Gibson P-90s with Alnico rods? HUh?

[Mark Hammer]

A buddy on another forum posted some pics of a 2014 Gibson Melody Maker he just picked up. I couldn't help noticing that the pickups do not have adjustable screw-poles, but flat-top rods instead. What's up with that?

I started looking for some info, but didn't find anything other than Lindy Fralin advertising Alnico rod P-90s. Pretty sure these weren't Fralins, since this is a 100% stock budget instrument. When did Gibson start making alnico rod P-90s, and how do they attach the the magnet structure or keeper bar underneath?

[jack briggs]

you mean like this?

Alnico Staple Pickup - Seymour Duncan Specialized

[big_teee]

When you make it with rod magnets, don't you end up with a Jazzmaster pickup?
A similar pickup to the jazzmaster that fits a P90 Cover.
http://mmguitarbar.files.wordpress.c...07/2115207.jpg

[JGundry]

Gibson make P-90's with Alnico 5 rods in the 50's. I have one.

[Mark Hammer]

So I'm curious to know what's underneath the cover. Are these rods simply used as passive/conductive slugs, with a pair of bar magnets underneath, like a traditional P90, or is there some other arrangement?

I'm not going to get all obsessive and picky about it, but my impression is that at least some of the traditional P90 tone stems from the impact of the adjustable screws and the keeper bar on the inductance of the coil. So are these P90s or should they have some other model number to indicate the design difference. After all, a cover does not a pickup make.

[jason lollar]

i dont know what the new melody makers with the soapbar covers have but rod magnets are a pretty obvious modification to do to a P-90- gives it a more fendery tone- splashier with less grit. Not quite a jazzmaster though. Gibson also made a pickup related to a P-90 that went in the BR 9 that has bar magnets and non adjustable steel poles. I make both but dont advertise them, its something I will suggest occasionally to meet someones expectations. It would be interesting to see if the coil form in the new melody makers are more like a P-90 or like a strat with a soapbar cover over it.

[Jammin'John]

Poles

I tried one from a canadian maker.
I didn't like it as much as a "real" soapbar.
It sounds more like a FAT Strat pup. NOT a bad thing.

JJ

[Tony Bones]

The pickups (Gibson calls them P90S's) have a wide flat coil like a real P90 but just replace the screws with Alnico slugs. This makes them very low profile. I've heard that a regular P90 will not fit on the cavity, but I don't know for sure.

The sound is P90 related, but a little brighter and clearer. A little in the direction of a traditional Strat pickup. They are very articulate, more than a regular P90. Some people like them.

Some people like them.

I have DCR and resonant peak measurements somewhere if anyone is interested.

[Mark Hammer]

First, I'd certainly be interested.

Second, thank you for this info. Very helpful. By "alnico slugs", I gather you mean that they are not charged, and there are still bar magnets on each side of the base of the slug?

[Tony Bones]

They are charged. There's a brass mounting plate below the coil but no bar magnets or keepers or anything else magnetic. Just the bobbin with relatively short Alnico pole pieces. I don't have the pups here. When I get home I can get some photos and measure the height (thickness) but I think the coils are P90 size in all respects.

[Mike Sulzer]

i dont know what the new melody makers with the soapbar covers have but rod magnets are a pretty obvious modification to do to a P-90- gives it a more fendery tone- splashier with less grit. Not quite a jazzmaster though. Gibson also made a pickup related to a P-90 that went in the BR 9 that has bar magnets and non adjustable steel poles. I make both but dont advertise them, its something I will suggest occasionally to meet someones expectations. It would be interesting to see if the coil form in the new melody makers are more like a P-90 or like a strat with a soapbar cover over it.

Your description of the tone change is what you might expect from measurements. The attachment shows impedance measurements for the same coil with steel cores and alnico. (Note that the measurement of coil resistance is the same in both cases as it should be, and the capacitance is very close. The capacitance is harder to measure, especially when one case has large eddy currents.)

AlAndSteelCores.pdf

As expected, the resonance is lower and broader when the cores are steel, but the range up to 5 Hz is what counts the most. Look at the yellow and green lines; these are the imaginary and real parts of the impedance with that part of the impedance resulting from the capacitance removed mathematically. This makes it easier to see the effects of eddy currents because it is possible to compare these lines with the dashed and dot-dashed gray lines. These latter two lines are the impedance of the coil without the effect of eddy currents, just the coil inductance and resistance. Notice that the measured impedance with alnico cores over the range unto 5 KHz is very close to these lines, and so the effect of eddy currents with alnico cores is small.

On the other hand, in the case of steel cores, the measured impedance with capacitance removed (yellow and green) differs greatly from the gray lines, indicating a large effect of eddy current. When the pickup resonates with the cable capacitance, somewhere under 5 KHz, the shape of the resulting impedance (and thus the frequency response of the pickup), differs significantly for the shape when eddy currents are small. Thus we expect that the sound to be different, even if the resonance frequency is the same.

[Tony Bones]

Don't know what I was thinking when I said there's a brass baseplate. There is no conventional baseplate at all. In the 2014 Les Paul Melody Maker (which I think is the only place these pickups have appeared) there is a galvanized steel plate screwed to the bottom of the pickup cavity. There's probably 1/4" or so of gap depending on the height adjustment. Close enough to have some influence I would guess.

The pole spacing is 49.2 mm. The bobbin is the 3.2" x 1.2" with 0.25" winding window.



I think the bridge pickup could use even more iron under the coil (my opinion) so for giggles I stuck the plate in the above photo directly to the bottom of the magnets and took another impedance scan. I'll leave it as an exercise to the reader to determine which curve is which.

[Zhangliqun]

Rod 90's

I've a made a few of these, I call them "Rod 90's". They are definitely Fendery sounding and in one case, a guy had a P90 guitar that he wanted a Tele bridge sound from so I got him as close as I could (can't do anything about the slant) by making one with a steel baseplate, forbon flats, and a twine coil cover for the finishing touch and he loved it.

But anyway, for the OP, these definitely don't sound anything like a standard screws-n-bar mags P90.

[big_teee]

I've a made a few of these, I call them "Rod 90's". They are definitely Fendery sounding and in one case, a guy had a P90 guitar that he wanted a Tele bridge sound from so I got him as close as I could (can't do anything about the slant) by making one with a steel baseplate, forbon flats, and a twine coil cover for the finishing touch and he loved it.

But anyway, for the OP, these definitely don't sound anything like a standard screws-n-bar mags P90.

Did you make the between the flats taller like a tele pickup?
That would make it brighter.

[Zhangliqun]

Did you make the between the flats taller like a tele pickup?
That would make it brighter.

Not as tall as a Tele, but taller than a standard P90 bobbin.