Pickup magnets touching springs

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Pickup magnets touching springs

Postby TDR1138 » Mon Jan 15, 2018 2:01 pm

I came across some Fralin P pickups in a trade and was going to put them in my LB-100 (the only split P bass I have at the moment), and was wondering about the mounting.

The stock LB-100 (older model with the Gotoh pickup) has springs affixed to the body, two per pickup half, that contact a brass baseplate that is permanently mounted to the bottom of each pickup. The Fralin pickup does not have such a baseplate; the magnets are exposed at the bottom.

Installing the Fralins without making any other adjustment to the bass would mean that the magnets on the pickups would be in contact with the springs. Not sure if this is an issue I should be concerned about or not. My initial reaction was to isolate the magnets somehow (foam or whatever), but then I got to thinking that the springs are in direct contact with the baseplate on the Gotohs, and I can't tell if there's anything isolating the baseplate from the magnets, so I'm wondering if I'm worrying for no reason. The springs do not appear to be grounded to anything in the body; just fixed to the wood, so I'm thinking it wouldn't be an issue.

Just wanted to get thoughts from the brain trust. Thanks.
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Re: Pickup magnets touching springs

Postby Ken Baker » Mon Jan 15, 2018 3:13 pm

I haven't seen the baseplate of the Gotohs. Are they solid brass or brass plated steel (or iron)? If solid brass, then any transmission of the magnetic field(s) would be through the brass but not affected (much) by the brass because, depending on the alloy, brass is non-ferrous. If plated, then the ferrous baseplates, even with a brass plating, will have a notable effect on the overall magnetic field. Having said all that, consider that the springs have relatively little mass compared to the baseplate and so would have relatively little effect on the magnetic field.

--so--

If'n it were me, I'd try the springs as-is and see what happens. Chances are you won't notice a thing odd. If things do seem wonky or you want to experiment, replace the springs with foam weatherstrip.

Ken...
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Re: Pickup magnets touching springs

Postby TDR1138 » Mon Jan 15, 2018 3:26 pm

Ken Baker wrote:I haven't seen the baseplate of the Gotohs. Are they solid brass or brass plated steel (or iron)? If solid brass, then any transmission of the magnetic field(s) would be through the brass but not affected (much) by the brass because, depending on the alloy, brass is non-ferrous. If plated, then the ferrous baseplates, even with a brass plating, will have a notable effect on the overall magnetic field. Having said all that, consider that the springs have relatively little mass compared to the baseplate and so would have relatively little effect on the magnetic field.


Metallurgy is not my strong suit. I'm just guessing it was brass. But I'll try and get a picture when I open it up.

Ken Baker wrote:If'n it were me, I'd try the springs as-is and see what happens. Chances are you won't notice a thing odd. If things do seem wonky or you want to experiment, replace the springs with foam weatherstrip.


Thanks for the input. That's what I was thinking I'd do. We'll see what happens...
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Re: Pickup magnets touching springs

Postby jim.i » Tue Jan 16, 2018 8:14 am

Subscribed...i may want to replace the pickup in my [fairly recent] LB-100...don't yet know what i will find underneath the pickups...
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Re: Pickup magnets touching springs

Postby TDR1138 » Wed Jan 17, 2018 9:02 am

So, had a spare 20 minutes this morning to swap the pickups out.

Here's the old pickups on the way out...

Gotoh.jpeg
Gotoh.jpeg (95.62 KiB) Viewed 621 times


(Sorry for the inverted photo. No matter what I do, I can't get it to upload the right way.)

You can see the springs and the baseplates on the pickups.

New pickups went in quickly and easily. I did not insulate them or anything. Just had a few minutes to test through a practice amp as I tuned it up, so I can't comment really on tone or anything. I was getting some crazy hum when not touching the strings. Didn't have time to try and isolate the problem yet, but I'll take a pass at it this evening or in the next few days. I don't think my house is well grounded and the cable I used was definitely not a high quality one, so there's always that. I don't remember having this issue before the swap, though, so I'll check the variables and see if I knocked the ground wire loose or anything when I get time. But I have a feeling that I should/will probably just order some copper tape and have a good ol' fashioned grounding party sooner than later.
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Re: Pickup magnets touching springs

Postby jim.i » Wed Jan 17, 2018 10:12 am

Is that foam inside each spring?
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Re: Pickup magnets touching springs

Postby TDR1138 » Wed Jan 17, 2018 10:17 am

Yeah, a real tiny strip. Guessing it's there to stop vibration or "spring ping" or something, but not sure.
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Re: Pickup magnets touching springs

Postby TDR1138 » Mon Jan 22, 2018 8:37 am

Shielding.jpg
Shielding.jpg (101.54 KiB) Viewed 580 times


Shielding the bass. Haven't tested it yet; I'm doing some work on the neck while it's all apart, so more to come...
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