Pickups - how to make a single-coil J-bass pickup

[SkuttleFunk]

You know them when you see them - a J-bass single coil pickup. Exceeded by only the famous P-bass split-coil design, the J-bass single coil is one of the most recorded pickups in history.

Over the next few posts I hope to remove a little bit of mystery about this style of pickup - what it's made from, how those parts are put together, how it's wound, a technique for charging the magnetic pole pieces, etc ...

In the process, feel welcome to ask questions if you have them. I may not have all the answers, but I'll answer what I can

all the best,

R

 

[SkuttleFunk]

Let's take a look at the parts that make up a typical J-bass single-coil pickup. There's not many to look at, and none of the materials used are state of the art by even 1980's standards

For a 4-string pickup, there are two sets of AlNiCo cast rod magnets (the pole pieces), to pieces of Forbon that are laser cut to tight tolerances (called flatwork), and a pair of eyelets that will be used to tie-off the coil wire and also to solder on the wire leads.

Yep - that's really it at this point. Nothing mystical or highly technical, just simple 1950's era technology

 

[SkuttleFunk]

The first step is to install the two eyelets into the bottom flatwork piece, and then use a specialized tool to swedge the opening to it has a tight fit and doesn't fly out when the coil wire is being wrapped onto the assembled coil bobbin.

 

[SkuttleFunk]

Once this is done, it time to move the work over to an arbor press ...

The second step is to press the AlNiCo rods into the top flatwork piece so that the rods protrude from the top at a specific distance. For this example, all of the rods will be set to protrude above the plastic pickup cover just under .015". To accomplish this I use a pair of flat bar pieces that have the same thickness as the rods will extend. I set these apart wider than the diameter of the rod, set a rod onto one of the holes in the flatwork, and then press it thru the flatwork until it bottoms out against the arbor bed. This is repeated for all eight rods in this 4-string pickup.

You can see the results here, with the rods sticking their necks thru the top flatwork piece

 

[SkuttleFunk]

Next, I utilize a pair of wooden spacers that have been carefully detailed to the exact thickness that the coil wire will be wound into. One piece is placed on each side of the rods and held in place with a rubber band

Finally, the bottom flatwork piece is set onto the rods and lightly pressed into place. If any of the rods are out of alignment, I use an ice pick type tool to massage them into place and then give them a bump with the press. Once all of the rods are fit into the flatwork piece, the flatwork is then pressed tight against the spacers (which are tight against the top flatwork piece, which is tight against the flatbar that allows the pole pieces to extend a set distance)

This is pretty simple to do once you've done it a few times, and a coil bobbin assembly can easily be brought to this point in the workflow in under five minutes.

 

[SkuttleFunk]

Once the coil is assembled it's time to give it a check to ensure the inside gap between the flatwork pieces is on target, and that the assembly is not racked. Several measurements are taken with a set of dial calipers to check the gap, and any massaging that needs to done is worked before proceeding.

After the gap check I validate that there is no racking, and massage if need be. In the case where racking was detected and massaging took place, the bobbin gap is again validated to assure it remained within tolerance. If not I backup to the previous step and repeat the gap and racking massaging until all is spot on. At this point a thin superglue is wicked into the joints around the pole pieces so that they are firmly locked into place.

Once the superglue is cured, the rods are wrapped with a tape insulation that prevents the coil wire from shorting against the rods should the insulating coating ever fail.

At this point the pickup bobbin is fully assembled and ready to have wire rolled onto it. That process will be the topic of my next post sometime in the coming week or so.

Until then ... R

 

[bagman67]

This is awesome, and fascinating.  I am grateful.


Would you please define the term "racking" for us non-manufacturing dudes?

 

[SkuttleFunk]

racking is where the two flatwork pieces are parallel on their faces, but twisted in a slight spiral (typically the result of removing the wooden spacers). when you lay the bobbin on one if its edges, it rocks on two opposing corners or leans to one side.

the bobbin needs to be adjusted/massaged so that it is parallel across the flatwork faces and also so that it is in square alignment and without a twist

make sense?

 

[bagman67]

Perfect sense, thank you very much.


Bagman

 

[SkuttleFunk]

Winding pickups is the simple process of wrapping a super thin copper wire around the bobbin. You need to achieve a couple things in the process - laying each wrap close to the previous one in a back/forth pattern that fills the bobbin with multiple players of wire.

The wire is thin, can break easily if you give it too much tension ... but you'll have a dead sounding rats nest if you use too little tension. There's a load of facts and mysticism out on the net about winding the wire, and you'll hear many terms like 'scatterwound' and 'eddy currents' tossed back/forth by different winders who have different perspectives on why their pickups are better than those of a different company ... it's the tone wood discussion topic for pickup builders

For our discussion here - let's just leave all that behind and focus on what is generally happening. The linked YouTube video demonstrates a DIY on the very cheap type approach to winding a single-coil pickup. Once you watch this, you'll probably have lost your awe for what a pickup is, and you'll also see that the technology is stooped simple.

http://youtu.be/rwngST_SRkw

So not only are the parts that make up a pickup bobbin simple, but the tools needed to make one are even more simple. This is perfectly fine for a DIY approach to making pickups for your own use, but it falls short on offering the consistency and production speed required in a name brand offering.

My workflow no longer utilizes a hand winding system, but instead utilizes a programmable CNC system that affords me the ability to 'record' the nuances of my winding motions ... and when that 'golden wind' happens, I can repeatedly play it back onto bobbin after bobbin after bobbin.

I'll show my CNC process in the next post or two

 

[stratamania]

Thanks for posting. it's interesting to see the process...