J-bass bobbins - standard spacing vs. Mojotone spacing

[Rodent]

Just a heads-up on Mojo J-bass bobbins - you NEED to use their covers together with their bobbins, as their pole spacing is narrower than standard exposed J cover spacing.

I now get why they had a disclaimer about their pole spacing on the bobbin flatwork (note that this disclaimer is missing on the assembled bobbin description page)

Top and Bottom flatwork (BLACK) - .093" thick. Vintage spec. The holes fit our .187" diameter magnets. Spacing is 2.29". These fit our covers. No guarantees as to fit in other products.

The covers have this disclaimer

American Fender spacing.

Didn't notice this until recently when I wound a set of coils to replace the stock pickups in a '68 J of my business partner (he's the original owner.) The original plan was to use the original covers with the new coils ... no go. Apparently this '68 J isn't vintage or American

Their bobbin length and width dimensions are good, it's purely the pole piece layout that is different. Because of this, covers from places like AllParts and WD won't work with the Mojo bobbins. Result when using their bobbin and covers is that, with the standard .75" bridge spacing, the strings are not centered between the poles. I'm guessing the person who worked their version had a preference for 18mm string spacing, or was looking to accommodate a range of spacing from 17.5mm to 20mm

I'll load up a CAD image of a standard cover overlaid with the Mojo cover for reference.


The convenience of assembled bobbins is nice to have, I give credit for this. Sadly I may have to look elsewhere for bobbin flatwork if the only way to get standard sized pole spacing is via custom order (and the associated higher pricing)

[Rick Turner]

It's no longer a big deal to get custom CNC laser cut Forbon bobbins made. I have a friend here in town with four (count 'em) Epilog lasers. Check around; it may be cheaper than you think.

[ScottA]

I'd like to get my hands on the dude that decided to do the J bass bridge and neck covers slightly different sizes, with just slightly different enough mounting hole spacings that you can't split the difference.

To me, that means two tooling charges!!!!!!!

ARRRRRGGGHHHHHHH!!!!

BTW, does anyone have a definitive drawing or dimensions for J Bass bridge and neck covers? I haven't found a good one. Would be much appreciated, Thanks.

[Rodent]

here's an image showing the two bridge coil versions overlaid on each other. the difference is not huge, but enough so that the narrower spaced Mojo bobbins won't fit a standard cover. (neck coil dimensional differences are similar)



@Rick - excellent advice, thanks


too bad it's not so easy/economical to get custom covers made

[Rodent]

I'd like to get my hands on the dude that decided to do the J bass bridge and neck covers slightly different sizes, with just slightly different enough mounting hole spacings that you can't split the difference.

My guess is that Leo & Team did this so that it was practically fool-proof to not mix-up the coils during final assembly, making it impossible for someone to put the wrong pickup into a specific cavity. Sure it's a second set of tools to make the bobbins, but it eliminates the need to disassemble and re-install a set of pickups installed opposite of what they should be.

BTW, does anyone have a definitive drawing or dimensions for J Bass bridge and neck covers? I haven't found a good one. Would be much appreciated, Thanks.

No authoritative drawings here at the ranch - just dial caliper work on many different sets of coils and covers to discoverer where there is consistency within reasonable tolerance, and where there is dimensional differences by design (or ?)

[David Schwab]

I'd like to get my hands on the dude that decided to do the J bass bridge and neck covers slightly different sizes, with just slightly different enough mounting hole spacings that you can't split the difference.

To me, that means two tooling charges!!!!!!!

ARRRRRGGGHHHHHHH!!!!

BTW, does anyone have a definitive drawing or dimensions for J Bass bridge and neck covers? I haven't found a good one. Would be much appreciated, Thanks.

It is good that Leo make the pole spacing closer on the neck pickup, unlike the way most pickups are, including Stats and Gibsons. It only made sense to make the mounting screws closer together to keep the over all proportions.

But he obviously didn't envision, or care about people making replacement pickups.

[David Schwab]

here's an image showing the two bridge coil versions overlaid on each other. the difference is not huge, but enough so that the narrower spaced Mojo bobbins won't fit a standard cover.

Well what's a "standard cover"? Mojo doesn't make the covers they sell. And Fender often has slightly different spacings on their pickup and bridges.

The mojo flatwork fits the covers they sell, so I don't see a problem.

[zparts]

Good news is we are getting a wider spacing jazz bass cover made for the bridge pickup that will line up with Fender. Our neck cover lines up. Also the edges will be more rounded. Should be later this Summer when we get them but enough folks have pushed us to having them made this way. The samples I received were fantastic.

[Rick Turner]

Get "no hole" covers and drill 'em. Make a hardened steel drill jig. Not a big deal.

And use zero rake drill bits on plastic, brass, wood, and copper if you're using twist bits. Google "zero rake drill mod".

Or laser them if the plastic doesn't off-gas chlorine...a problem with PVC. It's a no-no around the laser people.

[big_teee]

My answer is always rerout for soapbar humbuckers.
T

[David King]

Pole spacing was always too wide on most J basses for the 19mm string spacing. I see no point in trying to work with other people's new parts anyway. You're bound to be frustrated and limited. Forbon flatwork couldn't be any easier to make than it is already. Dump the hardened steel drilling guide, that's a waste of money and drill bits. Just put an alignment pin in your drill press table and locate your holes that way. I've been using that system for everything for a decade now and it's way more accurate and much easier to generate templates for. Drill presses were designed that way but I've almost never seen them implemented which tells me that no one ever took a shop class in the last 35 years.

[David Schwab]

My answer is always rerout for soapbar humbuckers.
T

Or Jazz pickups with closed covers/blades, like I make. No routing needed.

[big_teee]

Or Jazz pickups with closed covers/blades, like I make. No routing needed.

Would you please share a little more info, don't just tease us!
T

[David Schwab]

Would you please share a little more info, don't just tease us!
T

I make Jazz pickups like this:



But you can also do single coils, and use an alnico bar magnet as a blade, or a steel blade with magnets under the pickup like a P-90.

I gave up on pole pieces shortly after I started making pickups because there are too many different string spacings, even on just Fender Jazz basses.

The Mojo soapbar bobbins fit into Jazz covers.

[big_teee]

Thank you!
I was thinking of using 2 humbucker magnet bars, and glue a top and bottom flange on them.
I think they would be to fat.
In your diagram, looks like 2 of the small blade bobbins glued together on a longer blade.
I thought of that also, but the half round bobbins I have are too fat and would have to be trimmed.
Still if you have a router, it would be easy enough to install a soapbar rout, especially in my cheap imports.
Thanks, for sharing.
Like you say, there are options, if you want to get away from rod magnets, and away from single coils.
T