Eddy Current on Humbucker Pickups

[pablogilberto]

I'm thinking about this.

The metal parts in a humbucker pickups causes Eddy Current due to their permeability and conductivity.
This causes shifts in resonant peak, peak amplitude and quality factor.

If this is the case, why don't we just use plastic or wooden parts for the baseplates, spacers, metal covers and other parts?
Or maybe use some coating to make the metal parts less conductive and permeable?
That way, we will remove the Eddy Current issues.

Is this correct or am I missing something?

Thank you!

[mogeen]

I've done fiber base plates for Humbucker. Didn't make much of a difference but brass does not sound right to me.

[blademaster2]

I think what you are saying is correct - any metal in the vicinity of the modulated magnetic field will suck away some high frequencies from the signal due to eddy currents. I have experienced this myself when adding a metal cover to a pickup, which I subsequently removed because I could hear a sight difference. The different was pretty subtle, however, and it appears that the complete removal of all metal except for the poles themselves would similarly - but subtly - preserve the high frequencies.

I think the accepted response for a particular pickup design must include the effect of whatever metal is there, and perhaps it has the most profound effect when it is closest to the modulated region of the field (nearest the strings), which is why the usual place we see changes made is toward the top where covers can be either non-metal, removed entirely, or slotted metal (which might be due to eddy current losses but I do not have anything to confirm that). Perhaps the difference between metal and non-metal for the pickup base is less pronounced or imperceptible.

Then again, metal is the way we shield against electric-field-induced noise, so removing metal everywhere possible will lead to more noise (note that humbuckers address more of the magnetic-field-induced noise), so it becomes a trade-off. It seems that either way we do it, reducing noise ends up reducing high frequencies in some way.

[pablogilberto]

Jan 8, 2020 10:56:47 GMT -5 mogeen said:

I've done fiber base plates for Humbucker. Didn't make much of a difference but brass does not sound right to me.

Can you share your pickup analysis or measurements?

Thank you!

[stonewall]

There is so much more to consider here than just “metal” parts on a pickup. Different metals have different effects on the magnetic field(s); some are good, some are bad. Eddy currents seem to have become a “buzz word” with people talking about pickups: “no eddy currents”, “get rid of eddy currents”, “eddy currents bad”. But for some reason people don’t seem to realize that eddy currents are how a pickup actually work. Look at the bar trick of dropping a magnet down a copper pipe. A pickup works the same way but instead of the magnet or copper moving, the steel strings move inside the magnetic field that also has copper wire wrapped it. So not all eddy currents are bad; they’re in every pickup. There are bad eddy currents, of course. Those are caused by brass baseplates and covers. The eddy currents caused by brass are like invisible shields that keep the magnetic fields from doing what they want / should be doing. Generally speaking, less expensive pickups use brass baseplates and covers but they’re also machine wound coils so that’s just bad on top of bad. Tele neck pickups also, traditionally, use brass covers... which is why many people think it’s not a great pickup... which is why myself and a few other boutique pickup makers use nickel-silver Tele neck pickup covers. Nickel-silver is what we use for baseplates and covers to reduce the bad eddy currents to a point where the tonal intrusion is unnoticeable. Also, the thinner the nickel-silver, the better; keep in mind that nickel-silver is mostly copper which creates eddy currents. As for the remaining metals in pickups, they’re necessary. Obviously magnets are required, and they’re only metal. But the keeperbar and polepieces are steel and they’re required to transfer the magnetic field from the bar magnet(s) through the center of the coil(s). Eddy currents are not something to be concerned about here; instead, the carbon content changes the ... the amount of magnetic pull it will have by touching a magnet. 1010, 1018, 1022 all sound different because of this. I’m using two or three different grades of steel in each P90 and humbucker I offer. I’m not going to give you the answer to that, as it’s proprietary to my tone but if you’re interested in experimenting, buy twelve of each grade and spend a weekend swapping out polepieces in your humbuckers. You won’t need to take the pickups out of your guitar or even slack the strings to do this. Addiction FX carries all three grades.

I hope this response was informative. I actually created an account to ask a question in the wiring subsection (can you tell I’m new to forums??) but I didn’t want people think I was just a douche asking for free advice with nothing to offer in return. So I found this post in a subsection in my specific expertise and knew I could add to this thread. Hello all, I’m Stonewall.

[ziggystardust723]

Hello,
Late.. but I'm new on this Forum..
- Look at Stratos pickups:
= no Metal, only Rod-Magnets..
- 0n his LP: Jimmy Page pulled off the Cover of his Bridge pu..
> Now, there are many Covers in Plastic..
- Bye, Ziggy (France, 19h14)