Copper shielding & eddy currents

[fieldwrangler]

Folks -

So, in an effort to shield the inside of some closed plastic 'bucker covers I'm thinking about one wind along the sides (without closing the circle) and one strip across the top (connected at one end to the surrounding side wrap.) Does this seem like The Thing to Do?

The coils are sitting in the conventional orientation.

Bob Palmieri

[LtKojak]

Now that you mention it... I've seen Duncan p'ups come with the copper stripe in both bobbins soldered to ground. Stew-Mac single coils are shielded too.

What I'm interested in, is to see HOW you attach those plastic covers to the baseplate, as I haven't been able to come up with any idea... are you epoxying'em or how you attach'em to the nickelsilver baseplate?

I've been interested in doing'em for a long time, but never got myself together. Maybe your post is the push I needed to get off my lazy rump...?

[David Schwab]

What I'm interested in, is to see HOW you attach those plastic covers to the baseplate, as I haven't been able to come up with any idea... are you epoxying'em or how you attach'em to the nickelsilver baseplate?

There's two types of plastic covers. The ones I use don't need a baseplate, but you have to epoxy the pickup into the cover.



As far as shielding, I totally enclose the pickup.

[CRU JONES]

Folks -

So, in an effort to shield the inside of some closed plastic 'bucker covers I'm thinking about one wind along the sides (without closing the circle) and one strip across the top (connected at one end to the surrounding side wrap.) Does this seem like The Thing to Do?

The coils are sitting in the conventional orientation.

Bob Palmieri

I used to work CAD/CAM processing at a circuit board company, so I sent flatwork designs to the router for my experimentation. I used bare, single sided, and double sided copper clad circuit board. There is a slight difference in measurements. Especially when it came to the double sided. The capacitance increased a bit using double sided as the windings were directly laying on a ground. Once the copper layer was 0.062" away from the windings that effect seemed to be lost. I didn't get much losses do to eddy currents in any of the cases. I think the copper is too thin to cause much losses. I really didn't hear any difference. I was slightly disappointed as I was hoping an elaborate "eddy loss pattern" would possibly lead me down a path to "auditory nirvana".

I don't know how thick your copper tape is though...

I think you are safe to shield with tape as you describe. Hook up your inductance meter and then put the cap on. The reduction in inductance will tell you how much eddy losses you are experiencing. As far as adding capacitance... I don't think it will be much based on my experience. Measure resonant frequency before and after, maybe?

Ethan

[fieldwrangler]

Thanks Ethan!

I'll report back.

[David King]

I sprayed MG Nickel conductive paint inside a stack of Jazz bass covers and it totally killed the treble, I thought at first I was getting eddy losses but when I sliced through the corners it made no difference. It turned out to be the magnetic field disruptions from that nickel right on top of the magnet poles, I scraped the paint off and all my treble came back.

[fieldwrangler]

I sprayed MG Nickel conductive paint inside a stack of Jazz bass covers and it totally killed the treble, I thought at first I was getting eddy losses but when I sliced through the corners it made no difference. It turned out to be the magnetic field disruptions from that nickel right on top of the magnet poles, I scraped the paint off and all my treble came back.

Sounds like it might also have been associated with an electrical connection to the conductive alnico poles plus capacitance between the rods & windings, especially if the inner winds were connected to the hot lead.

Bob Palmieri