APPENDIX C: Balanced Lines, Phantom Powering,
Grounding and Other Arcane Mysteries
Balanced LinesWhat is it, exactly?
Balanced lines offer increased immunity toThe obvious external power source for any
external noise (specifically, hum and buzz).modern microphone is a battery. About the
Because a balanced system is able to minimize only electronic advantage that a battery has is
noise, it is the preferred interconnect method,that its output is pure DC. The only other ad-
especially in cases where very long lengths ofvantage is to the battery company N you have
cable are being used. A long unbalanced cableto keep on buying them.
carries with it more opportunity for noise toTube microphones require several different
get into a system N having balanced inputsvoltages for operation. This invariably means a
means very little noise will enter the systemmulticonductor cable and nonstandard (not
via snakes and other cables that typically must XLR) connectors. A tube microphone will al-
run a long length. But regardless of length,ways have an associated external power supply.
balanced lines are best.In the late 1960Os, Neumann (you know, the
folks that brought you the U47 and U87
Phantom Powering and Microphones
microphones) converted its microphones to
solid-state, adopting a system of remote
History
powering that they called, and trademarked,
Condenser (capacitor) microphones differ
Phantom Powering. Because of the trademark,
from dynamic and ribbon microphones be-
some manufacturers use terms like Simplex
cause they are not self-generating. That is,Powering, etc. Over the years, the trademark
they cannot generate electricity in response to
has become genericized and now refers to any
an impinging sound wave. A condenser micro-device that is powered according to DIN stan-
phone modifies an external source ofdard 45 596 (or maybe itOs DIN standard 45
electricity to reflect the effects of a sound595, weOre not exactly sure�).
wave striking its diaphragm.
So, why OPhantom� Powering? Because (like
Dynamic and ribbon microphones use
the Phantom in the old comic strip) itOs there
magnetism to generate electricity in response
when you need it, and invisible when you donOt.
to a sound wave: they are self-generating. Fur-
This technology is not new; it actually predates
thermore, both of these types of microphones
rocket science. Like many other things in
are inherently low-impedance devices. It isaudio, it was brought to you by the telephone
possible to connect a dynamic microphone ele-
company, who used it to get an extra circuit
ment directly to a balanced, low-impedance
from a pair of wires. In effect, so does your
mixer input. Many commercially made dy-phantom powered microphone.
namic microphones do just that.
What is important is: phantom powering is a
On the other hand, a condenser microphone compatible system. Your dynamic/ribbon
is an inherently high-impedance device. How
microphones as well as your condenser
high? Verrrrrrry high. On the order of a billionmicrophones work side-by-side, from the same
ohms (1 Gigaohm). This is high enough that
microphone inputs, without further thought on
the inherent capacitance of a foot of shieldedyour part.
cable would audibly reduce the output of theTechnically speaking, phantom powering
microphone. All condenser microphones have
refers to a system in which the audio signal is
an impedance converter, in the form of a
applied to the balanced line in differential-
vacuum tube or field-effect transistor (FET),
mode, and the DC power is applied
built into the microphone and located ex-
common-mode. The audio travels via pins 2
tremely close to the microphone element. The
and 3, the power travels between pins 2 and 3
impedance converter and the microphone ele-
simultaneously, and pin 1 is the ground for
ment itself require an external power source.both audio and power.1
1To be strictly correct, electret condenser microphones
are a bit different, as the microphone element does not require
a power source for operation (it is more or less permanently
self-polarized). Regardless, the impedance converter still re-
quires an external source of power.
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