Duncan Designed SC101, Analysis & Review

[antigua]

I've heard a lot about the Duncan Designed SC101s, which come stock in the Squier VM Stratocaster. In particular, there's curiosity over how they differ from Seymour Duncan SSL-1s. I saw this SC-101 loaded pick guard on eBay, and figured it was a good deal for the parts if nothing else, so I ordered it, and I've taken a look at the pickups.

They're quite different from SSL-1s, where to begin? Long story short, they're more Tele than Strat.

First, the bridge is a very "hot bridge". Not louder so much as darker. The DC resistance is 11.5k, the inductance is nearly twice that of a typical Strat pickup at 3.9H. It's not quite as dark as an SSL-5, but almost. Despite the hotter wind, the voltage output is only about 2dBV higher than the neck or middle pickup, so the intention here is treble attenuation more than it is increased volume output. This inductance is more typical of a Telecaster bridge pickup.

The second difference, and by far the most major, is that all three pickups have copper shielding around the coils, as can be seen in the pic below. A copper shield might seem like a good idea, but it capacitively couples with the coil, adding about 150pF capacitance, which is equivalent to several feet of extra guitar cable length. The resonant peak of a neck pickup with 2.8H inductance is typically around 3.7kHz, but with this added capacitance the peak frequency is brought down to 3.2kHz, which makes for a darker pickup, typical for a Telecaster, but not a Stratocaster.

The neck and middle pickups are typical Strat in terms of DC resistance and inductance, but because of that copper shielding, they end up being closer to a Telecaster neck pickups. The inductance is similar to an SSL-1, despite the DC resistance being higher at 7k per pickup. If not for the copper shielding, they would spec out very close to SSL-1's.

Another difference from SSL-1s that make them more similar to Telecaster pickups; they're flat poled. The gauss measures 950 at the tops of the center-most AlNiCo 5 pole pieces, down from a typical 1050 on center, due to the shorter size of the magnets.

The final difference is that the bobbins are plastic rather than fiber bobbin. This isn't really a big deal, but we're reached a point where you can get real fiber bobbin Strat / Tele pickups for bottom dollar, so there's no need to settle for plastic. One upside to plastic, though, is that the pole pieces can be pushed around without risk of destroying the coil. So they need not be flat-poled, a stagger profile could be applied manually.

If you have a set of these and want to make them sound even more Strat-like, you can carefully snip the ground connection to the copper shielding. This will prevent it from capacitively coupling with the coil, and will raise the peak frequency by about 500Hz for each pickup.

The copper shielding also causes eddy currents, which reduce the Q factor a small amount, about 1dB at the resonant peak. Removing the copper shielding entirely would win that small amount of resonance back.




Measurements:

Duncan Designed Strat SC101B/ADWH BRIDGE 1706
DC Resistance: 11.51K
Inductance: 3.875 H
Calculated C: 375pF (385-10)
Gauss: 950G

Duncan Designed Strat SC101M/ADWH 1706
DC Resistance: 7.00K
Inductance: 2.770 H
Calculated C: 274pF (284-10)
Gauss: 950G

Duncan Designed Strat SC101N/ADWH NECK 1706
DC Resistance: 6.93K
Inductance: 2.817 H
Calculated C: 263pF (273-10)
Gauss: 950G


Duncan Designed Strat SC101

Bridge
Unloaded: dV: 9.1dB f: 4.12kHz (black)
Loaded w/ 200k & 470pF: dV: 3.7dB f: 2.55kHz (blue)

Middle
Unloaded: dV: 8.9dB f: 5.67kHz (red)
Loaded w/ 200k & 470pF: dV: 5.0dB f: 3.24kHz (green)

Neck
Unloaded: dV: 8.1dB f: 5.74kHz (pink)
Loaded w/ 200k & 470pF: dV: 4.8dB f: 3.21kHz (lower black)

[pj]

Super analysis as ever. Makes my day when you post one.
A Jb sh4 I used to own had similar copper taped coils, and then I got an old Kramer pacer with a much older jb that wasn't taped and I always preferred that pickup, though in reality they were both far too hot for me.

I've had students with these pickups on squiers and I thought they had a kind of usable 'strat but tamed' tonality, which is explained by your findings. Personally I think the bridge is too far dark. I miss the light and dark effect available on a traditional strat switch extremes, that's just me though.

[antigua]

Mar 23, 2018 3:46:42 GMT -5 pj said:

Super analysis as ever. Makes my day when you post one.
A Jb sh4 I used to own had similar copper taped coils, and then I got an old Kramer pacer with a much older jb that wasn't taped and I always preferred that pickup, though in reality they were both far too hot for me.

I've had students with these pickups on squiers and I thought they had a kind of usable 'strat but tamed' tonality, which is explained by your findings. Personally I think the bridge is too far dark. I miss the light and dark effect available on a traditional strat switch extremes, that's just me though.

Yeah stratotarts observed this coil wrapping on a cheapo Chinese humbucker. Interesting that they go out of their way to try to improve these pickups that are supposed to be low cost, even aside from the fact that they arguably make the resulting tone worse. It makes me also question how much design input Seymour Duncan really exercised in the design of the pickup. It's a shame they didn't just create three SSL-1 copies. Cheap. Easy. That's what I had envisioned when I bought the loaded pick guard. 

[antigua]

I did a little more testing on the shield. It has two impacts, 1) capacitance and Q factor, so first, capacitance, as measured with a DE-5000 meter set to Cp /100kHz.

With coil shield and shielded hookup wire, red to ground: 197.48pF
With coil shield and shielded hookup wire, white to ground: 166.30pF
Without coil shield, with shielded wire: 165.74pF
Without coil shield, without shielded wire: 138.78pF

The SC101 has three conductors in all, red (coil start) white (coil finish) and a shield wire. As the picture below shows, these pickups are wired into pre-wired pick guards white hot and red to ground, but it appears that white is also the end of the coil, and that causes the shielding to add about 30pF added capacitance, because it brings both sides of the circuit into very close proximity, where the hot lead is at the outside of the coil, closely hugging the grounded copper tape.

If the red and white wires are reversed (coil end and coil start are flipped), two things happen, #1 the 30pF capacitance disappears completely because the hot side of the circuit is now on the inside of the coil, and the ground side is outside, beside the copper tape. Thing #2, since the outer layers of the coil are on the ground side of the circuit, the copper tape has become redundant as a shield, because both the copper tape and the outer layer of the coil are on the ground side of the circuit.

What this means for other pickups with copper taped coils that might not have separate conductors for coil start and end: if the coil end is going to ground, then the coil tape is doing virtually nothing, good or bad. If the coil start is going to ground, then the shield is having an effect as a shield, and adding about 30pF capacitance.

So you might think it's better to just always have the ground side of the circuit at coil end, but a downside to having the coil start at the hot side of the circuit is that the pole pieces, if not grounded (which these are not), can act as a noise receiver, you will especially hear noise when you touch the tops of the pole pieces. Ungrounded steel pole pieces will generate more noise than AlNiCo pole pieces due to their higher permeability and conductivity.

30pF capacitance added is equivalent to about 1 extra foot of guitar cable. If you remove both the copper tape and replace the shielded hookup wire with two strands of wire, like a vintage Strat pickup, you reduce the capacitance by 60pF, or two feet worth of guitar cable.


Then the Q factor:




The eddy currents caused by the copper tape brings the unloaded resonant peak amplitude by 7dB. Disconnecting the copper tape from the ground wire doesn't change the Q factor at all but the reduction of 30pF capacitance, as measured above, raises the peak frequency by 1kHz.

With a simulated cable capacitance and control pots, the copper tape reduces the resonant amplitude by about 2dB, which is just at the edge of being audible.

One thing I realized is that if you want to break the circular continuity of the tape in order to eliminate the eddy currents, all you have to do is heat up the solder on the copper tape, pull it up, and then just fold the tape back on itself until it's no longer touching the other side. The adhesive isn't conductive, so breaking that solder joint that's holding the tape to itself could be enough by itself, but it's hard to guarantee that the copper tape isn't making continuity if it's touching with itself in any way.

So as can be seen in how the two upper most sets of peaks having matching amplitudes, folding back the copper tape so it isn't make a full loop is virtually the same as removing it all together, but because it's still grounded, it's still acting as an electrostatic shield. But that being said, you could just switch the red and white wires, so that coil start is on the inside of the coil, and not the outside, and that renders the shield unnecessary, and reduces the capacitance a bit.

In conclusion, I'd say the fold back is a good mod, because it eliminated the eddy currents while retaining the shielding properties of the copper tape. There's just no reason that it has to have circular continuity.

Also keep in mind that the top and the bottom of the coils are not shielded, and that the shielding only blacks electrostatic noise, it doesn't block electromagnetic noise, which is generally the much bigger source of noise, and which humbucking blocks. That's why everyone agrees that humbuckers sound a lot quieter, but there's debates about whether shielding makes any difference at all.


Tape folded back in order to break continuity around the circumference of the coil:




Duncan Designed loaded pick guard, the white wires (coil finish) are hot, and red to ground. I bought this off eBay a while back, probably factory overrun.