J-bass 8-pole pickup magnet orientation- created 03-11-2008

Simpson, John - 03/11/2008.14:03:59

I'm sitting here looking at the parts to make me a couple bass pickups--and it occurs to me that I don't know the answer to a simple and basic question. On a single-coil J-bass style pickup with eight magnets, are all the magnets pointed the same way? It seems like they oughta, but then I've never known why they put eight magnets in there anyway except maybe to make response equalizing easier and to give it more oomph. Anyway, is north always the same direction

All 8 magnets are oriented the same. However, when you have two pickups, the other pickup should have the opposite magnetic polarity, and be wound in the opposite direction, so that they be humbucking when used together

Thanks much, Mark.

>but then I've never known why they put eight magnets in there anyway except maybe to ...

They have two per string. The original single coil P bass pickup had four magnets. Supposedly the double poles per string soften the attack a bit, since the string isn't right over the magnet, which helped with the early amps breaking up, and also it gives a wider field around each string

Well hell, I like my bass kinda attacky. Thanks, David

I just wound my first set of J pickups the other day. If you are using a 42AWG with double insulation build you need to really watch how the wire goes on as there isn't much room to spare. Stay away from the edges once you get past the 3/4 mark, you don't want stray windings getting sheared off on the edge of the Forbon as you're sliding the cover on and off. What this means is to build a very slight hump in the middle at the end.

My coils were a wee bit shorter as I was working around a slightly narrower (3/4") string spacing and I had to pile on 10500 turns to break the 8k ohms DCR.

Also be careful not to let the first few hundred turns short out against the magnets. I had to wrap the magnets with polymide tape to keep that from happening.

Lastly I'd recommend that you keep an extra wrap or two of the start wire handy outside of the coil in case your soldering doesn't work the first couple of times. My insulation was nearly impossible to strip off w/o breaking the wire. I used 1200 grit sandpaper and that finally worked.

Sounds like you did a good job, David! Winding is fun. I don't know about polymide tape, but teflon tape works OK to insulate the magnets.

>Well hell, I like my bass kinda attacky.

Me too, which is why I use blades. But those pickups are from a different time. bass was expected to me politely in the background and not over driving amps. <g>

>If you are using a 42AWG with double insulation build you need to really watch how the wire goes on as there isn't much room to spare.

I think they used single build formvar on Jazz basses. I seem to remember them winding about 6800 turns too, but with the double build you would want more to bring up the low end. I'm about to pick up some heavy build formvar to try out.

Did you try the pickups out yet? <g>

David K.,

David S.,

Thanks all.

I've never played a Jazz bass that didn't rip the roof off on the back pickup so I don't think the 2 poles per string in any way mellowed out the tone. That said, I've never played a '51 P bass with the single poles to compare

I wouldn't say the double poles mellow the tone, but I've read a bunch of times it was done to soften the attack, which was making the amp break up.

If you think about it, it's like moving the magnet away from the string, since it's not directly under it.

The other thing I've read a few times is it was done to accommodate the wider string motion.

I like to tape up my coils before putting tight covers on.

So David,

That's an interesting question for bass since it's mute for a guitar (guitarists seem to like distortion. )

I buy that the wider magnetic field of double poles is better for wider string excursion on a bass but I'd love to see a plot of the wave shapes for comparison.

Tape is pretty handy stuff.

You're certainly going to get a different shape field under the string. If you get enough poles distributed under the strings, you more-or-less have a blade type of thing going on. Blades do have a different tone from poles usually described as 'smoother" sounding. My first prototype of my current bass pickup design had two poles per string, but closer together than a Jazz pickup. I think I can hear a slight difference between that pickup, and the next one I made with blades, but it's hard to say what the difference is.

I think the initial attack might be stronger with a pole right under the string- just because the field is more concentrated- and it's very short in duration.

But that's not based on anything... just my very unscientific gut feeling. But it reminds me of Music Man bass pickups with those big poles. I once had a prototype MM bass in my shop that had a pickup case without the usual poles showing. When I took the pickup out of the bass I saw it had Jazz bass style dual poles. That's the only one I ever saw like that.

[edit] I just looked up patent # 5148733, which is for the Duncan Parallel Axis bobbins. Kevin Beller states in the patent that the dual poles under the strings creates "a magnetic flux pattern which minimizes the magnetic flux intensity in the area in which said string vibrates."

Interestingly, the patent talks about lessening the flux field as to improve the string's tone by minimizing the interference from the magnet. I had assumed the Parallel Axis trembucker was originally designed back when dive bombing was all the rage, and with a Floyd equipped guitar, you could push the strings down until they stuck on the pickup's poles! So having that gap there might minimize that.

I made some jazz bass pickups last year using heavy formvar (the stuff that David S. is looking at getting) and they're wound to the point where they're starting to lose highs (same deal with a couple of sets of strat pickups I made, but these sound really nice through a Fender amp). I cleared the 8K mark and the bridge is around 9K, wound with medium to tight tension. I'll be taking those down to see how I go.

The SPN sets I made were nice and the poly wasn't too bad at all. I'm currently experimenting with a spool of plain enamel and the set I made are on the bright side, so a little more work there.

I've been using poly, generally 42 and 43 gauge, single build. I also have a roll of 45 heavy build.

I think the original Fender pickups used Formvar, but single build. Heavy build is supposed to be brighter, due to reduced capacitance. But once your get past a certain point you are going to lose highs, unless you go with a different magnet, like ceramic or neo. Putting more juice into the pickup helps the impeded highs.

The notes I have on Jazz Bass pickups is the originals had 7,800 turns, and was 6.8K for the neck. Bridge pickup is longer, so it has higher DC resistance. Neck pickup usually north up, bridge pickup south up. They potted them in lacquer.

Interesting notes on the Jazz Bass pickups. The info I have differs in the turns and resistance, so looks like differences in wire. Where did you source the info for the turns and wire guage? There was talk out there that they used hf for the early JB's but the ones I've seen weren't.

I haven't potted the JB pickups I made, so I know they're way overwound for what I'm after. It should be interesting to listen to the results as I remove layers to get there.

>Where did you source the info for the turns and wire gauge?

Seymour Duncan.