Ground vs. +/- voltage

I'm a little confused: in most (audio) circuits, does the current go to ground or to the V-? I though it was just a current-flows-through-a-circuit-to-ground thing but now that I'm starting to look at all these schematics, this whole +/- thing is confusing me. And in the schematic for the Seventh Circle Audio N72, there are a few different grounds indicated! What's going on?

It's kind of like your house wiring, 120/240.

Your light bulbs go from neutral (ground in electronics) to one of the hot leads (+ or - in electronics, only dc)

But your dryer goes from hot to hot (- to + )

So you might have components where the current flows from - all the way past the ground to +, or you may have components that only have current flow from - to ground, or ground to +.

So you can have both in the same circuit.

Confused more or less?

[quote author="CJ"]

Confused more or less?[/quote]

Yes!

(But thanks....I guess I need to get really confused before these things start making sense.)

Cj was pointing out that current actually flows from *ground* to the *positive* in most systems except for multiphase systems.

twitchmonitor does bring up a point that hasn't been really discussed much.. if current goes from ground to positive, does a negative rail flow to ground?

:thumb:

A couple of points that may help:

1. Power supply rails (ie +15, -15, etc) supply DC current, but are usually an AC ground... that is to say, the big capacitors that help filter the DC will shunt any AC to ground as well.

2. Circuits that use dual positive and negative supplies (such as the ubiquitous +-15 volts), most often op-amp circuits, are usually set up with both positive and negative components. Op-amps are usually symmetrical inside, having matched pairs of transistors for positive and negative, which results in having no DC offset in inputs and outputs. Classical tube and transistor circuits, by contrast, need to have the signal at a DC offset of roughly half the power supply voltage so that the AC waveform can wiggle around "ground".

In op-amp circuits powered by a 9v battery you'll see a couple different grounds, a battery ground and a signal ground. The signal ground will be at 4.5 volts so that the AC signal voltage can have a range from maybe -4 to +4 volts.

+0- powerssupplies are usually 2 powersupplies in series. And that's how they work in a circuit too. You can have current flowing from - to 0 from 0 to + and from - to + depending on the resistance in the circuit.

I think in most opamp-schematics most current flows from - to + and the 0 is used to bias the signal voltage neatly in between the power rails.

Think of electricity as acting like water, it naturally flows downhill. Power supplies are like pumps that pump the water back uphill. Positive voltages are higher than ground and negative voltages are lower than ground. So the positive supply pumps current up to some level above ground. The negative supply pumps current up to ground level from some level below ground.

Ground is completely relative and can be defined wherever you like. For example the ground floor of a building up on a mountain isn't at the same level as the ground floor of a building down in a valley. Nonetheless, if you flush a toilet on the 2nd floor of either building the "water" is going to flow down towards the basement. :wink:

Make sense?

Thomas

I never liked the water analogy unless I was thinking in terms of the old, incorrect assumption that current flows from positive to ground. I prefer to think of voltage as a charge, like magnets, with current being made up of tiny magnets. If the polarity is one way, the current will be attracted to the charge. If you flip the polarity, the current will be repelled.

So a positive voltage attracts electrons and a negative voltage repels them.

Ground is just a reference point. The important thing is to have a difference between two charges.

Maybe we can combine this with the other recent thread on the same issue.

[quote author="electronaut"]I never liked the water analogy unless I was thinking in terms of the old, incorrect assumption that current flows from positive to ground. I prefer to think of voltage as a charge, like magnets, with current being made up of tiny magnets. If the polarity is one way, the current will be attracted to the charge. If you flip the polarity, the current will be repelled.

So a positive voltage attracts electrons and a negative voltage repels them.

Ground is just a reference point. The important thing is to have a difference between two charges. [/quote]

Huh?

By definition current flows from a more positive potential to a more negative potential ? unless somebody changed this 200+ year convention without telling the rest of the world.

Magnets are absolutely not the right analogy since electrons are monopoles and, as far as we know, there are no magnetic monopoles. In any case this whole electron flow thing just makes the issue more complex than it needs to be.

Current flows from positive to negative, pure and simple.

And water is a good intuitive analogy, at least for DC:

Voltage = Pressure
Polarity = Height (positive higher than negative)
Current = Amount of flow
Current direction = downhill (always from high to low)
Resistance = Pipe diameter (thin pipe high resistance, fat pipe low resistance)
Capacitor = Reservoir
Diode = Unidirectional valve
Battery = Pump
Etc?.

[quote author="barefoot"]Huh?

By definition current flows from a more positive potential to a more negative potential ? unless somebody changed this 200+ year convention without telling the rest of the world.

Magnets are absolutely not the right analogy since electrons are monopoles and, as far as we know, there are no magnetic monopoles. [/quote]

Jeeze. I'm thinking in very abstract terms here. What's intuitive for you may not necessarily be intuitive for others.

It is agreed that electrons flow from negative charges to positive charges, so for me it is sometimes easier to picture it that way.

The other thread

Generally speaking, assuming the same conductivity, fat wire will be "less resistant" than thin wire.

A thought I had today... Is there a point of inverse returns? Just focusing on resistance and nothing else like parasitic capacitance, or inductance, blah blah blah. At some point wouldn't there be more resistance in a really really fat wire, because of more surface area? Assuming the same voltage and current flowing through a really really fat wire and a thin wire.

I know that might sound strange and the answer is easily no if we go by the water analogy of electricity, but unlike water, electrons will flow throughout the whole wire and not just say the bottom half of a big pipe.
But then again, I suppose if you could get more of the water to spread out around the inner wall of the pipe, there would be more friction (resistance). OK, maybe I'm just babbling now. But to my electronically challenged self, it seemed interesting. Carry on.

The reason I was asking is, in part, because I'm trying to draw a schematic from a circuit that I have, and many components connect to one of two wires coming from the transformer (which is 6-0-6). One is a red wire, the other black. So in my diagram, I've been drawing red as +V (6 volts, I'm guessing, right?), and the black as -V, so instead of everything flowing to ground, as I was under the impression it need to, everything is going to the -, right? In which case, there is no proper "ground" for any of the circuit.

[quote author="twitchmonitor"]one of two wires coming from the transformer (which is 6-0-6).[/quote]

There's only two wires coming from the transformer? where's the '0' then?

[quote author="twitchmonitor"]So in my diagram, I've been drawing red as +V (6 volts, I'm guessing, right?), and the black as -V, so instead of everything flowing to ground, as I was under the impression it need to, everything is going to the -, right?[/quote]

No. Transformers work with AC, so current flows from red to black and from black to red alternatively.

Peace,
Al.

[quote author="alk509"]

No. Transformers work with AC, so current flows from red to black and from black to red alternatively.

Peace,
Al.[/quote]

Sorry....The wires from the transformer go to a bridge rectifier, voltage regulator and some caps, all of which is connected to the rest of the circuit via the red and black wires, so I'm assuming that I'm now dealing with DC at that point, correct? And if that's the case, what does the black wire signify?

And as for the "0", it is going nowhere. It just comes out of the tranny and has it's tip wrapped with shrink tubing.

[quote author="Ethan"]A thought I had today... Is there a point of inverse returns? Just focusing on resistance and nothing else like parasitic capacitance, or inductance, blah blah blah. At some point wouldn't there be more resistance in a really really fat wire, because of more surface area? [/quote]

In fact no. I see where you're heading, but no.

Electrons are lazy little bastards. If you "widen the highway" and gove them more lanes, electrons flow more easily, They indeed do take the path of least resistance, but not to exclusion of all other paths.

Look at it this way: if you made the wire a mile thick (ridiculous isn't it!) the path to the edge of the wire and back is so long that it would hae considerable resistance, but that resistance is still in parallel with the original "thin wire" path. Compare that to a 1Ω resistor. it measures 1 ohm. If you put a 100Ω resistor in parallel, the path now measures 0.99Ω. the 100Ω resistor is a lousy conductor compared to the 1Ω resistor, but it made things better, not worse.

As Bud Wyatt once sumed it up:

"What's shorter than a short circuit?"
"two shorts in parallel"

Diminishing returns? -Certainly. Inverse returns? -Never.

Though I see where you were heading... always remember that what you add is in parallel with the original path, adding more lanes to the hishway -even badly rutted lanes- will allow more cars to flow.

Keith

One more thought for everyone:

When I first came here, I was asked to teach a few basic electricity classes. I learned quickly that the "conventional current flow" which I was taught is in opposition to the "actual electron" current flow which many people in the US -and possibly elsewhere- seem to understand.

For me, Conventional current flow is how my brain figures things out best. Diodes "point" the right way, so too do the emitters of both PNP and NPN transistors. It's a beautiful thing. However, Electrons flow in the opposite direction. If cash flows one way, "debt" flows the other. -It's all how you look at it.

let's not fight about it, some folks have been taught using different methods, both are valid.

Keith