Gibson Bass pickup disection

[marku52]

Here is a Gibson bass pickup I was given to examine--Don't yell at me, I didn't break it!
It's kind of like a P bass, but with the 2 coils sharing a common central magnet, which energizes the inner of the 2 (??) pole pieces. Each coil has another, smaller magnet that energizes the outer pole piece.

Thankfully, one coil was not destroyed, here are the measurements, extech, series, 1kHz
L 2.623 H
Q 2.626
RAC 6.120K
RDC 5.117K

The wire looks to be .0018 - .0019", so guessing 44AWG. making a guess at bobbin path length and RDC gives me a guestimate of about 6500 turns.

Large magnet is quite powerful, about 140mT on the pole, dimensions are .200 X .550 X 2.35 "
Smaller magnet is not as powerful, dimensions are .185 X .185 X 1.18 "

Odd things: Why the 2 pole pieces per coil, with an air gap in between? Trying to limit eddy losses? And what is with the grounded copper foil wrapped around the magnet in the center of where each coil contacts the large magnet? If it was an attempt to ground the pole piece, it failed, neither pole piece is grounded or conductive to the other. It will increase the eddy current losses through that magnetic path, contravening the effects of the 2 pole pieces.

What where they thinking? Does anyone know?

[David Schwab]

What bass is that from? Is that from a newer Thunderbird? No wonder they are noisy.

Gibson really doesn't do well designing bass pickups. I have a neck pickup from an SG bass here to rebuild. It looks like a mudbucker, but under the cover are two bobbins from a mini humbucker with steel blades, two ceramic magnets on the bottom, and an aluminum piece on the top to hold the four dummy pole screws! And they put the blades the wrong way into the bobbins, so instead of them being right under the cover they are about 1/8" away front he top of the pickup. It's a dumb design. Also besides the aluminum piece on top, it has a brass baseplate!

The customer complained about how muddy and weak it was.

[marku52]

Wow, that is quite the horror story. How many things can we do wrong in one pickup? I especially appreciate the fake adjustment screws. Nice touch, that.

I don't know what bass that pup is out of, but I have several customers interested in it, saying that it is a nice aggressive pickup, sounds a lot like a good Precision. Just wondering if anyone had any insight to some of its "quirks"...

[marku52]

OK, I've got some feedback that it is probably from about a 1987 Thunderbird re-issue bass.

[David Schwab]

OK, I knew I saw that somewhere before. It's from a recent Tbird. I found these photos on the web (it's a shame people don't know how to use the macro setting on their cameras).
I'm not sure why they used the dual blades. Maybe they thought they couldn't stick two opposing magnets on one blade? The split coil arrangement makes sense if you want a single coil type tone.

[marku52]

Yeah, its a kind of clever architecture, I'll probably build one just to see what it can do.

2 magnets on a single pole? Oh yeah Gibson's never done that before, on maybe like a p90 or a melody maker....Sometimes they amaze me, like those fake adjustment screws. Way to show respect for your customers.

[David Schwab]

Sometimes they amaze me, like those fake adjustment screws. Way to show respect for your customers.

They could have made an updated sidewinder, much like the original, but wound less. But instead they came up with that thing, using parts they had on hand, like the mini bucker bobbins. The blades are T shaped, but they have the T on the bottom where the magnets are, so they don't stick up high enough. It's just weird.

Then there are those noisy T-bird pickups, because obviously the copper tape is not touching the blades. Maybe they foot that ceramic magnets are not conductive?

I mean these are really rudimentary mistakes!

[MrCandy]

They wrap magnet with copper foil to magnet itself 'produce' less spurious frequencies which are peculiar to ceramic magnets.
Since the advent of NIB magnets the use of ceramics has lost all meaning and they can be sent to the dustbin of history.

[marku52]

If I can make a guess at your meaning, "ceramic magnets are wrapped with copper foil to add some eddy current losses, as ceramic magnets by themselves have no such losses, and tend to sound harsh"

Close enough?

[David Schwab]

They wrap magnet with copper foil to magnet itself 'produce' less spurious frequencies which are peculiar to ceramic magnets.
Since the advent of NIB magnets the use of ceramics has lost all meaning and they can be sent to the dustbin of history.

I don't think so. The magnet is clearly not wrapped with foil. They have a piece stuck on it and grounded. This is normal for grounding your blades, but the foil has to extend over and touch the blades.

Also a lot of pickups, especially for bass, still use ceramic magnets. Not too many using neodymium yet. I ground my neo magnets/blades just like this. The neos are usually nickel plated, so it's each to ground them with copper foil.

[big_teee]

I don't think so. The magnet is clearly not wrapped with foil. They have a piece stuck on it and grounded. This is normal for grounding your blades, but the foil has to extend over and touch the blades.

Also a lot of pickups, especially for bass, still use ceramic magnets. Not too many using neodymium yet. I ground my neo magnets/blades just like this. The neos are usually nickel plated, so it's each to ground them with copper foil.

That logic of being in the DustBin depends on if your selling Ceramics, or NEOs, IMO.
David, on the Foil to touch the blades do they do it on the top or the bottom?
B_T

[David Schwab]

David, on the Foil to touch the blades do they do it on the top or the bottom?
B_T

I do it on the bottom where the magnet touches them.

[RedHouse]

it's a shame people don't know how to use the macro setting on their cameras

A-men to that brutha.

[MrCandy]

If I can make a guess at your meaning, "ceramic magnets are wrapped with copper foil to add some eddy current losses, as ceramic magnets by themselves have no such losses, and tend to sound harsh"

Close enough?

That it is. Shorted coil around magnet partly closes high frequency components on itself.
This process goes with evolution of heat,energy conservation has not canceled.

[MrCandy]

That logic of being in the DustBin depends on if your selling Ceramics, or NEOs, IMO.
David, on the Foil to touch the blades do they do it on the top or the bottom?
B_T

All logic is in getting better sound.