with parts that have been salvaged from an existing pickup or new parts available in after-market kits.
Mount one of the bobbins, top facing out, on the face plate of the coil winding machine. Place a short piece of tape on the edge of the face plate to secure the leading end of the coil wire after the next step. My coil winding rig is built around a Unimat miniature machine lathe with home-made face plate and wire guide parts and an Azonic wire tensioner.
This is the Azonic series 3000 wire tensioner. It provides control of the tension on the wire and compensates for variations in linear speed of the wire caused by the oblong shape of the coil bobbin. Thread the wire through the tensioner and wire guide, to the coil bobbin, tape the wire end to the edge of the face plate and set the guide stops so the wire leads to just inside the top and bottom flanges of the bobbin with the first turn against the bottom flange of the bobbin.
Rotate the bobbin by hand, winding a few turns to be sure the guide stops are set so that turns at the top and bottom of the bobbin lay inside the flanges. If during the winding process any turns of the wire “cast” outside of the bobbin it will have to be stripped and the procedure started again.
A white background will facilitate being able to see the wire during the winding process if viewed in line with the wire allowing you to judge how the coil is laying up.
Cut the wire from the supply and tape the tail end of the coil winding to the top of the bobbin.
Carefully remove the tape holding the “on” end of the coil wire to the edge of the face plate
Remove the wound bobbin from the face plate being careful to not pull the exposed ends of the coil wire, particularly the “on” or “start” end. Breaking wire at the “on” end will make it necessary to strip and rewind the bobbin, about a half-hour of work for each one. Tape around the middle of the bobbin in preparation for the next step.
Submerge the bobbins in wax heated to about 1650 F. Some plastic bobbins may deform if subjected to temperatures higher than 1750 F and some types of the very thin insulation on the wire may be melted by higher temperatures resulting in shorted turns and a spoiled coil.
Leave the coil in the wax until air bubbles stop coming from it.
After the coil has cooled very carefully remove the tape around the bobbin.
Tape around the coil being sure that no turns of the winding are exposed. Lead the “on” end out at the bottom of the coil and the “off” end at the top. Both ends should come out from under the tape along the sides of the bobbin, not at the ends.
Prepare four lengths of color coded #30 teflon coated stranded wire for the coil off leads, stripping and tinning about ½” of one end of each. Write down the colors for each of the leads to identify the polarity. (See step 14.)
Solder the off leads to the ends of the coil wire and secure each with a short piece of tape covering exposed coil wire and the splice. Hold the soldering device to the splices just long enough to flow the solder – too long will melt the coil wire. Position the off leads near the bottom flange of the bobbin, one on each side, with about an inch exposed beyond the end of the bobbin.
Tape around the coils being sure that no wire is exposed except for the leads at the ends. Here I have used black for the “on” or negative end of coil A (bobbin with the adjustable screws) and white for the “off” or positive end. The “on” or positive end of coil B is yellow and the “off” or negative end is blue.
To agree with the configuration of traditional Gibson pickups coil B “on” (yellow) should be the positive output and coil A “on” (black) the negative output or ground. Coil A “off” positive (white) and coil B “off” negative ( blue) are joined for traditional single wire output. With the magnetic polarity oriented with coil A north up a pickup wired thus will be in phase with traditional units.
Insert the plain pole pieces through the bottom of bobbin B.
Press them home so the top ends of the pole pieces are flush with the top of the bobbin.
Lace two pieces of .010” dia. guitar string around the pole pieces on the bottom of the bobbin.
Leave about ¾” of one of them extending beyond the end of the bobbin on the end opposite the end where the off leads emerge. This will make a reliable ground connection to the pole pieces.
Start the adjustable screw pole pieces in the top of coil A with the two end pole pieces just extending through the bottom flange.
Assemble the A bobbin and the pole carrier together.
Solder the four-wire output cable assembly to the base plate along the A side,, oriented as shown. Direction for making the cable and other basic wiring procedures are in the section on wiring.
Assemble the base plate and the A coil with its pole carrier.
Screw all six pole screws fully into the bobbin and through the base plate.
Identify the north pole of the permanent magnet.
Position the permanent magnet between the base plate and the A coil with the north pole facing the pole carrier of the A coil.
Secure the magnet and the Coil A assembly to the base plate using the two small brass screws inserted through the bottom of the base plate.
Assemble coil B and the base plate with the ground wire extension at the end opposite the lead wires.
Secure coil B with the two small brass screws inserted through the bottom of the base plate.
The ground wire should be at the end of the pickup assembly where the output cable emerges from the pickup.
Solder the ground wire to the base plate being sure that it is buried in the solder.
If the pole screws are not reliably grounded to the base plate remove the two small brass screws holding coil A and lace pieces of guitar string among them.
Press the grounding wires down to the base plate and replace the bobbin attachment screws as shown inside of where they cross between the pole screws for strings one and two and five and six. Replace the small brass bobbin mounting screws. Solder the ground lacing if necessary.
Use an ohm meter set on the lowest range to be sure that all of the pole pieces and screws are grounded. Any parts meant to be grounded should be less than one ohm off ground. The meter here is showing 0.2 ohms between output shielding cable and the pole piece being tested.
Check to be sure the magnetic polarity is correct; coil A north up, coil B south up.
Solder the ends of the coil off-leads to their respective output cable wires.
Cover solder joints with heat shrink tube.
Solder pickup assembly to the cover.
Tape over the cover.
Wax fill the assembled pickup.
Add wax to the bottom of the pickup as it cools and the wax contracts so that it is filled to the edges of the cover. After the pickup has cooled remove the tape and any excess wax.