Bose 1600VI Service Manual page 18

4.0 Operating Modes
The Bose 1600VI and 1800VI amplifiers are capable of being configured to operate in several
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different modes in order to allow greater flexibility in use.
4.1 Bridged Mono/Dual Mono Switching
The Stereo/Mono Switch (S1) on the Input Board is a three-position switch used to select
Normal Stereo, Bridged Mono or Dual Mono operation. In the Bridged Mono position, it con-
nects CH 1 in parallel with the CH 2 input, but inverts the signal to CH 1. The CH 1 input
connection becomes disabled. The speaker output signals are identical except CH 1 is 180
degrees out of phase. In this way, a single speaker can be connected between the two "+"
speaker terminals and receive twice the voltage as a single channel. When connected in this
way, each channel "sees" one-half the impedance of the speaker that is connected between
them. If an 8 ohm speaker is used, each channel will see a 4 ohm load. The result is twice the
rated power (per channel) into twice the rated impedance.
Note: Each channel can still be independently controlled with its own level control so it is
important that both level controls be set to the same position for a balanced output.
When S1 is switched to the Dual Mono position, CH 1 is connected in parallel with the CH 2
input, but in phase. The CH 1 input connection becomes disabled. This allows both channels
to be driven with the same signal without the use of special patch cords. Each channel can still
be independently controlled with its own level control.
4.2 Parallel Mono
To operate in Parallel Mono mode, leave S1 in the Normal Stereo position. Removing jumpers
JP201 and JP203 will disconnect the CH 2 predrivers from the output stage. Installing jumpers
JP102, JP104, JP202 and JP204 will connect the CH 1 predrivers to the CH 2 output stage. In
this way, both channels will operate at exactly the same level, and will be controlled by the
CH 1 level control.
In addition, removing JP1 will prevent the CH 2 clip LED from activating, and installing a 16 ga.
jumper wire between WL100 and WL200 on the Output Board will tie both amplifier outputs
together before the relays.
When operating in parallel mono, either of the speaker output terminals (CH 1 or CH 2) can be
used since they both have exactly the same signal present. When a speaker is connected to
the output terminals it can be driven with twice the current capacity of a single channel. The
result is twice the rated power (per channel) into half the rated impedance.
THEORY OF OPERATION
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