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required by the microphone (usually between 11 and 52

volts DC). If less than the minimum is available, the

condenser microphone performance may be

compromised with less headroom or more distortion. This

is not a concern with dynamic microphones (which do not

require power) or with condenser microphones powered

by an internal battery.

The bodypack transmitter presents the greatest range

of possible interfaces. The simplest arrangement is the

hard-wired lavaliere or headset microphone. Again, it can

usually be assumed that this design already provides the

optimum interface for the components provided. If various

hardwired microphone choices are offered, the selection

should be based on the intended application.

Most bodypack transmitters are equipped with an

input connector to allow the use of a variety of

microphones and other input sources. (See Figure 4-2.)

Microphones and input cables supplied by a manufacturer

with a given wireless microphone system can be assumed

to be compatible with that system. However, they may not

be directly compatible with wireless microphone systems

from other manufacturers. At a minimum, a connector

change is often required. In many cases, additional

circuitry or modifications to components will be necessary.

A few combinations simply will not work.

In order to determine the suitability of a particular

microphone for use with a particular transmitter it is first

necessary to determine the connector type(s) involved.

Connectors include eighth-inch and quarter-inch phone

jacks as well as a variety of multi-pin designs.

Next, the wiring of the microphone connector and the

wiring of the transmitter connector must be compared.

Unfortunately, there is no standard input connector, and further,

the wiring scheme of the same connector may

differ from one manufacturer to another. A quarter-inch input

jack is usually wired unbalanced with the audio signal at the tip

and shield on the sleeve. The typical multi-pin input on a

body-pack transmitter has at least one pin for the audio signal

and one pin for shield or ground. There may be other pins to

provide "bias" (a DC voltage for a condenser microphone

element) or to provide an alternate input impedance. Some

transmitters have additional pins to accept audio signals at

different levels or to provide a combination audio + bias for

certain condenser elements.

The electrical characteristics of the microphone and

transmitter should then be compared: the output level of the

microphone should be within the acceptable input level

range of the transmitter and the output impedance of the

microphone should be less than the input impedance of the

transmitter. In addition, the input configuration of most

bodypack units is unbalanced. Microphones intended for

use with wireless are also invariably unbalanced, though a

balanced output dynamic microphone can usually be

accommodated with an adapter cable.

If the microphone has a condenser element and does

not have its own power source then the transmitter must

supply the required bias voltage. Most transmitters

provide about 5 VDC, suitable for a typical electret

condenser element, though some elements may require

as much as 9 VDC. In this case, it is sometimes possible

to modify the transmitter to provide the higher voltage.

Many condenser elements and associated

transmitters use a two-conductor-plus-shield hookup in

which the audio is carried on one conductor and the bias

voltage on the other. A few condenser elements and some

transmitters use a single-conductor-plus-shield

arrangement in which the audio and bias voltage are

carried on the same conductor. Interfacing a microphone

of one scheme with a transmitter of the other may require

modification of one or both components.

In general, for non-standard combinations, it is best to

directly contact the manufacturer of the wireless microphone

system and/or the manufacturer of the microphone to

determine the compatibility of the desired components. They

can provide the relevant specifications and can usually

describe any limitations or necessary modifications.

Non-microphone sources include electronic musical

instruments and possibly outputs from sound systems and

playback devices. Though none of these sources require

bias or phantom power their interface presents a much

wider range of level and impedance than a typical

microphone source.

Musical instruments such as electric guitars and basses

can have output levels from a few millivolts (microphone

level) for instruments with passive pickups to a few volts

(line level) for those with active pickups. The transmitter

must be capable of handling this dynamic range to avoid

overmodulation or distortion.

Ordinary (passive) magnetic instrument pickups have

a high output impedance and require a transmitter input

impedance of about 1 Megohm to insure proper

frequency response. Active (powered) pickups have fairly

low output impedance and will work with almost any

transmitter input impedance of 20,000 ohms or greater.

Piezoelectric pickups have very high output impedance

and require a 1-5 Megohm transmitter input impedance to

avoid loss of low frequencies.

Selection

and Operation

of Wireless Microphone Systems

CHAPTER 4

Figure 4-2: examples of input connectors

1/4” mini XLR Lemo