Pickup Magnet - Affects "Output" and/or DC Resistance?

[ChrisN]

Assume I'm an electrical neophyte.

I changed the A5 magnet in my 498T to an A2 in order to cut some of the difference from the neck's 490R. I like the sound much better, easier to match on the amp, etc.

Today I measured DC resistance in my pickups (not done it before, but guitar believed to have stock/original pickup) and found that the 490R measured where it should at 7.67k, but the post-magnet change 498T, which I understand should measure around 14.7k, measures 7.58k, below the 490R with its A2 magnet.

Question - is the magnet change from A5 to A2 responsible for the DC resistance change by almost 50%?

I've seen commentary both ways, with some saying the resistance comes from the number of winds, thickness of wire, etc., not the magnet - "you could take the magnet completely out and still have the same DC resistance", and others saying "of course changing the magnet changes the resistance."

Question - is the DC resistance the "output"? The 498T is a high output pickup which statement is always supported by reference to its DC resistance figure, as if the two are related, cause/effect, etc.

I've seen commentary both ways, with some saying "output has nothing to do with DC resistance," and others saying "that's how you measure "output" in a passive pickup."

Any info appreciated.

[Rodger Knox]

It's actually the number of turns in the coil(s) and the strength of the magnet that determines the output.

DC resistance is proportional to the number of turns, and it's easier to measure. The magnets do not affect the DC resistance(although they do affect the output), that's only dependent on the length and size of the wire.

Did you disconnect the pickups from the pots/switch to measure the DC resistance? I'd guess that you are only measuring one coil of the 498T. With the pickups connected, it's difficult to be sure exactly what you are measuring.

Generally, the DC resistance is a pretty good indicator of a pickups output because most pickups use the same size wire, and differences in DC resistance are due to different lengths(number of turns). There are a few pickups (tele bridge is one) that use a different size wire, and their output will be different at the same DC resistance.

[ChrisN]

Originally Posted by Rodger Knox

It's actually the number of turns in the coil(s) and the strength of the magnet that determines the output.

DC resistance is proportional to the number of turns, and it's easier to measure. The magnets do not affect the DC resistance(although they do affect the output), that's only dependent on the length and size of the wire.

Did you disconnect the pickups from the pots/switch to measure the DC resistance? I'd guess that you are only measuring one coil of the 498T. With the pickups connected, it's difficult to be sure exactly what you are measuring.

Generally, the DC resistance is a pretty good indicator of a pickups output because most pickups use the same size wire, and differences in DC resistance are due to different lengths(number of turns). There are a few pickups (tele bridge is one) that use a different size wire, and their output will be different at the same DC resistance.

I measured the p/u's "installed" per this vid:



I have several electric guitars and the p/u on the rest (installed) all measured out fine (compared to what others have said about them), except for the 498T (in an LP w/3-way switch, no coil split).

Thanks for the info re: magnets not impacting DC resistance.

[Rodger Knox]

Originally Posted by ChrisN

Assume I'm an electrical neophyte.

Today I measured DC resistance in my pickups (not done it before, but guitar believed to have stock/original pickup) and found that the 490R measured where it should at 7.67k, but the post-magnet change 498T, which I understand should measure around 14.7k, measures 7.58k, below the 490R with its A2 magnet.

Question - is the magnet change from A5 to A2 responsible for the DC resistance change by almost 50%?

Any info appreciated.

I watched the video, and I agree with everything he did. That method should give you a pretty decent value, maybe a little high depending on the wires and pots. I don't know how much difference it makes, but the tone should be set to full treble. I don't know if that's 0 or 10 on an LP.

I'd say that switching out the magnets has nothing to do with the low reading, unless you shorted one of the coils doing the swap. It's time to take the pickup out of the guitar and see if you can test the coils individually, your readings so far indicate a bad coil.

Did you measure the resistance of the 498T before the magnet swap?

[ChrisN]

Originally Posted by Rodger Knox

I watched the video, and I agree with everything he did. That method should give you a pretty decent value, maybe a little high depending on the wires and pots. I don't know how much difference it makes, but the tone should be set to full treble. I don't know if that's 0 or 10 on an LP.

I'd say that switching out the magnets has nothing to do with the low reading, unless you shorted one of the coils doing the swap. It's time to take the pickup out of the guitar and see if you can test the coils individually, your readings so far indicate a bad coil.

Did you measure the resistance of the 498T before the magnet swap?

1. Tested on full treble (10) - all knobs to max.

2. I did not measure the resistance of the 498T before the swap.

3. If I shorted a coil, would the pickup still work at all? (It does)

4. If I shorted a coil, and the pickup worked, would it have more noise/hiss because it lost its hum-cancelling coil? (It does not)

It's been a long time since I replaced the covers on those pickups and memory does not serve well enough to confirm I actually had a 498T in there - I bought the guitar used with worn hardware and covers, which I replaced. I'm sure the pickups said "Gibson" on them, but not much else. In short, I may be wrong to assume it's a 498T - time to pull the pickup and see what's what. Thanks for the help.

[Dru Edwards]

I wonder if you have a 490T and not a 498T?

[paulp1960]

I think the 498T bridge pickup should measure around 9K.

[ChrisN]

Originally Posted by Dru Edwards

I wonder if you have a 490T and not a 498T?

Anything's possible - per this post set, however, it looks like my '93 Studio was supposed to come with the 498T: https://www.thegearpage.net/board/in...ckups.1871293/

When I bought the guitar 3 yrs ago, all wear was age-appropriate, including the pitted gold p/u covers which wanted to replace. The solder holding the cover on looked like original work. I can recall seeing "Gibson" on pickup's bottom, but no model number.

That said, the way people swap pickups today suggests a previous owner may have put some other Gibson p/u in there.

Originally Posted by paulp1960

I think the 498T bridge pickup should measure around 9K.

I've seen people saying up to 14k, but yes, I think it should be higher than what it's showing (7.3k, less than the neck p/c by a small margin).

Is anyone aware of a test to determine if a coil's shorted (whether in the guitar, or out)? The pickup doesn't sound like it's on one coil (like a coil split) or anything.

I also should mention that I replaced the cavity electronics with an RS Guitars drop-in - all new pots - and wired it up to the old output jack and switch that work fine. Not sure if anything in that process might have caused an issue that somehow reduces p/u resistance, but let me know.

Finally, when I a/b the pickups at the same volume/tone, there is no drop-off in volume between the neck and bridge, as there would be if the bridge p/u was coil split. Bridge p/u sounds a little less full than the neck, very "bridgey." Also, the neck is decked while the bridge is raised by 1/4" or so to make it close to the neck.

[paulp1960]

Chris, I just googled that pickup for the specification. 9K sounds about right to me. That's certainly hotter than a vintage PAF. A 14K+ pickup is very hot and I'm not sure that would balance with your neck pickup very well.

[ChrisN]

Originally Posted by paulp1960

Chris, I just googled that pickup for the specification. 9K sounds about right to me. That's certainly hotter than a vintage PAF. A 14K+ pickup is very hot and I'm not sure that would balance with your neck pickup very well.

You are correct about the imbalance, and that's why that's not a popular p/u combination. It's too unbalanced to go back/forth between the neck and bridge on the same amp settings. That's why I, thinking I have the standard 490r/498t set, changed the 498's A5 for an A2 - an effort to mellow it a bit for lower gain work and make it closer to the neck p/u.

Here's a cool Gibson pickup info bit - this one shows the 498 at 12.3 to 13.4:

Gibson Burstbucker Pro (sim: BB1,Alnico5, potted) 7.4 KO
Gibson Burstbucker Pro (sim: BB2, Alnico5, potted) 8.0 KO
Gibson Burstbucker 1 (Alnico2) 7.5 KO
Gibson Burstbucker 2 (Alnico2) 8.0 - 8.4 KO
Gibson Burstbucker 3 (Alnico2) 8.2 - 8.8 KO
Gibson '57 Classic (Alnico2) 7.44 - 8.5 KO
Gibson '57 ClassicPlus (Alnico2) 9.0 - 13.8KO(the 9.0 appears to be a screw-up or faulty PU)
Gibson Dirty Fingers (2xCeramic) 16.0 -16.6 KO
Gibson Mini-humbucker (Alnico2) 6.0 - 6.4 KO
Gibson 490R (Alnico2) 7.2 - 7.83 KO
Gibson 490T (Alnico2) 7.9 - 8.53 KO
Gibson 498T (Alnico5) 12.32-13.46 KO
Gibson 496R (Ceramic) 8.3 - 8.63 KO
Gibson 500T (Ceramic) 14 – 15 KO

The p/u under discussion seems to function fine, it's just got a lower ohm value than I thought was spec'd for this guitar. I understand some LP Standards in '92 came with the 490r/490t set, so I suppose it's possible my '93 Studio came with that set, as well, and not the assumed 490r/498t set.

Or, it could be a PO did a really good job swapping the old cover onto a replacement 490t, though I think that less likely.

[ChrisN]

Re: Test to determine if 1 of the 2 coils is shorted - I learned that the sound will be greatly diminished when 1 coil is disabled, and I do not have that here.

I also learned you could test the coils by tapping them individually with something magnetic when the pickup is powered/selected. I assume this test is most accurate with the cover off the pickup, which I have not done. I did tap both sides of the pickup with the cover on, and they sounded equal, but I doubt testing with the cover on is a good test of much.

My suspicion at this point is that I never had a 498T, but, as Dru mentioned, a 490T. If so, I'm happier with the lower output, which I was trying to achieve with the A2 magnet. If not, I'm still happy with how it sounds.

Thanks to all for the input.