Brass and eddy currrents

[David Schwab]

Yes, I'm purposfully oversimplifying the eddy current thing.

As it is for me, I just put a cover on a known good pickup, take a listen, if it's crappy it goes into the crappy parts bin under my bench and I don't buy those ones anymore.

You can try cutting a slit in the cover, up from the open end to the top, to break the closed loop portion of the cover.

Rowe Industries had a patent on that once. Theirs was open on the top though. (see attached)

It should improve the tone, if not the appearance.

Probably way too simple, minimal thought required, but I like to save my remaining brain cells for more important things...dang, where'd those darn wire cutters go...again....

I had three VOM's for a while because I kept misplacing them!

[Mike Sulzer]

You can try cutting a slit in the cover, up from the open end to the top, to break the closed loop portion of the cover.

But that will not help much if most of the effect comes from the top.

[David Schwab]

But that will not help much if most of the effect comes from the top.

Agreed. This is why you see holes in the tops of Filtertron pickups.

Ray Butts wrote in the patent (#2892371):

Additionally, the frequency discrimination effects normally attendant upon the usual enclosing of the electrical pickup components within a metallic shield or casing (due to the shunting effect of currents induced therein) are avoided in the pickups described herein.

It is important to note that the symmetrical arrangement of the coils within the metallic casing 1 formed by the two shielding and enclosing members 5 and 6 eliminates any possible shunting effects of currents induced in the metallic casing, and thus avoids discrimination by the attenuating of the higher frequencies. Any current induced in the casing due to the field of (coil 1) is balanced or cancelled by the equal and out-of-phase current induced by (coil 2).

The top wall (14) of the top (6) of the case is provided with a pair of slots (14a) extending parallel to one another lengthwise of the case in the planes of the rows of pole pieces. A slot (14b) extending between slots (14a) in the top wall (14) constitutes a gap for inhibiting circulating currents in top wall (14) around slots 14a.

So really... metal covers and baseplates are bad if you are concerned about high frequency attenuation. However if you are reproducing a pickup design that used these parts, then you need them for that tone, as long as they are of the correct specs.

People started taking the covers off for a reason. They look cool on certain guitars, and they are sometimes useful if you want a certain tone, but I've never personally liked the way pickups sound with metal covers.

There's no reason you can't design the tone of the pickup to compensate for the cover though.

[Mike Sulzer]

There's no reason you can't design the tone of the pickup to compensate for the cover though.

True, but it might not be so easy! Taking the cover off increases the Q of the resonant circuit, thus increasing the frequency response at and around the peak. It might not be so easy to find another way to do this in a humbucker if you want to keep the cover on.

[RedHouse]

...There's no reason you can't design the tone of the pickup to compensate for the cover though....

I'm definately in the minority on this, but this is exactly what I do. I shoot for cover-on, if the player want's cover-off, well it's his baby.
(usually works out in my favor though)