Effect of magnetic field on Half of a Bucker.

[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.

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.

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

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.

[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.



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)

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:

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:



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

Now an inductor:



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.



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.

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.

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]

I dissagree Mr Schwab

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.






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!!

[madialex]

And in case you didn't realise it Mr. 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.
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.

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.

[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.