76 en | *Amplifier, 600W 4-channel | PRA-AD604 PRAESENSA
2019.11 | V1.00 | Installation manual Bosch Security Systems B.V.
Loop (A to B)
A third loudspeaker connection topology is the so-called Class‑A loop, where the loudspeakers
are connected in a loop, starting at output A and ending at output B, with the end of the loop
being supervised with an end‑of‑line device.
In normal operation the loop is driven from output A only. In case of an interruption of the
loudspeaker line, this will result in the loudspeaker signal not arriving at output B and neither
at the end‑of‑line device. The disconnection of the end‑of‑line device will be detected at
output A, and as a result output B will be activated to drive the loop from the opposite side in
an attempt to reach all loudspeakers again. A loudspeaker line fault will be reported.
Follow the procedure below to connect the loudspeakers according to this scheme.
1. Connect all loudspeaker in parallel in a loop‑through fashion. Observe equal polarity for
all loudspeakers. Connect one side of the loudspeaker cable to output A, observing
polarity.
2. Connect the other side of the loudspeaker cable to output B. In this case maintaining the
correct polarity is especially important, as reversal on one end will short circuit the
amplifier channel, not immediately, but when output B is activated in case of interruption
of one conductor.
3. Connect an end-of-line device to the end-of-line connection terminals. These terminals are
connected in parallel to output B, internally in the amplifier, to include supervision of the
output B connection.
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