L-ACOUSTICS LA15a 115V Manual V1.0 27/01/2003
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7.1.2 TANDEM MODE
In tandem mode, two, three or four channel inputs are linked (A+B, B+C or C+D) and receive the
same signal. Linking is performed by depressing the rear panel LINK switches to the IN position. All level
attenuators are active, allowing you to set different levels for each channel. Remaining input
connectors are available for daisy chaining the signal to other amplifiers.
Note: only the inputs are connected in parallel and this is NOT a parallel output mode.
Never connect either output terminal to ground or in parallel
Note: Always disable linking when using the amplifier for bi-amplification of 2-way active
enclosures
7.1.3 BRIDGED MONO MODE
Figure 12: Bridged mono cabling
Bridged mono mode is used to deliver two channels' power to a
single load. The nominal impedance of the load must be more
than 4 ohms.
Set the Link switch (A+B or C+D, as desired) to the IN
position and use one of the input connectors (A or B, C or D, as
desired). The remaining input connector can be used for daisy
chaining to other amplifiers. Both Channel A and B (or C and D)
level attenuators must be at the same position and it is
recommended that they are operated in the 0 dB (full) position.
Connect the loudspeaker as shown in Figure 12.
7.1.4 BRIDGED MONO MODE FEATURES
Bridged mono mode combines the power of two channels into one speaker. This results in twice the
voltage swing, four times the peak power and just less than three times the full power of a single
channel.
One way to understand the load and power from the amplifier’s perspective in bridged mode is that it
is zero voltage at the center of the voice-coil winding. This is because the coil is driven with positive
voltage at one pole and an equivalent negative voltage at the other pole. If an 8 ohm load is connected
in bridged mode, one channel shares one 4 ohm part of the load and the other channel shares the
other 4 ohm part. The power into 4 ohms from an LA15a (MLS at -3 dB) is 380 W. Therefore, the
total bridged power into the 8 ohm load will be 2 x 380 = 760 W.
7.2 OPERATING PRECAUTIONS
Never connect either Channel A/B or C/D output terminals to ground or to some other
output or input terminal (see also warnings in Section 2.4).
For normal quad operation, connect each speaker load across its respective output channel’s positive
and negative terminals.
Pay attention to speaker polarity - loudspeakers connected out of
polarity degrade sound quality and may be damaged as a consequence.
WARNING: To prevent electrical shock, do not operate the amplifier with any of
the conductor portion of the loudspeaker cable exposed.
