One topic that intrigued me as a young guitar player was definitely modifying my guitar's electronics. I remember when I bought the harness for the "Jimmy Page" wiring. That was absolutely crazy—four push-pull pots doing SOMETHING. I was so happy to have so many sound combinations that I forgot to practice. Anyway, very soon I’d remove two faulty push-pulls and gradually revert to the old-school style of having no mods on a Les Paul and just focusing on playing. But it was so cool to explore that.
Now that I've expressed some feelings about memories long forgotten, I’d like to start the topic of parallel coils. So, what am I talking about here?
Jumping back into the memory of the Jimmy Page wiring, I clearly remember that two of the push-pull pots were wired to achieve a split-coil. Obviously, after switching from a Telecaster to a Gibson Les Paul, a thought was planted in my mind that I needed some single coils for my gigs. So, I gave those splits a try. And to be honest, I didn’t like them. I still don’t really like them. I will say that there are some humbuckers that sound good when split, but most of the vintage-style PAFs I usually play don’t sound that great when split.
After hours and hours of surfing forums and the internet, I came across this topic of coils in parallel. Apparently, there was another way to get this "brighter" and "thinner" sound that somewhat resembled the split coil. Also, apparently, there was a huge benefit to this new system—it didn’t hum!
Obviously, I had to give it a try! But before I share any subjective comments on the sound achieved, let’s dive in and explain what the parallel coil connection is all about.
Okay, most of us are familiar with how the humbucker works, right? There are two coils of wire, sometimes one next to the other (like the PAF), sometimes one above the other (like some single-coil sized humbuckers), and these two coils of wire are connected. Normally, in 99% of the pickups we use today, the connection between the two coils is done in series. That means that the end of one coil is connected to the beginning of the other coil, and we use the two "outer" wires to connect the pickup to the rest of the guitar's electronics.
To achieve the "correct" sound of a humbucker, it is mandatory that the magnets, or slugs, around which the coils are wound are of reversed polarity. Not only that, but in addition to being magnetically reversed, the two coils need to be electronically reversed. This can be achieved either by winding one coil clockwise and the other counter-clockwise, but nobody does it this way. Pickup manufacturers or winders usually have a winding direction that they are comfortable with, and they always wind the coils in the same direction. The polarity reversal is achieved simply by switching the wires of one coil. So, basically, you’d connect the end of the first coil to the end of the slug coil, and you would use the starting sides of both coils to connect it to the system. This is mandatory for achieving the recognizable fat and smooth sound of a humbucker and for noise cancellation (hence hum-bucker).
If the coils in the humbucker are not magnetically and electronically reversed, the pickup will not sound right. It will have a thin, nasal, or "phasey" sound. Or maybe it will sound right for someone - it did for Peter Green.
Now, there are many different humbuckers on the market today. New technologies have been implemented, and new designs have come to life, but fundamentally they are very, very similar. Usually, the coils are not wound exactly the same, with the main coil tending to have a bit more windings compared to the slug coil. But for the purposes of this demonstration and analysis, I will assume that the humbucker is made of two exactly the same coils. This just simplifies the math.
One more thing to point out: I will be using some slightly technical terms now, such as inductance, capacitance, and resistance. So, I highly recommend you check out my other article on pickups: The Pickup Equation: Resistance, Inductance, and Capacitance Demystified. Do your homework before continuing!
Assuming that we fully understand what resistance, inductance, and capacitance do in a guitar pickup, let’s take an example of a very nice vintage-style PAF pickup, consisting of two exactly the same coils, with the following measurements:
\[L = 3H\]
\[R = 4k\Omega\]
\[C = 200pF\]
So, what happens when we connect two coils like this in series? Well, let’s do some basic physics:
Inductors in series are simple—they just add up, so the equivalent inductance will be 6H.
Resistors in series are also simple—they add up, so the equivalent resistance will be 8k ohms.
Capacitors in series are a bit trickier and are calculated with the following formula:
\[\frac{1}{C_{\text{total}}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3} + \dots + \frac{1}{C_n}\]
Since we have only 2 capacitors here, our equivalent capacitance will be 100pF.
So our series connected humbucker will have the following traits:
\[L = 6H\]
\[R = 8k\Omega\]
\[C = 100pF\]
Now is the time to invoke the power of plotting. Take a good look at Figure 2:
In Figure 2, I have plotted three lines. The blue line represents what the response would be if we only had one of the coils active—so a simple split coil. Assuming we had a 500k volume and tone pot connected, a 5m cable, and an amplifier load of 1M ohms.
The green line, in turn, represents the frequency response of a classic series humbucker. It can be clearly seen that the resonant peak has been moved lower in the frequency range and that more of the presence has been cut. Keep in mind that we are only discussing the frequency response here, not the actual voltage output of the pickups, or, as some might say—the volume of the pickups. Split coils are usually about half of the voltage compared to a humbucker; however, it's not very easy to say exactly because the output voltage depends on the magnetic field, which varies from one pickup design to another.
Now we come to the red line. This is the frequency response of a humbucker pickup with coils in parallel. Quite interesting, right? Not only is it more "present" than the split coil, but it pretty much retains the voltage output of the full humbucker, since both coils are working, and it is still humbucking. One might think, this must sound really good. The way how you achieve this connection is by connecting the start of the first coil to the end of the second coil, and the end of the first coil to the start of the second coil, afterwards use those to connection points to connect to the rest of the circuit - one side obviously to ground, and the other, obviously, to hot. That's how the parallel connection is made.
The question remains: Why didn't this configuration achieve any success in the industry?
Well, to everyone’s surprise, I have an opinion on this.
There is a practical problem with a sound like this. Even though everyone is asking for more of that "top end" and "openness," when it comes to guitar pickups, a lot of high end isn’t always a good thing. That huge resonance is also not always desirable. In practice, with a lot of humbuckers wired in parallel, the sound can simply be overly bright and may need some work.
That being said, I will say this: I tend to like humbuckers in parallel. Some pickups that I’ve done this mod to sound absolutely great. It usually works well with some higher-output pickups. But why is that? Let’s do some math again.
Since we have our two coils in parallel this time, we need to apply some new formulas. Inductors and resistors in parallel use the reciprocal formula (as used for capacitors in series), where capacitance is simply added when in parallel. If we work the numbers, the result for the humbucker coils in parallel is:
\[L = 1.5H\]
\[R = 2k\Omega\]
\[C = 400pF\]
Kind of weird and out of the ballpark, right? That’s exactly why I said it tends to work better with higher-output pickups. The resulting inductance and resistance will not be as low, so the resulting resonance peak won’t be as sharp or as high in the frequency range.
Another good idea to tame the pickups in parallel resonance would be to use lower-value pots for volume and tone—perhaps a 250k. Just sayin’.
And one more thing: I mentioned that a lot of humbuckers have coils that are not equally wound. That also doesn’t work well with the parallel connection. You can try doing the math yourself, but the resulting inductance and resistance will always be lower than if the coils were equal.
