Connecting Audio; IQ Mixer / Multiplexer; 3.3 Connecting the Audio Ins & Outs (Step 3)- Page 15

Page 15

IQ Mixer / Multiplexer  Hardware Installation

Rev. 0

added to the audio lines. Use only the signal
lines which normally connect to pins 2 and 3 of
the XLRs. 

Note: Because typical mic cables

have high capacitance, the maximum possible
Crown Bus loop distance will be less.

Outside RF interference is seldom a problem for a
Crown Bus loop…especially if shielded twisted-pair
wire is used. However, there are extreme situations
when fiber optic wiring is recommended. For ex-
ample, locating a Crown Bus loop next to an AM
radio transmission line may require fiber optic ca-
bling. An extremely long Crown Bus loop distance
(greater than 10 miles) may also require fiber optic
cabling.

Some examples of twisted pair wiring follow. Figure
3.6 shows point-to-point wiring for the Crown Bus
using two female removable barrier block connec-
tors:

Some IQ components use separate 5-pin and 4-pin
DIN connectors for Crown Bus input and output
wiring. Connecting to them is shown below:

The IQ components in each Crown Bus loop are
wired in series. The output of one IQ component
÷loopsš to the input of the next and so on. This is
shown in Figure 3.9.

Fig. 3.10  An Audio Input Section

Pro audio

equipment

Semi-pro or

consumer

equipment

Dynamic

mic, speech

Condenser

mic, speech

Hot

condenser

mic, speech

Dynamic

mic, music

Hot

condensor

mic, music

Close-miked

dynamic mic,

bass/drums

Close-miked

dynamic mic,

kick drum,

guitar amp

dBm/dBV

dBu

Suggested

Setting

+4 dBm

+4 dBu

–4 (L)

–10 dBV

–8 dBu

+8 (L)

–75 dBV

–73 dBu

+21 (M)

–65 dBV

–63 dBu

+11 (P)

–45 dBV

–43 dBu

+18 (P)

–55 dBV

–53 dBu

+21 (M)

–25 dBV

–23 dBu

–2 (P)

–15 dBV

–13 dBu

–12 (M)

–5 dBV

–3 dBu

–12 (M)

or

+3 (L)

0 dBm = 0.775 VRMS with a 600 ohm load, 0 dBV = 1 VRMS, 0 dBu = 0.775 VRMS

Fig. 3.11  Suggested Audio Input Gain Control Settings

Fig. 3.12  Balanced Audio Input Wiring

+

–

Shield connected

at both ends

INPUT

+

–

2-wire line cord

(or battery power)

Output

Note: If more than one

input is driven from the same

source equipment, connect only

one shield at the source

equipment chassis.

Microphone

INPUT

Floating

source

+

–

3-wire grounded line cord

(or other ground connection)

Output

Shield not connected
at this end

INPUT

Grounded

source

+

–

+

–

+

–

AUDIO
IN

1

L

M

P

0

-5

-10

-12

5

10

15

21

ADD 25
FOR MIC

3.3 Connecting the Audio Ins & Outs (Step 3)

IQ mixer/multiplexers have 6 mic/line inputs and
2 stack inputs. (Input 6 of the 

AMB-5 is dedicated

for ambient sensing and is discussed in Section
3.3.2.) For output, there are two audio channels that
feed two main and two auxiliary bus outputs.

3.3.1  Mic/Line Inputs

Three-terminal removable barrier block connectors
are provided for the audio inputs. Each input has an
input selector switch. Slide it to the left (M) for
microphone signal levels up to +7 dBu (0 dBu =