Pickup Magnetic Polarity and Phase
In this article, Pete Biltoft at Vintage Vibe Guitars explains how the magnetic orientation and winding direction of single coil pickups affects their phase relationships and hum cancellation.
Thanks again to Pete for the permission to post this here!
Howdy!
In this newsletter I would like to cover how to “match” two single coil passive magnetic pickups.
Consider all of the possibilities for magnetic polarity (north up or south up) and winding direction (clockwise or counter clockwise) for each of the two pickups as well as series or parallel connection of the two pickups and the possibility of the pickups being in phase or out of phase with each other and things can get a little complicated.
Let’s try to sort it out.
Most players just want three good and useful tones from an instrument with two pickups:
- Bridge position pickup only
- Bridge and middle position pickups both on (and most often connected in parallel)
- Neck position pickup only
In switch positions 1 and 3 all is good- no phasing issues are possible as there is only one signal from one pickup, but in switch position 2 the possibility exists that the two signals from the two pickups could be in phase or out of phase with each other.
Why would you care?
Let’s just consider switch position 2 in which both pickups are contributing to the signal going to the output jack of the instrument.
If these two signals are out of phase the result is often a thin, nasally tone that is not hum canceling. The tone of out of phase pickups has been used quite successfully by some players to create a very characteristic sound found often in Funk and Reggae. James Burton could coax a thin, out-of-phase sound out of his Tele—he called it the “little Chinese tone”. You can hear this sound on some of his famous recordings with Ricky Nelson, including Travelin’ Man. Jimmy Page also used the out of phase combination to very good effect. I bring this up to make the point clear: having the signals from two pickups out of phase with each other is not necessarily a bad thing. In the table below these out of phase combinations are highlighted in purple.
If the two signals from the two pickups are in phase and the pickups have the correct magnetic orientation and winding direction the result is a strong tone that is hum canceling. In this case the two pickups have opposite magnetic polarity and opposite winding direction with respect to each other. This is the configuration used in most modern instruments and is called reverse wound reverse polarity and is abbreviated RWRP. In the table below these in phase and hum canceling combinations are highlighted in green.
In some vintage instruments both pickups have the same magnetic polarity and winding direction; this configuration produces a reasonably strong tone but is not hum canceling. In the table below these in phase and non-hum canceling combinations are highlighted in yellow.
There are a total of eight possible configurations for magnetic polarity and winding direction for two single coil pickups; here they are:
Once a decision has been made regarding which of these eight pickup configurations is desired the remaining task is to make sure the magnetic polarity and winding direction of the two pickups is correct.
Note that for a desired configuration (RWRP for example) one must get both the magnetic orientation and winding direction for both pickups correct (options 1 or 5 in the table above). Purchasing a matched set of pickups configured as you want from a pickup manufacturer is often the easiest path to getting a desired pickup configuration. If you are faced with matching two pickups of unknown magnetic orientation and winding direction, changing the magnetic orientation or the effective winding direction on one of the pickups may be required. Note that changing the magnetic orientation will reverse the phase of a pickup; changing the effective winding direction will also change the phase of a pickup; changing both magnetic orientation and effective winding direction will change the phase twice and will return the pickup to its original phase orientation.
1. Magnetic orientation.
I usually start with checking the magnetic polarity of the two pickups using a scout’s compass as shown in the photo below. Note that the compass in many cell phones use GPS data to determine direction and cannot be used to identify the magnetic polarity of a pickup.
If the top of a pickup attracts the red end of the compass needle the pickup I call this north up.
If you find that the two pickups you want to install in an instrument have opposite magnetic polarity and you intend to have the pickups configured RWRP then you are half way there and can skip ahead to part 2: Winding direction.
If you would like to have RWRP configuration but observe both pickups have the same magnetic orientation you have a few choices:
A. If one of the pickups is designed to allow the magnetic orientation to be reversed then making this change will allow RWRP configuration. Many of the pickups offered by Vintage Vibe Guitars are specifically designed to allow the owner to remove and replace the magnets.
B. You can purchase one new pickup with the correct magnetic orientation to be paired with the pickup you intend to use. When making this purchase you will need to let the pickup maker know the magnetic orientation you want for the new pickup and also communicate the method used to determine the magnetic orientation of the pickup you want to pair with the new pickup.
C. You can purchase a new matched set of two pickups which are configured RWRP.
2. Winding direction.
We will start here assuming that the magnetic polarity of the two pickups has been sorted out as described in section 1: Magnetic Polarity.
A. Using an analog multimeter to check phase orientation
Note: Detailed information on the proper use of multi-meters is available on: http://www.masonmonitoring.com/pdf/support/UsingMultimeter.pdf
To do this test, set the multimeter to the most sensitive DC voltage scale (1 volt full scale) and connect the probes of the multimeter to the output leads of the pickup. The leads should be connected as follows: red multimeter probe to the “Hot” lead of the pickup and the black multimeter probe to the “ground” lead of the pickup. With these connections made place a steel tipped tool on the top of the pickup then quickly pull the tool away from the pickup. You should observe a quick motion of the indicator needle of the multimeter either to the left or to the right. Most pickup manufacturers make pickups which will indicate a positive (right moving) deflection of the indicator needle in this test. If both of the pickups show deflection of the analog meter needle in the same direction the two pickups have the same phase orientation which is correct if you want the pickups to be in phase with each other. If you want to change the phase of the pickup go to section C. below.
B. Testing the pickups in the instrument
If an analog multimeter is unavailable I suggest installing the pickups into an instrument and listening carefully to the tone and output of the pickups in all three pickup selector switch positions. If you hear a low output, thin sounding tone in the middle (2) switch position it is likely that the two pickups are out of phase with each other. If this is the desired middle position tone, all is good, if not then the phase of the pickup must be reversed as described below in section C.
C. Changing phase orientation by reversing the effective winding direction
If you wish to change the phase of one pickup it will be necessary to reverse the assignment of the output leads on that pickup at the free end of the leads. First check that the output leads are independent of any grounded shielding on the pickup. In pickups with two leads and no shielding simply reverse the assignment of leads (use the black lead as the hot output and the white lead as ground). If the pickup has grounded shielding one would need to remove the connection between the ground lead (which usually has black insulation) and the copper shielding and install a new independent ground lead onto the shielding of the pickup. The new ground lead should be soldered to a known electrical ground in the controls cavity such as the casing of a grounded pot. If the pickup has an output cable with two independent conductors (often one with black insulation and one red or white insulation) inside a shield then one can simply reverse the assignment of the two internal conductors at the free end of the output cable. Maintain the connection of the external shielding to ground.
I hope you find this information useful.
Please visit the Vintage Vibe Guitars website (www.vintagevibeguitars.com) for more Tech Tips, wiring diagrams and of course a wide selection of pickups for guitar and bass.
Best wishes,
Pete Biltoft
Vintage Vibe Guitars
website: www.vintagevibeguitars.com
email: info@vintagevibeguitars.com
August 20, 2014 @ 8:30 am
Actually, two out of phase pickups will hum cancel if the windings are opposite, or they are wired in reverse. This is not shown in your chart. All humbuckers, or hum canceling pairs, have coils with opposite electrical polarity; they are always out-of-phase! This can either mean they were wound in the opposite direction, or are wired with reverse polarity, as with most Gibson style humbuckers.
The reason why you can have in-phase sounding coils that hum cancel is because the magnets are reversed polarity. The way this works is that two coils do not see the exact same movement of the strings at the same time. So the string might be moving down over one pickup, but up over the other. But electrical interference—and in this case specifically magnetic field interference—is picked up by both coils simultaneously, and cancels out.
Winding or wiring the two coils in opposite directions cause this noise to be canceled out when the signals are summed together. However, because one coil has a north magnetic polarity, and the other is south, the strings are picked up out-of-phase by the magnets, and put back in-phase by the windings.
So now you have the common mode noise being canceled, but most of the signal from the strings passes unscathed. But there are cancelations in the strings’ signal too. This causes a comb filtering effect, and is responsible for the slight canceling of high frequencies in humbuckers. And any two pickups will exhibit this comb filtering, which is why you get that mislabeled “out-of-phase” quack on a Strat in the 2 & 4 positions. On true out-of-phase wired pickups, you lose low frequency information, since that is common between the two pickups, while the higher harmonics are not.
One thing humbuckers can’t cancel is electrical field noise, such as from light dimmers. These signals vary with time, so they don’t hit both coils equally. They are also higher in frequency. Shielding helps with that noise.
August 22, 2014 @ 8:58 am
David- thanks for the comment. I would respectfully disagree, however with some of your assertions. In the chart I provided there are eight combinations of magnetic polarity and winding direction for two single coil pickups. If you believe this list to be incomplete or incorrect please post a chart or a detailed list showing the missing information. Also- “noise” as guitarists experience it in magnetic pickups coming from dimmer switches and other 60 cycle AC sources is electro-magnetic radiation which contains both an electric and a magnetic component as described in detail on the following website: http://en.wikipedia.org/wiki/Electromagnetic_radiation
When you refer to “electrical noise” in the last paragraph I believe the more correct term is electro-magnetic noise which has both electric and magnetic components.
In any event, please understand that I in no way am trying to “slam” you; my sole interest in publishing the original article and in writing this comment is to provide information on this topic in as clear, complete and technically correct manner as possible.
August 22, 2014 @ 12:35 pm
Pete, the chart is wrong. Any time you have two coils with *reversed electrical polarity*— and it doesn’t matter if they are wound in opposite directions, or wired in reverse—you will buck hum. This is how humbuckers work. The noise does not care about magnetic polarity, and does not need it to be induced in the coils, and indeed two coils without magnets will still hum cancel. This is how dummy coils work.
The reason why the tone is not thin on a humbucker, or with a RWRP Strat in the 2 or 4 position, is because of the reversed magnetic polarity. The magnets only affect sensing the strings, because they both magnetize the strings, and also the strings disturb the static magnetic field (variable reluctance). This causes current to flow. But has nothing to do with noise pick up of stray magnetic fields.
You can prove this yourself. Get two single coil pickups with the same magnetic polarity, and wire them out of phase. When you turn them both on they will hum cancel. But the tone will be thin.
So on the chart, every reverse or out-of-phase *coil polarity* will be hum canceling. Even with same facing magnets. However, if two coils have the *same polarity,* but the magnets are opposite, it will sound out-of-phase but will not hum cancel.
Regarding noise, your statement equating light dimmers and 60 cycle hum is also incorrect. To prove this, notice how humbuckers DO cancel 60 cycle hum (from AC power line transformers), but DO NOT cancel the noise from light dimmers. Shielding will help with that, which is in part why EMG pickups are so quiet (along with using a differential op amp circuit).
Now note that shielding a single coil pickup with copper foil does NOT effectively block 60 cycle hum. If it did, then the quest for noise canceling “single coil” pickups would have ended a long time ago, and humbuckers would never have been invented!
60 cycle hum from transformers is alternating (time-varying) magnetic field noise. The hash from light dimmers is electric field noise, and is not time-varying. They are kind of two sides of the same coin (electromagnetism), since all electrical fields create magnetic fields, and vice versa, but not exactly the same. The frequencies of the noise are also different.
How do I know all this to be true? I’m a pickup maker. That’s what I do every day. Recently a set of my pickups was on the Grammy’s in Ben McKee from Imagine Dragons white hollow body bass.
It’s not an easy concept to wrap your head around though, and I’ve heard pickup makers get it wrong too.
I’ll direct you here:
http://en.wikipedia.org/wiki/Humbucker
“Hum is caused by the *alternating magnetic fields* created by transformers and power supplies inside electrical equipment using alternating current.”
“How humbuckers work
In any magnetic pickup, a vibrating guitar string, magnetized by a fixed magnet within the pickup induces an alternating voltage across its coil(s). However, wire coils also make excellent antennae and are therefore sensitive to electromagnetic interference caused by alternating magnetic fields from mains wiring (mains hum) and electrical appliances like transformers, motors, and computer screens. Guitar pickups reproduce this noise, which can be quite audible, sounding like a constant hum or buzz.
The direction of a voltage induced across a coil by the moving string depends on both the coil winding direction and the direction of the fixed magnets. A humbucker has two coils wound in opposite directions, one clockwise and the other counterclockwise. The magnets in the two coils are arranged in opposite directions so that the string motion induces voltages across both coils in the same direction.
Electromagnetic interference, on the other hand, induces voltages in opposing directions across the coils because it is only sensitive to the winding direction. When the signals from both coils are summed together, usually by connecting the coils in series, the two noise voltages cancel, while the signal voltages add thus dramatically improving the signal-to-noise ratio. The technique has something in common with what electrical engineers call common-mode rejection and is also found in balanced lines in audio recording.”
December 16, 2019 @ 9:39 am
I think you both may be correct. The two coils in a humbucker are normally wired in series, while two single coil pickups are usually wired in parallel. Pete seems to be talking about two single coil pickups (thus wiring is in parallel), and David seems to be talking humbuckers (thus wiring is in series). Am I correct you are both correct?
December 16, 2019 @ 11:44 am
Once again, there are statements in David’s message which I believe are incorrect.
Here is an example:
“Regarding noise, your statement equating light dimmers and 60 cycle hum is also incorrect. To prove this, notice how humbuckers DO cancel 60 cycle hum (from AC power line transformers), but DO NOT cancel the noise from light dimmers. Shielding will help with that, which is in part why EMG pickups are so quiet (along with using a differential op amp circuit).”
In this statement David is asserting that the electromagnetic noise signal emanating from a dimmer switch (which operates on 100 Volts AC power) is somehow different from the noise signal emanating from an AC power line transformer. Both of these noise signals are AC electromagnetic waves.
Here is another statement from David:
“Actually, two out of phase pickups will hum cancel if the windings are opposite, or they are wired in reverse. This is not shown in your chart. All humbuckers, or hum canceling pairs, have coils with opposite electrical polarity; they are always out-of-phase! ”
Pickups (specifically single coil pickups or one coil in a HB pickup) themselves are physical objects and cannot be in phase or out of phase; coils can either be wound clockwise or counter-clockwise. The SIGNALS generated from two single coils can be in phase or out of phase. I think David gets confused when he assigns a phase (AC electromagnetic wave) to a physical object such as a coil.
I will agree with Kevin that in large part David and I are in agreement; it is just not clear to me why David took exception to information in my original post.
In any event, I stand by everything stated in my original posting which contains a chart showing every possible combination of two coils. For example, two coils which have the opposite winding direction (one clockwise, the other counter-clockwise) and the opposite magnetic polarity (one north up and one south up) will be hum cancelling if the two coils are connected in series or in parallel.
I hope this is helpful.
January 12, 2020 @ 12:20 am
Pete, I’m not sure if this is David’s point, but I believe numbers 4 and 8 in your chart are incorrect. These will both be OOP (as you state), but will be hum-cancelling.
Here’s how I think about it:
The typical RWRP pair is in-phase, and quiet. The coils have reversed magnet orientation, and reversed wind direction (or reversed hookup leads, same thing).
Hum vs hum-cancelling is purely a function of wind direction. Opposites are quite, sames are noisy.
Changing phase can be done by changing *either* magnet orientation, *or* wind direction.
So, if reverse magnets, reverse wind = in-phase, quiet…
– reverse magnets, same wind = OOP, noisy (wind change affects both)
– same magnets, reverse wind = OOP, quiet (magnet change only affects phase)
– same magnets, same wind = in-phase, noisy (changing wind affects both making it OOP, noisy; but then changing magnet affects only phase, making it in-phase, noisy).
Hope this is clear, and that it helps a bit.
January 12, 2020 @ 9:02 am
Okay, I see it now. #4 and #8 are definitely incorrect insofar as these arrangements would certainly be hum-bucking. The changing magnetic flux through the two coils from an external magnetic field (in other words, NOT from the strings) is in no way dependent upon the relative orientation of the magnets in the pickup. As far as external magnetic fields, the permanent magnets in the pickup might as well not be there. For external magnetic fields it is only the relative directions of the two windings that determine if the voltage generated in the coils is cancelled, or added. If the windings are opposite, the voltage generated with be cancelled, so “hum-bucking”, while if the windings have the same sense, the voltage will be additive, thus noisy. So, #4 and #8 are 100%, definitely incorrect as far as humbucking properties. The image needs to be changes because it is causing confusion to those who come here,myself included. At least it forced me to think about it further, but #4 and #8 are incorrect.
September 21, 2020 @ 9:23 am
The simple fact of the matter is that any configuration which cancels out humming from outside sources will also reduce the desired output of an AC waveform generated by manipulating the magnetic flux via the strings. The only difference is that the pickups are inherently designed to respond to nearby field changes where electrical hum induces direct harmonic resonance. Sadly, you can’t have your cake and eat it too; if you want lots of tone you’re going to have to eat noise as well.
And since noise doesn’t come into the signal path exclusively through the pickups, shielding is a big help but you can’t shield your pickups from the strings or you wouldn’t have any sound. And since your strings will also respond to EMF, they will always help route electrical noise into the pickups like a big antenna. That is precisely why the strings are grounded at the bridge: EMF is channeled to ground directly to try and mitigate the amount of induction they undergo as a result of responding harmonically to EMF. Unless you want to go with non-ferritic strings and optical or piezo transducers, you’re going to have SOME noise.
Best thing to do is find a pickup you like and can live with. And if it doesn’t exist, make your own. Music may have science behind it, but it isn’t based in science. It’s based in soul. That being said, my pacemaker REALLY annoys me when playing with single coils.
September 21, 2020 @ 12:16 pm
That’s crazy about your pacemaker coming through your pickups! I’m sure there’s a good pun in there about music being based in heart and soul!! 🙂
-John
October 8, 2020 @ 11:38 am
I have a chart that I’d be happy to email you that would correct the slight inaccuracies of your above chart.
October 8, 2020 @ 1:36 pm
Hi Eric- Sure. Send it over and I’ll see if I can attach it to your comment