Appendix D: Balanced Lines, Phantom Powering, Grounding, And Other Arcane Mysteries - Mackie SR40.8 Owner's Manual

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