When is a bobbin 'full'?

[larryguitar]

Hi, as I'm working on learning more about winding I'm trying to find out what a 'full' bobbin actually is; in my mind, it's when the coil wire nearly overlaps the top and bottom of the bobbin itself.

Doing that, and with my current process, I can get about 5,500-6,000 turns of 42AWG single build poly on a 50MM bobbin (I'm using the ones from Philadelphia Luthier Supply) before it gets too dicey to proceed. I've read about folks winding 10K worth of 42 on a humbucker, and I'm wondering if those are special bobbins, or my process (hand-guided traverse) simply isn't efficient enough to put a 'full' load of wire on the bobbin.

I'd welcome the opinions of you experienced pickup builders--

Thanks,

Larry

 

[ReWind James]

The first problem is that you’re trying to wind to DCR, and quoting others who have stated a DCR spec they wound to. That’s not a reliable way to discuss winding coils, especially when you’re talking such extremes. It’s possible that someone who discusses winding guitar coils using DCR as a measurement of how “hot” they are is inexperienced enough to not know they are stretching the wire. Stretching the wire increases DCR in two ways - it heats the coil up and it makes the copper thinner with increased resistance per foot. Maybe the others you mention are measuring a coil they have wound with 42 gauge wire but they stretched it as thin as 43 gauge and have even less turns than you, but don’t know it. A coil made like this will also read artificially high right off the winder, as the wire stretching heats the coil.

The second problem is that “42 AWG” isn’t specific enough of a descriptor to define what others really used or what you are working with. That’s a very broad spec and covers a very large (in this context) range of copper core and insulation thicknesses. You can fit twice as much single build on the same bobbin as you can triple build. Within the same type, you can also fit much more wire on a given bobbin that’s in the lower range of copper core thickness, and much less wire on that’s in the upper range of copper core thickness. That wire at the lower end of the range will also have a higher resistance per turn, so you can stack more turns on and each turn will also read higher, compounding your exponential DCR increase as the coil builds.

All this shows a few reasons why DCR is an absolutely terrible indicator of anything regarding sound from a pickup. I’ve shown why coils with higher DCR are the ones with fewer turn counts, in several different examples. That’s the OPPOSITE of the common thinking of “higher DCR of the same gauge wire = more turns = more output.”

Can it be done? Yes. Without stretching the wire? Yes. One a typical PAF bobbin (I don’t know anything about your 50mm bobbins)? Yes. With factory off the shelf common 42 AWG min-nom PE magnet wire? Kinda. I could do it on my machines, but the coil will likely be fatter in the center than the flanges of the bobbin by a little. I wouldn’t recommend trusting a pickup with coils like that.

Unless you’re stretching the wire, or using a very large bobbin, you won’t wind a coil nearly clean enough to get that much stock 42 AWG wire of any type on it without a precise wire feed system, a stable and accurate tension system, and a correctly set up auto traverse winder, set to wind the cleanest coils with your wire/bobbins. With that, and especially with a custom spec of wire, you could definitely do it, even on a PAF bobbin, but you’d really be pushing the limits of everything. That’s not to say it would sound any good, either!

 

[larryguitar]

The first problem is that you’re trying to wind to DCR, and quoting others who have stated a DCR spec they wound to. That’s not a reliable way to discuss winding coils, especially when you’re talking such extremes. It’s possible that someone who discusses winding guitar coils using DCR as a measurement of how “hot” they are is inexperienced enough to not know they are stretching the wire. Stretching the wire increases DCR in two ways - it heats the coil up and it makes the copper thinner with increased resistance per foot. Maybe the others you mention are measuring a coil they have wound with 42 gauge wire but they stretched it as thin as 43 gauge and have even less turns than you, but don’t know it. A coil made like this will also read artificially high right off the winder, as the wire stretching heats the coil.

The second problem is that “42 AWG” isn’t specific enough of a descriptor to define what others really used or what you are working with. That’s a very broad spec and covers a very large (in this context) range of copper core and insulation thicknesses. You can fit twice as much single build on the same bobbin as you can triple build. Within the same type, you can also fit much more wire on a given bobbin that’s in the lower range of copper core thickness, and much less wire on that’s in the upper range of copper core thickness. That wire at the lower end of the range will also have a higher resistance per turn, so you can stack more turns on and each turn will also read higher, compounding your exponential DCR increase as the coil builds.

All this shows a few reasons why DCR is an absolutely terrible indicator of anything regarding sound from a pickup. I’ve shown why coils with higher DCR are the ones with fewer turn counts, in several different examples. That’s the OPPOSITE of the common thinking of “higher DCR of the same gauge wire = more turns = more output.”

Can it be done? Yes. Without stretching the wire? Yes. One a typical PAF bobbin (I don’t know anything about your 50mm bobbins)? Yes. With factory off the shelf common 42 AWG min-nom PE magnet wire? Kinda. I could do it on my machines, but the coil will likely be fatter in the center than the flanges of the bobbin by a little. I wouldn’t recommend trusting a pickup with coils like that.

Unless you’re stretching the wire, or using a very large bobbin, you won’t wind a coil nearly clean enough to get that much stock 42 AWG wire of any type on it without a precise wire feed system, a stable and accurate tension system, and a correctly set up auto traverse winder, set to wind the cleanest coils with your wire/bobbins. With that, and especially with a custom spec of wire, you could definitely do it, even on a PAF bobbin, but you’d really be pushing the limits of everything. That’s not to say it would sound any good, either!

As always, I appreciate the detail and thoroughness of your replies, Sir. I've learned a lot from you, and continue to do so.

I'm glad to hear that it would be difficult to get that much wire on a bobbin, since I sure can't. I max out (single build poly wire from Remington, and the PLS bobbins) right around 5,500, and could *maybe* hit 6,000 with a perfect (for me and my process) wind.

I was just wondering at these spec's I've seen floating around with those resistance numbers on a PAF-style bobbin; I know resistance isn't a good guideline for much, but I know it would take a lot of 42 to hit that. Now I know about stretching the wire, and have to wonder how much of that goes on (and how much is smoke and mirrors in the specs, to be honest.)

Thanks again,

Larry

 

[ReWind James]

If I could never measure DCR again, it would have zero impact on anything I do with designing, building, or repairing pickups.

I mean that. I wouldn’t feel hindered in my work, at all!

 

[Elrathia]

So what is your criteria? Do you go by number of winds?

 

[ReWind James]

So what is your criteria? Do you go by number of winds?

That’s one of many factors, ya. An important one, but not nearly everything. Pickups are passive and work at such low amounts of energy that every little thing counts. …once you start getting into designs that are clear and detailed and breathy, every little thing counts even more!