Post by antigua on Nov 23, 2017 16:18:12 GMT -5
Seymour Duncan C.S. Stra-Bro 90
Mfg website: customshop.seymourduncan.com/stra-bro-90/
Mfg's description:
Unless a player wanted to seriously modify their guitar, getting the sound of a P90 out of a Strat sized pickup wasn’t do-able. Because we’re obsessed with insanely hard challenges, the Custom Shop developed the StratBro 90 to offer thick P90 tone out in a traditional single coil size. This pickup is tapped to offer different output levels.
DC Resistance: 7.4k top, 14.8k total
As the product copy states, this Custom Shop set is intended to give P-90 like tones from a Strat-sized pickup. The single bobbin is a double tall PAF type plastic bobbin with three filister screws and three AlNiCo pole pieces. Below the double tall bobbin, the three filister screws pass into a PAF / P-90 keeper bar that has been sawed in half, and is flanked by two halves of a mini ceramic bar (the type found in single coil sized humbuckers) that has been snapped in half. On the other end of the pickup, the three AlNiCo pole pieces are flanked by two halves of a PAF type plastic spacer. The bobbin is screwed to a nickel silver PAF-like base plate with convenient little clamps that secure the hookup cable (refer to pics below). While this is said to target a P-90 tone, it looks very "PAF" like, and there's nothing P-90 about powerful AlNiCo pole pieces. It's a really cool looking pickup, though.
Based on how the wire is fixed to the base plate, it appears that the screws are supposed to sit below the G/B/high E, and the AlNiCo 5 below the low E/A/D, though there is no flange, so you can orient it either way.
The magnetic strength at the pole tops is a little unusual. With most pickups, it tends to be rather uniform from end to end, with a little more strength at the far ends of the pickup. The Strat Bro 90's all show about 250 Gauss over the outer two screws, but only around 150 G over the center-most screw, and the reason for this is that it has a powerful AlNiCo magnet right beside it. Since this center-most screw is in the magnetic return path of the much stronger AlNiCo, it's magnetic strength is somewhat suppressed compared to the outer two screws. This means the string above this screw will have a softer sound to it, as though the pickup where lowered slightly, for that string alone. The AlNiCo pole pieces show some inconsistency in strength, with some reading just over 800 Gauss, and others reading over 1200G. It's hard to tell if this is due to inconsistent charging or different AlNiCo allows being used, but when the magnetic fields are this strong, above 800 Gauss, you can't really hear any difference.
As for electrical performance... the coil is a single large coil with a tap point. The wire uses a transparent poly insulation. The overall DC resistance is around 14k to 15k, overall inductance 8 to 9 henries, with tap points that bring the DC resistance down to 6k to 8k, and as low as 2 henries inductance. As I've noted in other analysis of tapped single coils, the three-lead design leads to a high capacitance when tapped, which is why the low inductance of 2H does not sounds as thin as you'd normally expect. The overall capacitance is around 350 picofarads, which average for coil with so many turns of wire, but the tapped capacitance is remarkably high at around 1.3 nanofarads. That's roughly equivalent to using a 50ft guitar cable, and this is because the two halves of the coil form a crude capacitor when the pickup is tapped. A fun fact about tapped pickups is that it doesn't matter whether you tap the inner or the outer coil, you get almost identical performance, so long as the two haves have similar turn counts, because the what one half lacks in inductance will be made up for by additional capacitance in relation to the other half of the coil.
But how close is it to a P-90? I've analyzed several P-90s, and most have an inductance around 7 to 8 henries, with loaded resonant peaks right in the area of 2.0kHz. These StraBro 90s have have a higher inductance of 8 to 9H, and loaded peaks around 1.6kHz, so that means about 400Hz less harmonic content, all other things being equal. When the attenuation is above 2kHz, most of the difference is perceived in the attack, or the transient, the only time when there is significant voltage above 2kHz, but when the attenuation dips down into the 1kHz range, the sound becomes noticeably darker in both the attack and decay phase.
The Q factor, which can be observed in the bode plots below, is remarkably similar to what I had measured with Tonerider's P-90 models, which is about +2dB, a very small amount, with a 200k ohm load. When tapped, however, the loaded Q factor is +5 to +6dB at resonance, which is very similar to what you'd get with a Strat pickup.
My feeling about the StraBro 90 in-situ is that the full mode was rather dark, as though you had a very long guitar cable, while the tapped tone was rather anemic. If anything stops these from sounding like P-90's though, it's probably more the fact that these pickups are situated in a Strat, where as most P-90s would be found in a Gibson, where the pickups are positioned differently, and the guitars themselves resonate differently.
At $140 a piece, or $420 a set, they're not a bargain in terms of what they do tonally, as you can get similar performance from an SSL-3T or an SSL-5T, but they might be worth the money for the aesthetics. They're just wound so hot though, literally they're comparable to JB humbuckers, even the middle and neck versions. You could probably fabricate something similar by using half of a JB, where each coil is similar to a Strat pickup by itself. The biggest challenge would be figuring out how to mount the lone coils, in lieu of a Strat sized base plate.
The StraBro 90's I received from Seymour Duncan didn't have any threadings in the mounting leg holes, so I have to mount the pickups with screws and nuts. Probably just an oversight. Also note that communication and turnaround time with the Seymour Duncan Custom Shop is really hit an miss. If you can find a good set on eBay, that's a probably a better way to go.
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As a technical aside, this pickup set is unique for having a mix of AlNiCo and steel parts within the core of a single coil. From that, something interesting can be observed; the higher permeable steel screws show in relation to the AlNiCo a) less magnetic reluctance, and b) higher eddy currents.
The three plots show, in order black, red, green, the test exciter coil over the screws, then in between the screws and AlNiCo pole pieces, and then over the AlNiCo. The lower gree line, representing the AlNiCo, shows a higher peak than the black or red lines. That means great resonance, less eddy current losses. But the green line is also 2.6dB below the steel pole pieces, that means higher magnetic reluctance, and less voltage all things being equal.
Even though the steel shows greater voltage than thee AlNiCo, in practice, they're probably produce similar voltages on either side. This is because the screw tops only show Gauss levels of ~250G, compared to the AlNiCo's ~1100G. The stronger magnetic strength of the AlNiCo means the guitar strings are immersed in a stronger magnetic field, which will offset the higher magnetic reluctance (which is analogous to magnetic resistance) of the AlNiCo. And though there are fewer eddy currents with the AlNiCo, it looks like the difference there is negligible, visible on a graph, but not audible to the ear.
Measurements:
Stra-Bro 90 Bridge
Full:
- DC Resistance: 14.88K ohms
- Measured L: 9.456H
- Calculated C: 332pF (342 - 10)
Tapped:
- DC Resistance: 8.05K ohms
- Measured L: 2.286H
- Calculated C: 1374pF (1384 - 10)
Bridge Full
- unloaded: dV: 8.9dB f: 2.80kHz (black)
- loaded (200k & 470pF): dV: 2.0dB f: 1.56kHz (red)
Bridge Tapped:
- unloaded: dV: 8.9dB f: 2.83kHz (green)
- loaded (200k & 470pF): dV: 6.3dB f: 2.44kHz (gray)
Stra-Bro 90 Middle
Full:
- DC Resistance: 13.45K ohms
- Measured L: 8.050H
- Calculated C: 357pF (367 - 10)
Tapped:
- DC Resistance: 6.86K ohms
- Measured L: 2.351H
- Calculated C: 1245pF (1255 - 10)
Stra-Bro 90
Middle Full
- unloaded: dV: 8.5dB f: 2.93kHz (black)
- loaded (200k & 470pF): dV: 1.9dB f: 1.69kHz (red)
Middle Tapped:
- unloaded: dV: 8.5dB f: 2.93kHz (green)
- loaded (200k & 470pF): dV: 5.7dB f: 2.47kHz (gray)
Stra-Bro 90 Neck
Full:
- DC Resistance: 13.56K ohms
- Measured L: 8.043H
- Calculated C: 342pF (352 - 10)
Tapped:
- DC Resistance: 6.34K ohms
- Measured L: 1.990H
- Calculated C: 1349pF (1359 - 10)
Stra-Bro 90
Neck Full
- unloaded: dV: 8.9dB f: 2.99kHz (black)
- loaded (200k & 470pF): dV: 2.0dB f: 1.67kHz (red)
Neck Tapped:
- unloaded: dV: 9.1dB f: 3.06kHz (green)
- loaded (200k & 470pF): dV: 6.5dB f: 2.67kHz (gray)
Pics:
