Magnets & Copper Wire: A Pickup Building Thread

[Bruce Johnson]

Hi all. I grew tired of dabbling around the edges of pickup construction and daydreaming about being able to tinker with my own so this weekend I placed an order for a few small DC motors, PWM boards, a counter, an AC-to-DC converter, and some odds & ends I knew I'd need off the bat. No supplies, just what I'll need to get a winder up & running. I have a lot of reading to do still, obviously, but once everything's here I'll order what I need to get a few P, J, and Tele pickups under my belt.

Welcome to the club of Crazy Pickup Winders! It's the pickups that are crazy, not us, really. There are a lot of posts on this thread showing how we've built our own pickup winding machines, but they are scattered throughout the 88 pages. Make sure you scan through. Many different types and levels of sophistication. You'll probably find something close to what you are thinking. You are welcome to ask questions. We've all stumbled around making ours and refining them.

 

[szyzk]

Welcome to the club of Crazy Pickup Winders!

Thanks! I pretty much know what I'm after design-wise, I just need to have the parts in front of me so I can figure out what I need to do for the base & shell. I don't aim to sell these but value being able to reproduce things to an extent, so I'm going to run the wire over a rod that's tensioned against a cam which spins at a low rpm so I can chose how quickly & when the wire spools or scatters. I need to figure out which "patterns" are useful right now -- for example (just examples, I have no idea what's reasonable right now): building up the wire for 900 winds at a steady 4rpm from bobbin-to-bobbin before letting it "scatter" for 100 winds at a faster 10rpm to create space between the wire.

I like knowing how things work, so this will help scratch that itch!

 

[Derek Kay]

There are other things that can influence the sound:
I have a PJ fender Player jaguar I bought second hand that came with this configuration of pickup/wiring:
View attachment 5387943

I felt the sound of my bass improved a lot just by rotating the P pickup 180º as follows:
View attachment 5387945

Rotating the P pickup sounds rather useful.

Could it be that the new orientation, with both PUs on, has E/A on north/south and D/G on south/north, and thus all strings are partially phase cancelled?

That would probably change the bottom end for better or worse.

 

[13ghosts]

?

They're just different steps in the scale of field strength. They aren't as commonly used and much more expensive.

They way most of us adjust the strength of our magnetic fields is with the size of the magnets. Increasing the diameter and length of the magnet increases the strength much more than going to a higher grade. Magnetic field strength is the product of the Volume (cubic inches or meters) of the magnet. Increasing a rod magnet from 3/16" dia to 1/4" dia nearly doubles the field strength, at the same length and grade. Increasing a 3/16" diameter magnet from 1/2" long to 3/4" long will be a 50% increase in field strength. I don't remember the number, but going from A5 to A8, of the same diameter and length, is more like a 40% increase.

The sound of a magnetic pickup comes from:

• The power of the magnetic field
• The shape of the magnetic field around the strings and the coil
• The number of turns on the coil
  
• The fit of the coil within the magnetic field's shape
• The wire gauge and impedance of the coil.

There are a few other little things, but those are the main design parameters. And that's the approximate order in which you should play around with these parameters when you are designing a new pickup.

Decide:

• What strength and size magnets you are going to use
• How the magnets are going to be positioned in relation to the string
• How the coil will be positioned within the field
• How many turns you need for that combination to get the signal level you want.
• Then, work with the wire gauge and impedance to shape the EQ curve of the signal "sound".

Thanks!

Most of the possible decisions are dictated by the special design and purpose of the pickups I use. Since the pickups in my bass have to be relatively small and I therefore can't increase the diameter of the magnets that much (at least I thought so, since I had used AWG 42 with 14,000 turns for the previous ones). Hence, I use two magnets in a row instead of one with a larger diameter.
So I have four parameters left to tune in this design:

1. the number of turns,
2. the type of the magnets (A1-9),
3. the length of the magnets,
   
4. the wire gauge.

Since I am rather limited in design options, I wanted to test magnets of different strengths. The current combination of Alnico 3+5 on the neck and Alnico 6 on the bridge harmonizes very well. However, flatter pickups would be an advantage for the construction in my bass.

My two current four-in-one pickups each have 10,000 turns of AWG43 wire and a resistance of 9.8K. The height of the coil is 15.5mm/0.59in. The magnets have a length of 18.5mm/0.72in and a diameter of 5mm/0.2in. Magnets with this diameter are available from between 15mm and 18.5mm (0.59in to 0.72in) as Alnico 5, 6, 8 and 9. For example, if I were to use 15mm/0.59in magnets, i.e. 12mm/0.47in coil hight instead of 15.5mm/0.59in, what would, based on Alnico 5, be the Alnico number that would have the same strength - 6, 8 or 9? Can this be roughly approximated?

In which direction would the wider but flatter coil affect the sound as this changes "the shape of the magnetic field around the strings and the coil and the fit of the coil within the magnetic field's shape"?

 

[ricardol]

Rotating the P pickup sounds rather useful.

Could it be that the new orientation, with both PUs on, has E/A on north/south and D/G on south/north, and thus all strings are partially phase cancelled?

That would probably change the bottom end for better or worse.

It is possible that, with both PUs on, this cancellation effect disappeared after rotating the neck pu... I felt that a significant improvement occurred as if the sound spectrum had become more balanced and without the cancellation of some frequencies. The original positioning created some sound discomfort that probably led the previous owner to sell the bass.

 

[Bruce Johnson]

In which direction would the wider but flatter coil affect the sound as this changes "the shape of the magnetic field around the strings and the coil and the fit of the coil within the magnetic field's shape"?

In my experience & knowledge, making the coil wider and flatter makes the low end less clear, more muddy and "wooly". This is assuming that everything else is the same; magnet strength and shape, wire size & turns, etc. In comparison, a tall narrow coil of those same specs will have more clarity of the bottom end.

The reason why this happens is because some of the turns are moved out further within the magnetic field around the coil, and as the coil becomes larger diameter, those outer turns become longer in length (circumference) around the coil.

As the string swings through the field, and the field swings through the coil, there is a teeny little electrical pulse in every turn of the wire. They all add together instantly to create the overall signal in the coil. The number of turns determines the level of that signal, because it's the sum of all those teeny pulses.

When the turns around the outside of the coil become significantly longer in length than the ones on the inside, there's a time delay on their teeny pulses catching up to the ones on the inside. The pulse goes through the wire at the same speed, so it takes longer for them to go the distance. This causes them to get a little bit out of phase. Which makes the signal less clear and more muddy. And that out of phase is greater at lower frequencies.

That's why a P-bass coil has a muddier low end than a J-bass coil. Leo did that intentionally. He made the P-bass coils short and fat to make the P-bass sound thicker and mushier down low. He was trying to make it sound more like an upright bass. The J-bass coils are tall and narrow to make the sound clearer and wider range. That's the sound he wanted for the J-bass.

 

[13ghosts]

In my experience & knowledge, making the coil wider and flatter makes the low end less clear, more muddy and "wooly". This is assuming that everything else is the same; magnet strength and shape, wire size & turns, etc. In comparison, a tall narrow coil of those same specs will have more clarity of the bottom end.

The reason why this happens is because some of the turns are moved out further within the magnetic field around the coil, and as the coil becomes larger diameter, those outer turns become longer in length (circumference) around the coil.

As the string swings through the field, and the field swings through the coil, there is a teeny little electrical pulse in every turn of the wire. They all add together instantly to create the overall signal in the coil. The number of turns determines the level of that signal, because it's the sum of all those teeny pulses.

When the turns around the outside of the coil become significantly longer in length than the ones on the inside, there's a time delay on their teeny pulses catching up to the ones on the inside. The pulse goes through the wire at the same speed, so it takes longer for them to go the distance. This causes them to get a little bit out of phase. Which makes the signal less clear and more muddy. And that out of phase is greater at lower frequencies.

That's why a P-bass coil has a muddier low end than a J-bass coil. Leo did that intentionally. He made the P-bass coils short and fat to make the P-bass sound thicker and mushier down low. He was trying to make it sound more like an upright bass. The J-bass coils are tall and narrow to make the sound clearer and wider range. That's the sound he wanted for the J-bass.

Thank you Bruce, as always! Much appreciated!
That's a very good explanation. I really like the sound right now so I'll leave it as it is for the time being.
I will certainly do a test with 15mm magnets at some point and then report on the results.

 

[ricardol]

In my experience & knowledge, making the coil wider and flatter makes the low end less clear, more muddy and "wooly". This is assuming that everything else is the same; magnet strength and shape, wire size & turns, etc. In comparison, a tall narrow coil of those same specs will have more clarity of the bottom end.

The reason why this happens is because some of the turns are moved out further within the magnetic field around the coil, and as the coil becomes larger diameter, those outer turns become longer in length (circumference) around the coil.

As the string swings through the field, and the field swings through the coil, there is a teeny little electrical pulse in every turn of the wire. They all add together instantly to create the overall signal in the coil. The number of turns determines the level of that signal, because it's the sum of all those teeny pulses.

When the turns around the outside of the coil become significantly longer in length than the ones on the inside, there's a time delay on their teeny pulses catching up to the ones on the inside. The pulse goes through the wire at the same speed, so it takes longer for them to go the distance. This causes them to get a little bit out of phase. Which makes the signal less clear and more muddy. And that out of phase is greater at lower frequencies.

That's why a P-bass coil has a muddier low end than a J-bass coil. Leo did that intentionally. He made the P-bass coils short and fat to make the P-bass sound thicker and mushier down low. He was trying to make it sound more like an upright bass. The J-bass coils are tall and narrow to make the sound clearer and wider range. That's the sound he wanted for the J-bass.

Assuming that everything else is the same a wider but flatter coil will have higher inductance and higher resistance... this should also result in higher voltage drop across the pu and consequentely in lower output signal, I suppose...

 

[13ghosts]

Hi all,
inspired by various discussions, posts and tests here and there:

• https://www.talkbass.com/threads/ch...cy-and-tone-with-a-loading-capacitor.1553278/
• https://guitarnuts2.proboards.com/thread/7166/effect-tone-capacitors

I have some questions.

My core question is whether it makes sense to passively adjust/reduce i) the resonance frequency with a frequency switch (capacitors) and ii) the peak intensity with a level switch (resistors) to "simulate" different pots and pickups.

Background:

• The level of the resonance frequency peak is determined by the resistance of the volume pot:
  
  
  
  Source: Der große Split-Coil-Vergleichstest

• The frequency of the peak can be reduced by capacitors connected in parallel:
  
  
  
  Source: https://guitarnuts2.proboards.com/post/72490/thread

• Each pickup has a characteristic resonance frequency and a characteristic strength of the peak.
• The resonant frequency depends on the resistance of the coil (and the latter is easy to measure). Here is an overview of some P-pickups tested in Gitarre & Bass (04/2024):
  
  

Plan:

• No volume pot but a switch with different resistors (100K, 250K, 500K, 1000K and 2000K, Off) to simulate the characteristics of different pots.
• Shifting the resonance frequency with capacitors from 1-5nF to simulate the characteristics of different pickups.
• In order to obtain a wide range of sound options, the pickups should of course not have a too low (starting) resonance frequency and therefore fewer windings than usual. 7kΩ might probably a good starting point.

Questions:

• Is this compiled half-knowledge correct?
• Why is such a circuit rather uncommon - or if it is more common, where can you find it, and if not, why does it make no sense?
• What values would you set for the resistors, capacitors, and the resistance of the pickup?
• What disadvantages might arise from such an approach?

TIA!

 

[ardgedee]

Why is such a circuit rather uncommon - or if it is more common, where can you find it, and if not, why does it make no sense?

I don't think it's overly rare -- Varitone type tone controls have been around for a very long time, usually for guitars rather than bass. I suspect in part because bassists who want a lot of tonal variety are more inclined to use an active onboard EQ which is more versatile and relatively easier to use in performance.

In terms of building something like this for the bench, a breadboard is going to be more flexible to experiment with (and easier to test) than soldering up a lot of switched circuits.

 

[Snert]

In terms of building something like this for the bench, a breadboard is going to be more flexible to experiment with (and easier to test) than soldering up a lot of switched circuits.

This. And I'd simply use clip leads to change values, then record each variation into the exact same set up of interface, gain and DAW so that you can compare as sonic memory is notoriously short and unreliable. With recordings you can easily and repeatedly compare.
Also be VERY consistent with your technique when playing the notes as this alone can swamp any differences.

PS: this reply is for 13ghosts and I was just quoting ardgedee to expand on what he said.

 

[Freekmagnet]

Questions:

• Is this compiled half-knowledge correct?
• Why is such a circuit rather uncommon - or if it is more common, where can you find it, and if not, why does it make no sense?
• What values would you set for the resistors, capacitors, and the resistance of the pickup?
• What disadvantages might arise from such an approach?

TIA!

• Is this compiled half-knowledge correct?

Yes, it is correct. Correct enough anyway.

• Why is such a circuit rather uncommon - or if it is more common, where can you find it, and if not, why does it make no sense?

Actually, these types of circuits are not uncommon. The Stellar Tonestyler is a commercial example, although it does not simulate different resistance values - only capacitance, AFAIK. There's a schematic DIY version floating around here on Talkbass someplace that does include additional resistors. I'll leave that search up to you.

I once built my own DIY Tonestyler and added it to one of my basses. In a real-world working environment, I did not find the feature to be very useful. Just having one set capacitor wired to a pot is far less awkward to adjust and dial in. It might have been a little more useful to wire the varitone to a pot in order to vary the degree to which the capacitor sends high end to ground. I'd say for you, that experiment might be worth a try. For me, it wasn't worth it enough to have more than two knobs on my control interface.

• What values would you set for the resistors, capacitors, and the resistance of the pickup?

As far as caps, a stock Fender cap is 0.047uf. Say you had 10 settings on a switch. You could make 0 your open setting, no cap. 5 your 0.047uf setting. Maybe 10 as your .1uf setting. Everything else you could set as increments in between. Every increment should be double the last. Personally, I found the mid-bump with the smaller value caps to be the most interesting. My prediction is once you get past 0.047uf, you'll find that you'll just have more bass.

As far as resistance, if your pickup is say, 7K, you'll find that once you get past a pot value of 500K, you're not going to hear much difference. The lower values have more effect on the sound of the pickup. I'm the last person in the universe qualified to quote anything even remotely related to electrical engineering, but just in case you want to know, it works something like this: Between a pickup (R1) and a pot (R2), you're wiring two resistors in series, so the the formula will be RT = 1/(1/R1 + 1/R2), with RT being resistance total. In this case, a 500K pot will give you 6.9K total and a 250K pot would give you 6.8K. 0.1K doesn't seem like a heckuva difference, but the pickup with the higher value pot will sound noticeably brighter.

Pickups wired straight to the jack can be pretty piercing - that's kind of the rational behind tempering the high end by using a pot.

• What disadvantages might arise from such an approach?

If you have the time on your hands to do an experiment like this, then I don't see any disadvantages.

 

[ricardol]

Between a pickup (R1) and a pot (R2), you're wiring two resistors in series, so the the formula will be RT = 1/(1/R1 + 1/R2),

Resistors in series, you simply add them... your formula is for resistors in parallel.

 

[Freekmagnet]

Resistors in series, you simply add them... your formula is for resistors in parallel.

You’re right - I should have written that a pickup and pot are wired in parallel instead of series. (Too late to edit)*

@13ghosts

 

[13ghosts]

Thank you all for the help and input! I really appreciate it!

 

[13ghosts]

• Is this compiled half-knowledge correct?

Yes, it is correct. Correct enough anyway.

• Why is such a circuit rather uncommon - or if it is more common, where can you find it, and if not, why does it make no sense?

Actually, these types of circuits are not uncommon. The Stellar Tonestyler is a commercial example, although it does not simulate different resistance values - only capacitance, AFAIK. There's a schematic DIY version floating around here on Talkbass someplace that does include additional resistors. I'll leave that search up to you.

I once built my own DIY Tonestyler and added it to one of my basses. In a real-world working environment, I did not find the feature to be very useful. Just having one set capacitor wired to a pot is far less awkward to adjust and dial in. It might have been a little more useful to wire the varitone to a pot in order to vary the degree to which the capacitor sends high end to ground. I'd say for you, that experiment might be worth a try. For me, it wasn't worth it enough to have more than two knobs on my control interface.

• What values would you set for the resistors, capacitors, and the resistance of the pickup?

As far as caps, a stock Fender cap is 0.047uf. Say you had 10 settings on a switch. You could make 0 your open setting, no cap. 5 your 0.047uf setting. Maybe 10 as your .1uf setting. Everything else you could set as increments in between. Every increment should be double the last. Personally, I found the mid-bump with the smaller value caps to be the most interesting. My prediction is once you get past 0.047uf, you'll find that you'll just have more bass.

As far as resistance, if your pickup is say, 7K, you'll find that once you get past a pot value of 500K, you're not going to hear much difference. The lower values have more effect on the sound of the pickup. I'm the last person in the universe qualified to quote anything even remotely related to electrical engineering, but just in case you want to know, it works something like this: Between a pickup (R1) and a pot (R2), you're wiring two resistors in series, so the the formula will be RT = 1/(1/R1 + 1/R2), with RT being resistance total. In this case, a 500K pot will give you 6.9K total and a 250K pot would give you 6.8K. 0.1K doesn't seem like a heckuva difference, but the pickup with the higher value pot will sound noticeably brighter.

Pickups wired straight to the jack can be pretty piercing - that's kind of the rational behind tempering the high end by using a pot.

• What disadvantages might arise from such an approach?

If you have the time on your hands to do an experiment like this, then I don't see any disadvantages.

Thanks @Freekmagnet for all the details and tips. I will definitely order a set of capacitors and resistors and do some tests. I'm curious to see how the possible changes in sound interact with the positions of the pickups. I will report back!

 

[Bruce Johnson]

For those of you interested in casting your own bobbins from polyurethane resin, I've been trying out a new casting resin: Model Pro Black from SPC. It's available on Amazon and in most hobby shops.

This is a fast cure polyurethane resin, pre-mixed with black pigment. Working time in the cup is 2.5 minutes and full cure is 15 minutes. And it really is that fast. I had previously tried Smooth-On's Fast resin, and had problems with it overheating and making wrinkled and distorted parts. This Model-Pro is working reliably so far.

It mixes 1:1. I'm using a scale to measure it.

I'm casting up some batches of pickup bobbins and headstock scroll inserts, and they are coming out very nice. The resin is low viscosity and flows easily into the deep recesses of the mold. Hardly any problem with bubbles. Fairly hard plastic when cured, but not brittle. And the parts are a nice solid opaque black color.

I'm happy with the results.

 

[Verner]

This is a great thread, I just stumbled across it looking into interesting pickup designs. There is some really great craftsmanship and ingenuity here. I am new to this side of things, so forgive my crude experiment, but I was hoping maybe someone could shed some light on the reason for my pickup experiment's failure.

My general problem set to overcome is extending the magnetic field through 1/4" of wood. I wanted to make a pickup that could be back-mounted, with long pole pieces and a small base. I figured a small 1/4" rout cavity for the pole pieces would be as unobtrusive as I could get. I also wanted humbucking pickups with a single focal point.

So I decided to try and reverse the sidewinder arrangement using rod magnets as the primary magnets, which would magnetize a baseplate going through two mini humbucker coils of about 5,000 winds each. I reverse wound the coils, making the assumption that the baseplate would be magnetized in the same direction as the magnets (North facing up, South facing down). My idea was the reverse coils would approach the poles from different directions, givng me reverse wound/reverse polarity. I also made a keeper for the neodymium rods to keep the same poles very close, the idea being an increased magnetic field, in the spirit of the Fender/Porky Freeman 60s Marauder 'invisible pickup' patent. I put together a prototype, and the pickup works, but the rods don't pick up much. The sides coming out of the coils, however, seem to be hum-free and give a strong signal. I 3d printed the magnet keeper and baseplate prototype, and did the metal forming by hand. Again, quite crude compared to what I see here, gives me a lot to aspire to. Here are some pics:

Very rough idea:

So, armed with only my high schools physics unit on magnetism from 30 years ago, I am ignorant as to why the field disruption only works efficiently at the coils. Is it the direction of magnetic transference? I have only made one pickup before, please pardon the extreme crudity (I know I keep mentioning that), but even though my concept was a failure, it was a fun project that has sparked my curiosity on the subject. I will definitely continue learning and seeing where this new corner of the build process takes me.

Thanks for this thread, I am only 5 pages in, but it is fascinating!

 

[tidbits]

I'm sure the more experienced builders can point you in the right direction, but I suspect your coils are too far from the strings...

As I understand it, the magnets in a pickup are meant to focus their magnetic field into the strings... thus magnetizing the strings themselves. It's actually the movement of that secondary magnetic field from the strings that's generating current in the wound copper coil of the pickup that's creating the signal.

So... if your coils are way down in the body away from the strings the strength of the secondary magnetic field from the strings is going to be pretty weak down there, not able to induce a strong current in the coil, and consequently a weak signal.

I'm not 100% on that, but if I've understood the theory covered in this thread that's my guess at the issue.

 

[Bruce Johnson]

I'm sure the more experienced builders can point you in the right direction, but I suspect your coils are too far from the strings...

As I understand it, the magnets in a pickup are meant to focus their magnetic field into the strings... thus magnetizing the strings themselves. It's actually the movement of that secondary magnetic field from the strings that's generating current in the wound copper coil of the pickup that's creating the signal.

So... if your coils are way down in the body away from the strings the strength of the secondary magnetic field from the strings is going to be pretty weak down there, not able to induce a strong current in the coil, and consequently a weak signal.

I'm not 100% on that, but if I've understood the theory covered in this thread that's my guess at the issue.

Hello tidbits;

Yes, you are generally right, with one clarification. There really isn't a primary and secondary magnetic field. It's one magnetic field, which surrounds the group of magnets and pole pieces. The size and shape and power of the field is a summation of the size, shape, power, and pole orientation of the magnets.

The whole idea of a magnetic pickup is that the strings pass through one end of the magnetic field, and the coil of teeny wire is positioned nearby, within the field. When the string wiggles, it makes the field wiggle, which creates a tiny wiggling electrical current in each turn of the wire in the coil. Multiply that times several thousand turns, and a wiggling audio signal comes out of the coil. Which is a pretty close match to the wiggling of the string.

If the output signal is weak, it means that something isn't getting enough wiggling. The string may not be immersed enough in the field, and not making it wiggle. Or, the coils may not be immersed in the field enough to detect the wiggling.