Magnets & Copper Wire: A Pickup Building Thread

[dwizum]

That was for the thick vulcanized fiberboard - for a piece of flatwork that's essentially 1/2" x 3" with a few holes and a slot for a blade - the larger of the two parts in my photo above.

How stiff was the thinner version? It's only $1.50 - still twice as much as the taskboard but less than $3! I didn't really even consider it as my home-made versions of this design are all .06" fiberboard and that already struck me as too flexy - I'd get a lot of flaring which was exaggerated thanks to the long length.

The blue tape works great. I cut the slots a little oversize then wrap the steel blade in tape before I press it in. Then I trim off the tape and run a bead of thick CA along the joint. They're pretty indestructible at that point.

 

[Freekmagnet]

That was for the thick vulcanized fiberboard - for a piece of flatwork that's essentially 1/2" x 3" with a few holes and a slot for a blade - the larger of the two parts in my photo above.

How stiff was the thinner version? It's only $1.50 - still twice as much as the taskboard but less than $3! I didn't really even consider it as my home-made versions of this design are all .06" fiberboard and that already struck me as too flexy - I'd get a lot of flaring which was exaggerated thanks to the long length.

The blue tape works great. I cut the slots a little oversize then wrap the steel blade in tape before I press it in. Then I trim off the tape and run a bead of thick CA along the joint. They're pretty indestructible at that point.

The thinner stuff is more flexy. Like I said, for the cardboard, I made an attachment to sandwich the coil while I wound it up. I’d leave it in the assembly until it was potted. After it gets potted, the coil stabilizes somewhat.

The thinner fiberboard is OK. It will still flex although it flexes less than cardboard. I have my winding dialed in so that the wire piles up mostly in the middle. That way there’s less stress on the bobbin flange. I switched to the fiberboard because it’s more durable than the cardboard. If for some reason I have to rewind the coil, I can reuse the fiber bobbin. The cardboard ones wouldn’t survive that. Besides, the fiberboard looks better in pictures.

On my new sidewinders, I took some cues from @slowburnaz and stared using PCBs for my flatwork. This is mainly for structural reasons - it’s a lot easier to build this pickup using PCBs and little right angle header pins to hold it together. It’s a little more pricey, but it’s significantly easier to make, so I think it’s worth it in this particular case.

 

[Bruce Johnson]

Here's an example of how I do my cast epoxy housings. This is a special pickup that I'm making as part of a full restoration of a '67 Ampeg AMB-1 Scroll Bass. I used a leftover pair of coils that I build for my new AMB-2 models. They are a matched humbucking pair, with 3/8" x 3/4" A5 rod magnets in cast plastic bobbins. Wound with 6000 turns of #41, potted in CPES epoxy. I'm fitting these coils into the housing dimensions and mounting plate, so the pickup will bolt into the '67 AMB-1 with no routing or modifications. I've made a few of these before for other AMB-1 owners. This is a standard pickup of mine, set into a custom housing and base plate.

Here's the two coils, stuck on a steel bar, all checked and tested. In front is the special AMB-1 size aluminum base plate, which I made from 1/8" aluminum plate. And the housing mold with the perforated brass shielding shell fitted inside. The wire sticking up is soldered to the brass shell, and will be connected to ground. I use the AMB-2 mold for these AMB-1 conversion pickups, but the brass shell is fitted about 1/8" shorter in length. The AMB-1 pickup is slightly smaller than the AMB-2 pickup, and I don't want to have to file out the opening in the original Ampeg pickguard.

Also notice that this is the one-piece pickup, with the two coils in one housing. All my AMB-2's up through #014 were one piece. I went to the split two-piece design on #015.

All the parts in the mold, poured full of black epoxy. West Systems 105/206, with a drop of So-Strong Black colorant.

Fresh out of the mold. Right now, the top surface is just black epoxy. The magnets are staggered in height to match the 7 1/4" fingerboard radius.

I picked a suitable chunk of ebony and trimmed it to be the top cap. It's stuck on that wood holder block while I cut the radius to match the pickup.

Gluing the ebony cap on the pickup with more black epoxy.

After it's cured, I grind the ebony cap down to about 1/16" thick, following the radius. Trim the edges of the cap, and clean most of the excess epoxy off of the brass.

The pickup is almost done. A little more cleanup work, and polishing the top surface of the ebony cap. And it'll be ready to install.

This is how I build the "housings" for most of my pickups: Cast solid in epoxy, with a brass shielding shell around the outside, an aluminum base plate, and a thin ebony top cap. I've been using this technique for about 15 years, about 50 basses, and I've never yet had one fail out in the field. They are sealed up and should last 100 years.

 

[Freekmagnet]

I've been working on building up one of my new sidewinders this week. I posted a picture of the empty bobbins yesterday. There's some interesting interactions happening with this pickup, so I figured I'd post a little more of the build today and explain what's going on.

First here's the loaded bobbins - this is going to get dunked in epoxy within the next day or two:

I've had to be pretty crazy about registration with this pickup. The side plates are 430 stainless steel poles. They're .02" thick and also serve as decorative plates when the pickup cast in resin. As you can see, everything has to line up perfectly, so I use PCBs as my flatwork and use right angle header pins to join the bobbins to the ba isseplate. The base plate is also a PCB. The baseplate and the outwork has a copper ground plane that provides shielding for the coils. Theoretically, the stainless side poles could do the job of the shielded flatwork, but I figured, "what the heck, it can't hurt." The copper tape is there to ensure that all of the blade poles and the magnets are grounded. It also provides a little shielding on the sides.

Here's the part I'm excited about: This is an AlNiCo 8 sidewinder. AlNiCo 8 is kind of known for rendering a really dense, almost congested-sounding mid range. AlNiCo 8 also happens to be a really strong magnet. Sidewinders on the other hand, tend to have a really neutral-sounding midrange and not a ton of output, unless you wrap it with a ton of wire. So what happens is the nasty mids from the A8 gets tempered by the nature of the sidewinder. Conversely, the tame nature of the sidewinder gets a kick in the pants from the AlNiCo 8. So it's a pretty powerful sidewinder with a fat, aggressive mid-range.

The side poles are interesting as well. Without side poles, sidewinders tend to sound really thin. I've built sidewinders before with 1/8" thick stainless steel poles. I always assumed that for whatever reason, the side poles needed to be at least as substantial as the center pole. But, the .02" thick poles seem to do the job just fine - perhaps even better. If anything, those thin poles are getting a lot of charge from the magnets.

I have this pickup loaded into my test bass at the MM position. @Passinwind has been helping me to find a good 2-band preamp to match with this pickup and I'm kinda settling in on one I like. I A/B'd this rig with my 2015 3-band StingRay and I couldn't say that I could tell much difference between the two. If anything, my sidewinder might have had more nicely defined lows. I'm going to install this rig into my gigging bass and work on Stage 2 testing.

Here's a picture of a finished pickup - I've posted it here before.

 

[Bruce Johnson]

I've been working on building up one of my new sidewinders this week. I posted a picture of the empty bobbins yesterday. There's some interesting interactions happening with this pickup, so I figured I'd post a little more of the build today and explain what's going on.

First here's the loaded bobbins - this is going to get dunked in epoxy within the next day or two:

View attachment 4344836

I've had to be pretty crazy about registration with this pickup. The side plates are 430 stainless steel poles. They're .02" thick and also serve as decorative plates when the pickup cast in resin. As you can see, everything has to line up perfectly, so I use PCBs as my flatwork and use right angle header pins to join the bobbins to the ba isseplate. The base plate is also a PCB. The baseplate and the outwork has a copper ground plane that provides shielding for the coils. Theoretically, the stainless side poles could do the job of the shielded flatwork, but I figured, "what the heck, it can't hurt." The copper tape is there to ensure that all of the blade poles and the magnets are grounded. It also provides a little shielding on the sides.

Here's the part I'm excited about: This is an AlNiCo 8 sidewinder. AlNiCo 8 is kind of known for rendering a really dense, almost congested-sounding mid range. AlNiCo 8 also happens to be a really strong magnet. Sidewinders on the other hand, tend to have a really neutral-sounding midrange and not a ton of output, unless you wrap it with a ton of wire. So what happens is the nasty mids from the A8 gets tempered by the nature of the sidewinder. Conversely, the tame nature of the sidewinder gets a kick in the pants from the AlNiCo 8. So it's a pretty powerful sidewinder with a fat, aggressive mid-range.

The side poles are interesting as well. Without side poles, sidewinders tend to sound really thin. I've built sidewinders before with 1/8" thick stainless steel poles. I always assumed that for whatever reason, the side poles needed to be at least as substantial as the center pole. But, the .02" thick poles seem to do the job just fine - perhaps even better. If anything, those thin poles are getting a lot of charge from the magnets.

I have this pickup loaded into my test bass at the MM position. @Passinwind has been helping me to find a good 2-band preamp to match with this pickup and I'm kinda settling in on one I like. I A/B'd this rig with my 2015 3-band StingRay and I couldn't say that I could tell much difference between the two. If anything, my sidewinder might have had more nicely defined lows. I'm going to install this rig into my gigging bass and work on Stage 2 testing.

Here's a picture of a finished pickup - I've posted it here before.

View attachment 4344837

What Jeremy is doing on this pickup is really fascinating, from a pickup design/theory standpoint. The magnetic poles are a pair of vertical razor blades!! Say what??? So, what shape is the magnetic field around the blades, and how does it fit around the strings???

An interesting experiment would be to test the core of this pickup alone, without the thin blades. Get an idea what part of the sound is coming from the magnetic field off the side (top) of the big A8 magnet. Then maybe try some taller thin blades, with the coils down lower, to see how much the blades themselves are doing. The total sound may be a mix of those two sections of the magnetic field, and you may be able to fine-tune it by adjusting the height of the blades?

What this shows overall is that there is still a whole lot of uncharted territory in the design of basic magnetic pickups. Open for exploration by brave souls.

 

[slowburnaz]

I've been working on building up one of my new sidewinders this week. I posted a picture of the empty bobbins yesterday. There's some interesting interactions happening with this pickup, so I figured I'd post a little more of the build today and explain what's going on.

First here's the loaded bobbins - this is going to get dunked in epoxy within the next day or two:

View attachment 4344836

I've had to be pretty crazy about registration with this pickup. The side plates are 430 stainless steel poles. They're .02" thick and also serve as decorative plates when the pickup cast in resin. As you can see, everything has to line up perfectly, so I use PCBs as my flatwork and use right angle header pins to join the bobbins to the ba isseplate. The base plate is also a PCB. The baseplate and the outwork has a copper ground plane that provides shielding for the coils. Theoretically, the stainless side poles could do the job of the shielded flatwork, but I figured, "what the heck, it can't hurt." The copper tape is there to ensure that all of the blade poles and the magnets are grounded. It also provides a little shielding on the sides.

Here's the part I'm excited about: This is an AlNiCo 8 sidewinder. AlNiCo 8 is kind of known for rendering a really dense, almost congested-sounding mid range. AlNiCo 8 also happens to be a really strong magnet. Sidewinders on the other hand, tend to have a really neutral-sounding midrange and not a ton of output, unless you wrap it with a ton of wire. So what happens is the nasty mids from the A8 gets tempered by the nature of the sidewinder. Conversely, the tame nature of the sidewinder gets a kick in the pants from the AlNiCo 8. So it's a pretty powerful sidewinder with a fat, aggressive mid-range.

The side poles are interesting as well. Without side poles, sidewinders tend to sound really thin. I've built sidewinders before with 1/8" thick stainless steel poles. I always assumed that for whatever reason, the side poles needed to be at least as substantial as the center pole. But, the .02" thick poles seem to do the job just fine - perhaps even better. If anything, those thin poles are getting a lot of charge from the magnets.

I have this pickup loaded into my test bass at the MM position. @Passinwind has been helping me to find a good 2-band preamp to match with this pickup and I'm kinda settling in on one I like. I A/B'd this rig with my 2015 3-band StingRay and I couldn't say that I could tell much difference between the two. If anything, my sidewinder might have had more nicely defined lows. I'm going to install this rig into my gigging bass and work on Stage 2 testing.

Here's a picture of a finished pickup - I've posted it here before.

View attachment 4344837

Do you happen to have a gauss meter?

It would be interesting to see the strength of the field at the tops of both of the different blade thicknesses.

 

[Freekmagnet]

An interesting experiment would be to test the core of this pickup alone, without the thin blades. Get an idea what part of the sound is coming from the magnetic field off the side (top) of the big A8 magnet.

Well, I can tell you right now what that would sound like. Removing the side poles would make the pickup sound really thin, not unlike a single coil. I guess with most of the action happening around that central blade, it would basically make it similar to a single coil. The added side blades bring the opposite poles closer to the central pole, making them more a part of the magnetic field while also increasing the aperture.

I've done tests with thicker poles. Generally, the more steel on a sidewinder, the more output and bass response you get. This makes sense because you're increasing your inductance. However, I haven't noticed that the added steel reduces the amount of brightness. I haven’t used anything thicker than .125” for a pole. Maybe that’s not enough to affect your treble response. Either way, in this case, it seems that I was able to "tune" the amount of bass in relation to the treble. When I used 3x.125” blades, I don’t remember being as impressed by this pickup.

Another interesting thing I've noticed is that depending on the sidewinders, once you get past a certain wind count, any additional turns of wire have a greater effect on the sound of the pickup. For instance, the difference between say 6000 turns and 6125 turns is a lot more than the difference between 5000 and 6000. I'm guessing that may be because the coil itself is actually getting physically closer to the strings, but I haven't really done any experiments to prove or disprove that theory.

Then maybe try some taller thin blades, with the coils down lower, to see how much the blades themselves are doing.

That sounds like an interesting experiment, but these coils have a hot date with epoxy resin tonight! I could try it with my prototype coils, but I'd have to fix one of the leads.

Do you happen to have a gauss meter?

It would be interesting to see the strength of the field at the tops of both of the different blade thicknesses.

I don't have a gauss meter, and at this stage in my pickup-making career, I really have no excuse for not having one. Then again, I could say that about a lot of things. I did a check with the magnometer on my phone, and it says that it's about 3000ut at the central pole and -1800ut on the side poles. I honestly don't know what that's telling me. I usually just use that meter to tell which pole is north or south.

 

[Jeff Siddall]

I don't have a gauss meter, and at this stage in my pickup-making career, I really have no excuse for not having one.

I am looking at building one of these out of an Arduino... someday. If I do I will post the design here. I purchased the hall effect sensor several months back as part of a bigger order, but the one I got maxes out at 100 mT and I don't thing that is enough for strong magnets.

it says that it's about 3000ut at the central pole and -1800ut on the side poles

OK, so I already gave the disclaimer above that I don't own a gauss meter, but I have researched them somewhat and my understanding is that a strong A5 cylindrical magnet could be as high as about 110 mT, and neo significantly more, so your numbers sound like only a small fraction of what I would expect to see. Hmmm...

 

[slowburnaz]

...and did you ever nail down how these sidewinders are supposed to be wired? ;-)

 

[Freekmagnet]

...and did you ever nail down how these sidewinders are supposed to be wired? ;-)

Yes. I was just about to log on and post the answer, and then there you are with the question!

Somebody else posted the correct answer a few posts back. I don't remember who it was, but I'm just confirming that it is true.

Sidewinders should be wired with the flow of electricity going in opposite directions.

If the coils are both wound in the same direction and are then placed side-by-side in the same direction, then they should be wired beginning > end > end > beginning.

If you took those same coils and flipped one of them over, then the direction of the wire would be reversed. In that case, you would wire them beginning > end > beginning > end.

Electricity doesn't care if it's going from the inside out or outside in as long as it's going in opposite directions.

 

[dwizum]

Can you remind us what the magnet polarity is in that design?

 

[slowburnaz]

Right on.. I think that's what I had assumed.

Basically like a standard humbucker if it were out of phase, right? Reverse wound, same polarity.

 

[Freekmagnet]

Right on.. I think that's what I had assumed.

Basically like a standard humbucker if it were out of phase, right? Reverse wound, same polarity.

¡Correctomundo!

Can you remind us what the magnet polarity is in that design?

Which design?

 

[dwizum]

Which design?

The sidewinder a couple posts up - or, I suppose, any sidewinder that's wired in the "backwards" method you just mentioned?

 

[Freekmagnet]

The sidewinder a couple posts up - or, I suppose, any sidewinder that's wired in the "backwards" method you just mentioned?

That one, the center pole is North to strings - but that shouldn't make a difference as long as the central pole is charged with one single magnetic polarity.

 

[dwizum]

The coils are wound right on bar magnets, if I remember? So what you're saying is that both coil's magnets have N facing in?

I guess that makes sense in terms of the right hand rule, the magnetic field would cross the coil's wires in the opposite direction so they need to be wired opposite to result in an in phase signal.

 

[Jeff Siddall]

It was kinda hot and muggy here yesterday so instead of working in the garage I worked inside at my electronics bench and designed, assembled and wrote the code for a gauss meter. Works great! Here is a link to a quick video of it in use:

Gauss Meter Demo Video

On power on it auto zeros itself and shows the battery voltage, in mV, before showing the field strength in gauss. It's a little hard to see in the video but the bottom LED in the lower window is a polarity indicator.

The sensor is a Honeywell SS49E and while the linearity should be pretty good at less than 1%, the absolute sensitivity is not that accurate with a specified range of about +/- 35%. Total cost was about $10, so I really can't complain about the performance. It should still be useful to compare relative strength of magnet fields.

If anyone is interested I can post details of the design.

 

[Freekmagnet]

The coils are wound right on bar magnets, if I remember? So what you're saying is that both coil's magnets have N facing in?

I guess that makes sense in terms of the right hand rule, the magnetic field would cross the coil's wires in the opposite direction so they need to be wired opposite to result in an in phase signal.

Yes, yup, and yeppers!

 

[A9X]

It was kinda hot and muggy here yesterday so instead of working in the garage I worked inside at my electronics bench and designed, assembled and wrote the code for a gauss meter. Works great! Here is a link to a quick video of it in use:

[Invalid or Expired Link Removed]

On power on it auto zeros itself and shows the battery voltage, in mV, before showing the field strength in gauss. It's a little hard to see in the video but the bottom LED in the lower window is a polarity indicator.

The sensor is a Honeywell SS49E and while the linearity should be pretty good at less than 1%, the absolute sensitivity is not that accurate with a specified range of about +/- 35%. Total cost was about $10, so I really can't complain about the performance. It should still be useful to compare relative strength of magnet fields.

If anyone is interested I can post details of the design.

Yes please.

 

[Freekmagnet]

It was kinda hot and muggy here yesterday so instead of working in the garage I worked inside at my electronics bench and designed, assembled and wrote the code for a gauss meter. Works great! Here is a link to a quick video of it in use:

[Invalid or Expired Link Removed]

On power on it auto zeros itself and shows the battery voltage, in mV, before showing the field strength in gauss. It's a little hard to see in the video but the bottom LED in the lower window is a polarity indicator.

The sensor is a Honeywell SS49E and while the linearity should be pretty good at less than 1%, the absolute sensitivity is not that accurate with a specified range of about +/- 35%. Total cost was about $10, so I really can't complain about the performance. It should still be useful to compare relative strength of magnet fields.

If anyone is interested I can post details of the design.

Yes, that’d be great. Thx.