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2-11
Separate shielded twisted pair cables: 50 feet (15.24 m). Balanced microphone input: up to 100
feet (30.48 m).
External Electret Microphone
An external electret microphone may be connected at the auxiliary connector and used in place of
a front-panel gooseneck microphone. Connect microphone high/bias to pin 15 and connect
microphone low to pin 2. When using an external microphone, do not connect a front-panel
gooseneck microphone.
Unswitched Microphone Output
The microphone audio is provided as an unswitched, balanced output at the auxiliary connector.
The in-phase signal is available at pin 1; the inverted-phase is available at pin 14.
External DC Power Source
The MCE325 may be powered from an external DC power supply in the 10 to 25 volt range (500
mA minimum).
If the external supply is in the 10 to 15 volt range, connect the positive lead to pin 13 of the
auxiliary connector and connect the minus lead to pin 10 or 11. A 0.5 Amp slo-blo fuse should be
connected in-line for 17 to 24 volt operation.
Remote Speaker Mute Control
When the MCE325 is used with an external speaker, the speaker may be muted from a remote
location. Applying a logic low signal to pin 25 of the auxiliary connector will cause muting.
Connect circuit common to pin 11.
Front Panel Headset Connections
Headset Requirements
Use headphones with an impedance of 25 ohms or greater. Low impedance 8 ohm headphones are
not recommended. Headphones with good acoustic isolation (20 to 40 dB) improve
communication in high ambient noise environments, and allow the user to use the headphones at a
less tiring, lower volume.
Headset Connections
Dynamic-microphone headset connector: XLR-6 type receptacle.
Table 2.8
Dynamic-microphone headset connector.
PIN # FUNCTION
1 Balanced mic low/unbalanced mic common
2 Balanced/unbalanced mic high
3 Headphone/mic switch common
4 Headphone left
5 Headphone right
6 Mic Switch high