Magnets & Copper Wire: A Pickup Building Thread

[Freekmagnet]

Since starting my own pickup-making project, it has been suggested by a few folks that it would be a good idea to start a thread here in The Luthier's Corner dedicated to building pickups. The intent is to have a thread for all the pickup builders here in LC to contribute, share projects and information about their processes of pickup building.

My most current pickup project has been exhaustively documented in another thread:

Build #3: La Charra: the Semi-Hollow Adventure Continues

but I will post here a video of my winder and the initial stages of a new pickup project.

Here's a video of my Arduino-powered winder. In short, the thread is guided by a 1/4 20 nylon screw that is driven by a stepper-motor. The zero position and the X-limit are set using the joystick. Once screw travels to it's X-limit, the stepper motor reverses direction and repeats the same operation using the zero position as it's new limit. The back of the bobbin plate is covered with a black/white/black/white pattern. I have an infra-red diode and an IR sensor that reads the transition between the light and dark sections and each transition sends a pulse to the brain which then tells the stepper motor to advance one increment. To help eliminate any complicated math, the stepper drives a 1/20 ratio gear - in other words, one complete rotation of the stepper drives the screw one inch. I can adjust both the size of the motor increments and the black/white/black/white pattern to control the wire spacing.



Although I am still wrapping another pickup project, I kinda started on a new design a few weeks ago. The idea is simple: I want to use some of the extra materials I have laying around and make something cool out of them.

I have a bunch of these 1/4" X 1" neodymium magnets and some really thin pieces of 430 stainless steel. I was hoping to make a really thin humbucker out of these materials. I've built neodymium sidewinders before, and I wasn't completely sold on the sound - I think that the neos in that context rendered a really "peaky" pickup - in other words, the crazy highs of the neos and extra low-end from the big steel blades made both the highs and the lows overwhelming. Instead, I'm going to try this thin steel and see how it works. I'm not sure where this is going, but I'll probably start by wrapping about 5000 turns of 44awg wire around each of the bobbins and see what happens. They may sound kind of tinny, but right now, this is an experiment. If they do work, I might try stacking four of these thin coils to make one quad-coil pickup.

 

[mapleglo]

Sub'd! I'll put together some of my home made pickup pics. Interested in how those thin humbuckers come out. The one set of humbuckers I made didn't seem to have the output I wanted.

 

[Jon Clegg]

Sub'd

 

[Jisch]

When I show people basses I make they invariably want to know how much of it I made. Some people assume when I say "made" I really mean "assemble". As I go down the list of what I made they sometimes ask if I made the pickups. I have to say "no" now, but it's on the list of things to learn for sure. That winder looks awesome.

 

[MPU]

Multicoils start with casting the bobbins. I use Smooth Cast urethane and silicone molds. Molds are sprayed with release spray before casting.
I measure urethane parts with a scale.

 

[MPU]

About an hour later the bobbins are hardened and I can release them and cast a new batch.

 

[NKBassman]

Following for interest sake. I have nothing to add.

 

[Freekmagnet]

M

Sub'd! I'll put together some of my home made pickup pics. Interested in how those thin humbuckers come out. The one set of humbuckers I made didn't seem to have the output I wanted.

Yes, please post pictures!

I also struggled with my pickup having low output for a while. I started to realize that there’s a kind of Goldilocks size/shape/wind count combo that works - but it’s different for every pickup! I chose to stick with one design and kept at it until it worked.

 

[Freekmagnet]

View attachment 3225017 View attachment 3225019 View attachment 3225018 Multicoils start with casting the bobbins. I use Smooth Cast urethane and silicone molds. Molds are sprayed with release spray before casting.
I measure urethane parts with a scale.

Wow, cool @MPU - I’m looking forward to seeing how your multi-coils are made! Thanks for posting!

 

[mapleglo]

The winder

Bobbins

Wound

Potting

Crock pot from Amazon was about $15.00

And final pickup, measuring about 9.4k Ohms

And Humbuckers

 

[GeraldMcG]

Subscribed!
I read the entire La Charra thread. Glad you followed through on your threat to start this pickup thread.

Mapleglo I think our winders are cousins. Lol.

This is the rough cut body of a pickup I am making to go on this two string bass project.

The bobbins are sewing machine bobbins and the body of the pickup is a scrap of maple with a scrap of rosewood on top.
The two string is based on an old Mechanics Illustrated artcle. The body of the bass is cut from a 2x4.

 

[Bruce Johnson]

I decided to start making my own pickups for my Scroll Basses in 2003. Up until then, I had been buying Quarter Pounder P-Bass coils from Seymour Duncan, mounting them in my own ebony and epoxy housings. They worked well, consistent quality and reasonably priced. I was buying the bare coil assemblies from them, without the covers or retail packaging, 10 sets at a time. I think back then they were like $25/set.

So, for any of you who want to get into unusual looking pickups in special housings, but don't want to make the jump into making your own coils yet, this is a good option. If you are a Luthier and buy a little bit of quantity, SD will sell you just the finished coil assemblies of any of their standard models. As far as I know, they still do. And they make a wide variety of models and specifications. You can pick from their stock and use them in unusual ways.

In my case, as I was planning out my Series IV model, I wanted to make some new pickups in unusual configurations, where commercially available coils and bobbins wouldn't work. So, I had figure out how to make my own.

I was starting from scratch, so I did a lot of research. I bought copies of Jason Lollar's book and Animal Magnetism, the two main books available on pickup making. I read probably every post on the Pickup Maker's Forum. I found that there isn't really that much good technical information out there about designing and building pickups. Particularly about making unusual configuration pickups. Most of the info out there is about making standard Fender and Gibson pickups, fussing over the little details to make precise replicas of old vintage models. Doing it just like Fender did in the '60's.

I dove into it on my own. I found that building unusual pickups is mostly about mechanical things. Figuring out how to build custom bobbins. Making a winding machine. Learning how to wind the tiny wire neatly without breaking it. Figuring out a good reliable way of terminating the tiny wire ends. Making up housings, shielding shells, mounting brackets. Lots of mechanical problems to work out.

Designing magnetic pickups is also mostly mechanical. Picking and arranging magnets to get a good shape magnetic field. Designing the geometry of the coil to put the wire turns in the best place within the magnetic field. The only "electronics" part is in working the specifications of the coil to work with the amp. These are the things that you can mess around with to adjust the resulting sound of the pickup.

If you limit yourself to winding wire onto purchased standard Fender-style bobbins, then you are really narrowing what you can change. There's only so much you can do with number of turns, wire gauge, wire insulation type, DCR reading. And everyone has already done every possible combination. If you want to experiment with pickups, you've got to get into the mechanical stuff of making custom parts.

 

[Bruce Johnson]

Like MPU, I decided to make my bobbins by casting them from polyurethane. I make them in two pieces, an upper and lower half. Each half is a flange and half of the center that the wire wraps around. I integrated my own idea for the wire terminations into the part; two U-shaped pieces of 20 ga buss wire to solder the wires to.

I've made up the tooling for about eight different special bobbins so far. Here's a quick layout of the parts for the bobbins of my AMB-2 model pickups. It starts with designing and making up a Master, then making up a set of silicone rubber molds from it. The bobbin halves are cast in the silicone molds, then get a little bit of cleanup and drilling. They are assembled on the magnets and go on to the winder. At the left are the finished coils, terminated and potted.

Here's a closeup of the Master. I usually machine them out of aluminum like this, working from an AutoCad drawing. It's a block of bar stock, with the holes precisely drilled and the flat sides and ends milled away. The end radiuses are shaped by hand with a file.

You don't have to make the Master from metal. You could use a block of maple for the base, and build up the master shape gluing together pieces of plastic. Or cardboard and CA glue. It doesn't matter to the silicone rubber.

Here are the rough-cast bobbins, right out of the molds. I use Smooth-On Slow Onyx Polyurethane Casting Resin. Very easy to work with. Mix 50:50, stir slowly, pour into the mold, cured hard in 30 minutes. It's a fairly hard machinable plastic. For cleanup, I hold them quickly against the belt sander to take the excess off the back side of the flange. I drill the small holes on the spots left from the Master. The large holes for the magnets are cast slightly undersize. I hand turn a 0.375" machinist's reamer through them to get them right to the right size for a gentle press fit on the magnets. The center hole is for the screw that holds the assembled bobbin on to the face plate of the winder machine.

And here are a couple of the finished AMB-2 coils for reference. The wire is wound on them and terminated onto the buss wires. Then they are potted with a special very thin epoxy, then the outsides of the coils are coated with West Systems epoxy for mechanical protection. More details on those steps in upcoming posts.

 

[Bruce Johnson]

Here's another set of custom bobbins, similar to the AMB-2 bobbins above, but for a 5-string. Narrower magnet spacing; a 2-string and a 3-string bobbin. In this case, I just machined the two bobbins on one aluminum block and a made double silicone mold.

Here's a shot of machining the master in the milling machine. Yes, life is better with a milling machine.

And the radiused ends are filed by hand. They don't have to be perfect. It's just a bobbin, a form for the wire to be wrapped around. No one will see it when the pickup is together.

And here's how my built-in terminals work. After cleaning up the bobbins and drilling the holes in them, I cut short lengths of uninsulated 20 ga tinned copper buss wire. I use a small pair of pliers to bend the wire into a narrow U-shape.

The wire gets inserted into a pair of the tiny holes between the magnets.

And pulled down through. Another one goes in the other side. Note how the notch makes room for the wire to go across between the holes.

Then the bobbin halves are assembled onto the magnets, a light press fit. I use a small arbor press to seat them together gently. You can see how the wire terminals are captured by the upper and lower halves. The lower half is the same cast part as the upper half, but without drilling the tiny holes.

After assembling the bobbins like this, I put one wrap of 1/2" Scotch tape around the center area. This keeps the coil wire from dropping into the gap between the upper and lower halves, during the winding.

The idea of these terminals is to make a solid mechanical connection to the bobbin, which the wires can be soldered to. The tiny coil wire goes out of the coil through the small hole in the bobbin flange, and is then lightly wrapped around the leg of the terminal wire next to the hole, and soldered. Later, when the pickup is all encapsulated in its housing, the hookup wire is soldered to the other leg of the terminal wire.

You've got to pay attention to how the coil wire is attached to whatever kind of terminal connection you use. That's the most fragile part of a pickup. Most pickup failures are caused by the coil wire snapping right at the solder joint to the terminal. If the wire is taut where it comes off the coil to where it is soldered to the terminal, any mechanical or thermal flexing of the coil will snap the wire. That little length of tiny wire needs to be slack and protected. These mechanical details are important!

You can see from all of our posts here that there are many different ways to make up custom bobbins. This design has been working well for me, but other approaches work for other folks.

 

[Bruce Johnson]

By the way, here's how I make up the silicone rubber molds. This is a different model bobbin than the ones above, but the same general idea. The master is machined from an aluminum block, leaving a nice squared-off rectangular base. I cut a set of four MDF blocks that make up a tight square box around that base.

I thoroughly wax the faces of those four blocks, and clamp them around the master, like this:

Then pour in the silicone rubber, up to the top surface:

Let the silicone rubber cure, pop it apart, and there's the mold (the one on the left). I usually make up multiple molds of the bobbin halves, so I can pour sets of them at a time. The molds will wear out eventually, so I mark and save the Master and the MDF blocks away. When necessary, I get them out and make another mold.

The mold on the right is for one half of the large round bobbins that I use in my mechanical percussive pickups. More on them later. Same casting process to make them.

 

[Bruce Johnson]

Here's my winding machine. It's more complicated and goofy looking than the others have built but, hey, I'm a professional Mad Inventor with a machine shop! I couldn't help myself. I built it in 2004, and it's worked very well for me since then. I make all my pickups on it, of many different sizes and shapes.

Yeah, you have to stare at it for a while to understand how it works....This is what happens when I'm left alone unsupervised with a sketch pad and machine tools.

Here are some notated pictures to help:

This is an automatic feed winder. It feeds the wire onto the spinning bobbin, moving sideways at a smooth accurate rate. This winds the coil in nice flat, evenly spaced layers. Like a spring or a screw thread. When it reaches one flange of the bobbin, it reverses direction and feeds steadily back the other direction.

This feeding motion is done with a leadscrew, a slowly spinning shaft with threads on it. The threads on the leadscrew drive the side-to-side movement of the feed assembly. It keeps the movement linear and accurate. The leadscrew is synchronized by the timing belts to the movement of the spindle. With every rotation of the bobbin, the leadscrew drives the feed mechanism sideways just over 0.002". Slightly more than the diameter of the coil wire. That's how it's able to lay down very flat layers on the bobbin, for tight, compact coils. And tight, compact coils are important in shaping the sound of a pickup.

The feed motion is able to change direction because the leadscrew is actually a double-ended reversing leadscrew. Which is obviously way cool. It has left hand threads on one end and matching right hand threads on the other end. Underneath the leadscrew is the Toggle Bar, which pivots in the middle and tips slightly either way. At each end of the toggle bar is a brass tooth sticking up, which can engage the threads on the leadscrew. Tip the bar slightly one way, and the left tooth engages the left hand threads, driving the feed to the left. Tip it to the right, and the right tooth catches the right hand threads, driving the feed to the right. It's almost an instant reversal in direction.

The wood Control Bar at the bottom is linkaged to the toggle bar. As the bobbin is spinning, I rest my hand on the control bar. Push lightly to the right, it feeds right. Push lightly to the left, it feeds left. Take my hand off the bar and it's in neutral, not feeding either direction. So, as the machine is running, I'm watching the buildup of wire on the bobbin, and controlling which direction the feed is going. But the rate of feed is fixed by the geometry of the machine. I watch and make subtle left/right corrections as needed to make the wire build up evenly.

When I first built the machine, the toggle bar was controlled by a spring and an electric solenoid, and a pair of limit switches with adjustable stops. It would operate fully automatic; it would feed across one way until it hit the stop, then reverse and go back the other way to the other stop. I could stand there hands-off and watch it. But I found that it was too fussy to get the stops perfectly dialed in for each bobbin size. If they weren't just right, the coils would get lumpy and mis-shapen. And really, I wasn't ever going to walk away from the machine while it was winding. I'm going to sit there and watch it carefully. Each coil doesn't take that long. So, I ripped out the automatic wiring and put in the wood control bar. I guess it's now a semi-automatic feed winder. It's comfortable to use this way, and I get neat, consistent coils.

Back to the overall structure: The top shaft is the spindle, driven directly by the motor. The bobbin mounts over on the right end of it on a flange. Most of my bobbins get mounted sandwiched between a pair of machined aluminum flange disks. These have shallow milled recesses that the bobbin flanges fit into. The disks make a smooth surface, so the wire can be fed right into the corner of the bobbin, without catching on the spinning corner of the flange.

The vertical plate slides side-to-side, driven by the leadscrew via the toggle bar. It has a total side-to-side travel of about an inch and a half. The plate is mounted on three black Delrin bearing blocks. They are simple blocks with bored holes, which slide on the spinning shafts. The upper one is on the spindle shaft, and the two lower ones are on the leadscrew shaft. Clamped to the vertical plate is the feed bar, with a narrow black Delrin feed pulley out at the end. You can see the path of the wire drawn in red. I comes off the spool in the back, through the tensioner, around the feed pulley, and on to the bobbin from underneath. I deliberately made the wire path short and straight, not bending the wire over any tight spots. That's why I use the pulley. These details are important to keep from damaging or breaking the wire as it feeds.

You'll notice that the feed bar has quite a range of adjustment of where it can be clamped on the vertical plate. I designed this machine so that I could wind bobbins up to 6" long. That's the reason why this machine is so tall; it's a fairly large diameter to swing. Shortly after I built this machine, I used it to wind some 7-string bass single coil pickups. Kind of ridiculous, but I made them. If I ever build another winder, it'll be more compact.

That's enough for now. I'm sure we'll all get into more discussion and detail about building pickup winding machines. There are lots of different ways, from simple to complicated. Mine is at the complicated end.

 

[Jisch]

That's impressive and your descriptions are easily followed, thanks for taking the time!

 

[Flying B]

Awesome machine Bruce! I keep reading about scatter-wound pickups though, is this possible on your machine? And are they really inherently any better?

 

[ctmullins]

Bruce, that is way cool!

 

[Novarocker]

View attachment 3225017 View attachment 3225019 View attachment 3225018 Multicoils start with casting the bobbins. I use Smooth Cast urethane and silicone molds. Molds are sprayed with release spray before casting.
I measure urethane parts with a scale.

This is similar to an idea I have, nice to see a visual representation, thank you.

I decided to start making my own pickups for my Scroll Basses in 2003. Up until then, I had been buying Quarter Pounder P-Bass coils from Seymour Duncan, mounting them in my own ebony and epoxy housings. They worked well, consistent quality and reasonably priced. I was buying the bare coil assemblies from them, without the covers or retail packaging, 10 sets at a time. I think back then they were like $25/set.

So, for any of you who want to get into unusual looking pickups in special housings, but don't want to make the jump into making your own coils yet, this is a good option. If you are a Luthier and buy a little bit of quantity, SD will sell you just the finished coil assemblies of any of their standard models. As far as I know, they still do. And they make a wide variety of models and specifications. You can pick from their stock and use them in unusual ways.

In my case, as I was planning out my Series IV model, I wanted to make some new pickups in unusual configurations, where commercially available coils and bobbins wouldn't work. So, I had figure out how to make my own.

I was starting from scratch, so I did a lot of research. I bought copies of Jason Lollar's book and Animal Magnetism, the two main books available on pickup making. I read probably every post on the Pickup Maker's Forum. I found that there isn't really that much good technical information out there about designing and building pickups. Particularly about making unusual configuration pickups. Most of the info out there is about making standard Fender and Gibson pickups, fussing over the little details to make precise replicas of old vintage models. Doing it just like Fender did in the '60's.

I dove into it on my own. I found that building unusual pickups is mostly about mechanical things. Figuring out how to build custom bobbins. Making a winding machine. Learning how to wind the tiny wire neatly without breaking it. Figuring out a good reliable way of terminating the tiny wire ends. Making up housings, shielding shells, mounting brackets. Lots of mechanical problems to work out.

Designing magnetic pickups is also mostly mechanical. Picking and arranging magnets to get a good shape magnetic field. Designing the geometry of the coil to put the wire turns in the best place within the magnetic field. The only "electronics" part is in working the specifications of the coil to work with the amp. These are the things that you can mess around with to adjust the resulting sound of the pickup.

If you limit yourself to winding wire onto purchased standard Fender-style bobbins, then you are really narrowing what you can change. There's only so much you can do with number of turns, wire gauge, wire insulation type, DCR reading. And everyone has already done every possible combination. If you want to experiment with pickups, you've got to get into the mechanical stuff of making custom parts.

Although I'm certainly far off from digging into the physical work, this has been the biggest road block I've had as well. The mechanical side is the most difficult and certainly where I have little to no practice. I much appreciate the whole breakdown. Your postings and the @Freekmagnet La Charra build have been so helpful for me to really understand the process.

It's nice to know that once I get the basics of the mechanical process down and get some hands on practice it's a matter of trial and error to find the ball park of what I'd like to do.

Anyway, one of the ideas I have had in my head for a while is something near the idea of the p rails guitar pickup. Take a coil with a narrower field and mate it to one with a wider field, ie similar to the rail and p90 coils in the p rails pickup. The real appeal to me, is to create a wiring system to effectively blend each coil. I think it would be interesting to be able to go from a jangly, spanky single coil to a thicker, throatier sounding coil.

Taking it even further would be possibly to make 4 coils elongated and parallel to the strings and mate them with a narrow field coil orientated normally across the strings. Add in the blending between coils and it may make some interesting tones.

All in theory (in my head lol) of course, especially since I don't have a lot of knowledge on the subject. But it does seem to make sense to me. I think the idea may be more appealing to those who use more dirt/harmonics, aka many guitarists, since the longer coils would have a larger apperature and sense a longer section of the strings.

Granted it could just be a bunch of snake oil and really just create a bunch of mud.