Wiring the Frankencaster #1

I was trying to think about how to discuss the guitar wiring. I know wiring diagrams and electronic components can be rather opaque to many people but they really aren’t that hard. I decided not to go into any kind of theory but just to look at my wiring diagram/proposal to see how things will work. Remember, electric guitars are, well, full of electricity. And electricity likes to flow. In many respects electrons flowing in a wire are just like water flowing in a pipe and in fact that’s how I’ll analyze my Frankencaster wiring diagram below.

When I realized I would need to connect all these components, I looked at various wiring diagrams on the web thinking I could just quickly borrow one. What I found was that they were all different and so I quickly realized I would need to do my own. I think I understand how to wire a guitar so I drew up the following schematic which I plan to use to wire the Frankencaster. I drew this diagram on a plane flight to Seattle and let me tell you I drew a lot of glances from the guy sitting beside me. I think he thought I was working on a bomb diagram. I was very tempted to start running my finger down a specific wire and then softly whisper “BOOM”.


The way to understand this schematic is to remember that electric signals want to flow from source (pickup) to ground, completing a loop, or circuit. The symbol for ground in the schematic looks like an upside down Christmas tree or pyramid and you read this symbol as saying all the grounded things share a common connection, which joins them electrically. You can imagine them all connected together by a big loop of wire though in practice that won’t be how I ground the components (see below).

In this wiring diagram, there are 10 basic components. There are two pickups (neck and bridge), each with its own volume control and its own tone control. These volume and tone controls are made from potentiometers, or variable resistors. A variable resistor, say 500 K ohms, is exactly what it sounds like – you turn the knob and this varies the resistance between the middle post and an outer post from 0 ohms (conductor) to 500,000 ohms. So that’s six components.

Each tone control also uses a capacitor (which adds two more components). Capacitors, in this context, can be thought of as components which, when combined with resistors, allow a direct connection to ground for certain frequencies. In other words, capacitors in series with resistors can subtract certain frequencies from the main signal, shorting them to ground before they get to the output jack. These circuits are called “filters”. By changing the resistance, one can change the frequencies which are subtracted. This is how a basic tone control works. Turning the tone knob alters the resistance and changes the frequencies removed from the signal from none to some. What you actually hear is treble being added or lost. In fact no treble is added, it is only removed.

Then there is a switch to switch between the two pickups, and finally there is an output jack, where the signal goes out to the amp and later returns to the guitar and to ground. Each of the pickup circuits is independent of the other so while they make the diagram look more complicated, it is really just two circuits on the same page, sharing a switch.

For the volume controls, the voltage from the humbucking pickup enters the variable resistor and leaves through the wiper (middle lead) of the variable resistor. If you turn the pot all the way in one direction, and the voltage may be zero; turned to the other side the output voltage approaches the input voltage. This is how the volume control changes the volume, by reducing the output voltage to near zero.

There are three questions at the bottom of the page and I’ll briefly mention them as they were items I wanted to research further. First, I want to make sure the end result had few to no ground wire loops. For example, both volume controls have one lead connected to ground. By connecting a wire between then and then running the wire to another place to ground the components, potential ground loops are created. Ground loops are potentially bad because, since they are wires, it is possible to induce currents in them inadvertently (the same ways we induced currents in the pickups). The result can be  a significant source of noise or hum. What I have decided to do is to wrap the body cavity and the entire underside of the pickguard with copper tape, thus at once grounding the various bits as well as providing a shielding cage around all the electronics. I’ll post pics when I get that done.

I will use the same solution for the bridge ground – tape overlapping the bridge to ground the bridge.

Finally, I wanted to double check the frequency which the particular RC choices I had made (0.022 uF and 0.047 uF capacitors – recommended choices by Seymour Duncan) will affect with the tone controls. I have not done this yet.



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