Advice on LOOOONNNNGGG pickups

[chad h]

So, with some extremely helpful input from expert forum members, I rewound my first J-bass pickup - a small job for a friend. He was so happy, he immediately asked me if I could make pickups for his next custom creation. Of course, I said yes. Then he told me the next custom job is a 10-string bass. I gather these pickups will end up being 6" + long.

I know there are many people here who do this sort of thing for a living, so I'm not looking for recipes or anything. But some general advice of the, "This issue always ends up being tricky" variety would be great.

These are things that struck me immediately as potential problems:

1. A big, long pickup is likely to pose greater physical difficulties in winding. I'm hoping my sewing-machine motor winder will do the job.

2. Off-the shelf parts don't exist for these things. The luthier said he'd happily make the bobbin, and is intent on doing his own custom work for the covers. But even things as simple as bar magnets won't come in the ideal size. At this stage, I'm imagining the length will enable us to use two bar magnets end-to-end in place of a single bar magnet.

3. There's obviously some experimentation that will be required to find the appropriate number of turns and the appropriate wire gauge for the job. But that's really just busy work.

It seems I'll have quite a lot of freedom with regards to the style of pickup. The luthier imagined that either a J-bass style arrangement, or using dual coil/humbuckers would be fine. And, at least conceptually, these are both designs I can wrap my head around. There's some appeal to using rails, though, but I don't really know in which designs the unusual length of the pickup will pose the biggest problems.

Any insights will be gratefully received.

[rjb]

I'm definitely not an expert- but here's an untested semi-wacky idea using off-the-shelf parts:

- At your hardware store, find a 6" bar of low-carbon steel to use as a central rail.
- From Mojotone, order 2 sets of 3" rail bobbins with matching ceramic magnet rails.
(For part IDs, refer to the recent thread on Soapbar Bass Pickups.)
- Wind both bobbins identically (same direction, same magnetic orientation).
- Wire the bobbins in series.
- Face the bobbins into the steel rail in offset configuration (e.g. one from top-left, one from bottom-right).

So, you'll have something vaguely like a PBass pickup- but with sidewinder coils and a central steel rail.
Or like a Gibson mudbucker with half a coil on each side....

With this configuration, I think you'll get less "subtracting mutual inductance" (is that the right term?)
than with a normal sidewinder- so will require fewer turns per coil.

But, as I said, I'm definitely not an expert.

-rb


ps- If the steel blade is exposed, I suppose you'll want to plate it. But it doesn't have to be exposed.
pps- You may also want to ground that blade. And, of course, I've ignored a ton of pesky assembly details.

[Mark Hammer]

Seems to me that the principal challenge here is one of maintaining appropriate wire tension. Turns always fit snugly at the ends of the coil, when pressed up against the polepieces. But they bulge out at the middle, where there is no pivot point. And the longer that "middle part" is, the bigger a challenge finding the right winding tension can be.

In a perfect world, the polepieces at the highest and lowest strings would be a little bit slimmer than those in the middle strings, such that polepieces in the centre of the coil would provide the luxury of a pivot point, albeit not quite as sharp a turn, but better than nothing.

Ultimately, I suspect that slowing down winding speed will play a big role in this.

[Mike Sulzer]

If winding a such a long single coil is difficult, why wind a single coil?

You might upset the balance of power between strings by using larger pole pieces. I suppose that you could taper the center piece of the bobbin so that it is thicker in the middle, possibly combined with a slight increase in pole piece diameter.

Seems to me that the principal challenge here is one of maintaining appropriate wire tension. Turns always fit snugly at the ends of the coil, when pressed up against the polepieces. But they bulge out at the middle, where there is no pivot point. And the longer that "middle part" is, the bigger a challenge finding the right winding tension can be.

In a perfect world, the polepieces at the highest and lowest strings would be a little bit slimmer than those in the middle strings, such that polepieces in the centre of the coil would provide the luxury of a pivot point, albeit not quite as sharp a turn, but better than nothing.

Ultimately, I suspect that slowing down winding speed will play a big role in this.

[Mark Hammer]

Alternatively, just stagger same-diameter pole pieces along the horizontal plane a little, such that this one sticks out a little more neckwards, and that one sticks out a little more bridgewards, so as to provide some additional pivot points to reduce the mid coil slack a bit.

[rjb]

If winding a such a long single coil is difficult, why wind a single coil?

Why, indeed? That's why I proposed a scheme that uses two 3" bobbins rather than one 6" bobbin, and seems relatively easy to assemble.*

Another scheme would be to wind 2 JBass style pickups RWRP, and mount them offset like PBass pickups.

If you want short coils, you could go whole-hog and make a pickup with 10 or 20 round coils- one around each polepiece.
Some forum members have made Wal clones- you can "just" take that design and extrapolate it for 10 strings.

* One obvious flaw with my initial KISS design is lack of a way to adjust volume balance between strings-
other than filing the top of the blade, like some Charlie Christian pickups.


EDIT:
Then again, you may find winding a long coil less difficult than you fear:

I have made several 18 inch long blade pickups I call "knuckle busters"- sewing machine motor had no problems

But then again again, Jason is a very experienced builder....


EDIT2:
If you haven't already, try Googling 10-string bass and check out what others have done.
I've seen several offset coil designs and one long modified pedal steel pickup.

[big_teee]

There are several ways to do the long pickup.
You could do a humbucker, by putting two bobbins end to end.
Do the stagger split P humbucker pickup.
Or do a humbucker 2 bobbins end to end and then put the two pair side by side(4 bobbins). Wired either Series-Series, or Series-Parallel.
If you want a sidewinder do like the humbucker above, but layed side ways, with a single blade in the middle, with 2 pairs of bobbins, wired in series, (4 bobbins).
Lots of options there.
GL,
T

[chad h]

I appreciate everyone's insights.

I'm getting the sense here that most people would be worried that they simply couldn't wind a straight, 6" long bobbin without having the middle of the coil sag.

Two clear solutions to this:
1) winding multiple coils to deal with different sets of strings. This potentially has the advantage of allowing hum cancellation. I thought RB's initial suggestion (while not hum cancelling) was quite elegant. And using blades, it becomes very versatile as string-spacing issues become irrelevant. It also avoids the problems of putting coils end-to-end, which potentially places significant constraints on the size of your coils, as the "end" of two coils have to fit between the middle strings. (I presume this is why the P-bass uses offset coils).
2) making a single bobbin that doesn't put the poles in a straight line. What I don't know about this idea is what impact this has on the way different strings would be picked up. For example, the poles on the top and bottom strings would have coil directly around them on each side. But the poles on middle strings would have coil only on one side. Would this reduce the output from the middle strings? If so, could I compensate for this by varying the pole height/weight/strength between strings?

Could I make a narrow, diamond-shaped coil, oriented with acute vertices on the top and bottom strings and the obtuse vertices between the 5th and 6th strings, with the bobbin shape formed by blades running along the NW and SE sides? And how do we think it would differ from winding two separate coils, each around a single blade, and then putting them in the same configuration?

[Bruce Johnson]

Chad;

I've built and wound some single coil pickups that were nearly 6" long, and it wasn't really that much of a problem. Obviously, your winder has to have a big enough diameter face plate and spin clearance. And you need to keep the RPM's down to minimize the centrifugal loads. But the wire will lay down reasonably well on the long straight sides. The bundles will be kind of loose, so you have to be careful handling the bobbin, and get it securely potted and wrapped to keep it all in place. My bobbins used normal 3/16" A5 rod magnets as the poles, all in a long line. The pickups worked fine.

[rjb]

I thought RB's initial suggestion (while not hum cancelling) was quite elegant.

Thanks, Chad.
Um, that suggestion was meant to be (mostly) hum cancelling.
It uses two counter-wound coils mounted on parallel planes- although not aligned like "normal" sidewinders.
Not to hijack the thread, but does anyone see a reason this wouldn't work?

-rb

[chad h]

Hi RB -

Thanks, Chad.
Um, that suggestion was meant to be (mostly) hum cancelling.
It uses two counter-wound coils mounted on parallel planes- although not aligned like "normal" sidewinders.
Not to hijack the thread, but does anyone see a reason this wouldn't work?

-rb

In your earlier post, you suggested

- Wind both bobbins identically (same direction, same magnetic orientation).

I must be missing something, as I don't understand how your pickup would cancel hum.

Chad

[rjb]

I must be missing something, as I don't understand how your pickup would cancel hum.

Same way as a "normal" sidebucker.
It's a little confusing, but it's right.

A thought experiment:
Wind 2 coils, both CW from Start to Finish.
With both coils facing "up" (or "toward you", whatever you choose that to mean), wire them in series;
that is, connect Finish of the "1st" coil to Start of the "2nd" coil.
Now flip the 2nd coil over so it is facing away from you.
Now trace the path from the Start of the 1st coil to the Finish of the 2nd coil.

[chad h]

Gotcha!

The term "sidebucker" doesn't mean much to me though. I hadn't realized that you were pointing the "tops" of the coils towards the center, so they were pointing at each other. But now it makes perfect sense. Thanks.

[Rick Turner]

And the reason for not simply trying to wind a long coil is?

I'm seeing solutions to problems that may not exist. I would make the flat work so I could tie some #34 wire around the bulk of the coil in a few places in the middle of each long run. My first pickups were done like this without bobbins. I had coil flanges and laid in about eight lengths of wire...something like wire-wrap wire...that I could just tie off. Then I'd pop the flanges off, and pull the coil off of the center former. No problem. You can also then curve the coil to match a fingerboard radius.

[Bruce Johnson]

That's my experience too. It wasn't a big deal to make those long custom single coil bass pickups. Other than the larger diameter faceplate and the custom bobbins, construction wasn't really any different from a standard Fender-style bass pickup. Plastic flatwork, rod magnets, wind & pot. And the results were quite predictable, based the usual magnets, turns, and DCR. I don't remember the specs offhand.

This particular project was a custom 7-string bass, but with unusually wide string spacing. The customer had huge hands. It was a classic Jazz setup with two long single coil pickups with slightly different pole spacing. They were wound RWRP, and wired to be a humbucking pair when used together. I stayed close to a mild Jazz pickup in the formula. The bass had a slight fingerboard radius, so I staggered the rod magnets a bit in the bobbins to match. It worked right the first time. He was very happy with the bass overall and with the sound of the pickups.

On a one-off custom job, keep it simple. The more complicated you make it, the more experimenting you'll have to do. And R & D never pays off on one-off custom jobs.