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 Post subject: Pickups - how to make a single-coil J-bass pickup
PostPosted: May 1st, 2014, 5:23 pm 
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Joined: March 10th, 2008, 7:00 pm
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Location: Seattle, WA USA
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

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 Post subject: Step 1 - the parts
PostPosted: May 1st, 2014, 5:31 pm 
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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

Attachment:
MakePickups_Step01_Parts.jpg
MakePickups_Step01_Parts.jpg [ 83.59 KiB | Viewed 6527 times ]


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

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 Post subject: Step 2 - initial assembly
PostPosted: May 1st, 2014, 5:43 pm 
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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.

Attachment:
MakePickups_Step02_EyeletInstalled.jpg
MakePickups_Step02_EyeletInstalled.jpg [ 88.62 KiB | Viewed 6527 times ]


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.

Attachment:
MakePickups_Step03_PressRodsIntoTop.jpg
MakePickups_Step03_PressRodsIntoTop.jpg [ 117.62 KiB | Viewed 6527 times ]


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

Attachment:
MakePickups_Step03a_PressRodsIntoTop.jpg
MakePickups_Step03a_PressRodsIntoTop.jpg [ 130.29 KiB | Viewed 6527 times ]


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

Attachment:
MakePickups_Step04_Spacers.jpg
MakePickups_Step04_Spacers.jpg [ 111.7 KiB | Viewed 6527 times ]


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)

Attachment:
MakePickups_Step05_PressBottonOntoRodsAgainstSpacers.jpg
MakePickups_Step05_PressBottonOntoRodsAgainstSpacers.jpg [ 132.75 KiB | Viewed 6527 times ]


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.

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 Post subject: Step 3 - initial QA & insulation install
PostPosted: May 1st, 2014, 5:52 pm 
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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.

Attachment:
MakePickups_Step06_ValidateCoilSpace.jpg
MakePickups_Step06_ValidateCoilSpace.jpg [ 102.03 KiB | Viewed 6526 times ]


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.

Attachment:
MakePickups_Step07_InsulateRods.jpg
MakePickups_Step07_InsulateRods.jpg [ 104.13 KiB | Viewed 6526 times ]


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

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 Post subject: Re: Pickups - how to make a single-coil J-bass pickup
PostPosted: May 2nd, 2014, 2:16 pm 
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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

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 Post subject: Re: Pickups - how to make a single-coil J-bass pickup
PostPosted: May 2nd, 2014, 4:17 pm 
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Joined: August 1st, 2009, 6:19 pm
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Location: Lake Tahoe, Ca
Fascinating! I am a big pickup freak :D


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 Post subject: Re: Pickups - how to make a single-coil J-bass pickup
PostPosted: December 3rd, 2014, 9:01 pm 
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Joined: October 20th, 2014, 7:57 am
Posts: 41
Thank you for posting this! I am afraid the only way to get the pups I need
for a restoration that I have coming up is to reproduce them. You are an
inspiration!


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