Clear-Com SB-704 - Manual (Page 14)

S B - 7 0 4 M A I N S T A T I O N 1 - 8
• TALK LATCH DISABLE: Four DIP switches (one for each channel)
disable the latching action of the selected channel.
• PROGRAM ON/OFF: Four DIP switches (one for each channel) enable
feeding the main program input to the selected intercom channel. The
main program input is the one on the XLR-3F on the rear panel.
The other four program inputs in the auxiliary connector feed their
respective intercom channels all of the time. The only way to turn off the
auxiliary feed to a channel is to turn its individual control off.
• LINE LENGTH: Four DIP switches (one for each channel) allow the
optimization of the nulling circuitry for each channel. The default (up
position) is for lines less than 400 ft. (122 m). The down position is for
lines greater than 400 ft. (122 m).
Hidden Adjustment Controls
Various adjustments are available beneath the front access panel.
• PANEL MIC GAIN: This control trims the panel microphone
preamplifier gain to compensate for different uses of the station.
The unit is shipped from the factory in the minimum gain position (fully
counter-clockwise). This level matches the headset microphone level
when the panel microphone is worked up close. Raising the gain from the
factory setting should be done carefully as too much gain will increase the
background noise in the intercom making it unusable.
• CHANNEL NULL ADJUST: The screwdriver-adjustable control
beneath each talk push-button marked null allows nulling of the hybrid
circuitry associated with each listen channel.
The amount of null in the listen circuitry varies with the length of the
intercom line. Adding or removing stations and intercom cable will
change the null. For optimum performance, the null control will need to
be adjusted each time there is some change in the intercom line wiring.
If a panel microphone and speaker is being used, the setting of the null
control is critical to prevent feedback.
To adjust the null control on a given channel:
1. Turn the sidetone adjust control just below the headset connector to
minimum.
2. Set a talk to the channel to be adjusted or send some program to the
channel and adjust the null control for the channel for minimum level
in the headphone. If the headset microphone is being used, hum or
gently scratch it for a continuous signal source to null on. If a good
null is not attainable, switch the long/short DIP switch for the channel
(to the far right of the hidden adjustments) to its opposite setting. Use
the setting that produces the best results.
3. Repeat the adjustment for all four channels on the station.