Crown IQAMB-5, IQSMX-6 Technical Information, Crown Local Net IQ-SMX-6only, Audio, Input Section

AMB-5 /SMX-6IQ 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

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.

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

IQ–AMB-5 / IQ–SMX-6 Reference Manual Page 19