Post by antigua on Sept 25, 2016 18:55:09 GMT -5
I had loaded a Strat with three SSL-4's, each one with a little tap dip switch, with the idea that the neck and middle would be tapped most of the time. It was actually a very versatile setup, and the tapped tone was nice, but ultimately I felt it just looked too ugly, and so I tried the same thing again with tapped SSL-5's, and it's pretty much the same equation, but with a stock Strat appearance.
Strat pickups this hot should be thought of more as humbuckers, and paired with 500k, or even 1meg pots.
DC Resistance: 13.85K
Resonant Peak: 4.31 kHz
Calculated C: 172pF (192-20)
tapped: 606pF (626-20)
Coil width: 0.5775"
DC Resistance: 13.48K
Inductance: 6.740 H
Resonant Peak: 4.46 kHz
tapped: 4.46 kHz
Calculated C: 169pF (189-20)
tapped: 597pF (617-20)
Coil width: 0.5525"
DC Resistance: 13.67K
Inductance: 7.240 H
Resonant Peak: 4.22kHz
Calculated C: 176pF (196-20)
tapped: 615pF (635-20)
Coil width: 0.5760"
Pole pieces: 0.2525" diameter (typically 0.18"), Flux density at top center: 600G to 1000G .
Amplitude / frequency bode plot:
The very low loaded Q factor and resonant peak makes the SSL-4 similar to hot PAF type humbucker, from an electrical standpoint, although this pickup gets there with a higher wind count, rather than steel core components. It's safe to assume that this was the design goal of this pickup.
The measured results show a very surprising thing, a wildly large amount of unwanted capacitance when tapped, around 600pF capacitance when tapped. That's roughly equivalent to a 20 foot long guitar cable's worth of capacitance. The cause is obvious, but I would have never imagined the capacitive coupling would be so dramatic. When the outer section of the coil is disabled, it's still connected at one end, causing the unused portion of coil to capacitance couple with with the used portion. If they wanted the tapped sound to be reminiscent of a vintage type Strat pickup, they could have got a lot closer.
Design flaw? I'd say so. Unless you consider 20ft capable capacitance a good thing. This flaw could be corrected by giving the pickup a proper "four conductor cable" instead of three, as with three conductor, it's impossible to disconnect the unused outer coil. Due to the short wire leads, it's also impossible to correct the problem at home.
The way a tapped coil is made, is after so many turns, they pull the wire through one eyelet, solder it, and then continue winding. The red wire connects to the "tap" eyelet. If they terminated the coil at this eyelet, and then started a new strand of wire from another eyelet, then four conductor cable could have been used to offer access to each coil in isolation of the other, eliminating the capacitive coupling.
The result of this design is that, shockingly, the "unloaded" resonant peak of the tapped mode is just barely higher than the full mode's resonant peak. The Extech LCR meter puts the untapped inductance at 7H and the tapped inductance at 2H (though this might be inaccurate). They should have resonany peaks that are oceans apart, but due to that huge tapped capacitance, they end up close, at 4.3 and 4.4 kHz.
The loaded peaks are a little further apart, thanks to the swamping cable capacitance (470pF). The loaded tapped resonant peak is 3.4kHz,and that's dark by Strat standards, but then the Q factor is 2.5 (suggesting / confirming a rather low inductance), where 1.6 to 1.8 is more typical of a vintage Strat pickup, which wins back some treble. It's easy to see, though, that this combination of factors makes the tapped tone somewhat dissimilar to a vintage output Strat pickup.
Bode plots are made with a Velleman PCSGU250 and the supplied probes in 10x mode, with the function generator feeding a driver coil of 0.48mH, placed on top of the pickup and driven with 2Vpp. The pickup is connected to an integrator circuit, designed by Ken Willmottkenwillmott.com/blog/, with a Velleman 10x probe, and fed back into the Velleman PCSGU250. I measured the probes' capacitance at 20pF, so that amount is subtracted from the capacitance calculation.
The inductance and Q measurements are made with an Extech 380193 in "SER" series mode, and the mean value between the 1kHz and 120Hz modes is recorded. The capacitance value is derived from the inductance and measured resonant peak.
Magnets are tested with a Spin Doctor ER gravitastech.weebly.com/spin-doctor-er.html