S&S BiPolar pickup details

[antigua]

I ordered a loaded pick guard of BiPolar pickups from www.bipolarpickups.com/ . I'm interested in trying some other wiring schemes that they don't allow for with their loaded pick guard, so I'm going to rewire it, but I have to document what's what in order to get the phases correct. I'm sharing this information here, and the info also gives some insight into how the pickups will probably sound too.

These Strat pickups have two coils per pickup, side by side. They were made by cutting neat looking orange colored Strat bobbins into two halve, winding little three pole pickups, and then combining them together on a third piece of fiber board that is shaped much line a base plate for Strats.

The pole piece stagger is nearly flat, but not quite. The pole pieces having reversed polarities on each side of the pickup, three north and three south, which isn't actually necessary since there are no "in between" positions. You only need reverse magnetic phase when any given string is sense by two pickups, but with the pre-wired pick guard, every string is sensed by one pickup at a time, in all five positions, so all that is required is reverse phase, but the reverse polarity could be ignored. Here's a video showing the different positions, I think the guy in the video is the one who thought it up 

My plan is to change all the magnetic polarities to be the same, remove the hum cancelling and set up dual blade toggles to allow for almost any combination of coils. I don't know what they sound like other than what I've seen in demo videos.




Wires:

White - start EAD
Black- finish EAD
Green - start GBE
Red - finish GBE


Pole pieces: 1100 Gauss, EAD north up, GBE south up


Bridge with combined combined (black white):
L: G-RB-W: 1606H G-RW-B: 1718H
C: G-RB-W: 86.98 G-RW-B: 88.98pF
R: 6.489k

Bridge pickup - low EAD strings (white to black):
L: 892.6H
C: 136pF
R: 3.364k

Bridge pickup - high GBE strings (green to red):
L: 772.1H
C: 192.94pF
R: 3.127k


Middle pickup - low EAD strings (white to black):
L: 895.1H
C: 155pF
R: 3.311k

Middle pickup - high GBE strings (green to red):
L: 795.3H
C: 157pF
R: 3.183k


Neck pickup - low EAD strings (white to black):
L: 860.2H
C: 162pF
R: 3.316k

Neck pickup - high GBE strings (green to red):
L: 619.8H
C: 238.7
R: 2.831k


Based on these measured values, these are very under-wound relative to a typical Strat pickup, about 1.7 henries. Normal Strat pickup achieve at least 2.4 henries with the usual ~8,000 turns. The capacitance of two of the coils combine is around 90pF, which is also typical of Strat pickup. The resonant peak wound be rather high, over 10kHz, and around 5kHz with 470pF added load.

The electrical values of the GBE side of the neck pickup have really low inductance and DC resistance compared to the others, and really high capacitance, which possibly suggests an internal short in the coil, but I'll try it out before seeing if it needs replacing or rewinding.

Usually when you add inductances together from two coils, the add together, but there is a second mutual inductance factor based on how the coil are geometrically aligned, so that their magnetic fields are near each other. If the magnet fields are in phase with eachother, the overall inductance goes up slightly. If they are out of phase, the inductance drops. Looking at the inductance of the bridge pickup's coils by themselves, and comparing that to the inductance of the two coils in series, it can be seen that the mutual inductance increases the overall inductance by 3.2% when wired in phase (G->RW->B), and drops by about the same amount when wired the out of phase (G->RB->W). Overall that bump up is not too impressive, since the magnetic connection between the coils is through the air, and not steel or iron.

Concluding thought: these are really well priced for what they are. $225 for some exotic split coil Strat pickups that can make sounds from a Strat that few people have ever heard before. I was a little disappointed that their pre-wired pick guard only offers five out of a potential 47 tones. Of course to get all 47 you have to do some exotic control, and guitarists tend to shy away from exotic controls. I think I can to with with two push-pulls and two blade selectors, though. The Eastern style blade switches are smaller and will fit nicely side by side, but the larger all metal American style ones probably wouldn't. I might do a demo video when it's all done. I don't love making videos, otherwise I'd have a Youtube channel by now, but in this case I think a video would be valuable. Conceptually, the wiring is like having two electric guitars connected to each other in series, with each controlling with three strings, with a master volume and tone.

[stratotarts]

Jan 12, 2020 6:31:10 GMT -5 antigua said:

The pole pieces having reversed polarities on each side of the pickup, three north and three south, which isn't actually necessary since there are no "in between" positions. You only need reverse magnetic phase when any given string is sense by two pickups, but with the pre-wired pick guard, every string is sensed by one pickup at a time, in all five positions, so all that is required is reverse phase, but the reverse polarity could be ignored.

Sorry, you lost me there. If you select a single pickup by itself, don't you need both magnetic polarities to make it hum canceling? Or, wouldn't you want to have a choice of using a single pickup?

[antigua]

Jan 12, 2020 8:08:46 GMT -5 stratotarts said:

Jan 12, 2020 6:31:10 GMT -5 antigua said:

The pole pieces having reversed polarities on each side of the pickup, three north and three south, which isn't actually necessary since there are no "in between" positions. You only need reverse magnetic phase when any given string is sense by two pickups, but with the pre-wired pick guard, every string is sensed by one pickup at a time, in all five positions, so all that is required is reverse phase, but the reverse polarity could be ignored.

Sorry, you lost me there. If you select a single pickup by itself, don't you need both magnetic polarities to make it hum canceling? Or, wouldn't you want to have a choice of using a single pickup?

The stock wiring does not offer the possibility to use one pickup by itself. It sounds crazy, but it's true. 

[antigua]

It is done, I mounted the BiPolar's into a custom wiring scheme. It's in a special guitar too, the third guitar I ever bought, and the one I went the most places with back in the day.




Note two selector switches. The two tone knobs are push/pull pots. I didn't realize the screw hole pattern for this pick guard was fubar until after I had cut out the second selector switch and was done with everything. I made new holes in the plastic and plan to fill the old ones.

This is the insides:




The controls are sort of two dimensional; the EAD wound strings are all on the upper selector switch, and the GBE plain strings are on the lower selector. Each selector behaves mostly like a Strat switch:

B
B+M
M
M+N
N

but then if the push/pull pot is pulled up, it becomes:

B
B+M
M
B+M+N <-- new
B+N <-- new

Only the last two positions are different when the push pull pot is pulled up, but that's a total of seven pickup combinations with one five way and one push pull pot. (the way this works is by re-purposing the second side of a stock selector switch that would normally be used to dedicate the two tone controls to specific pickups to make the bridge optionally active when the neck pickup is selected, and position four in turn).

Each pickup is split into two coils, one on each side, each side has one five way selector and one push pull pot, so that 7 * 7 = 49 combinations.

Then there's the tone controls. The top knob is a master volume per usual. The bottom tone knob is global, but the middle tone knob affects only the wound strings, or one side of the circuit. With a third push/pull pot I can make it so that this tone control one side or the other, and I'm planning to make this change since I've tried it out since having wired it this way.

The two tone controls, global and EAD, are interactive, unfortunately. It would be nice if they behaved independently. Decreasing the tone value on the EAD's tone causes the global tone to become less effective, so in effect the GBE strings become brighter as the EAD strings become darker. Also the EAD's tone does rather little until the botton of the sweep is reached. It probably need a lower value pot, or a resistor across the lugs to make effectively a low value pot.


How it sounds....

The low inductance makes them very bright, but a tone control fixes that up easy. Where a normal Strat might need to be rolled back to 8, these might need to be rolled down to 6, but otherwise they sound good and the output level is decent enough.

Having the sound of two different pickups selections all at once; when strummed, frankly it sounds like a bit of a mess. You mostly hear the brightest strings, the GBE string. The EAD strings sort of disappear into the cacophony of harmonics, so it doesn't really matter so much where the EAD selector switch is set, of course you get more bass when the neck pickup is selected, or more treble when the bridge is selected, but the timbre differences between them is hard to hear when strumming. Meanwhile, selecting between the GBE strings changes the tone the most, pretty much as if you were switching between pickups on a stock Strat. I haven't had a chance to use the guitar in a jam with a drummer yet, there might be some benefit to using the two selectors as a sort of on-the-fly EQ, which is sort of how BiPolar markets the loaded pick guard to begin with.

Picking out individual strings, or finger style is a different story though, in that cause you can distinctly hear the difference. Imagine playing a finger style, and as you play the pickup selector switch magically flips back and for between the neck and bridge pickup (or whatever), it's like that, sort of surreal. If I were the rhythm guitarist in a band, I think I'd love to have this, because if effectively gives you as a musician two voices at one, your thumb making one sound, you other digits are making another. With the tone knob dedicated to the lower strings, you can get the bass strings to deliver a bump-bump-bump while the GBA strings are used to pick the lead line out. Of course a low tech way of doing it is to just slightly palm mute the wound strings.

But as a lead guitarists, I think this could be killer. You play a lead line on the EAD strings, it's one sound, then in the next measure you move up to the GBE strings, and there's a whole different tone. It sounds like dueling guitars, like the Hotel California lead, where it switches from Felder using a bridge pickup to Walsh with his Strat in the notch position, back and forth again.

Even though there is a good use for a dedicated tone control on the lower wound strings, I'd like to try the dedicated tone on the GBE high strings, because they're so dominant in the mix that I think something might be gained from having a way to hush the GBE strings so that the wound strings have a chance to shine.

Another practical problem, on a Strat everyone knows the notch positions are lower output, and that the neck is the highest output, when all the pickups are set to about the same height. When you have the ability to divide it up and use a notch position and the neck position at the same time, of course the strings assigned to use the neck pickup are much louder, so the volume sounds imbalanced, especially when strumming. When picking one string at a time, it's a lot easier to compensate for that by picking softer or harder.


Dead spot between the D and G pole pieces..

These types of humbucking Strat pickups have always had the problem that in between the D and G, there the magnetic fields of the two sides form a "figure eight" flux pattern, if you bend the G string up into the center, the center of the figure eight, the volume drops. This pickup set is configured that way, so I best the G string in the middle to test it, and the volume drop is shocking. Imagine turning the volume control from ten down to two. It's never dead silent, but it sounds like an electric guitar for ants when you set the string right to dead center. In order to overcome this problem I'm going to reset the polarity of all the pole pieces to be uniform.


I'll make some sound demos soon.