...How do you know that's not what they're talking about? I was under the impression all scientific discussion was archaic sorcery under a technobabble shell, but even mastery of sorcery requires education.
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Scientific: How does physics apply to the different sound of particular basses?
- Thread starter WarriorJoe7
- Start date
Potentiometers, as they're used in instruments, are not just variable resistors. The middle pin on a potentiometer is called the Wiper. It's potential (Voltage) varies between that of the other 2 pins, but if the Wiper is the source, the other 2 pins vary with the wiper. Typically, Pin 1 is Ground, Pin 2 is the (+) lead of the Pickup, and Pin 3 is the output. As the potentiometer turns, the resistance decreases in one direction, and increases in another. For example, if you have a linear taper 500K potentiometer, with Pin 1 grounded, Pin 2 connected to the pickup, and Pin 3 connected to the output jack, when the volume is all the way down, the resistance between Pin 1 and Pin 2 is 0, and between Pin 2 and Pin 3 is 500kOhms. This is oversimplifying it, but electricity tends to travel the path of least resistance. So all of the pickup output goes to ground. When the volume is halfway, the resistance is the same, 250K, between Pin 2 and 1, and 2 and 3. So the output is split. When the volume is wide open, the resistance between 2 and 3 is 0, and between 1 and 2, it's 500kOhms.
This is not a realistic example, as volume pots are not linear taper, but logarithmic, it's just a simple example to help understand how potentiometers work.
But as for how the sound changes when both pickups are on vs when 1 of them is on, obviously each pickup 'feels' different frequencies, but I think what you're talking about is how the neck pickup can have more bass by itself than with both pickups on. This has to do with phase cancellation, I would think. Think of vibration as pushing and pulling. When a string is plucked regularly, the whole string pushes and pulls together, like a jump rope. This is not the case with harmonics, so I'll leave that one alone for now. But basically, the whole string moves to one side, then to the other side, and back again. The bridge pickup 'feels' the string pull to one side, and translates that into an electrical signal, as does the neck pickup. But due to their different locations, different windings, different wires, etc, when the signals are combined at the output, the translated pushing and pulling is not synchronized for all the frequencies. They're not completely out of phase, if they were, there wouldn't be any output, but they're out of phase just enough so that certain frequencies are empasized while others are de-emphasized.
Interesting. You could do the reverse with an inductor correct?
A little background on me, I am studying EE right now, but the school I am at doesn't cover this stuff till quite a bit later(they seem to want to emphasize Computer Engineering). I really like analog systems so I may ask a lot of questions.
Yeah. I just mess with the stuff. No formal training of any kind.
But yes. If you put an inductor to ground, it would kill everything except the high frequency. Of course, in both cases this is assuming your input is a high impedance source at the frequencies in question (like a pickup).
With a low impedance source (like the output of your amp) it'll draw a lot of current since it looks like a short at those frequencies, so you're better off using a series element to block it instead. Just an example, of course. Most people don't make a habit of filtering at the output of their amps.
Quite interresting to me. I've got a bit of electronics experience, but have never applied it to guitars until now. (I'm building one right now)
That configuration is actually kind of a creative hack. Normally you would use a pot as a voltage divider with the output on the wiper, like Pin 1-Ground, Pin 2-Output, Pin 3-Pickup. And what this does is gives your pickup a relatively constant load at the rating of the pot. With a 500k pot, the pickup is always feeding about 500k (very slightly less at high volumes due to amp loading, but negligible)
Turning the pot just chooses the percentage of the pickup's voltage that the output will get.
Problem with this setup is that if you have 2 volume controls feeding the same output, turning one of them down actually pulls the output towards ground, and allows that to pull the other pickup's signal down.
With the pins configured as you describe, the pot is actually grounding the pickup itself, and letting the output have whatever's left. I'm not sure, but I've a hunch that this will cause a bit of a change in tone depending on volume since the reactance of the pickup is constant, but its load impedance is changing.
Maybe one of you EE's can confirm?
That said, it's a clever trick.
If you only need 1 volume control though, I'd just wire it conventionally.
-Nick
Right, I know the pot is not a variable resistor per say, but to make the example a little more "graspable" that is what I equated it to. Thank you for the greater explanation though, like I said, I am just a student and I want to learn.
Whoa.
Awesomness abounds round here... You guys just answered a lot of questions floatin' around in my head about my basses. Much obliged, good sirs.
No worries, love doing it
Can someone explain the mechanics of multiple-piece laminated necks? What benefit does having a maple-walnut-maple sandwitch bring?
You more or less nailed it. A passive P Bass is wired with the output on the Wiper. This seems like a more intuitive approach, but as you pointed out, with more than 1 pickup, this causes problems. Hence, Jazz basses, and I imagine, all passive basses with more than 1 pickup in parallel, have the pickups wired to the wiper instead.
Hmmm, I wonder if wiring a volume pot on a P Bass the way you wire one on a J Bass would change the tone.
Different woods react to humidity differently. They all will flex, but the amount of humidity needed for them to flex, and the degree to which they flex, vary from species to species, and, to a lesser degree, piece to piece.
So, for example, if you have a 1 piece maple neck, all of the grain moves in one direction. So perhaps the humidity will cause this neck to flex down, towards the ground. Kinda sucks. This is where quartersawn necks came from. Take the same piece of wood, cut it up, and reassemble it, but facing different directions. So instead of the neck flexing in unison, all of the pieces push against each other, and the overall flex is minimal.
As for necks with multiple woods, it's a similar idea. When the humidity reaches a certain point, only a part of the neck wants to flex, the rest remains rigid. When the humidity/temperature changes, and the other wood wants to flex, the first wood will hold it in place.
Actually, I could see why it would if I have you correct. So a P bass pickup is wired in series to the wiper and the two jazz pickups in parallel to the wiper correct? If this is so, changing the combo on the jazz would cause phase cancelation, but I don't know about the P
WOW you guys are helping me understand more of this stuff, and about basses!! cool thanks!!
b.c. thanks for suggesting i go on this thred. As far as volume pots go, look at it as going from the pickup to the output with the pot between the source and the destination. See if how the pot is wired really matters for the single pickup configuration.
Now add a second pickup for both configurations and see what happens. (hint: draw them out and see what goes to ground as the pots are turned.)
The J bass configuration is a classic passive mixer.
Phase cancellation has more to do with the relative positions of the pickups along the string when both pickups are on.
Yeah. I've been meaning to look into it, but I've noticed that the tone of my bass changes when I adjust the volume knobs in a non-linear fashion.
I can't remember exactly whether it was going from both full on, to one slightly off, or if it was one pick up only, with the other slightly on.
Anyways. the tone changed, in a non-linear fashion. Not just phase cancellation, as that should occur at a constant rate, but a change in brightness. I figured that's probably a change in the load on the pickups killing the treble. I noticed it, but was busy at the time so I didn't figure it out yet.
but when I was looking at how a jazz bass was wired, it kind of made some sense.
It's a vantage p+j. Kind of cheap in general, so who knows how it's wired.
-Nick
the bass I'm building right now is going to have the pickups fully phase/parallel/series switchable, with a shunt pot over each pickup, and a standard volume pot for each as well, all feeding into a master pot.
I should be able to experiment with all this stuff just by playing with knobs.
I'll also be able to see what effect the magnetic drag has on the strings in a shorted pickup, vs an open one and other crazyness.
-Nick
I should be able to experiment with all this stuff just by playing with knobs.
I'll also be able to see what effect the magnetic drag has on the strings in a shorted pickup, vs an open one and other crazyness.
-Nick
And, on the subject of pickup placement...
...the closer the string is to the end of its vibrating length, the more constrained its vibrations: the string will more readily vibrate at higher frequencies and less readily at lower ones.
If you place a pickup nearer the bridge, it'll sound as though it has more treble than an identical pickup placed nearer the neck. A pickup at the 12 fret would produce the most bass for the simple reason that, at that point (midway between the nut and saddle), is where the string excursion is widest.
So pickup placement is an art (even though the vast majority of bass manufacturers go with Leo Fender's ideas on the subject) and the sound of a bass is partly determined by where the pickups are.
And then, of course, there's the physical and electronic characteristics of the pickup, the resistance of the potentiometers (to give the formal name), the value of any capacitors in the circuit, did I mention the scale length, or the strings and their material makeup, wrapping material and so on?
Tell ya what: get a Precision, put a set of TI Jazz Flats on it, and all will be revealed.
...the closer the string is to the end of its vibrating length, the more constrained its vibrations: the string will more readily vibrate at higher frequencies and less readily at lower ones.
If you place a pickup nearer the bridge, it'll sound as though it has more treble than an identical pickup placed nearer the neck. A pickup at the 12 fret would produce the most bass for the simple reason that, at that point (midway between the nut and saddle), is where the string excursion is widest.
So pickup placement is an art (even though the vast majority of bass manufacturers go with Leo Fender's ideas on the subject) and the sound of a bass is partly determined by where the pickups are.
And then, of course, there's the physical and electronic characteristics of the pickup, the resistance of the potentiometers (to give the formal name), the value of any capacitors in the circuit, did I mention the scale length, or the strings and their material makeup, wrapping material and so on?
Tell ya what: get a Precision, put a set of TI Jazz Flats on it, and all will be revealed.
Widest excursion just means it'll be louder, not bassier. The reason for the most bass is because that is the point where the fundamental mode has the most excursion. (nit picking, but it's a good detail to understand) Also, the second harmonic (typically the next loudest) is pretty much null at the 12th so the purity of the fundamental is higher, with nothing at the next octave.
