Toa EXES-6000, Operating And Troubleshooting

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1. Operation Principle of the Voice Switch Circuit
1-1. Hands-free to Hands-free Mode
Given below are operation procedures of the
voice switch when stations A and B are talking to
each other in the hands-free mode and sound
pressure level at a mic of station A is higher than
that at station B. See Fig. 22
(1) A signal flow from mic A:
Similarly, a signal from mic B flows as follows:
(2) A comparator compares signal strength from
stations A and B.
(3) Since a signal level from station A is higher
than that from station B, switch SW(A) closes and
SW(B) opens, thus permitting transmission of the
signal from mic A (signal A) to speaker B.
At the same time, ATT(B) is activated and the
signal from mic B attenuated by ATT(B) is trans-
mitted to the comparator. In this event, ATT(A) is
not activated. The signal A, therefore, is sent to
the comparator without being attenuated.
(4) Therefore, the signal A that is fed from
speaker B back to its mic is sent to the compara-
tor after being attenuated in ATT(B), allowing not
only signal A to be still kept higher at the
comparator but also the status of (3) above to be
maintained.
* The EXES-6000 system uses FET's for the
switches SW(A) and (B). This makes transient
response at switching longer than that of the
EXES-5000.
Fig. 21 Voice Switch Transient Response
Fig. 22 Main Circuit Activated in Hands-Free
to Hands-Free Mode
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