Is there some "conventional wisdom" wrt J-Bass & P-Bass magnet diameters?

[kayakerca]

A local guitar tech that I deal with wants me to wind him a J-Bass bridge and a P-Bass neck, both with custom string spacing, for his personal 6 string bass he made. The bass currently has a set of Bartolini 6 string soap bars, but the magnets do not extend far enough to provide sufficient power for the treble string. This is a total one-off, so I'm looking to hit the target first shot.

Is there any conventional wisdom that goes along with magnet diameter for bass guitars? .187" vs .195" Alnicos. He wants to use .195" - A5 double magnets for each string location (.195" - A5's because he has some kicking around). I was concerned that with a pair of the larger .195" - A'5s per string combined with the reduced wire on top of each (reduced thickness of the wind because of the much wider pickup for the same amount of wire) might have some "non-conventional/non desirable" impact on tone. Thoughts?

[big_teee]

Since he has soapbar routes, I would build something in a soapbar cover.
Either a Humbucker, Sidewinder, or Multi-Coil.
T

[David King]

I would make them split 3 + 3 humbuckers. I think Fender used the .195"(5mm) magnets early on before switching to the .1875". I doubt it makes much of a difference. What's your string spacing? If you do the splits try to make as much room for wire on the bobbins as possible so you can stick with 42AWG. I compensate for the losses at the split by using A5s for the A and D strings and dropping to A4s or A2s for the others. That can make a really nicely balanced set.

[kayakerca]

I would make them split 3 + 3 humbuckers. I think Fender used the .195"(5mm) magnets early on before switching to the .1875". I doubt it makes much of a difference. What's your string spacing? If you do the splits try to make as much room for wire on the bobbins as possible so you can stick with 42AWG. I compensate for the losses at the split by using A5s for the A and D strings and dropping to A4s or A2s for the others. That can make a really nicely balanced set.

String space at the bridge location is 3.558" and at the neck position it's 3.410".

Edit of OP....................

Correction, the existing were Wilkinson not Bartolini.

[David King]

With the bridge I calculate you only have .131" of winding depth available at the split if you use .260 magnet spacing and .187 magnets.
At the neck 3.4/5= .680" - .260-.187=.233/2= .115". If you managed a perfectly even wind you could only get about 7000 turns on a .5" tall bobbin space. With a .6" tall bobbin space you can hit 8500 with a good machine wind and 42SPN.
With 43 you should be able to hit 10K turns no problem.

So use the thinner forbon and push it out to the ends of the magnets. Moving your magnet pairs in so that they almost touch (.2" center to center) will gain you .030" of depth which is more than enough for a safety factor or another 1500 turns.

[big_teee]

To add to what david just said.
If you go to single 5/16", .312" diameter magnets, you can put them in the center of the 2 .187" magnets.
Thus giving more room on the ends like my 4 string project I have documented here.
That gives more room, and more turns.
T

[David King]

Or stagger them diagonally the way Markku showed us á la Nordstrand. The stagger would also separate the poles a tiny bit more to reduce the cancelling effects. Personally I'd go with a P bass configuration inside those soap bars just to minimize the cancellation.

[kayakerca]

Thanks David. Thanks Terry. You've given me some things to think about.