Quarter Inch Pole Pieces

[Squawky]

What effect on tone and signal do quarter inch pole pieces magnets (as in Seymour Duncan Quarter Pound pickups) have? Is there a significant difference between using them and standard diameter pole pieces or are they largely used for cosmetic reasons?

[big_teee]

Bump, Anyone?

Plus- easier to center the strings, over .250.
Minus- on a strat sized bobbin, you lose winding room
That is why the SD version has no cover.
Minus- You lose that bell ringing big wire tone IMO
you would probably need to go to taller magnets.

On the smaller sizes you have .187, .195, and .205 or somewhere in that ball park.
My choice for most fender style SC pickups, are the .195s.
YMMV, GL,
T

[Antigua]

I only have SSL-4's for Strats and the STL-3 for Tele to refer back to. It's functionally aesthetic. The wider a pole piece is, the more it will cancel out high harmonics that are physically narrow, but the frequency of these harmonics is so high that the issue isn't relevant. Suppose the scale length is 25.5 inches, the difference from 0.2" to 0.25" in width is about one thousandth the overall length of the guitar string, harmonics of that width are very high in frequency and don't last for more than a short instant once the string is plucked. If the could be heard at all, it would only be in the transient pick attack, but when I have tapped the SSL-4 in order to coax a high resonant peak, the high end responses sounded no different to me than an ordinary Strat pickup. When not tapped, the SSL-4 has a very low resonant peak, and that might trick some into believing the large diameter pole piece costs treble response, but with that pickup in particular it can be attributed to the low resonant frequency, when not being tapped.

The measured magnetic strength is actually a little weaker than a narrow AlNiCo pole piece. With the SSL-4 and STL-3 I measure between 750 and 950 Gauss, they're spec'd as AlNiCo 5, with typical pole pieces they reliably measured about 1050 Gauss, center over over the D or G poles. The reason most likely being that AlNiCo is most efficient when it's length is at least four times the width of the polar faces, due to it's lower coercivity relative to modern magnets, and the quarter inch pole pieces have a more lower length to diameter ratio than typical Strat pole pieces. Even though the flux density in any given spot is lower, because the quarter inch pole piece has a wider area, the overall magnetic flux is probably about the same. I would bet the height of AlNiCo poled Fender pickups werer originally intended to get optimal strength from the AlNiCo pole pieces, because they happen to be about three to four times as tall as the pole piece diameter, although the Jazzmaster pickups have shorter AlNiCo pieces than other Fender single coils, and they also measure a weaker strength as a result, around 750 Gauss.

[Squawky]

Antigua

Any thoughts on the role the difference in magnet diameter has on the difference in you measurements between the SSL 4 and SSL 5, which otherwise seem like pretty much identical pickups? The larger magnet size would alter the ratio of height to width of the coil, which I understand will affect the inductance (I believe Fender did something similar with the Twisted Tele bridge by using a squatter bobbin). How about the difference in Q though?

[Antigua]

Antigua

Any thoughts on the role the difference in magnet diameter has on the difference in you measurements between the SSL 4 and SSL 5, which otherwise seem like pretty much identical pickups? The larger magnet size would alter the ratio of height to width of the coil, which I understand will affect the inductance (I believe Fender did something similar with the Twisted Tele bridge by using a squatter bobbin). How about the difference in Q though?

Here are two bode plots, full and tapped, unloaded and loaded with 470pF and 200k ohms. The Q factors are very close, but in theory the SSL-4 should have very slightly lower Q factor, due to higher eddy current effect in the larger volume of conductive metal in the core. AlNiCo 5 is conductive, but less so than steel poles or lower numbered grades of AlNiCo.

It looks like they have roughly the same DC resistance of about 13.5k, but the SSL-4 has one henry greater inductance at 7.1H, versus 6.1H with the SSL-5, likely due to the wider coil area of the SSL-4. We just have to assume both use AlNiCo 5 and that the composition of the AlNiCo is about the same for both, but varying amounts of iron in AlNiCo could also vary the inductance.

[Helmholtz]

AlNiCo 5 is conductive, but less so than steel poles or lower numbered grades of AlNiCo.

A5 has less resistivity/higher conductivity than the lower grade alnicos, so somewhat more losses.

[Antigua]

A5 has less resistivity/higher conductivity than the lower grade alnicos, so somewhat more losses.

I found a data sheet that agrees with you, but I always see a lower Q factor with A2 and A3 compared with A5. I have multiple bode plots of Stratocaster and Tele pickups indicating as much.

[Helmholtz]

I found a data sheet that agrees with you, but I always see a lower Q factor with A2 and A3 compared with A5. I have multiple bode plots of Stratocaster and Tele pickups indicating as much.

I found several reliable sources confirming the lower resistivity of A5.

But - everything else being the same - higher L lowers the resonant Q.
That might explain your measuring results.

[Zhangliqun]

In my experience, 1/4" rods have a significantly beefier tone than standard .187-.159, whether A2, A3 or A5. It stands to reason that if the magnet sees a longer segment of the string, it would see the longer wavelengths of the lower freqs a bit better. I don't know about the effect of length-to-width ratio but I use .800" length.

[Antigua]

It stands to reason that if the magnet sees a longer segment of the string, it would see the longer wavelengths of the lower freqs a bit better. I don't know about the effect of length-to-width ratio but I use .800" length.

Voltage is produced when the guitar string moves towards and away from the pickup, and it's proportional to the rate of change of the magnetism through the coil, so the width doesn't factor into in terms of seeing more fundamental. If the pole piece is wide enough, it will suppress harmonics that are more narrow than the pole piece itself, but the difference in width here is about a thousandth of the overall length of the guitar string, so that harmonic would be a very, very high one. I still suspect that people come to the conclusion that fat pole pieces sound fatter because popular pickups that make use of large pole pieces tend to also be made to have a higher inductance, maybe because if something looks fat, guitarists probably think it should sound fat, too.

[Zhangliqun]

I don't buy it. A 6k humbucker humbucker sounds a great deal fatter than an 8k Fender single. Neck P90s are notoriously tubby, including the ones I made -- until I started using narrower magnets. Width matters.