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Post by antigua on Jul 27, 2019 18:10:33 GMT -5
I've recently bought another Jazz Bass set, which makes this my third or fourth set. I recorded technical values of those here . Fender Custom 60's Jazz Bass
Bridge - DC Resistance: 7.35K ohms - Measured L: 2.837H - Calculated C: 183pF ( - 10) - Gauss: 1000G (AlNiCo 5)
Neck - DC Resistance: 7.05K ohms - Measured L: 2.480H - Calculated C: 172pF - Gauss: 950G (AlNiCo 5)
Bridge unloaded: dV: 14.8dB f: 6.89kHz (black) Bridge loaded (200k & 470pF): dV: 6.7dB f: 3.51kHz (blue) Neck unloaded: dV: 15.9dB f: 7.81kHz (red) Neck loaded (200k & 470pF): dV: 7.0dB f: 3.81kHz (green)This Fender Custom 60's set has less wire than the Pure Vintage 74 set, therefore lower inductance and increased treble response. With 470pF capacitance thrown in to represent a ~12 foot guitar cable, the Custom 60's have about 500Hz of additional reach into the upper 3kHz range. Both sets use AlNiCo 5 pole pieces. Fender also sells the "Yosemite" Jazz Bass set, which I haven't measured, but which I see uses AlNiCo 5 pole pieces also, and has DC resistances of 7.3k and 7.0k, which is exactly what I measured with the Custom 60's set, so it appears these pickups are more or less identical, aside from the hookup wire, and they cost about $30 less. There is also the Original Jazz Bass set, which cost less than the Yosemite set can have the nicer cloth hookup wire, too, except that this set features AlNiCo 2 magnets, and a bridge pickup with a DC resistance of 7.7k on the bridge, and 7.2k on the neck. AFAIK, Fender only used AlNiCo 3 some time in the early 50's, due to cobalt being expensive, possibly in relation to the Korean War, and I've never heard that they used AlNiCo 2 at all, so in the interest of achieving a good vintage Jazz Bass sound, I'd personally stick with pickups having AlNiCo 5 pole pieces. The reason I bought a new Jazz Bass pickup set is that a recent purchase came with stock ceramic pickups with steel pole pieces. Even though the DC resistance of stock steel poled ceramic pickups measured a DC resistance of 5.7k ohms, the highly permeable steel pole pieces in such pickups causes the inductance of the pickup to increase way beyond what it will be with AlNiCo pole pieces, so even though the pickup only reads a DC resistance of 5.7k, the frequency response with 470pF capacitance didn't even break 3kHz in testing, while the Fender PV '74 and Custom 60's both exceed 3kHz, despite having DC resistances in the 7k ohm range. This is true of all stock single coil pickups that have steel pole pieces; they are a lot darker and louder than their AlNiCo counterparts, even if the DC resistance shows that they have so much less wire on them. The steel pole pieces also causes eddy currents, robbing the single coil of a high resonant Q, that gives vintage Fender AlNiCo pickups a bite (some say ice pick) that they're well known for.
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Post by wgen on Jul 28, 2019 7:16:46 GMT -5
Thank you Antigua, very interesting as always. I seem to recall that you explained in the past the reason of the relative high Q factor of jazz bass pickups, when alnico poles as in this example. Could you please explain this again? Is there a design thing to take note about pickups, to assume that a higher Q factor is to be expected? Thank you!
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Post by straylight on Jul 28, 2019 12:52:09 GMT -5
Thanks for this, it's really handy, there's not enough analysis of bass pickups.
For a given inductance, less winds and more steel appears to give a lower Q. I don't have the maths relating to this. I don't know if it's just eddy currents or to do with the permiability of the core, but using fillister screws and more winds or alnico rods and a LOT more winds to get the same inductance gives a much higher Q.
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Post by antigua on Jul 28, 2019 23:08:18 GMT -5
I seem to recall that you explained in the past the reason of the relative high Q factor of jazz bass pickups, when alnico poles as in this example. Could you please explain this again? Is there a design thing to take note about pickups, to assume that a higher Q factor is to be expected? Thank you! The reason I figured was that these pickups must have a higher ratio of air to pole piece in the core (a pure air core yields the highest Q factor possible, a purely conductive core, the lowest). The only other explanation would be a low series resistance, and these pickups do not have a low series resistance. But I've subsequently found another reason why a single coil pickup can have a high Q factor, the very flat and wide coils of a Jazzmaster pickup yield a high Q factor also guitarnuts2.proboards.com/thread/8311/fender-vintage-jazzmaster-analysis-review . It think that with these short and wide coils, it's the same idea as the air core, except instead of air, you have the inner mass of the coil, which is effectively the same as air, with respect the outer portion of the coil. The Jazz and P-Bass pickups both have a rather high Q, I think in the case of the Jazz Bass pickups, it's that there is a lot of space in between the pole pieces, more "actual" air, and in the case of the P-Bass pickup, the coils are flat and wide, more "virtual" air.
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Post by antigua on Jul 28, 2019 23:25:49 GMT -5
Thanks for this, it's really handy, there's not enough analysis of bass pickups.
For a given inductance, less winds and more steel appears to give a lower Q. I don't have the maths relating to this. I don't know if it's just eddy currents or to do with the permiability of the core, but using fillister screws and more winds or alnico rods and a LOT more winds to get the same inductance gives a much higher Q.
I think you're contrasting the damping factor of eddy currents versus series resistance, and in general, series resistance with guitar pickups has a negligible effect on the Q, compared to eddy current losses. Even with an SSL-5 guitarnuts2.proboards.com/thread/8022/seymour-duncan-ssl-analysis-review , with about double the series resistance of a typical Strat pickup, the Q factor is still rather high. Or comparing the JB and Jazz humbuckers guitarnuts2.proboards.com/thread/8032/seymour-duncan-jazz-analysis-review , both had Q factors that were about the same. I think there is a lot of variation in terms of how fillister screws effect the Q factor, depending on the screw and coil dimensions, because it's been observed that the fillister screws in Filter'trons cause much greater damping than the filiister screws in PAF style humbuckers, which have both smaller screws and wider coils.
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Post by straylight on Jul 30, 2019 7:50:51 GMT -5
It's easily demonstatable that bigger cores of the same material increase inductance and decrease Q, i'm not sure i have data assembled to present something good on this but i'll have a look. That i'm throwing more winds into the problem is more of a design question as it's fairly easy to manipulate wind counts to achieve the required inductance and thus cutoff frequency, but in order to build a pickup with the same cutoff frequency but a higher Q it appears to be a question of construction. Of course the coil size changes with winds.
What's particularly piqued my interest is the similarity in inductance between some strat pickups I've made and individual coils from a slightly hot conventional humbucker, which have wildly differing Q. I'll post up analysis of what comes out of this soon, but I need to get a few projects out the door before I can wind the set I have in mind.
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