ICM-400 Series Intercom Stations
Page 8
Document IM-ICM-400-2.14
Talkback Kit Installation Complete
Make the electrical connections to the talkback kit for the loudspeaker and optional switches. The loudspeaker
connection must be made to a 45-ohm loudspeaker, or through a matching transformer. For an 8 ohms speaker a
matching transformer is required. The ideal transformer tap setting of 25 V/13.9 watts will provide an output of 1
watt into an 8 ohm speaker. You should select a transformer tap setting as close to the ideal values as possible.
Selecting a setting of 25 V/10 watts will give an output of 0.97 watts into an 8 ohm speaker, while a transformer
tap setting of 25 V/5 watts will provide an output of 0.77 watts. The pigtail leads for the speaker and switch
connections of the ICB-400 Intercom Board (Talkback Kit) are color coded as follows:
Wire
Signal
Green
Spkr +
Black
Spkr -
Yellow
Switch B In+
Yellow
Switch B In -
Orange
Switch A In +
Orange
Switch A In -
The intercom talkback unit is connected to a station audio board the same as any other intercom station via the
MTA connector. The following table gives the pin configuration for the MTA connector.
MTA Pin
Signal
1
Audio +
2
Audio -
3
N/C
4
N/C
Connections to
transformer from
Spkr+ and Spkr-
Trim and insulate
unused switch
leads
Trim and insulate
unused transformer tap
leads
