Pickup phasing
- Thread starter dj92
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octavedoctor
New member
Re: Pickup phasing
OK.
First of all, the term phase is incorrectly used in relation to pickups. Phase is a term that refers to the relative position of two waveforms in their vibration cycle.
When people talk of phase they usually mean polarity. A pickup can't be reverse polarity in isolation, it can only be so relative to another pickup, just as a waveform can only have a phase relationship to another waveform.
The most common application of reverse polarity pickups is in noise cancellation. A humbucker is a reverse wound, reversed polarity pair. The middle pickup of a modern strat is also reverse wound and reversed polarity, or rwrp for short.
In its simplest form a pickup is just a coil around a magnet. When something magnetically sensitive, such as a steel guitar string moves inside the pickups magnetic field, small disturbances in the field ripple out and cause proportional currents to be induced in the surrounding coil; these currents create a fluctuating voltage at the coil terminals which are used to signal the input of an amplifier.
The problem with this arrangement is that the coil can also pick up noise from the electromagnetic ocean in which we are immersed; typically 50 or 60 Hz hum, depending on where you are in the world.
Flipping the polarity of a coil by simply reversing the coil terminals relative to the other pickup with which it is in circuit also flips the polarity of the noise signal so that a + voltage flagged at the signal terminal of one coil is matched by a - voltage at the same terminal of the other coil, causing them to cancel each other. This will also flip the signal induced by the string and cause this to cancel as well, but because the signal from the string is dependent upon the polarity of the magnetic core, by flipping the polarity of the core we can restore the polarity relationship of the signals induced in each coil. Because the noise signal is not dependent on the magnetic polarity of the core the noise cancelling effect of the pickup pair is maintained.
OK.
First of all, the term phase is incorrectly used in relation to pickups. Phase is a term that refers to the relative position of two waveforms in their vibration cycle.
When people talk of phase they usually mean polarity. A pickup can't be reverse polarity in isolation, it can only be so relative to another pickup, just as a waveform can only have a phase relationship to another waveform.
The most common application of reverse polarity pickups is in noise cancellation. A humbucker is a reverse wound, reversed polarity pair. The middle pickup of a modern strat is also reverse wound and reversed polarity, or rwrp for short.
In its simplest form a pickup is just a coil around a magnet. When something magnetically sensitive, such as a steel guitar string moves inside the pickups magnetic field, small disturbances in the field ripple out and cause proportional currents to be induced in the surrounding coil; these currents create a fluctuating voltage at the coil terminals which are used to signal the input of an amplifier.
The problem with this arrangement is that the coil can also pick up noise from the electromagnetic ocean in which we are immersed; typically 50 or 60 Hz hum, depending on where you are in the world.
Flipping the polarity of a coil by simply reversing the coil terminals relative to the other pickup with which it is in circuit also flips the polarity of the noise signal so that a + voltage flagged at the signal terminal of one coil is matched by a - voltage at the same terminal of the other coil, causing them to cancel each other. This will also flip the signal induced by the string and cause this to cancel as well, but because the signal from the string is dependent upon the polarity of the magnetic core, by flipping the polarity of the core we can restore the polarity relationship of the signals induced in each coil. Because the noise signal is not dependent on the magnetic polarity of the core the noise cancelling effect of the pickup pair is maintained.
Last edited:
Re: Pickup phasing
Wow,
Thanks for that.
You have now educated me in ''phasing'' - ''polarity switching''.
I will try some experimentation on this minihumbucker I have as I just thought it might add a new tone to the guitar I am building.
What would I need to switch the polarity on just the one pup?
I would guess some sort of double pole switch but do not know enough about this subject to be confident in doing it.
Many thanks,
Regards,
Wow,
Thanks for that.
You have now educated me in ''phasing'' - ''polarity switching''.
I will try some experimentation on this minihumbucker I have as I just thought it might add a new tone to the guitar I am building.
What would I need to switch the polarity on just the one pup?
I would guess some sort of double pole switch but do not know enough about this subject to be confident in doing it.
Many thanks,
Regards,
octavedoctor
New member
Re: Pickup phasing
Indeed, although the error is understandable and only irksome to a borderline Asperger's pedant like myself...
It originated because for a simple sine wave a mirrored - i.e. reversed polarity waveform - is exactly the same as a 180 degree phase shift. However many noise profiles are spike waveforms with assymetric mark/space ratios (mark/space ratio is an expression of the time the signal spends in the negative voltage range versus the time spent in the positive) an AC signal may have a mean voltage of zero but have a high, short value in the positive and a longer but lower value in the negative. Such a waveform shifted through 180 degrees won't result in noise cancellation but in a doubling of the frequency of the noise signal. Mirroring by reversing the polarity is effective at cancelling the signal though.
A double pole, single throw switch is what you need for polarity reversal, although the benefits it produces in terms of tone are dubious. The circuit is simplicity itself. You just connect opposite corner terminal lugs of the switch and take the wires from the pickup to the top two terminal lugs of the crossover, the connect one of the centre lugs to earth and use the other as the pickup output.
Indeed, although the error is understandable and only irksome to a borderline Asperger's pedant like myself...
It originated because for a simple sine wave a mirrored - i.e. reversed polarity waveform - is exactly the same as a 180 degree phase shift. However many noise profiles are spike waveforms with assymetric mark/space ratios (mark/space ratio is an expression of the time the signal spends in the negative voltage range versus the time spent in the positive) an AC signal may have a mean voltage of zero but have a high, short value in the positive and a longer but lower value in the negative. Such a waveform shifted through 180 degrees won't result in noise cancellation but in a doubling of the frequency of the noise signal. Mirroring by reversing the polarity is effective at cancelling the signal though.
A double pole, single throw switch is what you need for polarity reversal, although the benefits it produces in terms of tone are dubious. The circuit is simplicity itself. You just connect opposite corner terminal lugs of the switch and take the wires from the pickup to the top two terminal lugs of the crossover, the connect one of the centre lugs to earth and use the other as the pickup output.
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