Australian Monitor Audio Telex ACM250 - Manual (Page 4)

Phantom Power
This button enables or disables the 18 volts DC phantom power which is available on all microphone inputs (XLR’s). The
“in” position indicates that phantom power is on for all mics. The “out” position means that phantom power is switched
off for all mics. Phantom power is required for electret condenser microphones which require DC power to operate. While
some of these microphones can operate from an internal battery, having phantom power available on the amplifier
eliminates the need to regularly change batteries in the microphone. While phantom power is not required for the more
common Dynamic microphones, it will not damage them providing that they are balanced. Do not plug an unbalanced
microphone in any amplifier or mixer when phantom power is switched on.
Line Output
The balanced XLR line level output provides a maximum of 700mV to allow for connection to up to 6 power amplifiers.
Simply run a balanced cable from the line out of the ACM250 to the line input of the power amplifier. Pin connections are:
pin #1-earth; pin #2-signal (high, +); pin #3-signal (low, -).
Tape Output
Dual RCA output connectors provide a line level output with a maximum of 350mV into 10K Ohms which is ideal for a
connection to most standard tape recorders. This output is sourced before the master gain control and as such, the tape
output level is not influenced by the operation of the master gain control.
Microphone Inputs
The mic input sensitivity is 1mV @ 200 ohms. Pin connections are: pin #1-earth; pin #2-signal (high, +); pin #3-signal
(low, -). Phantom power of +18 volts is available on all microphone inputs. Reading from left to right across the rear panel,
the connection are for microphone inputs 6, 5, 4, 3, 2, & 1 respectively.
Line Inputs
Line inputs 1, 2, 3, 4, & 5 have an input sensitivity of 75mV @ 47K ohms. Input 6 has an input sensitivity of 300mV @
47K ohms making it suitable for high level inputs such as a CD player. Reading from left to right across the rear panel,
the connections are for inputs 6, 5, 4, 3, 2, & 1 respectively.
Other Features
Tone Generator
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. To activate the bell chime for example, just
run a pair of wires from the Tone generator common and the Bell terminal to an external switch. Activating the switch, or
closing the pair of wires, will activate the bell. When any tone is activated, all inputs (except for inputs one and two) will
automatically mute. To adjust the level of the tone generator, disconnect the power lead, remove the amplifier lid and
locate the pot labeled R6. (located behind the Bass adjustment pot). This pot adjusts the level for all 4 tones.
Tones available on the ACM250 include:
Evacuation Tone (to Australian Standard AS2220.1.2)
Alert Tone (to Australian Standard AS2220.1.2)
Bell Tone
Pre-Announce Chime
Muting
A VOX muting card is installed in the ACM250. This feature provides automatic muting of some channels when others
are active. It is normally used so that a paging microphone can have priority (by muting) over background music. VOX
muting is available from channels 1 and 2 meaning that any signal on channels 1 and 2 (mic or line) will mute channels 3,
4, 5 & 6. The muted channels will automatically ramp back up to normal volume when the signal on channels 1 and/or 2
is no longer active. The amplifier ships with the VOX muting function enabled. To disable the VOX muting, disconnect
the mains power lead and remove the lid of the amplifier. Looking down from the front of the amplifier, a three position
jumper (labeled JP2) is located just to the left and behind the level pot for channel 1. To disable VOX muting, move the
jumper to the middle and left pins.
(The factory setting is with VOX enabled with the jumper on the middle and right pins).