Appendix E: Bridged Mono Mode (Servo-550 Only)
The Servo-550 amplifier provides a rear-panel switch that allows it to be used in
a bridged mono mode. When this switch is placed in the “Stereo” (up) position,
the Servo-550 functions as a true stereo amplifier, where both of the two
independent amplifier channels (left and right) can receive different input signal
and produce independent output signal. However, when the switch is placed in
the “Bridged Mono” (down) position, both amplifier channels process only the
signal present at the left input, thus producing a monophonic output signal with a
true 550 watt output (into 8 ohms).
The illustration on the left shows how this works. In bridged mono mode, the
polarity (phase) of the right output signal is reversed relative to that of the left
output signal. Both channels then process the same signal, with the speaker
load connected so that power is derived from both channels. The effective
voltage swing seen by the load is thus doubled so that the power output is
doubled.
When using the Servo-550 in bridged mono mode, be sure to connect the
loudspeaker as shown in the illustration below, with the hot (+) terminal of the left
channel connected to the positive input of the speaker and the hot (+) terminal of
the right channel connected to the negative input of the speaker.
Do not use
the ground output terminal of either channel (the speaker load must “float”
away from the amplifier chassis).
15
TO PREVENT SHOCK DO NOT OPEN. NO USER
SERVICABLE PARTS INSIDE. REFER SERVICING
EXPOSE TO RAIN OR MOISTURE.
FUSE AS INDICATED.
MEME TYPE.
WARNING: Bridged mono mode is to be used only when the Servo-550 is
connected to an 8 ohm speaker load. Use of bridged mono mode with
speaker loads of 4 ohms or less can result in severe damage to the unit
due to excessive heat and current limiting and will void your warranty!
Never use bridged mono mode during stereo operation. If loudspeakers
are connected to both channel outputs of the Servo-550 when used in
bridged mono mode, they will be severely out of phase with one
another (there will be an extreme loss of low end).
