Question about Guitar circuit in its relation to oscillatng sin wave - Pic included.

[Joel]

First post here at music electronics forum and wanted to say hi for starters. I've been reading a lot of posts here in the last week and learning quite a bit; am stoked that a forum like this exists.

I've been playing guitar for over 10 years and have never paid much attention to the electronic workings of it and have gotten the bug recently to really understand what is taking place in a guitar circuit.

I've also been reading quite a bit about electromagnetic induction -- from ohm's law, faraday's law, to lenz's law about how an alternating current works, and how a charge can be created by disrupting the magnetic flux in a coil of wire and can generate a current through a circuit.

My question is probably very simple -- I was hoping someone could either confirm or clear up my understanding of a guitar circuit.

I created a picture below with different colors representing the direction of the current in circuit in its relation to the sin wave. Am I understanding this correctly?

[booj]

Your drawings make sense in that the signal alternates in direction, but your question would be clearer to me if you were relating it to a guitar signal. A sine wave is generally fed to an amp using a signal generator. A guitar doesn't to generally create a sine wave although it can come pretty close using harmonics.

[Alex/Tubewonder]

Current changes direction (flow of electrons reverses, if you prefer) where the sinewave crosses =-line. At the peaks of the sine it only reaches its maximum and then decreases in magnitude to 0 a.s.o. At the 0-crossing current & voltage change polarity.

[rjb]

I created a picture below with different colors representing the direction of the current in circuit in its relation to the sin wave. Am I understanding this correctly?

No.

Relating your sine wave & guitar rig drawing conventions:
1 (0-90 degrees) current flows toward the amp ("up" the sine wave).
2 (90-180 degrees) current flows away from the amp ("down" the sine wave).
3 (180-270 degrees) current continues to flow away from the amp (further down the sine wave).
4 (270-360 degrees) current flows toward the amp (back up the sine wave).

[Chuck H]

rjb covered a root misunderstanding. But I wanted to add... based on your verbiage I think your giving too much credit to the guitar amp symbiosis. The AC from the guitar is actually able to operate from it's own 0V reference. And that's a good thing because the AC impedance of most amplifier inputs is so high as to have very little affect on what the guitar is doing. The guitar puts out AC that is unhindered (or nearly so) by the amps input. There is no significant current between the amp and guitar that can change the behavior of either. Provided everything is working correctly. The only thing the guitar AC output cares about is impedance. And the amp input doesn't have significant impedance to consider as it relates to the guitar. The amp only cares about voltage differential. There is no real power exchange between the two ends of the patch cord.

[Alex/Tubewonder]

Only 50% correct
Current changes direction at 0-crossings. In between 0-crossings it goes from 0 to max positive magnitude back to 0 to max negative magnitude and back to 0. At the 0 crossings voltage changes polarity. The sine wave in question is not same thing as a cable laid out in shape on sine wave.
Also, for a voltage to be developed on amplifiers input impedance there must be current flowing through it. Chuck got it wrong too, sorry.

No.

Relating your sine wave & guitar rig drawing conventions:
1 (0-90 degrees) current flows toward the amp ("up" the sine wave).
2 (90-180 degrees) current flows away from the amp ("down" the sine wave).
3 (180-270 degrees) current continues to flow away from the amp (further down the sine wave).
4 (270-360 degrees) current flows toward the amp (back up the sine wave).

[Chuck H]

The AC from the guitar is actually able to operate from it's own 0V reference. And that's a good thing because the AC impedance of most amplifier inputs is so high as to have very little affect on what the guitar is doing.

I'll stand by this.

The guitar puts out AC that is unhindered (or nearly so) by the amps input.

This too.

There is no significant current between the amp and guitar that can change the behavior of either.

This is could be taken as incorrect. But note the word "significant". I didn't mean this to imply that there is no current needed for the system to operate. I meant to demonstrate that the power exchange is small enough that it doesn't affect either units independent operation. But yes, there must be current. That's why I didn't say there was NO current. Probably an important distinction WRT circuit analysis. So thank you for being vigilant.

[Alex/Tubewonder]

My remarks were qualitative, not quantitative. AC current changes direction at the zero crossings, not at the peaks/valleys.
Even if it is a mere 1/100th of a microampere. But let's not split hairs, of which I don't have many left.

[Joel]

I think I see where I may have made my mistake -- I think I may have conflated the current's sine wave and the guitars signal as the same thing.

Chuck said, "The AC from the guitar is actually able to operate from it's own 0V reference.", and booj said, "A guitar doesn't generally create a sine wave although it can come pretty close using harmonics."

Am I understanding these two statements correctly when I say the guitar signal acts from its own potential difference, and the current acts from its own potential; meaning the guitar signal is creating an alternating current that is within the alternating current of the sine wave? Or in other words, the waves of the guitar signal are 'riding' the wave of the current?

I sincerely apologize ahead of time if any of this is nonsensical.

I used another graphic to better illustrate my question.

[Chuck H]

Nope.

The guitar signal has too many harmonics to be considered a sine wave. Nothing more to it than that.

The blue line you have representing current would be a sine wave. The AC modulation wouldn't move positive/negative along a current of a frequency as you have shown. In fact, current doesn't have a frequency. It's a property that, relative to voltage, quantifies power. The current would be analogous to the sine wave. I'm finding this very difficult to explain to someone green enough to draw the graphics you've provided. I really don't mean to offend. I don't really know if I could draw a simple graphic that would make it clear. If the concepts were easy enough to digest that a simple drawing explained it there would be no need for text books.

I would suggest you get a basic electronics book. I wish I could suggest one but all the books I have still go over my head?!? And they don't offer much for anyone who doesn't know calculus and electronic symbols and insignias (guilty). Which I don't actually know. Which is probably why I can't explain this to you. I have just developed an intrinsic understanding from decades of exposure.

I'm hoping someone here will suggest a book (I'll probably buy it!). But guessing at it and asking if your wrong is definitely NOT the best or quickest way to learn this.

[rjb]

EDIT:
Hunh, did I say this?
I've obviously recently suffered severe multiple brain farts; please disregard my posts in this thread!

PS- I was "only 0% correct"; the total current flowing through a guitar cable is always 0.

Only 50% correct
Current changes direction at 0-crossings....At the 0 crossings voltage changes polarity.

I concur; current does change directions when voltage changes polarity.
But you are assuming that the OP's sine wave represents voltage.
He didn't say that. His diagram could just as well represent current magnitude.
I interpreted his question as "how is a sine wave"?

[Joel]

I'm finding this very difficult to explain to someone green enough to draw the graphics you've provided.

Lol, I definitely have more experience with computer graphics than I do with electrical circuits, though I didn't draw any of these graphics, found them off the net and added a few little things to them.

I'd also say after reading your responses and the others, it has already helped significantly, and I plan on referring to this forum as I progress through conceptualizing this stuff. I've also been going through this site Volume I - DC : All About Circuits , it has a lot of fundamental info laid out in a lesson plan. I don't know of any books that are good, but this site has definitely been sufficient so far.

[J M Fahey]

For the discussion forget waveform, consider this signal a sinewave and don't get entangled in irrelevant details.
Not forgetting that a guitar *can* and *does* produce a siinewave if you want .
And that it *is* a generator.

Back to the main point: Alex/Tubewonder was closest: within this very simplified explanation, voltage is positive from 0º to 180º (no matter that it's rising or dropping, it's still positive polarity) so under that convention "current flows from the guitar to the amp" .
From 180º to 360º polarity is negative all the time and current thus flows from amp to guitar, all that time.

[Enzo]

Don't over-think this. I think the OP is trying to get at VERY rudimentary concepts. I may be wrong.


Your first post showed a sine wave. The guitar rarely make a sine wave, it makes something more complex. BUt as I read the question, that was just a detail. OP is asking which way current flows. I interpret that to mean he wants to know what the waveform represents when applied to the real world. SO imagine the guitar DOES make a sine wave. Now we can look at the waveform without bogging down on overtones.

Your first four part drawing has twice as many reversals as it needs. When your sine wave starts up, it starts at zero then the voltage gets higher and higher in the positive direction until it peaks. Then in part 2, it is STILL moving in the positive direction, just less and less. And then it is back to zero. Now it changes polarity/direction, and section 3 shows the negative flow increasing until peak. And finally in section four, the current is still moving in negative direction, just less and less voltage until we are back to zero. SO your arrows are not right. sections 1 and 2 should both be running towards the amp, and sections 3 and 4 return from the amp. The sine wave shape represents the voltage in a circuit over time. Above the zero line is positive and below it negative (unless someone does it the other way for a reason). The fact that the voltage/current is falling at some point does not mean it is negative. Only being below zero makes it negative. SO in sections where the voltage is falling, the TREND is negative, but hte voltage is not. Until it crosses zero.

Don;t try to separate voltage and current so hard. They are parts of the same thing. If I hand you a 8x10 photo, it is 8 on one side and 10 on the other. SO is it an 8 or a 10? Well, it is both. A battery, sitting on a table by itself, has a voltage between its terminals. There is zero current flowing. (We will ignore any small leakage within the battery) Once you connect a circuit between its terminals, then current flows. (OK OK I know we could hook a backwards diode "circuit" and no current would flow, but any reasonable circuit...) Likewise the guitar. The pickup generates a voltage. If it connects to the amp, then there is a circuit across that voltage, and when there is a circuit across a voltage, current flows through it. It may be microscopic, but it is there.

Voltage and current are related in a simple circuit by Ohm's Law. It isn't a matter of one going one way and the other going the other. They may have an inverse relation somewhere, but that is not the same thing. Let us pretend the amp is a resistor, so we need not get into phase relations through reactive components. If the voltage is zero, then the current is zero. As the voltage rises, so does the current. If the voltage rises unevenly, like your little wiggles in post #9, then your current does the same thing. One is not within the other.

DC circuits is the first step, and you do need to understand it. But AC is different, at least in form, so read that chapter as well, and some of this will fall into place. And then over the years, electronics is all a matter of more things falling into place. Those things have been falling into place for me for almost 60 years now, and there is still PLENTY of room for more things. It never ends.

Oh, and one other detail. A "circuit" means a complete path to and from a point. Your guitar cord has a signal through the center conductor, but the outer shield is also a conductor. And any current that flows down the center is matched by a return current through the shield. SO your arrows in the four-part show ONLY the center conductor, your shield would be carrying the exact same current, but going the other way.

If that is confusing, think about a speaker. Your amp sends power to the speaker through a pair of wires. The current in those wires may be moving either direction at any instant, but the current flowing towards the speaker in one wire needs to flow back the other way in the remaining wire. If you don;t think so, disconnect ONE wire from the speaker and see what you hear. Nothing. The speaker might be taking 100 watts, and your guitar is making only a millionthy of a watt, but they are both CIRCUITS.

[Enzo]

There, while I was yapping, Fahey summed it up pretty well.