Magnets & Copper Wire: A Pickup Building Thread

[MPU]

Gyancey; Christoph Dolph at Bassculture pickups in Germany has those covers. Urethane casting resin really cures fast, I’ve had similar problems when casting bigger parts. I’ve used toothpick to take the bubbles out.

 

[Bruce Johnson]

It's interesting how balanced you noted the harmonics. I had thought that increasing the length of aperature would increase harmonic content, but goes to show theory is only that, theory.

Think about how harmonics work. When you pluck the string, it goes into a complicated vibration motion that also includes some nodes (the blobs where it swings the widest) of the harmonic frequencies, like the octaves. For one given note played on the string, the nodes are in fixed positions along the length. But as you walk up the scale on the string, the nodes get closer together, shifting toward the bridge. In between the nodes are the anti-nodes, where the string has the least movement.

If you have a normal pickup with a narrow aperture along the length of the string, and mount it in a fixed position, the window it can sense is limited. On some notes, the octave node will end up right over the pickup, and the harmonic will be quite loud. On other notes, the anti-node will be right over the pickup, and the harmonic will be quiet. And that's why people fuss so much about pickup position, particularly on guitars. It's about getting the pickup in the right position so the harmonics are loud on the most commonly used notes and chords. But they'll be weak on the other notes.

So, with a pickup like my Quad, the long aperture along the string means that the harmonic nodes always end up somewhere over the sensing area, for all the notes. The harmonics aren't necessarily louder than a normal pickup, but they are more even in volume as you go up the scale.

 

[Bruce Johnson]

I used a polyurethane casting resin that's already jet black. TC-808 from BJB Enterprises. Need to work on my squish technique though as I did have two troublesome bubbles:

You only get two minutes working time with this stuff, so no time for vacuum degassing! Still though the walls of the pickup shell are pretty thin and I'm impressed with the color and opaqueness of this resin.

Nice work for your first attempt at casting parts!

It sounds like you are using Smooth-On's Fast mix polyurethane resin. Many of the other brands that you see are actually made by Smooth-On, relabeled. I used the Fast mix for a while, and it's troublesome. The working time is so short and it tends to heat up and make bubbles.

I recommend the Slow mix. The working time is about 5 minutes and the part is cured in 30 minutes. Much easier to work with, fewer problems with swelling and bubbles.

I buy it through Reynolds Advanced Materials, a California distributor. There's probably another distributor around your area.

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I normally haven't been using any release agent when casting the polyurethane parts in the silicone molds. It hasn't seemed to be necessary. I use Johnson's Paste Wax as the release agent on the aluminum masters when pouring the silicone molds, and any time I'm pouring epoxy into a silicone mold.

 

[GeraldMcG]

Nice work for your first attempt at casting parts!

It sounds like you are using Smooth-On's Fast mix polyurethane resin. Many of the other brands that you see are actually made by Smooth-On, relabeled. I used the Fast mix for a while, and it's troublesome. The working time is so short and it tends to heat up and make bubbles.

I recommend the Slow mix. The working time is about 5 minutes and the part is cured in 30 minutes. Much easier to work with, fewer problems with swelling and bubbles.

I buy it through Reynolds Advanced Materials, a California distributor. There's probably another distributor around your area.

Invalid Link Removed

I normally haven't been using any release agent when casting the polyurethane parts in the silicone molds. It hasn't seemed to be necessary. I use Johnson's Paste Wax as the release agent on the aluminum masters when pouring the silicone molds, and any time I'm pouring epoxy into a silicone mold.

Great info as usual Bruce. Thank you.

I have been wanting to add mold making/casting to my skillset and Reynolds is on my way home from work.

Nice that they have classes too.

 

[Novarocker]

Think about how harmonics work. When you pluck the string, it goes into a complicated vibration motion that also includes some nodes (the blobs where it swings the widest) of the harmonic frequencies, like the octaves. For one given note played on the string, the nodes are in fixed positions along the length. But as you walk up the scale on the string, the nodes get closer together, shifting toward the bridge. In between the nodes are the anti-nodes, where the string has the least movement.

If you have a normal pickup with a narrow aperture along the length of the string, and mount it in a fixed position, the window it can sense is limited. On some notes, the octave node will end up right over the pickup, and the harmonic will be quite loud. On other notes, the anti-node will be right over the pickup, and the harmonic will be quiet. And that's why people fuss so much about pickup position, particularly on guitars. It's about getting the pickup in the right position so the harmonics are loud on the most commonly used notes and chords. But they'll be weak on the other notes.

So, with a pickup like my Quad, the long aperture along the string means that the harmonic nodes always end up somewhere over the sensing area, for all the notes. The harmonics aren't necessarily louder than a normal pickup, but they are more even in volume as you go up the scale.

Excellent way to put it, brings back the memories of quantum mechanics in college. Certainly a d'oh moment for me and you're definitely right. It's not a matter of getting increased signal strength of harmonics, instead just not missing any versus a small aperature pickup.

 

[Freekmagnet]

Sandwich Sidewinders, Pt 3

I get my 430 stainless steel blade poles cut by water jet from my local fabricator. The plate was pretty pricey - $70 for a square foot - and the water jet service ran me about $6 each.

Once I clean the blades up with files and sandpaper, I glue the sandwich together with black epoxy.

Then, these cast polyurethane ends...

And these handy nubs on the side of the cast coils...

...I glue the ends and an aluminum base plate on the bottom. My little fantasy is to make this part of the process a snap-together process. That would take some more advanced engineering.

Once it’s all assembled, I give the blades a final polish.

Here’s an image of the bottom of the pickup.

And here’s a picture of the pickup installed in a bass:

 

[Jon Clegg]

Sandwich Sidewinders, Pt 3
Once it’s all assembled, I give the blades a final polish.

View attachment 3241586

That's gorgeous drool

 

[Slidlow]

Now if I could get for 6 string.

 

[tbrannon]

If that thing sounds half as good as it looks, you've got a winner.

 

[Freekmagnet]

Here’s an iPhone recording of the pickup being used in the field. This is my first iteration with the neodymium magnets and the 1-band preamp. The upcoming ceramic 8 version with the two-band preamp is an enormous improvement.

If that thing sounds half as good as it looks, you've got a winner.

 

[Matt Liebenau]

Sounds good. I'd be interested.

 

[MPU]

I have a small cnc-mill at work. Base plate is drawn in CamBam.

And plates milled, ready for drilling the bobbin holes.

 

[Freekmagnet]

View attachment 3246266
I have a small cnc-mill at work.
View attachment 3246267

Oooooh - I want one of those.

 

[celeste hall]

A general plea to the readers of this thread:

This thread is for Luthiers who are thinking about getting into building their own custom pickups. Specifically weird, unusual, non-mainstream pickup configurations. We're mainly comparing notes on the techniques of how to build unique pickups. Making parts, building the winding machines, details of fabrication, etc. Farther down, we'll get more into the basic principles of designing pickups; what parameters affect the sound in what ways.

But, for now, Please let's not load up this thread with ten pages of commentary on which pickups sound better than others and what makes them sound different, etc. That kind of discussion belongs over in the Pickups & Electronics Forum section. When you get into how and why pickups sound the way they do, there are all kinds of theories and arguments. Mostly from people who buy and use pickups, rather than the people who actually build them.

Mentioning Scatter-winding gets into those arguments. If you aren't familiar with it, Scatter-winding is deliberately winding the wire on the coils in a loose, messy, random way, with the turns scattered and crossing over each other. That's the way the ladies at Fender did it back in the '60's so it just has to be a good thing, right? Most of the Boutique Winders today have latched onto Scatter-winding as one of those magic techniques for making beautiful sounding pickups. In reality, they mostly like it because it's so much easier to do than Neat winding. Most of them haven't built automatic feed winders, and don't have the patience to hand-wind neat precise coils. Making them sloppy and random is easier.

To specifically answer your question, no, my machine doesn't do Scatter-winding. I built it specifically to do the opposite of Scatter-winding; to wind my coils in accurate, even layers. Tight and dense and compact. I have my technical reasons why I want to make my coils that way, to get the sound that I want. We'll get into more of that later. If I wanted to Scatter-wind, I'd disconnect my automatic feed, and guide the wire by hand in a random sloppy fashion. But I don't want to.

Obviously, what I've said here will start the feathers and beer bottles flying. But, Please, if you want to argue about whether Scatter-winding is good or bad, start a thread over on the Pickups & Electronics Forum.

Oh my, a winder that seems to be willing to share knowledge, not just tease with it, you sir are a rear bird. Thank you, I think I am really going to enjoy this.

 

[MPU]

I’ve finally done all the evaluation discussions with kids and their parents and now I have time to focus on my hobbies too. I’ve wound the coils, soldered the wires to them and tonight I made the keeper bars. Now all the parts are done, time to put them together.

 

[MPU]

I used a template for drilling holes thru the base plate and cover. Coils were glued with ca using the template on top of the coils to make sure that the pole screws line to cover holes. Keeper bars are under the base plate.

 

[MPU]

Magnets are also glued with ca. Pickup is ready for wax potting. I solder the coils to the base plate after potting. I want to make sure that the coil wires don’t break. Wax potting solidifies the coil wires to the coil just enough.

 

[I-Am-The-Slime]

I have no clue what's going on, but that looks seriously badass!

 

[bigbri5050]

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.

View attachment 3228037

View attachment 3228036

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:

View attachment 3228038

View attachment 3228039
Wonderful work on your pickups Bruce. A few thoughts from an ex-coil winder that might help you. When you pot coils, we used to find that the contraction of the epoxy while setting can put stress on the windings and especially the leadouts. You can put small rubber sleeves over the leadouts to shield them, but you can also dip the whole assembly into hot candle wax. this provides a protection to the coil. It also prevents individual coil wires from moving. When the windings are loose the pickup becomes 'microphonic.' In any case, thank you for putting your work on this thread.

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.

 

[Bruce Johnson]

Wonderful work on your pickups Bruce. A few thoughts from an ex-coil winder that might help you. When you pot coils, we used to find that the contraction of the epoxy while setting can put stress on the windings and especially the leadouts. You can put small rubber sleeves over the leadouts to shield them, but you can also dip the whole assembly into hot candle wax. this provides a protection to the coil. It also prevents individual coil wires from moving. When the windings are loose the pickup becomes 'microphonic.' In any case, thank you for putting your work on this thread.

Hello bigbri5050;

We haven't really talked much about coil potting yet on this thread but, yes, we all do it to prevent microphonics. Most pickup winders use the hot wax dip method, and there are lots of variation and technique to that.

I do my potting with a special epoxy called CPES (Clear Penetrating Epoxy Sealant) made by Smith & Co. It's very thin, with a viscosity almost as low as alcohol. It also doesn't dry rock hard; always stays just a little bit rubbery. It's made for reinforcing rotted wood by soaking down deep inside it. I've found that it's perfect for potting pickups. It soaks down all the way through the coil and dries to a rubbery mass, gluing all the turns together. It stops the microphonics and protects the wire from mechanical and thermal shock.

I think it's better than wax. I've been making all of my pickups like this since 2005, and I've never yet had a failure out in the field. But most pickup winders stay with wax because......wait for it....that's what Leo Fender did! Only a few of us bold pioneers use epoxy.