20 December 2013

Wiring DIY: in-phase, out-of-phase and hum-cancelling concepts


While dealing with just a single pickup or coil, it makes no sense to be worried about things as "out-of-phase" or "hum-cancelling" but, as soon as you combine together a couple of coils or pickups, those concepts have big impact on resulting sound.

If you are interested on pickups and on moding your guitar wiring to achieve alternative sounds to those few that came stock then, the wording "in-phase", "out-of-phase" and "hum-cancelling" would be part of your language but, what at the does it mean and, how do we know if we get one or the other when trying to combine one or the other coil of a humbucker with a true single coil pickup?.

Along this blog entry, I will try to let you understand what is behind this concepts and how to achieve your wanted results and, how to avoid the wrong ones.

How coils are wound, phase and polarity stuff

Usually, coils are made of a continous thin (42 to 44 AWG) isolated (formvar, etc) copper wire wound around  a frame to form a coil. Since engines rotate usually clockwise (CW from now), the CW winding direction is the usual way as EVERY coil is being wound.

The starting side of that single wire that forms the coil, after so much turns stays in the inner part of the coil while the finish of that single wire stays in the outer part of the coil (since it belongs to the last turn).
Usually, that start "wire" is connected to ground, while the finish "wire" is connected to hot (to the signal path).

That means that we assign positive electrical polarity to the finish wire and, negative electrical polarity to the starting wire but, for this to be true, the magnetic field should have South polarity.

So, most of COILS are of type CW-S (wound ClockWise with South Magnetic Polarity).
The typical Fender Strato coils are CW-S and, most of strato direct replacement pickups are, also.

In the case of humbucker pickups, both coils were wound in the same direction (once again, CW) but, since they are being placed over two different poles of the same magnetic bar, one has a North magnetic polarity and, the other South magnetic polarity.
Usually, the screw coil (adjustable) has North polarity (CW-N), while the slug coil (not adjustable) has South polarity (CW-S).

To get rid of hum in notch positions, Fender started to produce RW/RP (Reverse Wound / Reverse Polarity) middle pickups, to achieve hum cancellation in positions  2 and 4 of a typical strato.
But, take also into account that some models of Fender were historically mounted with flipped magnet rods, which created pickups of type CW-N (instead of CW-S).

A RW/RP pickup has a reverse wound and reverse polarity RESPECT OF THEIR model pickups.
That means that if for a certain model or group of models, the standard coil is CW-S, the corresponding middle RW/RP will be of type CCW-N (Counter ClockWise, North polarity) but, if the original set had pickups of type CW-N (ClockWise, North), the respective RW/RP will be of type CCW-S (Counter ClockWise, South).

Most of Fender Strato pickups are of type CW-S and, their middle RW/RP is CCW-N but, certain models, as the Texas Hot are of type CW-N and their respective RW/RP is of type CCW-S.

Following picture (click for full size), shows the different scenarios we can find when combining the 4 different types of coils described above.

You can see that for each two coils combination, we have two different columns in this table.
First one (in-phase) will have a YES if both pickups are electrically in-phase or NOT if they are electrically out of phase.
Second one (hum-cancel) will have a YES if the combination is good for hum-cancelling or NOT, if not the case.
Best scenario (in-phase / hum-cancelling) is shown in green, worst scenario (out-of-phase / not hum-cancelling) is shown in red and the in-between scenario (in-phase / not hum-cancelling) is shown in yellow.

When two coils are in-phase, they produce full sound, they just sound good.
When two coils are out-of-phase, the sound becomes thin, weak, hollow, nasal and sharp, do to the fact that most of the signal originated by the movement of the strings and caught by each coil have oposite sign and they are being cancelled.
When two coils are arranged in a hum-cancelling configuration, most of the noise (not signal) caught by both coils has oposite sign and therefore is being cancelled while the signal remains intact, in-phase.

But you should take into account that the signal produced by two different coils isn't exactly the same, never and, neither the hum or noise present.
For two coils to generate the exact same signal and noise, those should be exact clones one of the other and, stay in the exact same physical place.
As you can easilly understand, this is practically impossible, in real terms. So, even two twin coils of a humbucker will get the signal and noise slightly different and, therefore, the resulting signal will be slightly different to the signal we would get from one or the other coil alone and, also because of this, not all the hum will be completely cancelled.

The more equal that two coils will be and the more close they can be physically, the purest the signal and the lowest the hum.
The same coil placed in different spots along the guitar strings will produce different signals and noise levels.
You should have noticed that the neck (or front) pickup is always rich in harmonics and generates a strong signal, while the bridge (or rear) pickup sounds weaker, thinner and brighter.

If pickups makers didn't changed the number of turns or wire type or magnet strength in the differently placed pickups (bridge, middle, neck) we wouldn't be able to balance their output levels.

To reverse the phase (electrical polarity, in fact) of a pickup, swapping which wire goes to hot and which wire goes to ground has same effect as to reverse winding the coil.
So, if you have a CW-S coil and you solder to hot the start (natural negative) and to ground the finish (natural positive), you pickup is now acting as a CCW-S pickup. The oposite is also true.
Just understand that you are not able to change the magnetic polarity that way, just the electrical polarity.

To reverse the magnetic polarity, you need to flip 180ยบ the magnet bar (humbuckers) or the magnet rods (single coils) and, this is always harder and very specially with single coil pickups.

So, if you have two CW-S coils, swaping the hot and ground wires in one, will leave you in a CW-S / CCW-S scenario, which (take a look to the table) is a very bad one!.

To achieve an in-phase / hum-cancelling scenario, you need two coils with reverse phase (electrical polarity) and reverse polarity (magnetic polarity).

We said that both coils of same humbucker pickup were wound in the same direction (CW) but, one is placed over the North side of the magnet bar, while the other is over the South side of the magnet bar.
So, in a humbucker we have a CW-N coil and a CW-S coil. But search that case in the table above!. That's a bad case!.

If we link the start of each coil to negative and the finish to positive, we have exactly that case CW-N / CW-S but, if you remember, by swaping the two wires in a coil we are achieving the same as winding such a coil reverse so, if we just swap the wires of the North coil, we achieve a CCW-N coil and, now our scenario is CCW-N / CW-S. Take a look to the table. Yes, in-phase / hum-cancelling !!!.

This little trick allows the makers to achieve in-phase / hum-cancelling configurations even using coils wound in the same direction (CW). And that's why the typical arrangement of wires in a humbucker is as follows:

south start -> to ground
south finish - north finish (linked together, coils in series)
North start -> to hot

or you can swap ground and hot in south and north starts.

Which start goes to ground depends on each pickup maker, because for braided single conductor pickups (old school humbuckers), the start wire that is ground, is ground together with plate ground wire.

As we explained in other articles, a covered pickup creates some kind of Faraday's cage, which will get the noise in cage's walls and that noise will be thrown to the trashcan if that cage is being soldered to ground.
In braided single conductor pickups, the cage is in contact (soldered to) with the "humbucker ground wire" and, therefore, if we try the trick of swapping both coil wires we will positivize the cage, achieving an antenna that will catch lots of noise that will be thrown to the signal, instead of to ground!!!.

That's why some special mods make no sense with such a kind of pickups. You have braided single conductor examples in humbuckers, mini-humbuckers and P-90 single coils, by example.
But some Fender' single coils have a metallic plate on its bottom that is usually connected to the start (negative) of the pickup.
Once more, swapping the two conductors, we are positivizing such a plate with unwanted side effects.
That's why Telecaster mods that use out-of-phase or that need both pickups in series use a neck pickup with three wires (start, finish and plate ground).

This is not an issue with a humbucker having 4 conductors (start and finish of each coil) and an extra bare wire (for plate / cover ground).

Typical scenarios

Now that we have the background info of the previous version, it will be really easy to understand typicall scenarios and what to do in each case.

Let' start with Strato single coils.
In positions 1, 3 and 5, nothing of what was discussed here has any relevance, since each coil is being selected alone.
In positions 2 and 4 we are combining the middle pickup with either the neck or the bridge pickup.

As we explained above, most of coils are wound in CW direction and, they way as Fender mounts their magnet rods, give to that coils South polarity. So, each pickup is a CW-S case.
The black wire is the start wire and should be grounded.
The clear wire (white, yellow or alike) is the finish wire and should be linked to the hot path (pickup's output).

For those notch positions, in a standard Strato, we have an scenario CW-S / CW-S and, if you look that table above, that means that those positions are in-phase but not hum-cancelling. The sound, in this case has a nice bite and quack but, it's noisy.

Standard Strato coils, with a RW/RP middle pickup, will correspond to the scenario CW-S (neck or bridge) / CCW-N (middle) and, if you look to that table above. This is an in-phase and hum-cancelling scenario.
Since both pickups aren't exact clones and, since they are distant one from the other, some of the original signal will be cancelled and not all the hum would be removed.
The resulting sound has less presence than in the standard case, the quack isn't so pronounced but, the noise is clearly reduced.

So, sometimes, to achieve hum-cancelling positions can make slightly duller the tone of two coils combined together.

In the way the coils of any regular humbucker are being arranged, with the two finish wires soldered together and used to split the to one or the other coil (grounding the linked wires or, linking them to hot), there is the risk of splitting to the coil that, combined with that Strato single will lead to a wrong scenario. So, to understand what are we doing at every time is key for success.

When combining two humbuckers of the SAME maker (and I would say, model also), when splitting to North coils or South coils in both humbuckers, we will get in-phase but not-hum cancelling scenarios and, when splitting one to North coil and the other to South coil, we will achieve an in-phase and hum-cancelling scenario.

As explained in the case of Strato singles, which one to choose will depend on the wanted effect. If you can stand the noise and get a punchier sound, go to split same coils in both pickups. If you cannot stand the noise, go to split oposite coils in each pickup.

So, let say that we have a bridge humbucker with following color wires (Seymour Duncan's example):

You can see that the North wires were swapped (start wire goes to hot, instead of finish), to achieve that CCW-N type, while the South wires are standard (start to ground, finish as positive) so, we have a coil type CW-S.

Now, if we have to split that bridge pickup in position 4 (middle + bridge), in a Strato-alike guitar then ...

If we have a standard Strato pickup in the middle position, that would be of type CW-S.
If we wanted to achieve a typical position 4 (with the quack and the noise), we need to get a CW-S / CW-S scenario (by example, not the only possible). Since the South coil is just that, a CW-S, splitting the humbucker to South will give us that typical standard 4 position.
But, if we wanted to get a hum-cancelling position, we need to get a CW-S / CCW-N scenario and, that corresponds to split to the North pickup.

But if we are in the case of a standard RW/RP middle pickup, we have a coil type CCW-N.
If we wanted to achieve the typical positon 4, this time we need to select a CCW-N coil in our humbucker, that is, the North coil.
And, if we wanted a hum-cancelling position with that middle, we need a CCW-N / CW-S scenario and, therefore, we need to split to the South coil, this time.

Which color was used to identify which wire (north and south coils starts and finishes), widely changes from pickups maker to maker but, once you are clear about the scenarios described in the table above and the tricks we already discussed here, you will be able to always get what you wanted to achieve, while designing your wiring project.

Taking as example the above color wiring, if we put black to hot and white linked to red, the North pickup is type CCW-N and the South of type CW-S.
If we put white to hot and black linked to red, instead, we have North of type CW-N and South of type CW-S and, what we get is a  humbucker with their own coils out-of-phase. This will result in a weak signal with a nasal, hollow, thin, and sharp characteristic sound. But, maybe this is what we wanted to achieve!.

If we leave the North pickup linked as in the picture but, we swap red and green, we are having a CCW-N / CCW-S scenario and, once more, we get that characteristic out-of-phase sound.

To get a scenario with coils in-phase but not hum-cancelling isn't possible inside a humbucker. Look at the table above and, you will see that for that, you need two pickups with the same phase and polarity and, this is not possible since each coil has a different magnetic polarity.
So that kind of scenario takes place just when combining one coil of a humbucker with other coil of another humbucker or single coil pickup.

So, at the end, we can achieve following distinctive sounds out of a humbucker:

North coil alone (split to North coil)
South coil alone (split to South coil)
Coils in series and in-phase (regular humbucker sound, strong and warm, also hum-cancelling)
Coils in series but out-of-phase (weaker than previous one, thin, nasal, hollow and sharp)
Coils in parallel and in-phase (slightly weaker than a coil alone, open, clear, defined, bright and hum-cancelling)
Coils in parallel but out-of-phase (the weaker of all, thin, nasal, hollow and sharp)

Same is posible if we talk about two coils of two different pickups (being those another humbucker or just a single-coil pickup).

While for most of people the out-of-phase sound is unusable, Peter Green's typical tone was achieved with two out-of-phase humbuckers, in the middle position of the pickup selector switch (rythm + treble).
I personally like the OOP sound mainly under high distortion, when you need a razor-sharp screaming sound. I don't like so much for clean stuff, to be honest.

When dealing with Reverse Polarity Fender pickups (as the Texas Hot, among other models), which are CW-N, you will often need to swap the south and north start wires to get the wanted combinations with the trick to solder to ground or hot the link between both humbucker coils to achieve one or the other coil split.

1 comment:

  1. Great article, thank you for sharing your knowledge!


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