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In some cases you may want to invert the phase of one of the microphones. One example of when you
might want to do this would be when you use two mics on opposite sides of a vibrating plane, such as
an acoustic guitar soundboard. With one mic on the bottom (inside the body) of a guitar soundboard,
and another mic on the top (outside the body) of the soundboard, these mics should be out of phase
with each other. This can be accomplished by reversing the two piezo disc conductors (the red and
white wires in PZ1 and PZ2) on only one of the mics. But manually reversing these wires may not be
necessary if the equipment you are using has a phase switch.
A WORD ABOUT CABLES
In some cases you may find it useful to extend the distance between the piezo pickup and the circuit
board. This is possible by replacing the 18" cable with a shielded balanced cable of your desired
length. The maximum cable length that you can use without experiencing signal degradation will
depend on the quality of cable used, but in most cases it should easily be over 100 feet. The length of
the XLR cable could also be extended, theoretically even further than the piezo cable (assuming it is
connected to a good quality receiving circuit). One of the main things to keep in mind when using long
balanced cable lengths is the quality of the shielding. Only use cable that has a tight shield. The more
area the shield covers around the internal wires, the better.
PHANTOM POWER
The Cortado microphone circuitry does need power to operate. This is provided through phantom
power via pins 2 and 3 of the XLR jack. The circuit works best at 48Vdc phantom power, but can
function with much less voltage. It is not recommended to use less than 18Vdc or the mics headroom
will be too low for most applications. If the device you are plugging the microphone into doesn't
provide phantom power then you need to use an external phantom power supply (available at most
pro-audio stores). Zeppelin Design Labs is currently developing an external phantom supply DIY kit
which should be available soon.
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