Understanding Guitar Wiring

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Understanding Guitar Wiring

Postby Benn Roe » Wed Jul 25, 2018 11:54 am

The subject of this thread is both my goal and the title of a Stew Mac resource that feels to me like it's missing some crucial pieces of information. I figured I'd go through it here to see if anyone could help me fill in the gaps. As I'm beginning to plan the wiring for my first build, it'd be easy enough for me to reverse-engineer some online schematics and trial-and-error my way through it, but I want to actually know why it all works, not just get it working. Here goes:

How a magnetic pickup works This section seems pretty comprehensive when it comes to the internal workings of a pickup, but it doesn't really tell you anything about actually wiring them. The humbucker phase chart is interesting, but how do you actually connect wires to go about reversing the phase on one coil, or wiring the two coils in parallel? How do you split the coils? And why do these processes work this way? Each coil has a start and a finish, so I'd guess wiring a finish to a finish would reverse the direction of a coil and, thus, invert the phasing. That seems intuitive enough. Wiring in parallel would just have the finishes each going somewhere else (like a volume pot) instead of one going to the other's start? I can intuit a lot here, but nothing's really explained.

What is a potentiometer and how does it work? This section was pretty unclear when I first read it, but reading the next two sections cleared it up for me. The sweeper outputs a signal with resistance based on the knob's position, right?

How is a volume pot wired? I'm not really sure what the jazz bass short-circuiting example is getting at, but otherwise this is pretty clear. If the pickup were wired directly to the output jack, with no volume pot, how would that affect tone, since a higher resistance pot prevents loss of upper frequencies? Would it be the equivalent of a really high or really low resistance pot? I'm guessing high, as pickups are high impedance?

What is a capacitor and how does it work? There's no difference between a tone pot and a volume pot, right? The tone pot just has a cap in the mix? As for the cap itself, when it says "the higher the value of the cap, the more upper frequencies are allowed to travel through it", does it mean a higher value will result in more upper frequencies going to ground or going to the amp? I guess I'm just not sure how exactly the cap interfaces with the pot. For volume, I understand why higher resistance would yield an overall brighter tone, but is the highest value of a tone cap always the "true" output of the pickup, or is the choice of cap somehow brightening or darkening your tone at its highest setting?

Selector Switches There's really no explanation here to indicate why things are wired the way they are, but I kind of hate selector switches, and will probably always use a Jaguar-esque system for my guitars' pickup selectors, so this isn't a big priority for me, but I guess I should still figure it out.

Mini toggle switch basics and push-pull pot basics I understand the idea, but I don't know if I understand the diagrams. I assume the black dots are the poles (terminology?) that are active in that position, but are there specific inputs and outputs, or do you just have four connection points to do whatever you want with? SPDT means one row instead of two? SPST would I guess mean each position of the switch would only correspond to one pole? Is that even useful? Is there a DPST? Is there any disadvantage to using a DPDT switch when SPDT would have done? Or, in other words, can I leave poles unused without causing problems?

Output Jacks I have no questions. This seems basic enough.

Grounding and Shielding At the risk of sounding like an idiot, I understand the importance of grounding, but I don't really know what it is. Does connecting the wire to any piece of independent metal get the job done? You just need something conductive that's not part of the circuit?

Understanding impedance and impedance matching This doesn't seem to explain almost anything to me, but a lifetime of amp usage has armed me with some understanding of impedance and associated math.

If anyone can help me fill in any of these gaps, I'd appreciate it! Hopefully this can serve as a resource for other wiring newbies down the road.
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Benn Roe

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Re: Understanding Guitar Wiring

Postby Adamadamadam » Mon Jul 30, 2018 11:46 pm

Okay. I'm not an expert but I'm an enthusiastic hobbyist for about a decade now. Take the answers for whatever that means.

Magnetic Pickups
A magnetic pickup is a coil of wire inside a magnetic field. One end of the wire is hot, and the other is ground, and these labels are basically arbitrary. The electricity (generated by something ferrous-the string-vibrating in that field) doesn't care which end is hot, as long as there's a hot and a ground.

As applied to pickups, phase basically deals with which end is hot and which end is ground. Changing the phase of a pup is to flip those two ends. A single pickup can never be out of phase with itself, but two pickups (wound in the same direction) will be out of phase if the 'hot' side of one and the 'ground' side of the other are both sent to the output.

Parallel: the hot ends of each coil are connected; the ground ends of each coil are connected, and the hot signal goes to the switch.

Series: the hot end of the first coil connects to the ground end of the second coil, and the hot signal from the second coil goes to the switch. Tends to be hotter than the humbucker in parallel.

A humbucker out-of-phase will have one of the coils' ground wired to the others' hot, like it's parallel. You'll get some frequency cancellation, which will lead to a thinner sound.

Right. Put most simply, a volume pot has one lug as full signal (hot), the opposite lug as no signal (ground), and the middle lug as where you want your guitar to be on that spectrum. Don't worry about tapers for now.

If you're just getting your feet wet don't sweat how multi-volume-control axes (Les Pauls, Jazz Basses, etc) can cause the signal to short out if one knob is set to zero. It's a quirk of passive electronics. Learn to live with it and move on.

In most applications, capacitors are used to store a charge for a short time and then discharge it rapidly. The most extreme example is a railgun. In audio applications they're used as frequency filters, because magic. Mechanically, a capacitor has dozens of layers of alternating conductive and non-conductive material between the two leads. A tone pot is completely passive, so the cap value basically determines at which frequency things begin to cut off, and the pot's value/taper determine how that cutoff happens.

Selector Switches
I'm guessing you're talking about the Gibson sort? There's a left hot, a right hot, and a middle both (hot, parallel). The contacts are pretty easy to see if you have the switch out.

Poles are the number of connections, throws are the switch orientations. A SPDT switch will have three lugs and two orientations: up will connect the top and middle lug, and down will connect the bottom and middle lug. DPDT will be the same, but the two sides (top/middle/bottom) will share the same switch. Buy a cheap digital multimeter and get to probing. I say that as someone who's been in your position.

It sounds like you don't need to worry about impedance matching. Unless you're building your own amps or winding your own pickups you'll be fine.

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Re: Understanding Guitar Wiring

Postby challengerdeep » Wed Aug 01, 2018 12:28 am

These are two movable resistors that form an adjustable voltage divider.
(in actuality it's one horseshoe shaped resistor and the center contact moves)

Two very close parallel plates. DC cannot pass. Being a wave, AC can pass because the plates still influence each other's charge. Higher frequency more freely travels through a capacitor than low frequency.

There are *many* special uses for a capacitor, but in a guitar we're only concerned with High-pass and low-pass filters.
http://www.experimentalistsanonymous.co ... ilters.png
Once you understand a voltage divider, you might understand these as frequency dependent voltage dividers.

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