Theoretical Dilemma about Humbucking PUs

[xachangea]

Hi, I was wondering whether it might be possible to stack two single coils to create a humbucker, but not the usual way, with one "dummy" single coil just for the sake of hum canceling, and only one operational.

The ideas is thus: to have one single coil mounted under the strings, and another right above the strings...

How would you need to wind the wire and what would be the magnets orientation so that the signal from both PUs adds?

For instance, in the classic horseshoe PU there's only one coil under the strings, but strings are magnetized with different poles above and under them. Could you add a second bobbin above, to create a sort of humbucker? (forget practical considerations, as to the space needed to fit the coil)

Regards,

X

[T-Bird]

Hi.

Welcome to TalkBass xachangea.

Your post doesn't make much sense.

Using a dummy coil is used only if a single coil sound is what You're after. Is this what You're asking about?

The usual construction for a humbucker is to have two coils in the magnetic field.
Either the winding direction or the magnetic field orientation has to differ between those "two" single coils in order to have the hum cancelling effect.

Google humbucking theory or something like that and there's reading for hours.

http://www.google.fi/search?hl=fi&q=...=&oq=&gs_rfai=

Regards
Sam

[line6man]

Yeah, your post doesn't make much sense.

A dummy coil is a pickup without magnetic pole pieces.

Since a dummy coil does not produce a signal, it does not need to be, nor should it be, in the path of the vibrating strings.

Most people put dummy coils either under the pickguard, or in the control cavity.

[Stealth]

Originally Posted by xachangea

Hi, I was wondering whether it might be possible to stack two single coils to create a humbucker, but not the usual way, with one "dummy" single coil just for the sake of hum canceling, and only one operational.

The ideas is thus: to have one single coil mounted under the strings, and another right above the strings...

How would you need to wind the wire and what would be the magnets orientation so that the signal from both PUs adds?

Same as you'd do with a normal humbucker. The lower (internal) one would be wound in one direction and polarized in one direction, say, clockwise-wound and north facing the strings. The upper (hovering) pickup would be counter-clockwise-wound and south facing the strings. I don't believe anything else would be required.

As to whether the top coil would be magnetized or non-magnetized (dummy), that's anyone's choice. line6man is right in the sense that the dummy coil should be nowhere near the strings, so it'd only make sense to have both coils magnet-loaded.

[xachangea]

Hi, first of all thanks for the replies...

Unfortunately the word "dummy" lead to a wrong interpretation of my post.

What I mean is AS IN THE CASE OF STACKED PUs, with dummy coils, but in this case the TWO COILS ARE OPERATIONAL.

That's my question, to re-formulate it again: can you create a humbucker PU by placing the two single coils instead of one next to each other, one on each side of the strings? One sensing the strings from below, the other from above.

That's it. If it may be possible, what would be the correct wiring and polarity to cancel the hum and add signal from both PUs?

Thanks,

X

[bassbenj]

Originally Posted by xachangea

Hi, first of all thanks for the replies...

Unfortunately the word "dummy" lead to a wrong interpretation of my post.

What I mean is AS IN THE CASE OF STACKED PUs, with dummy coils, but in this case the TWO COILS ARE OPERATIONAL.

That's my question, to re-formulate it again: can you create a humbucker PU by placing the two single coils instead of one next to each other, one on each side of the strings? One sensing the strings from below, the other from above.

That's it. If it may be possible, what would be the correct wiring and polarity to cancel the hum and add signal from both PUs?

Thanks,

X

I suppose it is possible. People make "stacked coil" humbuckers with the second coil under the pickup so I presume you could do one with a second pickup over the strings. Only problem is the covering pickup would tend to interfere with playing and did I mention that at least the stacked coil pickups I had were really bad in the tone department?

[xachangea]

Originally Posted by bassbenj

I suppose it is possible. People make "stacked coil" humbuckers with the second coil under the pickup so I presume you could do one with a second pickup over the strings. Only problem is the covering pickup would tend to interfere with playing and did I mention that at least the stacked coil pickups I had were really bad in the tone department?

I'm only interested in the theory here, whether it would be possible to generate signal that adds constructively with two pickups, one placed over the strings, the other under the strings,...

and at the same time getting some humbucking effect so that the radio signals that they sense get cancelled...


Two put it shortly...

HOW TO WIND, ORIENTATE POLARITIES IN TWO PUs, one under the strings (as tradition dictates) one above them (as never seen on guitars/basses), so that the ACOUSTICally useful SIGNAL ADDs (for the most part) and the interfering RADIO SIGNALS GET CANCELLED....

NONE OF THE COILS IS DUMMY, both should sense the string motion, from different perspectives...

[T-Bird]

Hi.

Thanks for the clarification, Your question makes much more sense now.

The magnetic fields can't repel eachother because in that case the string would be in the 0 field plane.

For the same reason, in theory, the coils have to be wound CW and CCW.

What makes things complicated is that the interference in the magnetic field between the two coils is 180 degrees apart. The frequency response may be really erratic.

Using two magnets (magnetic fields) instead of one will create additional problems.

Regards
Sam

[FunkMetalBass]

Interestingly enough, a magnet on either side of the strings might allow for greater sustain, because the string is no longer suffering a unidirectional forced decay. Instead, the magnetic pull is (ideally) equal and opposite on both sides of the string, so it is equally pulled in both directions.

However, the complete opposite could be true in that additional magnets around the string would force it to dampen much faster. Sounds like a cool experiment that you should try.

[xachangea]

The magnetization from both sides is nothing but the original horseshoe pickup by Rickenbacker.

In that case, there's two magnets that surround the strings and create a magnetic field in which the strings are fully immersed.

What Rickenbacker did, on the other hand, is put only one coil to sense the strings...

And you're right about sustain, the equilibrium effect is positive from the standpoint of music,....

The idea would be how about putting a second coil. Can you ever find a way of getting the signal from both coils reinforcing each other, instead of canceling each other out??

I agree, maybe you cannot avoid having to experiment... maybe it sounds cool two have a stack-bucker... the idea was to get any comments from the theoretical experts before putting it into practice.

Cheers,

X

[FunkMetalBass]

They'll likely be hum-cancelling already because of the reversed magnet polarity, but assuming you're placing the second pickup (of identical make and design) directly over the first pickup, you wont get any tonal effects from it.

[M0ses]

My hypothesis: this pickup will NOT produce any noise at all if they were WIRED in phase.

Since the string is vibrating back and forth, when it goes toward one, it is moving away from the other: creating an "up" and a "down" in the other. So if they were wired the standard "in phase" way, then actually they would be totally out of phase. Humbucking properties should be the same as any, I think.

Thoughts?

[line6man]

Originally Posted by M0ses

My hypothesis: this pickup will NOT produce any noise at all if they were WIRED in phase.

Since the string is vibrating back and forth, when it goes toward one, it is moving away from the other: creating an "up" and a "down" in the other. So if they were wired the standard "in phase" way, then actually they would be totally out of phase. Humbucking properties should be the same as any, I think.

Thoughts?

Shamefully, I don't know as much about physics as I should, so I can't comment on how the movement of the string near the magnets will affect the phase of the signal, but from an electronics perspective you're correct about that.
Two identical signals, with 180 degrees phase separation would cause a destructive interference that would totally cancel them out. If indeed the pickups were producing equal waveforms, 180 degrees apart, you would want them wired out of phase.

[xachangea]

Originally Posted by line6man

Shamefully, I don't know as much about physics as I should, so I can't comment on how the movement of the string near the magnets will affect the phase of the signal, but from an electronics perspective you're correct about that.
Two identical signals, with 180 degrees phase separation would cause a destructive interference that would totally cancel them out. If indeed the pickups were producing equal waveforms, 180 degrees apart, you would want them wired out of phase.

And by wiring them out of phase... you would get the constructive interference?

If I get it right, since the signal in each of the pickups of humbuckers is IN PHASE, by wiring it OUT OF PHASE, you get a very thin sound (that could be described as the little difference between the two signals)...

In this hypothetical case, of having two coils producing already an OUT of PHASE signal, by wiring them IN PHASE you should get a thin signal, but wiring them OUT of PHASE would get you a better sound (conversely to the other case of figure).

Interesting enough... by the way, sorry about my utter ignorance, what are the factors that determine whether two pickups are wired IN or OUT of phase?

Cheers,

X

[line6man]

Originally Posted by xachangea

And by wiring them out of phase... you would get the constructive interference?

If I get it right, since the signal in each of the pickups of humbuckers is IN PHASE, by wiring it OUT OF PHASE, you get a very thin sound (that could be described as the little difference between the two signals)...

In this hypothetical case, of having two coils producing already an OUT of PHASE signal, by wiring them IN PHASE you should get a thin signal, but wiring them OUT of PHASE would get you a better sound (conversely to the other case of figure).

Interesting enough... by the way, sorry about my utter ignorance, what are the factors that determine whether two pickups are wired IN or OUT of phase?

Cheers,

X

Yep, you've pretty much got the concept.

[walterw]

Originally Posted by M0ses

My hypothesis: this pickup will NOT produce any noise at all if they were WIRED in phase.

Since the string is vibrating back and forth, when it goes toward one, it is moving away from the other: creating an "up" and a "down" in the other. So if they were wired the standard "in phase" way, then actually they would be totally out of phase. Humbucking properties should be the same as any, I think.

Thoughts?

actually, since a coil needs to be opposite magnetically as well as winding-wise, the coil above the strings would in fact have its magnets facing the string with the same pole as the pickup underneath. they would be repelling each other with the string right at the null point.

and since this coil would be reproducing sound in the same polarity as the underneath coil if the string were on the other side of it (like it would be if it was a regular side-by-side humbucker), then it should be reproducing the signal reversed from its bottom; couple that with the idea that it gets a reversed signal from the string, and it might in fact work perfectly!

[T-Bird]

Hi.

Originally Posted by xachangea

The magnetization from both sides is nothing but the original horseshoe pickup by Rickenbacker.

In that case, there's two magnets that surround the strings and create a magnetic field in which the strings are fully immersed.

Nope, just one magnet producing the magnetic field for a pair of strings, mounted so they don't interfere with eachothers fields (much).

Having two separate magnets to produce the field is asking for unpredictable results.

Originally Posted by xachangea

Interesting enough... by the way, sorry about my utter ignorance, what are the factors that determine whether two pickups are wired IN or OUT of phase?

Cheers,

X

No offense, but You have to be kidding us.

That, and the particle/wire/interference in the magnetic field is upper secondary school physics stuff. At least it was when I was young.

Before taking the matter any further You may want to brush up a bit .

Regards
Sam

[FunkMetalBass]

Originally Posted by xachangea

Interesting enough... by the way, sorry about my utter ignorance, what are the factors that determine whether two pickups are wired IN or OUT of phase?

From a simple, applied point-of-view, it's really just a matter of which of the two wires (we are assuming passive pickups) is the ground and which is the signal lead.

For more conceptual understanding of wave propagation, check out:
http://en.wikipedia.org/wiki/Interfe...propagation%29

[xachangea]

Originally Posted by T-Bird

Hi.



Nope, just one magnet producing the magnetic field for a pair of strings, mounted so they don't interfere with eachothers fields (much).

Having two separate magnets to produce the field is asking for unpredictable results.

I'm sorry, but you are wrong.

Actually the horseshoe pickup contains two magnets "C" shaped, in such a way that the magnetic field goes through the strings' plane, perpendicularly.

It would be different if you put two separate magnets, but only marginally different. In fact, that's the way in which plenty of pickup builders produce their copies of the original Rick's horseshoes, since "C" shaped magnets are pricey today.

They put magnets under and above the strings, with opposing polarities facing them (strings).

There is only one coil, under the strings, to sense the string motion, but the strings are fully immersed in a magnetic field.

[xachangea]

Originally Posted by T-Bird

No offense, but You have to be kidding us.

That, and the particle/wire/interference in the magnetic field is upper secondary school physics stuff. At least it was when I was young.

Before taking the matter any further You may want to brush up a bit .

Regards
Sam

Well, I'm not kidding YOU, so if you can point out to any source of reading that deals with those matters, I would gladly study them.

You had more luck that I did in Finland, with your physics class, so it seems, since what I learned in the subject doesn't allow me to disentangle this issue.

I have never seen a detailed explanation of how pickups work other than the general "a disturbance of the magnetic field, that induces a current in the coils, and blah blah"

Regards,

X