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HOW THE PHASE SWITCH WORKS
The phase switch on the
master volume control
board of the
Tri-Star Pro
Preamp
is a white miniature
switch that moves left/right
(2 positions). As long as
your amplification
equipment does not reverse
the phase, the “in phase”
setting should be with the
white switch to the left –
away from the volume
wheel.
What is phase?
Phase switches are usually marketed
as a feedback-controlling device, but they accomplish
more than just that. Phase determines at what point
in time a sound wave has its peak or trough.
This picture shows 2
(basically identical) sine
waves, but the wave on the
right (2) is inverted in
respect to the wave on the
left (1). Interestingly, if these two waves were played
back simultaneously from the same speaker-source
with the same volume, they would completely cancel
each other out and no sound would be heard. There
would be silence.
Out-of-phase guitar sound reproduction also suffers,
to a degree, from phase cancellations. Amplification
systems, effect units, or any electronic audio device
may or may not invert the phase in of the signal
coming in. In most cases the manufacturers do not
specify.
Every acoustic instrument projects sound waves in a
certain phase when it is played unplugged. The
phase that is projected from the amplified speaker
source needs to be "in phase" with the acoustic
instrument’s own sound waves or the result will not
be optimal.
An out-of-phase problem is indicated by early
feedback and tinny, unbalanced sound, which may be
tolerable in some tone ranges (positions on the fret
board) and quite noticeable in others, even resulting
in sound cancellations on some notes.
The phase switch allows for instant correction of this
problem. Toggling the phase switch back and forth,
you will notice fuller, warmer and nicely balanced
tone with less feedback in one setting. Test especially
the low E sting up the B on the 7th fret. Phase
problems are easier noticeable in the low register.
The warmer/fuller tone is the correct phase switch
setting. Keep in mind that it may be different with
different amplification systems.
