12
Installation and Maintenance Manual
Model 300MB-SD CommCenter Series D1
Figure 3 Model AM25CK connections (balanced line)
300GC
TERMINAL BLOCK (TB1)
ON REAR OF 300MB
AM25CK
300GC
AM25CK
14 13
290A7443
SHIELDED TWISTED PAIR
SIGNAL LINE TO ADDITIONAL
SELECTONES
For 25 Vrms line-operated speakers, connect them directly to the balanced signal output of the 300MB.
Remove the labeled jumper from terminals TB1-13 and TB1-14 of terminal block TB1. Connect the
speakers in parallel to the terminals TB1-13 and TB1-14 of terminal block TB1 on the 300MB. Unlike the
unbalanced line output, this output is not switched.
IMPORTANT:
This output is to be used only if there are no SelecTone system devices connected to the
unbalanced signal output (across TB1-15 and TB1-16).
Unbalanced Line Application
See Figure 4. For existing SelecTone systems using the 300CK Connector Kit, use the unbalanced signal
outputs on the 300MB. A 300CK Connect Kit is required to connect a 300GC, 300GCX, 300X, 302GC,
302GCX, 302X or 50GC to the unbalanced signal lines. The 300CK properly terminates the signal lines
to the amplifier in the 300GC, 300GCX, 300X, 302GC, 302GCX, 302X and 50GC. Connect the blue wire
on the 300CK to the
SIG COM
wire from the 300MB. Connect the yellow wire on the 300CK to the
SIG HI
wire from the 300MB.
Figure 4 Model 300CK connections (unbalanced line)
290A7332
300GC
TERMINAL BLOCK (TB1)
ON REAR OF 300MB
YEL
BLU
YEL
BLU
300CK
300GC
300CK
COM SIG
HI
16 15
SHIELDED TWISTED
PAIR SIGNAL LINE TO
ADDITIONAL SELECTONES
Connecting a Low-Level Audio Input
See Figure 5 on page 13. There is a provision for a low-level, low-impedance audio signal input at the
rear of the 300MB. It is designed to accept a cascaded input from a master CommCenter (TB1-12. But it
also accepts audio from a telephone system, radio receiver, CD player, or tape player. When the
ENABLE
pin (TB2-2) on the cascade input is pulled to circuit ground, audio on the cascade-in signal line is gated
through the CommCenter and output on the signal lines. This input is the lowest priority. The audio-level
input should be 1 Vpp. When cascading units, connect the cascade-out
ENABLE
and
SIGNAL
terminals
and the ground of the slave unit to the cascade-in
ENABLE
and
SIGNAL
terminals on the master unit.The
SIG COM
terminals (TB1-16) of both units also need to be connected together as shown in Figure 5.