THE T-60 PHASE SWITCH & PICKUP PHASING

by Mike Frederick

Some Background:

When a string is plucked or struck on any musical instrument, the sting vibrates at frequencies determined by the gauge (mass) of the string, it's length and tension.  However, the string doesn't simply vibrate with one single tone but many tones called harmonics.  Each harmonic is a multiple of the basic or fundamental frequency

The fundamental frequency (or first harmonic) is the vibration generated as the entire string moves up and down with the center of the string moving the greatest amount.  But the string also vibrates at twice the fundamental, three times the fundamental, four times, and so on.  Each successive harmonic is also weaker than the previous one, which explains why the string still sounds predominately like the fundamental tone.

The figure below shows the various vibrating modes of a string.  You may notice the second harmonic has a null point in the center where the sting hardly moves at all.  On a guitar, this corresponds to the 12th fret.  Guitarists know that by lightly touching a string at this (or any) null point, the fundamental tone (as well as some harmonics) is suppressed and the string takes on a bell-like tone.  One of the better known uses of this effect was the introduction to the Yes song, Roundabout

Of course, in real life, all of the harmonics are combined into one sound.  But combining all of them into a single graph gets a little confusing and it becomes impossible to pick out the different harmonics.  But  Here's what it could look like:

Pickup Placement:

As we can see, the vibrations of the string vary a great deal over the length of the string.  It stands to reason then that where the pickup is placed along the string will have a lot to do with the sound of the guitar. 

The T-60, like a great many guitars, has two pickups referred to as neck and bridge due to their positioning on the body.  And, like many guitars, it has a switch to allow you to select either or both pickups.  Anyone who has spent more than a few seconds with a two pickup guitar knows that the neck pickup sounds rather mellow while the bridge pickup sounds much brighter. 

The reason is, of course, because the neck pickup is placed closer to the point of maximum swing of the fundamental while the bridge pickup is farthest away.  Both pickups do hear all the tones but at different levels.

Phasers on Stun!

If you read the article on Humbucker and Single Coil pickups

(Stop.  Go back and read it now so you won't get lost!)

you know that by wiring pickups in different ways you can combine and/or cancel signals.  In the case of the Humbucker, it was noise we were trying to kill off.  But in this case, it is primarily the lower harmonics we want to eliminate.

If we wire the pickups so the signals are in phase (both signals going up and down approximately the same at the same time), the signals will add together.  This is what gives us the fuller sound of the typical both pickups position.

However, if we reverse the wiring of one of the pickups so that the signals are out of phase (one signal going up while the other is going down), the signals will tend to cancel each other out.  Much like Seth Lover's humbucking pickup did to noise.

But!

Unlike the humbucker, where the noise was expected to be the same from both coils and cancel out, the signals from the neck and bridge pickups are NOT the same.  They are mounted in different positions and do not hear the same combinations of harmonics.  They have slightly different signals.

When we combine these two out-of-phase signals, the common components of the sounds will cancel out but the dissimilar components will not.  As a result, a good deal of the original sound is lost and the result is a thin, hollowness that will - with a little boost from a compressor -- have a sound all it's own.

Here is a portion of the wiring of the T-60.  Notice that the signals from the two coils of one pickup are cross-wired on the phase switch (S1) with the output and ground wired to the common center connections.  That's the trick.  In one position, the black wire is grounded and the white wire is hot.  In the other position, the situation is reversed.  The white wire is grounded and the black wire is hot.  Electrically flipping the pickup over -- like standing it on its head.  So a simple cross-wired switch is used to reverse the phase of the pickups.

Though this still doesn't answer the question of who was first guy to mis-wire his pickups and say "Hey......That sounds pretty cool!"