Reference post: Bisonic hack

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This is a technical thread for historical purposes. If you have no interest in bass, or in re-engineering pickups, please do not posts veers.
Thank you

Lunginsam had a Bisonic that had been dropped and had shattered. As it wasn't more than a paperweight, I volunteered to repair it. Having not actually seen one in the wild before, I cut a piece of self-adhesive pickguard material and used a filler piece of another abs plastic.

 

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I wasn't happy with that. There wasn't enough space to replace the stock surround that broke, and the fabricated surround wasn't strong enough, in my judgement.
Another issue was one magnet had broken loose from the bobbin. The yellow glue was brittle, and didn't adhere well to either the bobbin, or the magnet.

 

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I scraped it off with a fingernail.

 

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Before I knew it, the other magnet, uh, fell off.

 

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While trying to figure out how in blazes Guild held the pickup together, I noticed that there was a ground connection to the metal face of the pickup. Really? That is the only shielding in a single coil bass amp? That started bugging me.

Did I mention that I had no idea how these pups were made?

 

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Ok, this sucker is broken, let's break it until it works!

There are a number of difficulties with shielding a Bisonic. The pole piece side of the pickup mounting is very thin, the mounting itself is very shallow, and the adjusters for the pole pieces take up a lot of room. Additionally, the pickup mounting ring is oval, reducing the room I had to work with.
I tried making a em shield, using some copper I use for shielding amp cabs.

 

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This turned out to be unsatisfactory for a couple of reasons, and potentially adding a mechanically induced "flutter" to the signal because there was no good way of securing it to the pickup. Bending aluminum to form a backplate was also problematic, due to the tight confines of the mounting ring.

I made the spacer to mount the pickup to the shell out of the thinnest and purtiest stuff I had.

 

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I didn't take any pictures of this part.
I fabricated a mount so I could fit the pickup into the metal shell. Looking at that, I was struck again by how little shielding there was. I was also not happy with the flexibility of the mount I had made as it's really no better than stock. I had some aluminum tape on the table and I thought, this might actually work as a structural element"
I lined it up with the "domino" on the face of the Bisonic and wrapped it around the bobbin where it would not visible. This had the benefit of stiffening up the surround that I had constructed and made this a more solid unit.
Since it was also an EM shield, I figured that, a metal backplate being out of the question, I could just wrap the tape over and create a shield on the back of the pickup. So I took the adjusters and the pole pieces out, cut holes somewhat crudely, for the adjusters and the pole pieces to go through, and wrapped the rest of the pickup.
In retrospect, I should have ordered copper shielding tape because it is conductive on both sides. The aluminum tape I was using was not conductive, so I had to create ground points in the foil. This had the result of making the pickup look roughly like the tin Man from the wizard of Oz, but I checked continuity with my meter and the pickup was safely shielded.
The only unshielded part of the pickup is the face. It's about as good as it can get for a single coil pickup.
Having decided that I would solve a problem that nobody asked me to solve, I looked at mounting the pickup itself. This is the third time I've mentioned that I had no idea how these things go together, so I won't bring it up. But looking at the metal shell, the only mechanical connection I could see, was the ground wire to the metal surround via one solder joint. I fit the pickup back into the metal ring and tried silicone as an adhesive. It would not adhere to the metal ring. So I did a little internet research,remembering the black rubbery coating that covers the terminals of the HB-1 and anti-hum reissues. I went through a number of products, and finally decided on using the Permatex brand.
I finally decided on Permatex gray as it promised the most mechanical strength. Using this material, I ran a bead around the top of the plastic pickup mount around the bobbin. When hardened it provided a very acceptable level of adhesion to the metal pickup ring and the pickup itself. These items are not bonded together from the factory. They're just loose. So I've again solved a problem that nobody asked me to solve.

 

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Yes, it's wearing a tinfoil raincoat.
I learned a few things about the construction of this pickup. For one thing, do not attempt to solder to the terminals that the ground and the signal lead are soldered to. The plastic will melt almost immediately. If you use shielded cable (and you should ) strip insulation from existing leads and solder on to them. Speaking of which, I had two conductor, foil grounded wire on hand, so that is what I used. I much prefer foil over braid as a shield, because it comes with a separate, uninsulated lead. Ive bought wire in the past and have been disappointed in the density of the braid.
Having soldered the shielded wire in place of the stock leads, I secured the cable with a bit of metal tape. At least, I think I did. Typing makes my head hurt.
In any case, I was able to get it back to 'sam after a somewhat ridiculous length of time.

"You want me to use gasket in a tube from an auto parts store???"

Using Permatex Gray will secure the pickup to the metal ring, and kill two birds with one stone, i.e. make the pickup mechanically stronger, and eliminate any potential buzzing with a loose surround.

"Why tape??? It's going to suck if I get it rewound!!!!"
It's the best way I could come up with. The tape does come off, but something tells me you're going to spring for a Novak anyway. The tape does come off, the Permatex does peal off with a knife point. Within the limitations of the pickup design, I had little other options. If I were an engineer, I would make half a dozen changes to the design to make it "better", but, I'm not.

I hope this helps Newark Street Starfire bassists with any noise issues they might face. Happy thumping!

 

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Thanks to frono for wearing the duck costume!

Done, comment away!

 

[lungimsam]

When I got it back I put it in my then shielded Starfire bass and there was total silence except for when I played notes. No RF or AC hum was heard anymore. Pickup is now better than Guild made it. They could learn a thing or two from Default.
The pickup is still going to be used in my Starfire after I finish modding it (the Starfire) with a neck Bisonic and v/blend/tone harness. I call this Bisonic that Default overhauled the “Silversonic” since it is all silvery looking now.

 

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Well, it beats "tinfoil hat" as a descriptor!