Jazzbass 5 string

[Mike Sulzer]

Alnico has an incremental permeability of 3 to 5, so alnico is almost air. Mild steel is more like 2,000. Ceramic is almost exactly 1.00, so it is equivalent to air.

3 to 5 is significant if you are trying to balance hum, if one coil has 3/2 times as many magnet cores.

Remember, with short open cores, the increase in sensitivity to B does not increase linearly with mu, but rather increases less than you might expect when mu gets large.

[David King]

Schwab, I had a customer a decade back who's name was D@vid Schw@nke, I'll bet that's were I picked it up from.
Mike, I can't make head or tail out of what you are saying but I guess it means turns * area is important when different numbers of alnico poles are present.

[Mike Sulzer]

Schwab, I had a customer a decade back who's name was D@vid Schw@nke, I'll bet that's were I picked it up from.
Mike, I can't make head or tail out of what you are saying but I guess it means turns * area is important when different numbers of alnico poles are present.

With air alone, the area turns thing works pretty well as long as the geometry of the two coils you are comparing is not very different.

As Joe wrote above, it is more complicated with iron.

But the other extreme is simple: a toroidal iron core. Now the area of the turn (as opposed to the iron) makes almost no difference because nearly all the flux is confined to the core. It is the area of the core that counts.

Iron cores that partially fill the coil: a mess to analyze. The paths of the flux lines have to change abruptly when they go from iron to air. I do not know of any good way to think of this, you just have to solve the math (as FEMM does).

I do not think you can both cancel hum perfectly (in principle) and get the string outputs the same with a 3-2 pair of coils. You have to go after a reasonable compromise.

[David Schwab]

Schwab, I had a customer a decade back who's name was D@vid Schw@nke

There is a name "Schwabe" as well as variations like "Schwabb", etc.

All Swabian (Schwäbisch) names I guess.

I know very little about my German heritage as it's so distant. All the culture I got growing up was Italian and Irish.

[David King]

Mike, Thanks!
I get it!

As I see it the alnico poles have little to do with an iron core since by definition the lines will go outside the magnets no?

[Mike Sulzer]

Mike, Thanks!
I get it!

As I see it the alnico poles have little to do with an iron core since by definition the lines will go outside the magnets no?

Alnico does respond to an externally applied field, but less so than the steel we work with. So it does tend to "attract" field lines more than a vacuum, but less than steel. Neodymium is even closer to a vacuum in that way. Magnetic materials are complicated, but one could say that Neo has nearly all its internal atomic currents lined up and frozen in place. So it has a very strong permanent magnetic field, but does not respond much to external fields.

[Knarleybass]

I have been trying to make a split coil 5 string jazz bass pickup, with poor results, the A string has a dampend or low output. I have tried winding both coils to the same resistance, also tried winding them with the same amount of turns, flat poles and staggered poles, nothing seems to get that A string up so that it matches the other strings... what am I missing here? I am running out of hair to pull out...

thanks

Howard

[David King]

Hi Howard,
These are notoriously tricky and you'll have to work out of the box to get something that sounds just OK. The two adjacent magnets with opposite polarities are interfering with each other's fields so you either have to over compensate with more powerful magnets in the center or use weaker magnets on the other strings. Another option is to keep all the polarities the same and let 2 strings be out of phase with the others. You can try to angle the coils so that there's more distance between the opposing poles or even put little steel plates over or under the weak mags in an attempt to buck them up a bit. Let us know what you figure out.

[Achiles]

Check the polarity of both pole pieces and A string quality.

[big_teee]

I agree with David.
The two reverse polarized string magnets in the middle of the pickup are close together, causing the conflict.
That is why fender built the Split P pickup in two pieces.
That way they could get greater separation.
As mentioned, you could have them all the same polarity, all north or all south, with the two halves reverse wired.
You would only have a polarity conflict on two strings when played with the other pickup.
That may not be a big deal either?

T

[rjb]

I agree with David.
The two reverse polarized string magnets in the middle of the pickup are close together, causing the conflict.
That is why fender built the Split P pickup in two pieces.
That way they could get greater separation.

Yup. Agree.

As mentioned, you could have them all the same polarity, all north or all south, with the two halves reverse wired.
You would only have a polarity conflict on two strings when played with the other pickup.
That may not be a big deal either?

Not a deal if you play one pickup at a time (maybe replace 2 volume pots with 2-position selector switch + master volume?)
Big deal if you play both pickups at the same time.
Out-of-phase pickups nearly cancel low frequencies (because space between pickups is small compared to wavelength, so signals are nearly 180 degrees out of phase).
(If the parts in parenthesis are too nerdly for you, ignore them.)

[big_teee]

Just thinking out loud?
When I did some of these experiments.
As long as both pickups are fed both north or both south?
The best I can remember, the second half of the pickup didn't seem to care?
example.
Neck N/S R/W split P
Bridge N/N R/W split J.
If you experiment with this please report back with results.
Thanks,
T

[rjb]

The best I can remember, the second half of the pickup didn't seem to care?

Hunh.

[Knarleybass]

Thanks for the suggestions, i'll get back to you...