Alnico 5 for multicoil pickups?

[JayGunn]

I have a few newbie questions before I start to wind my first pickups, multi-coil neck pickup for my next 4-string scratch build.

1) I browsed all I could find here on one-coil-per-string wal-style pickups. I found someone who got 10,000 turns of 42ga wire onto a 3/8" pole piece and it came out to 3/4" diameter. Must have been a pretty tall bobbin methinks(!) So I am wondering if there's an online or downloadable calculator that will help me figure out the relationship to bobbin diameter and length, # of turns, wire diameter and overall resulting diameter?

2) On this site http://www.magnetsales.com/Alnico/Alrods.htm I found the following text: "Alnico 8 magnets have a lower remanence, but a higher coercivity than Alnico 5 magnets. This means that Alnico 5, though stronger in the right circumstances, is easier to demagnetize. Alnico 5 rod magnets should have a length to diameter ratio of about 4 to 1 in order to avoid self-demagnetization". Elsewhere I have read a suggestion of 5:1 ratio of length to diameter for Alnico 5. So are you experienced pickup winders concerned about this when using a 3/8" diameter alnico v pole piece that's roughly 3/4" long or even less (thus less than 2:1 ratio)?

3) Last Q: If I decide to go with a mild steel pole piece or maybe a 416 stainless pole piece instead of alnico (it will definitely be 3/8" or 10mm diameter) AND if I decide to put a little neodymium magnet under it, can you suggest a starting size--those things are awfully strong. I have some 6mm x 1mm in stock, but I'm thinking I may need something weaker...

Thanks in advance, John

[big_teee]

Probably the round bobbin data you refer to is mine.
The magnets are A5 x 3/8" x 3/4", gauss is around 1400-1500.

Question 2, I wouldn't worry about a5 magnets of normal pickup length demagnitizing.
Question 3, I have no experience with NEO magnets.
I prefer Alnico, and Ceramics.

[big_teee]

You can adjust this estimator round spool data, for your use.
Coil Estimator

[JayGunn]

Great! That calculator will really help me. And I'm happy people find that the 2:1 ratio works okay.

I'm planning to build a neck pickup that looks like it 'goes with' a Musicman bridge pickup. So the big pole pieces will really match the look nicely. I'll wire it like a P-bass, with 2 coils in series, parallel to the other 2 in series, RWRP.

Very helpful.

[big_teee]

Here's mine.
The P pickup is a multi-coil, and the bridge is a split coil.
That is my test bass and I mount and test bass pickups with it.
T

[JayGunn]

Am I using and reading this right? Here's an example try:



As I read it, I have described a round pole just over 3/8" (0.380" vs 0.375) to allow for a piece of tape or a film of epoxy. The inner space of the bobbin in 5/8" high (0.625"). I keep adjusting the DC resistance until the number of windings for the fill factor of my choice (e.g. 9093 windings here at 78.5%fill) approaches but does not exceed the max winds for that fill factor (9100). I am assuming 'max winds' is the calculator's estimate of the number that shape of bobbin will hold without overflowing.

So in this run it's telling me how many turns and how much DCR I'll get when I fill the bobbin. And 4 poles in series would net out to about 9K, i.e. in the Pbass ballpark.

This is great! Hope I'm using it right. Thanks Big_Teee

Great that we can tweak the wire diameter, because some Pickup Winder guys are finding 4 ga wire that's thinner, like .00265

[big_teee]

Yes, that looks ok.
The wire diameter change doesn't do anything. It is fixed to the .0028 size for 42.
You can change the wire diameter, but it doesn't change the resulting data.
You can however change the wire size from 42 to 43, 44, etc.
That function does change the wire size parameters.

T