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.

[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]

Half a humbucker isn't lame....

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.

[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?

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

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....

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.

[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...

[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