I Don't Understand Guitar Wiring: Where's the Circuit?

[RobRed]

I am fighting to get a handle on how guitar wiring works. I am confused. In most wiring that does anything, you see circuits--the wire starts at one place, goes through some components and maybe a switch, and then it comes back to complete a circle.

As I see it, with guitar wiring you have one side of a pickup that is "hot" and/or "live", and which, after passing through pickup selector(s) and a volume pot, goes to the tip connector of your jack. The other side of the pickup is negative and, after passing possibly through tone control pots and caps, goes on to the sleeve component of the jack, which is apparently tied to ground. The other part of the negative side that I find confusing is that every component in the control cavity is connected to that same ground--certainly most of that has nothing to do with producing sound. Generally several pickups are hooked up in the same manner, with some switching options to allow them to run in parallel or series, in phase or out of phase, but with the same ultimate characteristic of one positive end going to the tip of the jack and the negative end being grounded to the sleeve. No circuit is completed within the guitar control cavity.

It would be another thing altogether if I could understand that the circuit was completed in the amplifier to which the guitar is connected, but I am confused there because one wiring guru that I ran into along the way on some web site claimed in no uncertain terms that there is absolutely no current running from the amplifier back to the guitar, unless there is a short somewhere. It would be one thing to say that there is a tiny current, just adequate to convey a guitar signal, and that one needs not worry about getting zapped by it, but it is another altogether to say there is no current going back to the guitar.

Then there is the issue of switches. In most circuits (at least I think so), switches are used to open and close circuits, but with guitar wiring, they do not appear to do that. They simply determine which of the several pickups or individual coils of pickups are active at a given time and whether they run in series or parallel or in or out of phase. Inasmuch as there is no circuit completed, I find it really confusing, for example, to see a switch in a wiring schematic with one terminal going off to ground, for instance. I have more specific questions about switches regarding which I am going to put up a separate thread, but here I will put up one of several switch schematics I have where, without anything resembling a circuit in the picture, it is very hard for me to conceive of why the switch is doing what it is supposed to be doing and what role the connection to ground plays (see Super Switch with HSS).

Can anyone enlighten me regarding what sort of electricity we're dealing with here that does not involve circuits and why the negative pole of the pickups runs to ground rather than to something akin to the neutral pole in household current (where we have hot, neutral, and ground as three separate components, not just hot and ground, and circuits are completed if we want to get anything useful from the electricity.

Thanks in advance for consideration and any assistance offered. Rob R

[Chuck H]

I'll start by saying that what you don't know about electronics has been written in books and takes time and study to understand. I doubt you'll get an answer here that fills in all the gaps for you simply because it would take too much time. Now, that said...

The magnets in the pickups are the voltage source for the "circuit". The coils impedance prevents the needed AC from passing directly to ground and this is why the circuit is not shorted. The ground reference is needed to complete the circuit as this is an AC circuit and could not work without a + and - polarity exchange.

The magnetic field holds the coil at a potential. The vibrating strings alter the magnetic field and also the potential in the coil. It is this difference between the static and altered potentials in the coil that is the AC signal sent to your guitar amp.

[big_teee]

I recommend starting on basic wiring and repairs.
Buy a cheap Multi meter if you don't have one and start checking things on the ohm scale.
You will answer most of your own questions.
Later,
Terry

[RobRed]

Thanks a lot chuck! You know, you hit the nail on the head. I've been reading everything I can get my hands on from guitar wiring sites and a couple of books on the topic, and even reading them with these questions in mind, I'm not finding the answers. For the most part, they just treat you like an idiot and tell you to connect wire A to terminal B, rather than giving a clear idea of what you're actually accomplishing. Perhaps I should have asked instead if someone could recommend a book that would cover the topic reasonably thoroughly?

I do understand and recognize most of what you've said. I know that vibrating a string in a magnetic field creates an electric potential, and that that has the potential to generate an electric current, but where I'm hung up is on the question of where the current is going--again, my main problem is I don't see any completed circuit here. Our household AC current has a much greater potential behind it than the AC current in a guitar, but until you close a circuit by flipping a switch to "on", it is nothing but electrical potential. I am missing how striking the strings and producing an electrical potential in the magnetic fields of the pickups is converted to a useful signal when none of the diagrams show what I can recognize as a completed circuit. Of course I recognize there must be a circuit for a current to be generated, so perhaps what I didn't put as clearly as I might have is the question, where is the circuit closed between the positive and negative poles in guitar wiring? I'm just missing that connection.

[RobRed]

You know, I have one and I keep meaning to pull it out. I don't have all the hardware yet, but it occurred to me that that would be a good approach once I get my hands on the switches and what-not. I haven't used it since I wired my workshop, so it may take me a while to find it. Obviously, I have more experience with electricity than with electronics, but I suspect that is going to change fast! Actually, I suppose I could pull out some of my other electric guitars and play around with the multimeter just to see how things work in them. Of course, it's going to involve the same concepts. Thanks, Terry.

Rob R

[RobRed]

Joe: That was a great idea, but I'm not sure I'm any more comfortable that I've got the answer after doing what you recommended. I actually started out using a single pickup with volume and tone, then a single coil with volume alone, and ended up with the pickup alone. In the first 2 cases, I could readily find a circuit, and I could see obviously how the volume and tone pots influenced the signal through the circuit, but in none of the 3 cases could I see a circuit actually carrying current to the amp, and in the case of the pickup alone I did not see any circuit completed. The fact that in any of these the connections to the jack are positive and negative and nowhere connect is where I'm having trouble. It looks like a potential difference across the jack, but if the circuit is not completed in the amplifier, then I just don't get it. I've uploaded my three diagrams. In the first two, the circuit is marked with red arrows and the part of the wiring (involving the jack), where I could find no completed circuit, is circled in a broken line. In the third, the whole thing shows no circuit, unless I am missing something. I was very happy though to see the completed circuits that I did. That helps me to understand the role that a connection to ground from a switch terminal might have.

Thanks, Rob R

[JoeM]

Well I was hoping to get you thinking about it without the switches pots etc complicating issues. But it wont look like a simple DC circuit where you 'see' current flowing, at least not in the way you may be thinking about it.

[big_teee]

Joe: That was a great idea, but I'm not sure I'm any more comfortable that I've got the answer after doing what you recommended. I actually started out using a single pickup with volume and tone, then a single coil with volume alone, and ended up with the pickup alone. In the first 2 cases, I could readily find a circuit, and I could see obviously how the volume and tone pots influenced the signal through the circuit, but in none of the 3 cases could I see a circuit actually carrying current to the amp, and in the case of the pickup alone I did not see any circuit completed. The fact that in any of these the connections to the jack are positive and negative and nowhere connect is where I'm having trouble. It looks like a potential difference across the jack, but if the circuit is not completed in the amplifier, then I just don't get it. I've uploaded my three diagrams. In the first two, the circuit is marked with red arrows and the part of the wiring (involving the jack), where I could find no completed circuit, is circled in a broken line. In the third, the whole thing shows no circuit, unless I am missing something. I was very happy though to see the completed circuits that I did. That helps me to understand the role that a connection to ground from a switch terminal might have.

Thanks, Rob R

Your red current arrows on the first 2 are not correct.
The whole signal path does not go through the tone pot.
The circuit is from the tip of the jack, to the center of the volume pot, through the Vol Pot, out of the vol. pot through the pickup. Returns on black wire to ground back to the jack. the tone ckt is a secondary ckt, with some current flow that effects tone. In fact to make a very short ckt. if you short the jack tip to sleeve, that is the circuit. when the tip goes to vol pot. when you turn it up and down that determines the current out of the vol. pot.
Terry

[JoeM]

Even though you wouldnt want a guitar with just a pickup and no tone or volume, it would work just the same. Imagine a very high impedance speaker (say 1 meg ohm), that can produce sound even with mv AC, connected between hot and ground. That could be your completed circuit, but in practice you'd have the input stage of the amp getting the signal from the pickup, not the imaginary speaker. (The pickup being an AC signal generator.)

[RobRed]

OK...Now we're talking. It's too late at the moment, but I'm going to have to review those drawings I did today in reverse and look at the tone control part as a separate circuit. I'm still stuck on how we can view it as a circuit if the positive side ends at the tip and the negative side at the sleeve. A circuit has to be closed to function as a circuit. It seems to me that Joe's last comment suggests there actually is a completion of the circuit across the jack in the amp/speakers that the guitar connects to...that makes sense to me. If there is completion of a circuit involving the connection between the guitar and amp, though, then am I mistaken to believe that there must be a current, presumably minute, traveling from the amp back to the guitar? I know that question has next to nothing to do with understanding wiring within the guitar, itself, and I think the outcome of looking at the circuits in the drawings I did in response to Joe's suggestion will help me tie that all together, but I am really stuck on this idea of having a circuit that isn't a circuit!

Thanks, all. I hope I'm not driving you crazy, but I have a tendency to obsess until I understand something. Rob R

[Sweetfinger]

A circuit has to be closed to function as a circuit. It seems to me that Joe's last comment suggests there actually is a completion of the circuit across the jack in the amp/speakers that the guitar connects to...that makes sense to me. If there is completion of a circuit involving the connection between the guitar and amp, though, then am I mistaken to believe that there must be a current, presumably minute, traveling from the amp back to the guitar?

You can think of the input circuitry of the amplifier as completing the guitar's "circuit". This is rarely referenced because it is essentially a given that the guitar WILL be plugged into an amp. If you want to get really complicated there are subcircuits in the guitar that are operating without it being plugged into anything, but there's no need to discuss them much because it isn't really useful to ponder what a pickup is picking up when it isn't connected to the amplifier.

The answer you received about there being no current flowing from the amplifier to the guitar is correct for the general context. The amplifier in no way "powers" the electric guitar. There is a small ac signal flowing BETWEEN the guitar and the amplifier but the signal is generated by the guitar. Even though half the time there are electrons flowing backward into the guitar as part of the ac current, for pretty much all purposes relating to guitars and amps, ac signals(currents, voltages) can be understood to "flow" from the generating point outward.

Some audio IS wired like electrical outlets, with a hot, neutral, and ground. They are called "balanced line". It is possible to wire a guitar this way, but is rarely done.

[Steve Conner]

The answer you received about there being no current flowing from the amplifier to the guitar is correct for the general context. The amplifier in no way "powers" the electric guitar. There is a small ac signal flowing BETWEEN the guitar and the amplifier but the signal is generated by the guitar.

Yes. The situation is pretty much identical to the AC current in your wall outlets, except the current is much smaller.

The pickup is a generator, current flows out of it through one wire, down the guitar cord, through the first stage of the amplifier, back along the other conductor of the guitar cord, and back into the pickup through the other wire, completing the circuit. (Obviously the current is alternating, so half of the time it runs round the circuit in the opposite direction, but it is still the same circuit, and the pickup is always the generator of power and the amp the consumer.)

An amplifier is required because the output from the pickup is too feeble to power a speaker directly. Or put another way, because Leo Fender thought the world was ready for something louder than a Dobro. The pickup supplies a tiny amount of power to the amplifier's first tube (or transistor or whatever) which amplifies it by adding power derived from the wall outlet, then this amplified signal is fed to the next tube, and so on until you have a deafening 100 watt stack.

The confusing mass of volume pots, tone pots and switches fitted to some guitars complicates things, but it doesn't alter the basic principle I described above. They are all just ways of regulating how much signal from which combination of pickups reaches the amp.

There are two basic ways of doing it: An impedance can be inserted in series with the pickup, which makes it harder for the signal to fight its way through to the amp. The extreme example being an open pickup selector switch, which allows no signal at all.

Or, an alternative path can be provided in parallel, that the current will go through in preference to taking the long trip down the guitar cord and through the amp. A tone pot with its capacitor is an example of this.

A volume pot, as usually wired, does both of these things simultaneously.

"Ground" is a fiction beloved of EEs and techs. In reality, everything is a circuit, and every current must have a wire to go out in, and another to come back in. But, several circuits can share a single wire. Ground is one of these shared wires. You can think of it as a kind of meeting place of currents, where a bunch go in, and another bunch go out, but according to Kirchhoff's Current Law they must all add up. If it helps you, redraw the schematic with wires between all the points that had ground symbols on them.

[GaryR125]

Maybe this will help:

http://ocw.mit.edu/ans7870/8/8.02T/f...nce/1_edit.wmv
Think of the meter as the amp.

[RobRed]

Sweetfinger: I'm getting closer and closer to an understanding that fits what I know about things and makes sense to me. That is comfortable. One of the biggest problems that has had me stuck on this (and I will acknowledge I can take things out of proportion to their level of importance and probably have done so here, but they need to make sense to me) is that one writer on another discussion group that I read while just starting to dig into this stuff came out and said, as if in no uncertain terms, that there is absolutely no current traveling from the amp to the guitar. Now perhaps what he meant to say was that there is absolutely no current generated by the amp that runs to the guitar, and that is true and obvious and a good thing to know, I imagine :<) (I recall in childhood some evening serial where a rock musician was killed by a significant current running from the amp to the guitar, and it turned out someone had messed with the wiring in the amp intentionally in order to murder him).

Of course the current we're talking about here is minute, not something that one would even feel, never mind worrying about getting killed by it. But I was stuck because of the stark statement that there was absolutely no current running from amp to guitar, and to look at the positive and negative ends of the circuit just coming to an end at the jack, where they don't tie together until you plug in, does not show what one would ordinarily think of as a completed circuit. I can understand it if folks who wire guitars regularly come to take that concept so for granted and see the current as so insignificant that they don't find it useful to think about it, but I had to hear it straight after being informed that there was absolutely no current. The pickup influenced by vibrating strings generates an electric potential, but until you close the circuit, there is no current. We know we are generating current in the guitar to send it to the amp for processing, so we come to think of it as using the guitar to send a signal to the amp, but a circuit can't be a one-way street (that's why it's called a circuit!). After the amp does its dirty work, some small amount of current has to come back to the guitar. I think I can see the meeting of the male and female jacks as representing a STDP switch, where you obviously need one at both ends of the cord to complete the circuit (and if electrical power generated was only moving from the guitar to the amp, you'd only need a cord with a single wire and a single connection at the guitar's output jack, and that is obviously not the case). It gets silly to say, but we all know from experience you can have the amp turned on, have pickups selected, and bang-away like mad on the strings generating all sorts of electric potential and wonder where the sound is, until you look down on the floor and see that you forgot to plug in.

The one thing you said that leaves me a bit troubled yet, after you acknowledged that there is a tiny current traveling as there must be in a circuit, is "Even though half the time there are electrons flowing backward into the guitar as part of the ac current (saying which, you have acknowledged the circuitous flow of electricity between guitar and amp), for pretty much all purposes relating to guitars and amps, ac signals(currents, voltages) can be understood to "flow" from the generating point outward (by which you seem to want to turn around and deny it)." First, considering that issue on the same scale, we can describe the current that returns from the amp to the guitar as minute, but we have to recall that the current we sent out in the first place was minute too...that's why it had to be amplified! Second, considering the issue on a bigger scale, when I wire up a light fixture in my bathroom, I don't harbor any misgiving that if I turn the light on I'm going to burn down the plant that generated the power. At the same time, I know that if I don't hook up the neutral connection on the fixture to return unused power to the power plant, that light is not going to do anything. While the business end of using a light fixture is to be able to operate a lamp, and we all reasonably think of having power delivered to our house (as if it was all unidirectional, like we're trying to see between the guitar and amp), the return of power to the generator that we don't have much reason to think about in our daily use of a light, in this much bigger context, is an essential part of reality and the physics of utilizing electric power. If there is no completed circuit and no return of current to the generator, we have no light. I have to see guitar electronics as analogous to that, but just on a much smaller scale.

Anyway, my mind is at peace now on this one issue. Now I can get around to studying the business end of the circuit that is within the guitar itself. Thanks.

Rob R

[Steve Conner]

one writer on another discussion group that I read while just starting to dig into this stuff came out and said, as if in no uncertain terms, that there is absolutely no current traveling from the amp to the guitar.

Well, he was wrong, meh. As you say, the whole thing is indeed a circuit, and it's incomplete until you attach it to an amp using a suitable guitar cord.

While the business end of using a light fixture is to be able to operate a lamp, and we all reasonably think of having power delivered to our house (as if it was all unidirectional, like we're trying to see between the guitar and amp), the return of power to the generator that we don't have much reason to think about in our daily use of a light, in this much bigger context, is an essential part of reality and the physics of utilizing electric power.

Well, not quite. Current goes out in one wire and returns in the other, but power flows unidirectionally from the power plant to the lamp. And even though the current alternates, the flow of power is always in the same direction. Current and power are two different things.

This is why people talk casually about "signals" and "power" flowing from the generating point to the point of consumption. Power is the real tangible thing that obeys the laws of thermodynamics and that you pay the utility so many cents per kilowatt-hour for. Nevertheless, the power can't be delivered without that essential flow of electrons arriving through one wire and leaving through the other.

You seem like one of these people who won't be happy until you understand the whole situation, and that's great. But right now it is best just to take this simplified view as true and not think too hard about why. The rabbit hole goes down a long way, and there are horrid things like Maxwell's equations and Poynting vectors lurking at the bottom.