AUSTRALIAN MONITOR AMIS120XL Series, Руководство по обслуживанию

Страница: 6 / 33

Tone Generators
Four separate tones are available from the in-built tone generator board. All four tones can be activated
individually via a contact closure connected to the screw terminals on the rear of the amplifier. When any
tone is activated, all inputs (except for inputs 1, 2 and 3) will automatically mute. The level of the tone
generator is controlled by the pot labeled R63 (located behind the Bass adjustment pot). This pot adjusts the
level for all 4 tones.
Tones available on the AMIS250 include:
- Evacuation Tone
- Alert Tone
- Bell Tone
- Pre-Announce Chime
Theses inputs are pulled up to 5VDC internally through 1k resistors.
The tones are generated through a combination of digital frequency modulation and analogue amplitude
modulation. The output of the microcontroller IC6 (PIC16C54A) on pin 17 is a 0-5V square wave of
varying frequency (depending on the tone selected). This signal is amplitude modulated using a VCA IC18
(M5222P). The envelope is controlled by the charging and discharging of the electrolytic capacitor C22
with the sink and sourcing of current on the microcontroller outputs pins 1, 2 & 13.
VOX Muting
The AMIS120XL includes a priority/muting system which is installer adjustable. When shipped, the
AMIS120XL has three priority inputs. From the factory, Input 1 has overall priority and mutes inputs 2-8
when signal is present. Input 2 has secondary priority and mutes inputs 3-8 when signal is present. Input 3
has a third level of priority and mutes inputs 4-8 when signal is present. Inputs 4-8 have no priority and are
mixed. All muting in the AMIS120XL is activated by signal (VOX) whether it be on the XLR or RCA
inputs.
A number of muting options are available and can be altered via a series of internal links located on the
front mixer board behind inputs 1and 2.
Muting for any of the first three inputs can be disabled. The jumpers are located on the front mixer PCB
behind input 1 and 2’s level controls.
To disable muting from input 1, move jumper JP1 towards the back of the chassis.
To disable muting from input 2, move jumper JP2 towards the back of the chassis.
To disable muting from input 3, move jumper JP3 towards the back of the chassis.
Another feature of the muting circuit of the AMIS120XL is the ability to have inputs 1 and 2 on the same
priority level. In this mode, both inputs can be used at the same time and both will mute all remaining
channels. To set inputs 1 and 2 to the same priority level, move jumper JP4 towards the front of the chassis
and remove and discard jumper J6. Please note that both jumpers (J4 moved and J6 removed) need to be
adjusted for this feature to work.
Channels 4, 5, 6, 7 & 8 are summed through IC7B (LM1458 or equivalent) to the VCA IC13 (M5222P)
which does the muting. The VCA is held on (i.e. no attenuation) by R90 (33k) pulled to the reference
voltage and the reverse biasing of diodes D14 (BAV21 or equivalent), D15 and D16. This is to eliminate
any attenuation by the op amp IC1B (LM1458 or equivalent) and its ½ supply which may be different to
the internal reference voltage of the VCA. Channel 2 signal passes through IC2B and VCA IC10. Channel
3 passes through IC3B and VCA IC5. These operate in a similar manner.
The control pin of the VCAs are pulled down by either op amp IC1A, IC2A or IC3A. These op amp runs at
very high gain to activate on even very small signal. The jumper shorts out the feedback resistor thus
removing the sensitivity. The attack of the muting circuit for channel 1 is controlled by the charging of C4