Using Copper clad board for flatwork.

[Mark Hammer]

Soem folks have had success employing PCB material for flatwork. I'll be attempting to do so myself, shortly. Assuming it is single-sided copper clad board, which side ought to go on the "outside" (i.e., away from the coil itself): the copper or the fibreglass part?

I'm quite open to choices made on the basis of any consideration: avoiding wire snags, inductance concerns, shielding concerns, etc.

[Dave Kerr]

I'd put the copper on the outside for no reason other than to protect against a short just in case you have an outside winding with a nick in the insulation.

[Mark Hammer]

I like your thinking. Thanks.

I was thinking as well that at least the bottom piece should have the copper on the outside such that one could etch the piece beforehand to mimic having solder rivets.

[Joe Gwinn]

Some folks have had success employing PCB material for flatwork. I'll be attempting to do so myself, shortly. Assuming it is single-sided copper clad board, which side ought to go on the "outside" (i.e., away from the coil itself): the copper or the fibreglass part?

Double-sided boards are pretty cheap, so why decide? Etch the copper away from the coil areas, so there is no possibility of snagging the wire on the rough edges of the etched foil, and use plated vias and pads in place of the traditional brass-rivet terminals.

Another reason to keep the copper well away from the winding is to reduce coil self-capacitance.

Another trick: drill through holes near the terminal vias, and thread the leads through these holes, then solder the wire to the vias. This acts as a strain relief for the wire leads, greatly reducing the incidence of solder joint breakage.

[Mark Hammer]

Good advice. I tend to have single-sided only, so there is less to etch away.

I like the strain relief suggestions and will definitely follow up on that. I may also etch some additional pads for actual coil-tapping at different points along the coil.

At one point (I think it was daydreaming during a very long drive), I was contemplating making a sort of "universal dummy coil" that would have multiple tap points on it. Etching pads for them on a PCB bottom would assist in that endeavour.

[David Schwab]

I made this stacked tele bridge pickup with double sided copper clad board. It was hand shaped so it's a little crude.

[Rick Turner]

A cut line through the copper would prevent the shielding from being a large shorted turn...

[Mark Hammer]

I'm not sure what you mean. Could you elaborate a bit?

[Dave Kerr]

Rather than an "O" made of copper, cut a narrow slit to make it into sort of a "C".

[salvarsan]

Rather than an "O" made of copper, cut a narrow slit to make it into sort of a "C".

That's what Joe Gwinn spoke of in making cuts perpendicular to the windings direction.

Conceivably, you could make four cuts like the 15 minute marks on a clock face.

[Mark Hammer]

You guys are operating on a different plane than I, here. I'm still not grasping something. Are you talking about organizing the ground plane on the bottom (and maybe top, too) flatwork in some specific strategic fashion?

If so, there's an underlying purpose that is eluding me. I'm not questioning it. I just don't understand or anticipate it.

[FunkyKikuchiyo]

The idea is that you shouldn't be able to "trace" a conductive circle around the coil. It needs to break somewhere. If you can make a circle around the pickup then you get eddy current loading. If you look at David's first picture, you can make a loop around the whole thing - if you broke continuity somewhere to make it a C shape then you couldn't do that. It would of course be all conductive, but only one way. I find myself following it with my finger a lot...

[Mark Hammer]

Okay. Gotcha. Thanks.

[Joe Gwinn]

The idea is that you shouldn't be able to "trace" a conductive circle around the coil. It needs to break somewhere. If you can make a circle around the pickup then you get eddy current loading. If you look at David's first picture, you can make a loop around the whole thing - if you broke continuity somewhere to make it a C shape then you couldn't do that. It would of course be all conductive, but only one way. I find myself following it with my finger a lot...

This is exactly right.

[Mike Sulzer]

You guys are operating on a different plane than I, here. I'm still not grasping something. Are you talking about organizing the ground plane on the bottom (and maybe top, too) flatwork in some specific strategic fashion?

If so, there's an underlying purpose that is eluding me. I'm not questioning it. I just don't understand or anticipate it.

Mark, think of magnetic field lines passing perpendicular through some imaginary flat surface. Draw an imaginary loop in this surface. Now let the magnetic field change in time. This changes the density of the field lines. You can think of field lines crossing the loop if you want. Now the key thing: there is an ac voltage around the loop from the changing field (or crossing lines). Its value depends on the area of the loop, that is, the square of the linear dimensions. Think of it as a bigger loop having more flux lines inside. Now put a conductor where the loop is. A current flows, dissiapting energy and loading whatever circuit is involved. You want this in a transformer; not as much in a pickup.

Now think of a loop containing the most time varying flux flux lines in the field of a pickup. This is one that goes all the way around the pickup, and so it is the one to avoid if you want to minimize the effect. There wil always be smaller loops with smaller voltages around them.

The nest level of understanding of the details of this is to realize that power is proportinal to V^2/R. And also it is important to realize that field lines have a direction, so that one passing through the loop and then "looping" back around and passing back through again has no net effect. That is why a really big loop around the pickup has no effect at all.