5 Technical Information; 5.1 Audio; 5.1.1 Input Section- Page 19

Page 19

IQ–AMB-5 / IQ–SMX-6

 Reference Manual

AMB-5 / SMX-6

  IQ Mixer/Multiplexer

increase in the ambient signal level above the
Threshold setting.  A 4:1 Expansion Ratio set-
ting will raise the output gain 1 dB for every 4
dB that the ambient signal increases. Choices
are 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 4:1, and 5:1.

• Threshold:

 determines at what ambient sound

level the Ambience function will begin to oper-
ate.  It is the sound pressure level of the ambi-
ent sensing input (Input 6).  When the signal
level of Input 6 exceeds the Threshold setting,
the Ambience function begins to increase the
gain  of Channel 1 at a rate dictated by the Ex-
pansion Ratio control. Control range is from
–100 to +25 dB in 

1

/

2

-dB steps.

• Ambient Offset:

 the level below Max Gain to

which the Channel 1 gain will be set until the
ambience level exceeds the Threshold setting.
As the ambience level increases above the
Threshold setting, the Channel 1 gain will be
increased above the Ambient Offset according
to the Expansion Ration setting.  The Max Gain
setting always limits the maximum possible
gain which any input can receive. Control
range is from 0 to +40 dB in 

1

/

2

-dB steps.

4.3 Crown Local Net (IQ–SMX-6 only)

The Crown Local Net (CLN) allows multiple IQ–SMX-
6 units to be linked so that their Duck Priority and
Gate Count functions work together.  For example, a
duck priority 1 in one unit will override a priority 2 in
another unit.  Likewise on the gate count side, the
number of open mics can be totaled among all the
IQ–SMX-6 units in a CLN and all open inputs attenu-
ated to prevent feedback in a large system. Use of
this feature requires that the serial port of each IQ–
SMX-6 be dedicated to CLN use, meaning that if the
IQ–SMX-6 is to be used with CLN, it cannot be used
as a system interface. Successful setup of a CLN
requires that the setup be performed in a particular
sequence of steps. Please refer to the IQ software
documentation for setup procedures. There are five
parameters which control this feature:

• System On/Off:

 activates the Crown Local

Net. 

This control should only be turned on

for the first time after all of the following pa-
rameters have been set.

  Please refer to the

IQ software documentation for setup proce-
dures.

• Master On/Off:

 selects the master IQ–SMX-6

as required by the start-up procedure. Only
one IQ–SMX-6 should be the master. Neither

5 Technical Information

Following is a technical description of the operation of
the IQ–AMB-5 and IQ–SMX-6 mixer/multiplexers. Re-
fer to the block diagrams on the following pages for
illustration of signal flow.

5.1 Audio

5.1.1 Input Section

Each audio input signal first passes through a bal-
anced filter designed to eliminate RF interference. The
RF filters are a balanced network of chokes, ferrite
beads and capacitors that attenuate both common-
mode and differential-mode signals above 500 kHz.
Optional input isolation transformers can also be
added by the factory.

The signal then enters the input switching circuit. This
circuit can insert a 25 dB pad for line level signals or
apply phantom power to the input terminals (44 volts
through two 6810 ohm resistors). The signal is filtered
again to eliminate lower-frequency RF energy such as
interference from the AM broadcast band. The signal
then goes to the preamp stage.

Each of the six input preamplifier stages is a balanced
circuit providing from 13 to 46 dB of voltage gain. The
preamp consists of a pair of low-noise transistors, fol-
lowed by a high performance op-amp. The transistors,
in effect, convert the input voltage to a current while
maintaining reasonably high input impedance. Their
transconductance (output current divided by input
voltage) depends on the setting of the gain control.
The op-amp then converts the current back to a volt-
age to drive subsequent circuits.

5.1.2 VCA Sections

Each preamplifier output drives two VCAs which then

the Crown Local Net nor the IQ–SMX-6 units
will function properly if more than one unit is se-
lected as a master.

• External Functions On/Off:

 setting this control

to ON allows the IQ–SMX-6  to participate in the
Crown Local Net.

• Duck On/Off:

 setting this control to ON allows

the IQ–SMX-6 to respond to external Duck Pri-
ority functions.

• Gate Count On/Off:

 setting this control to ON

allows the IQ–SMX-6 to respond to external
Gate Count functions.