Effect of magnetic field on Half of a Bucker.

[CraigJC]

If a humbucker is wired for single coil operation, does anyone think the magnetic field of the non-active coil has an effect on the active single coil and the overall tone? Just curious. Might explain why half a humbucker rarely has a true single coil tone or response (in my opinion).

[David Schwab]

If a humbucker is wired for single coil operation, does anyone think the magnetic field of the non-active coil has an effect on the active single coil and the overall tone? Just curious. Might explain why half a humbucker rarely has a true single coil tone or response (in my opinion).

Half a humbucker is a true single coil pickup, but it is not made like a typical Strat pickup. That's why they sound different. You could take two Strat pickups, with reverse magnet polarity on one, and either reverse winding, or just wire it up reversed, run them in series, and you would have a humbucker that would sound like a Strat pickup when split. However, it probably wont sound like a typical Gibson humbucker with both coils on.

And there's the problem. Anytime you change the size, shape, windings, and magnet circuit on a pickup, you change the tone.

I'm not so sure the other half of the humbucker's magnetic field is any different from the return of any magnet in a pickup. You always have the flux lines from the other side of the magnets coming around. But every little detail changes something.

I think we need to stop obsessing on certain guitar tones as if they are the only ones. Personally I'm perfectly happy with a guitar that does not sound like a Strat or Les Paul. It's cool to have different sounding guitars. :D

[soundmasterg]

Yah its called a Tele! :)

Actually I prefer to have guitars different than the norm for myself. Rickenbackers and Gretsches come to mind. Then there are strange designs I've done for myself too. It makes you stand out if nothing else.

Grge

[CraigJC]

I understand all of the mentioned concepts of pickup shape, magnet structure, materials, etc. and how they affect tone.

I was just wondering if there was a reason why, if half a humbucker is probably somehwere between Strat and P-90 pickups in design, it's typically lacking in character compared to those two pickups. To me, half a humbucker sounds very much like the same humbucking pickup only brighter and lower in output, and somewhat lacking the single coil bite/attack. This is the basis of my curiosity about the humbucker's magnetic field still being in place and the possibility of it affecting the tone of the pickup. I would expecy half a PAF, at about 4.5K, to be quite thin and bright...more that what I'm hearing...or at least have a lot of "chime".

I understand that is may just be, due to design, that half a humbucker is a relatively lame single coil pickup.

[Sweetfinger]

You have to realize that half of a PAF is nothing like a strat pickup and not anywhere near a P-90. Think of it as somewhat like a lipstick tube pickup, only wound on a plastic bobbin. It also has a bit more compression, and a slightly warmer sound due to the other coil. In order to get half of a humbucker that sounds more like a P-90 or strat, you need to look at distortion-type pickups in the 14 to 16K range.
Many times over the years I've removed the center magnet from various humbuckers and placed a half-size magnet under just one of the coils. If you choose the right pickup, you can get a nice smooth sound, and increase the sustain because of less magnetic pull on the strings. That is, in fact, my secret killer slide tone! You can also remove the adjustable poles from one side of a covered humbucker and replace them with brass screws which are non-magnetic.
If you're really lazy and don't want to futz with magnets or pole-pieces, just place a coupling cap in series between the pickup hot lead and the vol. pot. Anywhere from an .005 to .003 mf is where the magic happens. I do this to a lot of cheep-o guitars with muddy overwound neck pickups. I've said too much......they're coming for me!.......

[CraigJC]

You're using the backwards tone control trick. Very good. I've used this as an actual bass roll-off tone control, and it works nicely.

Also, I probably shouldn't have slammed the half a 'bucker tone as much as I apparently did. I have this option on most of my humbucker guitars. It is very useful.

[David Schwab]

I understand all of the mentioned concepts of pickup shape, magnet structure, materials, etc. and how they affect tone.

I was just wondering if there was a reason why, if half a humbucker is probably somehwere between Strat and P-90 pickups in design, it's typically lacking in character compared to those two pickups.

You just answered your own question. Half a humbucker is nothing like a Strat or P-90, that's why. It's precisely because of the "pickup shape, magnet structure, materials, etc." You are saying you know the effect these things have, and then asking why they sound different!

A P-90 has a shallow wide coil. This changes the tone drastically. Look at the difference between a Strat and a Jazzmaster. They are both made pretty much the same... but they sound quite different because of the shape. A wider coils senses more of the string, and also the outter wraps are farther away from the magnets. Another example is a Jazz Bass and a Precision Bass. The Jazz has tall narrow pickups, and the P has squat wide pickups. The taller Jazz pickup has a narrower coil, and more of the wire is close to the magnets. That senses a narrower part of the string, for a brighter tone, and less highs are lost in the winding.

Then the P-90 has a different magnet system, and has two magnets.

Then we take a Strat. The coil is a different shape, the wire is wound directly onto the magnets, on a humbucker there is a space between the coil wire and pole pieces due to the bobbin. In a Strat pickup the poles are usually alnico rods, or steel rods with a ceramic magnet. On a humbucker the poles are screws and slugs, usually charged by an alnico magnet. Steel poles increase the inductance and warm up the tone.

The bobbins are a different width and hight, and a Strat pickup usually has more wire wound on it.

You have to realize that half of a PAF is nothing like a strat pickup and not anywhere near a P-90. Think of it as somewhat like a lipstick tube pickup, only wound on a plastic bobbin. It also has a bit more compression, and a slightly warmer sound due to the other coil.

Lipstick tube pickups are wound directly on the magnet, and don't have pole pieces. This lowers the inductance. They sound quite different from half a humbucker. The only thing similar is the amount of wire wound.

Humbuckers sound warmer for two reasons. One is the pickup has a wider aperture, so it senses more of the string. The other reason is the same hum canceling effect also cancels some high end because the harmonics are so close together on the string.


In order to get half of a humbucker that sounds more like a P-90 or strat, you need to look at distortion-type pickups in the 14 to 16K range.

Strat pickups are not usually wound that much. How would that make a humbucker sound like a Strat?

Many times over the years I've removed the center magnet from various humbuckers and placed a half-size magnet under just one of the coils. If you choose the right pickup, you can get a nice smooth sound, and increase the sustain because of less magnetic pull on the strings. That is, in fact, my secret killer slide tone!

This is because you are using a weaker magnet, so you will get a duller (warmer) tone. That's not taking the other coil out of the circuit, unless you switch that coil out. The only reason you would get less string pull is from using a smaller magnet.

You can also remove the adjustable poles from one side of a covered humbucker and replace them with brass screws which are non-magnetic.

So why put the brass screws in there at all? They aren't doing anything, except maybe killing some high end due to eddy currents.

If you're really lazy and don't want to futz with magnets or pole-pieces, just place a coupling cap in series between the pickup hot lead and the vol. pot. Anywhere from an .005 to .003 mf is where the magic happens. I do this to a lot of cheep-o guitars with muddy overwound neck pickups. I've said too much......they're coming for me!.......

That's not a "coupling cap" ... that's a simple high pass filter. :D

[CraigJC]

OK. You're making me sorry I asked a question about a magnetic field (my original question). I'll do my own experiments and get my own answers.

Where's Jason Lollar when you need him?

[David Schwab]

OK. You're making me sorry I asked a question about a magnetic field (my original question). I'll do my own experiments and get my own answers.

You're sorry someone took the time to give you some info? :confused:

I answered your question. I guess you just don't like the answer! :rolleyes:

Where's Jason Lollar when you need him?

Do you think Jason will tell you something different? ;) Facts are facts.

Doing your own experiments wont tell you why something is happening, only that it is.

Alrighty then.... :D

So... the wider magnetic field, might have some effect, but I doubt it. Not unless that coil senses it. Also, you never have just the single pole of the magnet charging the strings... there is always the return path. It's still the one magnet. Doesn't matter if there is a coil above it. You don't even need the magnet once the strings are magnetized... Try removing the magnet from a pickup and see what happens.

[CraigJC]

So... the wider magnetic field, might have some effect, but I doubt it. Not unless that coil senses it. Also, you never have just the single pole of the magnet charging the strings... there is always the return path. It's still the one magnet. Doesn't matter if there is a coil above it. You don't even need the magnet once the strings are magnetized... Try removing the magnet from a pickup and see what happens.

Now that is an interesting and intelligent answer. Thank You.

[David Schwab]

Now that is an interesting and intelligent answer. Thank You.

I haven't seen you say anything "interesting and intelligent" yet. It's not my problem if you don't understand what I'm talking about. I'm giving you some examples that will demonstrate the effect of the magnets on the pickups. All that matters is the strings cutting through the flux field in the vicinity of that coil. If there's another magnet from another pickup close by, it has little to no effect on the sensing coil in question. Both sides of the magnet on a humbucker is part of the same magnetic field. Pull the poles out of one coil and the field from the opposite pole is still there.

The difference in tone you are talking about is due to bobbin size/shape, coil structure, and magnet circuit.

If you want to replace the screw/slugs/bar magnet in a humbucker for alnico rods, and then wind each coil similar to a Strat, then you will have a hubucker that will sound more like a single coil when split.. as much as the size of the bobbins will allow. Duncan already makes one of these. If you don't understand why it makes sense, go argue with him. :p

[SK66]

If a humbucker is wired for single coil operation, does anyone think the magnetic field of the non-active coil has an effect on the active single coil and the overall tone? Just curious. Might explain why half a humbucker rarely has a true single coil tone or response (in my opinion).

There IS a big difference in how the remaining coil interacts with the field in comparison to a singlecoil (when speaking of side by side HB's). Because the opposite pole of the magnet is offset to one side the resulting field is to the side of the active coil; effectively only exposing one half of the coil to the primary field. In a singlecoil the field reverses *equally* on both sides enveloping both *halves* of the coil. In a HB with both coils active each coil sees *1/2 the field* but combine in series to = a whole. The HB's overall aperature is narrower as well.
There may also be a difference in tone depending upon "which coil" is cut to and "how" you cut the coil. If you cut the coil by grounding the series link (typical) you get a basicly "unloaded coil" remaining. If you cut by making the series link the hot (creating a "hot loop" from the other coil) you get more of a "loaded coil" remaining. The output of active coil still "sees" the cut coil to some extent.

[David Schwab]

There IS a big difference in how the remaining coil interacts with the field in comparison to a singlecoil (when speaking of side by side HB's). Because the opposite pole of the magnet is offset to one side the resulting field is to the side of the active coil; effectively only exposing one half of the coil to the primary field.

SK, I have to respectfully disagree with you here... Primary field? What primary field? That implies there is a secondary field. The two poles of the magnet are not separate entities. The magnet is horizontal, so BOTH sides are facing the same way... one side is not offset. That doesn't matter anyway. What matters is how the field is directed towards the strings via the pole pieces. I've seen your FEMM simulations, but really any change in flux shape is either going to sound different, or not. Very often what looks different doesn't sound all that much different. And north or south does not matter. One is not lesser than the other.

Duncan explains it this way:

416. What are the various magnetic field patterns on popular pickups?

4 effect: A standard Gibson style humbucker where the adjustable polepieces extend out the bottom of the adjustable side of the pickup. You have a slight loss of magnetic field out the bottom of the pickup. The stud side has direct flow of the magnetic field to the strings and is the brighter side of the pickup.

1 effect: This is the standard magnetic pattern for a single coil pickup with no ferrous bottom plate to direct the magnetic field. The majority of Fender style pickups have this effect where the magnetic field extends from the top and bottom. You lose efficiency from this pickup design but they have a unique tone and output.

H effect: This is the magnetic field pattern of a humbucker that has a double row of adjustable pole pieces such as the Gretsch Filtertron and other modern humbucking pickup designs. In this design, there is also a loss of magnetic field out the base of the pickup but these are great pickups designed by Ray Butts and have a unique sound and tone.

U effect: This is a magnetic field pattern where the polepieces are flush and in direct contact with the bar magnet within the pickup. There are no extensions from the bottom of the pickup where there might be magnetic field loss. These pickups tend to be brighter and gain slightly more output. Many “rail” type pickups have U-effect and are pretty loud for their size.

The magnetic field pattern is an important factor in determining the output and sound of various pickups. The idea came from looking at the side profile of the pickup and trying to see how the magnetic field traveled through the coils. I then came up with these terms as an aid to help explain the mysterious magnetic patterns that travel through a coil and when the magnetic field is disturbed. As the string movement occurs it produces a small amount of alternating current that tailored by the controls before going to the amplifier. I feel the more direct and concentrated the magnetic field is to the string helps produce brighter and tighter sounding pickup that retains the high-end and less loss of magnetic field that will give the pickup more power. This all depends too the type of coil, number of turns, proximity of the coil to the magnetic field etc.

So as you can see a Fender style pickup with just the one pole facing up is less efficient than a humbucker. You can take a humbucker and install the same polarity magnets on each coil. It wont sound all that different, but it will hum. The opposite polarity magnets, combined with the coils wired out-of-phase* is what cancels the hum. (* In reality it is not out of phase, but opposite polarity. Phase relationships are strictly time domain based).

So the point is that each coil is the same as far as magnetic fields is concerned.. there is no primary and secondary field. If you have a symmetrical design, with the same poles in each coil, charged by a bar magnet, then the coils are equal, but opposite. In my bass pickups each coil sounds exactly the same if I cut a coil, because each coil is exactly the same... with the slight variation due to placement under the strings.

Also, having an asymmetrical magnetic field can be a good thing. This is the basis of Bill Bartolini's two patents for his Hi-A pickups.

Bill bartolini wrote:

"Basically, the tone of a plucked or a struck string instrument is judged by the richness and complexity of the acoustic output in the 'attack' or beginning portion of a note. In acoustic string instruments, the bridge structure constrains the motion of the soundboard such that those components of string motion which are perpendicular to the plane of the soundboard are well amplified, while those components of the string motion which are parallel to the plane of the soundboard are not."

"For variable reluctance pickup systems to have good tone (by acoustic instrument standards), it must be highly asymmetrical in converting string motion to electrical signal output."

"The prior art variable reluctance pickup systems are characterized by separate pole tip and/or pole pieces for each string. Each pole tip and/or pole piece provides a distinct magnetic field region around the quiescent position of each string. The distinct magnetic field regions of prior pickup systems render them relatively insensitive to the plane of vibration of the particular string.

For example, pickup systems with circular pole pieces provide a magnetic field having the form of a symmetrical sinusoidal shell and a string vibrating within such a magnetic field will generate approximately equal magnitude electrical signals for string vibrations both parallel and perpendicular to the string plane."




In a singlecoil the field reverses *equally* on both sides enveloping both *halves* of the coil. In a HB with both coils active each coil sees *1/2 the field* but combine in series to = a whole. The HB's overall aperature is narrower as well.


Well you can see from the above example that this is not really true at all. There is no "half" of the field. There is always a return from the one side to the other. It's the single coil that loses some of it's field strength. Plus once the strings are magnetized you can actually remove the magnets from the pickups, and they still work. As long as there is a flux field for the string to interrupt, current will flow in the coil.

How is a HB aperture narrower? The two coils sum together additively, and together they are twice as wide as a single coil. This is part of the reason that HB are fuller sounding than Strat pickups. It's also the reason way a Jazzmaster sounds different... wider aperture.

There may also be a difference in tone depending upon "which coil" is cut to and "how" you cut the coil. If you cut the coil by grounding the series link (typical) you get a basicly "unloaded coil" remaining. If you cut by making the series link the hot (creating a "hot loop" from the other coil) you get more of a "loaded coil" remaining. The output of active coil still "sees" the cut coil to some extent.

The reason they sound different is because each coil is in a different position under the strings, and in the case of a Gibson style humbucker, the two coils sound different as well due to different pole piece designs. If you short out a coil it has no electrical properties. It's not loaded or unloaded, because it's a short circuit. The coil itself generates its own magnetic field which opposes the variations in flux induced by the string. However, if the coil is shorted no current can flow in the coil. The short has lower resistance than the coil.

Now if you wired the split coil up as a loop, it might self resonate... :D

[SK66]

Ok, in a HB there is a primary and a secondary field. The primary field loops from top of one set of poles to the top of the second poles and thru those poles completes the primary loop. There is however a smaller secondary loop going from the top of the poles in the opposite direction in a much longer weaker loop. because the primary field is going from the top of one set of poles to the top of the other set the primary loop is to the side of either coil..each coil is only 1/2 in the primary field loop.
Because the pole tops are within 1/2" of each other you get a quick primary return and a smaller lower aperature. Dual rail designs and other similar further amplify this.
A singlecoil has a larger aperature and higher peak (for any given field strength) this is due to the "opposite pole" being so far away from the "cast filed". The field goes higher and takes a wider arc in returning and does this in all directions resulting in a wider aperature and the full coil being in the field. In fact the cast is emphasised up and out to the sides of the coil assembly due to same polarity of each pole (as it does in the HB coil but the emphasis is towards the other coils "pull".)
As for Duncans claim about lower efficiency in a singlecoil design, this is true as far as a "magnetic circuit" is concerned, but direct/indirect analysis/measurement shows the field is stronger higher for a singlecoil. There is always a
I can't explain it much better and it's about the best I can do to define "aperature".
While you are correct in that there a differences due to position and poles, I said MAY sound different. A hot loop "within" the circuit may generate no significant signal, but the coil mass does create a load on the circuit. Maybe it's the capacitance/inductance, maybe it's eddy currents I really don't know for fact.
Feel free to disagree....

[ken]

snip)
How is a HB aperture narrower? The two coils sum together additively, and together they are twice as wide as a single coil. This is part of the reason that HB are fuller sounding than Strat pickups. It's also the reason way a Jazzmaster sounds different... wider aperture.

I'm wondering.... if a Jazzmaster has the same 42gauge wire and magnetic aperture as a P90, why do they sound so different? Is it only the magnetic/metallic design structure of the pickup? Both the coil bobbins are roughly the same height.

Ken

[Sweetfinger]

Lipstick tube pickups are wound directly on the magnet, and don't have pole pieces. This lowers the inductance. They sound quite different from half a humbucker. The only thing similar is the amount of wire wound.

Ummm...yes, I know how Lipsticks are constructed. Thank you for expanding my short, generalized analogy. I WILL say that I have seen with my own eyes, and heard with my own ears, half a humbucker that was INDISTINGUISHABLE from a lipstick pickup.

Strat pickups are not usually wound that much. How would that make a humbucker sound like a Strat?

Because you are only using HALF of the pickup, i.e. ONE coil, which would be in the 7 to 8K range for the examples given.

This is because you are using a weaker magnet, so you will get a duller (warmer) tone. That's not taking the other coil out of the circuit, unless you switch that coil out. The only reason you would get less string pull is from using a smaller magnet.

Ummm...again, thank you for restating what I just said.:confused:

So why put the brass screws in there at all? They aren't doing anything, except maybe killing some high end due to eddy currents.

The brass screws are there to fill the ugly gaping holes in the front of the pickups on your LP custom or whatever. I think they're crazy, but some folks kinda care about how their guitar LOOKS. In older unpotted pickups they'll keep the metal spacer from shifting around. Think before you type, It will help you figure some of these things out.:D

That's not a "coupling cap" ... that's a simple high pass filter. :D

I'm afraid that you are completely flat-out wrong. It IS a coupling cap. Feel free to look up AC coupling capacitor on whatever search engine that floats your boat. Yes, the aforementioned capacitor is acting as a high pass filter, but it IS by the very use in series in an AC circuit, a COUPLING CAP.:cool:

[David Schwab]

Ok, in a HB there is a primary and a secondary field. The primary field loops from top of one set of poles to the top of the second poles and thru those poles completes the primary loop. There is however a smaller secondary loop going from the top of the poles in the opposite direction in a much longer weaker loop. because the primary field is going from the top of one set of poles to the top of the other set the primary loop is to the side of either coil..each coil is only 1/2 in the primary field loop.

You are talking as if the two ends of the magnet are separate. Each pole of the magnet has the same strength. So if one coil is seeing the North and the other the South, they have the entire field, since they don’t use both poles. We are interested in what goes on over a pole. Look at a magnet. You can clearly see that we are interested in the ends, and not the middle of the field, where the loop is. The field extends from the end of the magnet. Try putting a string in the side field of a magnet and see if the pickup works. The field more-or-less cancels its self out in the middle.

http://upload.wikimedia.org/wikipedia/en/5/57/Magnet0873.png

The two coils add their signals back together. So even if each coil is only getting half the field, which it’s not, they still sum together. This is why humbuckers are louder than single coils. Now as far as the magnet laying on its side... what about P-90’s? Same thing. The magnets are on their sides with one pole touching the ends of the screws. You still have the other pole not attached to anything, and its return path is up the side of the pickup.

Because the pole tops are within 1/2" of each other you get a quick primary return and a smaller lower aperature. Dual rail designs and other similar further amplify this.

The aperture of a pickup is the width of the string sensed by the pickup. The horizontal aperture is what we are interested in. A wider pickup senses a larger portion of the string. A dual rail pickup still has the other ends of the rails attached to the bar magnet, but most of the energy of the magnet is directed towards the strings. This is the U shape Duncan talks about. The magnetic circuit is completed mostly between the rails. If you drop a keeper between the rails you eliminate most of the output of the pickup.

The ferrous plate under a Tele pickup helps boost the signal, by redirecting the field from the bottom magnets.

A singlecoil has a larger aperature and higher peak (for any given field strength) this is due to the "opposite pole" being so far away from the "cast filed". The field goes higher and takes a wider arc in returning and does this in all directions resulting in a wider aperature and the full coil being in the field. In fact the cast is emphasised up and out to the sides of the coil assembly due to same polarity of each pole (as it does in the HB coil but the emphasis is towards the other coils "pull".)

Taller apertures are actually narrower.

(from the Line 6 patent # 6787690)
http://www.sgdlutherie.com/images/aperture.gif

As for Duncans claim about lower efficiency in a singlecoil design, this is true as far as a "magnetic circuit" is concerned, but direct/indirect analysis/measurement shows the field is stronger higher for a singlecoil. There is always a
I can't explain it much better and it's about the best I can do to define "aperature".

I know the definition of aperture. It's the window in which the pickup senses the string, and it's the width of the section of the string being sensed. A wide aperture pickup senses a wider area of the string. An example is that a Music Man bass pickup is a wider aperture unit than a Jazz Bass pickup.

A Fender style single coil has six magnets right under the strings, so of course it will read as having a stronger magnetic field. This is what causes Stratitus!

Why would we care about how high the magnetic field is? As long as it is disturbed by the vibrating strings (which in turn act as their own magnet), it doesn't matter. The width of the field is more important. And higher always isn’t better. A high field will sense more side to side motion of the string at the expense of the up and down motion, since the string is not able to cut through the horizontal lines of flux, because they are positioned higher than the string.

You have to picture the lines of flux which are in layers link an onion. It's the act of cutting through those layers that causes the variable reluctance of the pickup.

As far as the inefficiency of the traditional Fender design, Leo Fender himself filed a patent (4220069) on a new design which he felt was more efficient than his previous design. The way he did this was to redirect the magnet pole that's away from the string back to the top:

http://www.sgdlutherie.com/images/fender.gif


According to the embodiment of FIG. 2, pole pieces
21-26 are individually magnetized and arranged so that
their poles extend in the same direction. As shown, all
of the north poles may be positioned closely adjacent to
strings 14-19 and the south poles positioned relatively
remote from strings 14-19. The orientation of pole
pieces 21-26 may be reversed. With such a pickup 20A,
the magnetic field lines for each pole piece are as shown
at 29.
In order to strengthen the magnetic field and create a
magnetic field which has a better defined pattern of
field lines, the embodiment of FIG. 2 may be modified
as shown in FIG. 3. That is, FIG. 3 shows a pickup 20B
which is identical to pickup 20A except for the addition
of an elongate, generally U-shaped, metallic keeper 30.
Pole pieces 21-26 and coil 28 are positioned within
keeper 30 with the ends of pole pieces 21-26 remote
from strings 14-19 in contact with the base 31 of keeper
30. With such a modification, the magnetic field lines
for each pole piece are as shown at 32 and extend from
the ends of pole pieces 21-26 adjacent strings 14-19 to
the free ends 33 and 34 of keeper 30.

Leo also felt the reason for the inefficiency of the standard dual coil design using a bar magnet and ferrous poles, is that the magnetic flux had to bend 90 degrees from the magnet to the poles. Maybe so, but we also have to see that adding iron or steel to the magnetic circuit increases the inductance and makes the pickup more efficient... up to a point.

While you are correct in that there a differences due to position and poles, I said MAY sound different. A hot loop "within" the circuit may generate no significant signal, but the coil mass does create a load on the circuit. Maybe it's the capacitance/inductance, maybe it's eddy currents I really don't know for fact.
Feel free to disagree....

Coil mass? What the heck is coil mass? A pickup coil is an inductor, and as such it follows the same rules. It's also a generator, but in this case it's been shorted out.

Let's picture a circuit.

First with a resistor:

http://www.sgdlutherie.com/images/short1.gif

You can see that even though the resistor is wired into the circuit, it's effectively bypassed, and has zero effect.

Now an inductor:

http://www.sgdlutherie.com/images/short2.gif

Same thing. The coil is shorted out. Any current that might be induced by the reluctance of the magnetic circuit (magnet, poles, strings, etc.) are shunted to ground.

Now we can take it a step further and look at a dual coil system with one coil bypassed to the "hot" side.

http://www.sgdlutherie.com/images/short3.gif

If you picture current trying to flow in the shorted coil, you can see that it has no place to go. The load through the active coil is lesser than the load through the potentiometers, or even itself.

You can try this for yourself... just wire a four conductor pickup to some switches. I did a lot of experiments with this back in the late 70's. I came up with a circuit that bypassed the coils with different capacitors, so you could actually get a bridge position humbucker to sound like a neck position pickup, and also some interesting resonant effects. In this case you are kind of using the non voicing coil as an inductor, except it's also producing current because it's in the magnetic circuit. You can also wire the non used coil as a loop, and depending on the coil design, will self resonate. It's subtle, but you can hear it.

The capacitance of a pickup coil is pretty negligible, and as with inductance wont have any effect if the coil is not in the circuit.

A lot of this is pedantic... we can do simulations, which are almost always inaccurate due to things never being quite what we think they are (i.e., we don't know all the parameters)... in the end we like the sound of things that are familiar, and might be wrong in theory.

[David Schwab]

I'm wondering.... if a Jazzmaster has the same 42gauge wire and magnetic aperture as a P90, why do they sound so different? Is it only the magnetic/metallic design structure of the pickup? Both the coil bobbins are roughly the same height.

Give it a try and see. I modified a P-90 to fit in a Jazzmaster pickup cover once for a guy I used to play with.

The magnetic circuit of a P-90 is quite different from the Jazzmaster. I'd imagine the steel screw poles and keeper plate would add to the inductance, which would give more mids. Then you have the bar magnets.

I had a Gibson ES-330TD which had chrome cover dogear P-90's. They would wound a lot lower than the 70's P-90's in the SG's, and they really sounded a lot like warmer strat pickups.

[SK66]

Ok, last time I'll try to explain myself....
Your picture of the fields in a bar magnet are irrelevant considered seperate from the pole pieces. A HB IS more of a "U" design. The bottom of the U is the magnet one leg is N(slug tops) and the other is S (screw tops). The screw pole is slightly less efficient due to the keeper bar/screw interface but the result is basicly the same. Not much magnetic field bypasses the metal poles, but some does creating the secondary fields.
The aperature we generally care about is "length of string sensed" not the "width". The "aperature" is actually the field in ALL directions.
A taller aperature IS narrower "of the same design". A HB ("4" or "U") is narrower than a singlecoil.
http://www.ampge.com/SKGS/sk/Images/pickups/Pickup%20stuff/HBfield.gif
I know a shorted coil "shouldn't" affect anything, but neither should your tone/vol controls when they are full on. It "can", may be other factors involved (like minor coil faults ...) but I've witnessed it. My coil select schematic uses both methods of shorting the coils and generally works without issue.

[ken]

Hello all...

Tone and volume controls actually do affect tone even when fullly on, due to high frequency resistive attenuation effects, and also the control's interaction (impedance matching) with the input of whatever amp you play through. This is why Strats use 250K pots, and Les Pauls use 500K pots.

The Strat is an inherently bright pickup, so Leo used 250K pots to form a treble bleed circuit. The HB pickup has a much wider aperture and much more wire than the Strat, so higher value pots are used there to 'brighten up' the pickup's response. 1960's Teles with 1 Meg volume pots are famous for their trebly feedback squeals.

I learned this the hard way with a Paul somebody put 250K pots in - with the HB's in it, it was 'mud city'. Put the 500K pots in, and it brightened right up.

Bassists in general tend to like 500K or 1 Meg pots with passive pickups, slapping and popping effects are easier and much better defined with the added treble.

Ken

[David Schwab]

Ok, last time I'll try to explain myself....
Your picture of the fields in a bar magnet are irrelevant considered seperate from the pole pieces. A HB IS more of a "U" design. The bottom of the U is the magnet one leg is N(slug tops) and the other is S (screw tops). The screw pole is slightly less efficient due to the keeper bar/screw interface but the result is basicly the same. Not much magnetic field bypasses the metal poles, but some does creating the secondary fields.

Yes, yes, you said all this. And what's your point? I'm not sure about the accuracy of your simulation. If you measure the distance between the two coils on a HB it is wider than a single coil's field, so the aperture is wider, or longer if that's what you want to call it.

The aperature we generally care about is "length of string sensed" not the "width". The "aperature" is actually the field in ALL directions.

We? The length of the string sensed is the width I was referring to. You kept talking about hight. The field in any other direction does not sense the string.

Such as in this example.

http://www.bartolini.net/structures/strct_1j.gif


I know a shorted coil "shouldn't" affect anything, but neither should your tone/vol controls when they are full on.

OK... obviously you don't have a background in electronics. Yes, the volume and tone controls should and do have an effect when they are full on. They are both resistive loads. On a guitar with 250K pots, each one is loading the pickup down. Plus they are in parallel, so for two 250K pots there is a load of 125K on the pickup. Try removing all the controls from a guitar and wire the pickup directly to the jack. It sounds very different. Now take a 250k resistor and wire that from the hot to ground. You will hear less highs and less volume. Now try a 125K resistor.

When the tone control is all the way up, there is still a bleed through the 250K resistive element, so it's just like wiring a cap to a 250k resistor and connecting that from hot to ground.

The higher the DC resistance of the pickup, the more of an effect the controls will have, since the pickup is a higher impedance, and the same load will be greater. Two pickups in parallel will sound brighter with the same control values.

This is precisely why Fender has the TBX tone control. To remove the effect of the tone pot from the pickups. Well as much as a 1 Meg pot can remove it. It's also why a buffer amp cleans up the tone of a passive guitar.

[madialex]

Yes, yes, you said all this. And what's your point? I'm not sure about the accuracy of your simulation. If you measure the distance between the two coils on a HB it is wider than a single coil's field, so the aperture is wider, or longer if that's what you want to call it.



We? The length of the string sensed is the width I was referring to. You kept talking about hight. The field in any other direction does not sense the string.

Such as in this example.

http://www.bartolini.net/structures/strct_1j.gif




OK... obviously you don't have a background in electronics. Yes, the volume and tone controls should and do have an effect when they are full on. They are both resistive loads. On a guitar with 250K pots, each one is loading the pickup down. Plus they are in parallel, so for two 250K pots there is a load of 125K on the pickup. Try removing all the controls from a guitar and wire the pickup directly to the jack. It sounds very different. Now take a 250k resistor and wire that from the hot to ground. You will hear less highs and less volume. Now try a 125K resistor.

When the tone control is all the way up, there is still a bleed through the 250K resistive element, so it's just like wiring a cap to a 250k resistor and connecting that from hot to ground.

The higher the DC resistance of the pickup, the more of an effect the controls will have, since the pickup is a higher impedance, and the same load will be greater. Two pickups in parallel will sound brighter with the same control values.

This is precisely why Fender has the TBX tone control. To remove the effect of the tone pot from the pickups. Well as much as a 1 Meg pot can remove it. It's also why a buffer amp cleans up the tone of a passive guitar.

SK has done a lot of research of magnetic fields and expeirementing with such and I fully beleive he knows what he is talking about. Further more, SK was around way before I even heard of you. True you may have been working with guitars and stuff for a long while and you do know a bit about electronics but SK has been in the pickup business a long time himself and has done a lot of research on the subject and I dont appreciate your snobish attitude towards him or anyone else on this forum who has been around a lot longer than you. You sir need to respect the guiys here who were making pickups long before you ever thought about it!!:mad:

[madialex]

Ok, last time I'll try to explain myself....
Your picture of the fields in a bar magnet are irrelevant considered seperate from the pole pieces. A HB IS more of a "U" design. The bottom of the U is the magnet one leg is N(slug tops) and the other is S (screw tops). The screw pole is slightly less efficient due to the keeper bar/screw interface but the result is basicly the same. Not much magnetic field bypasses the metal poles, but some does creating the secondary fields.
The aperature we generally care about is "length of string sensed" not the "width". The "aperature" is actually the field in ALL directions.
A taller aperature IS narrower "of the same design". A HB ("4" or "U") is narrower than a singlecoil.
http://www.ampge.com/SKGS/sk/Images/pickups/Pickup%20stuff/HBfield.gif
I know a shorted coil "shouldn't" affect anything, but neither should your tone/vol controls when they are full on. It "can", may be other factors involved (like minor coil faults ...) but I've witnessed it. My coil select schematic uses both methods of shorting the coils and generally works without issue.


The picture you see is of an actual magnetic field. Are you going to disagree with that as well??? You have become a real ass here and not many people post here anymore because of it. You are always ready to pounce when someone brings up anything about something you think you know more about. So you are trained in electronics, big whoop... Does it make you an expert, a big NO!! I for one have seen this place going to crap because of you sir David. You started off great, kinda reserved, quiet then overnight you became a legend in your own mind. Please stop it!!

[David Schwab]

OK, first off I don't have a snobbish attitude, but I do have a background in electronics and worked in defense communications for a large well known company back in the late 70's. I only mention this because I have certain knowledge on some subjects related to what we are all talking about. I'll be the first to say that many things concerning music and instruments are very hard to measure in a scientific way. People have been trying it for years. There's too many variables. But there are certain laws of physics and magnetics involved, and that information is readily available.

The simulation of the magnetic field is not an actual picture, but is a computer model. Try using some magnetic viewing film and you will see the actual field around a pickup. And even then you will see more information than is actively producing sound. The problem with computer simulations is that they are only as good as the parameters you enter, and the software doing the rendering. For each part of a pickup we need to know the exact permeability, etc. for the given material. You can't just plug in some numbers for known materials and expect a realistic model. You will end up with a generalization.

There's a lot of misinformation and mumbo jumbo going around in this field. For example, many people who can wind a good pickup don't really understand how humbuckers work, you hear people insisting you need to reverse wind one coil... which is nonsense. There's no basis in fact for claims like that, but people keep propagating things they see that others do because it makes them feel like they know some kind of obscure information.

Magnetics and induction is a fascinating subject. Magnets are just plain weird. They are a power source that has a flowing current that comes just from having aligned molecules. Pickups are both generators and inductors. The pickup coil itself produces its own magnetic field when current is flowing, and any conductive parts that are in the presence of the magnetic fields also produce magnetic fields. This is known as Lenz' Law. Before you can do a computer model of a pickup you need to take all this into consideration.

I have nothing against anyone here, and I wasn't even arguing with SK. He was giving his view on the subject, and I was giving mine. I was using some citations to back up what I was saying. There are many more. He seemed to think I didn't understand the concepts he was talking about, and since he doesn't know me, or what I know, that's understandable. But I am very familiar with the subject and found fault in some of what he was saying. I started with the attitude that he has a lot of knowledge on the subject, up until he started saying things that are just wrong... such as the effects of parallel resistance of the volume and tone pots.

I post things to try and give people information. If someone asks a question, and I have a good idea of an answer, I'll post that answer and the reason why I believe it's accurate. I'll post links and pictures. This all takes time. I'm trying to be helpful. I don't have to do any of this. I could just keep what I know to myself. And that's making this place go to crap?

As far as me being an expert on a subject. What is an expert? Do you know that I'm not? Give your reasons for such a statement... don't just say things. Do you really think so called experts are any different than you are? My brother is a professor and teaches digital photography. He's an expert in the field of historical photographic techniques. He still calls me and asks questions about Photoshop, because I'm very knowledgeable in that area. I'm actually a certified Photoshop expert. Big deal. Does that mean I know everything about the subject? Of course not. No one knows everything. We can all learn from someone else. I can learn from SK as much as he can learn from me. If I'm correcting someone on a subject I'm not pouncing on anyone... I'm giving helpful information. If that makes you defensive... that's not my problem. If you want to continue believing incorrect nonsense... that's fine too. Yeah I've been around a while... yeah I built guitars played by famous people, yeah I designed guitars made by Kramer... Big deal. Everyday I learn something new. That's why I'm here.

If you think I'm an ass... well that's one of the problems with communicating via the internet. You can head over to the Musical Instrument Makers Forum (www.mimf.com) and read some of my posts. While you are there, register and check out the archives and read some posts from someone like Rick Turner. Now's there's an expert on all these things. You might think he's a jerk too! He corrects a lot of people, and he's quite blunt about it. Shame he doesn't post there anymore.

But no matter what you think, my intention is to be helpful. :D

[CraigJC]

I think it's great you're trying to be helpful, Dave. I've been helpful to loads of people all around the world over the years, too. I spend significant time and effort to provide information to folks and ask nothing in return. Hats off to people like that. I've found that lots of folks in the guitar community are like that.

I think that everyone appreciates information and intelligent discussion. We all learn from that. I think your approach might be a little hard on folks, though. Rather than assuming people are ignorant, maybe just give your professional expertise on a topic and leave it at that. You obviously have a passion for this science, but in text passion sometimes doesn't translate too well.

I do not and never have meant any disrespect to anyone in this topic. I, however, have felt a tad bit insulted, as apparently others have as well. I assume at was just the way things looked in black and white. I imagine that if we all had this conversation in person, it would have been very different.

Thanks to everyone for sharing a lot of information.

[SK66]

FWIW, I never "felt" attacked. I did feel misunderstood as the basics of what I said I firmly believe and have justification for.
I have done all of the FEMM calculations and standardized as best I could to get usefull information from them. I used industry standard information for the data input and I made everything as close to scale as possible. I also have "ferrofluid", magnetic viewing film, and a commercial/calibrated Gaussmeter...I have looked at all of this and have experience that valididates it as well. Beyond that, I am not an expert either.
I am not educated in electronics other than self taught....I have a hard time designing a circuit and making use of IC's and OpAmps etc....but I've done it.
I do understand the difference between the circuits mentioned, the parallel resistive ground and the HB...I recognized the issue as I typed it but let it go. To my limited theoretical knowledge, the path the signal SHOULD take is not thru the potentiometers, and it's basicly "a leak". In my mind it relates "similarly" to what can happen when cutting coils...WHY it happens I cannot explain; thus the difficulty...

The only point of contention that really bothers me is the magnetic fields/aperature. I guarantee you that if you take an a5 bar with N/S oriented vertically and measure the surrounding fields it will be both Taller and Wider than the same bar in a HB configuration.
I believe the field is important in "every direction" because a string will oscillate in a series of rotating ovals within the field, and this varies with player technique (hard/soft picking, plucking, strumming etc etc). The height and the strength of the field are both important in determining character of a pickup as well as the "aperature" as typicly defined. They help determine attack and "brightness" and also affect the very way the string oscillates within the field. Also, I would question just at what point the field strength becomes irrelevant...I don't know. As some have stated it doesn't take much, just residual magnetism in the strings themselves is enough...
Some of this is like discussing Helicopter Aerodynamics at a high level... In it's essence it's "THEORY" and "definitions" don't always make sense....it's too complex to really discuss clearly or fully understand in a "conversation"; especially if there are issues with common terminology/background.