Mackie CR1604 Owner's Manual download pdf (Page 46)

APPENDIX C: BALANCED LINES,

PHANTOM POWERING, GROUNDING

AND OTHER ARCANE MYSTERIES

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 advantage

is to the battery company — you have to keep

on buying them.

Tube microphones require several different

voltages for operation. This invariably means a

multi-conductor cable and non-standard (not

XLR) connectors. A tube microphone will always

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 accord-

ing to DIN standard 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 au-

dio, 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 where the audio signal is applied

to the balanced line in differential-mode, and

Balanced Lines

Balanced lines offer increased immunity to ex-

ternal 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 regard-

less of length, balanced lines are best.

Phantom Powering and Microphones

History

Condenser (capacitor) microphones differ

from dynamic and ribbon microphones because

they are not self-generating. That is, they cannot

generate electricity in response to an impinging

sound wave. A condenser microphone 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. Furthermore, both of these

types of microphones are inherently low-impedance

devices. It is possible to connect a dynamic micro-

phone element directly to a balanced, low-

impedance mixer input. Many commercially

made dynamic 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.

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-po-

larized). Regardless, the impedance converter still requires an

external source of power.

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Mackie CR1604 Owner's Manual Page 46

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