L-ACOUSTICS LA15a 115V Manual V1.0 27/01/2003
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L-ACOUSTICS switch mode amplifiers use primary switching, i.e. the mains power is rectified directly
before the transformer, which means that the power supply is insensitive to the mains frequency and
will operate from DC to 400 Hz.
If the supplied power plug is not appropriate for your country, it can be cut off and wired to a suitable
connector in the following manner:
BLACK
or
BROWN
LIVE
WHITE
or
BLUE
NEUTRAL
GREEN or GREEN/YELLOW
EARTH
Once the AC connector is connected to a suitable AC supply, the amplifier can be started with the
power switch. When you power up the amplifier it takes a few seconds to check its circuits (this is
known as the soft or slow start sequence), the fans blow at high speed before going into idle, then the
two bottom green LED’s come on to indicate that output circuits are receiving the correct rail voltage.
5.4 GROUNDING
There is no ground lift switch or terminal on this amplifier. The signal ground is always floating via a
resistor to chassis and the grounding system is automatic. If a potential above 0.6 V presents itself
between signal ground and chassis ground, a short circuit is introduced between the two, thereby
enabling electrical protection. If a unit in the system is faulty, its mains fuse will blow due to this
automatic ground system.
If you wish to tie the signal ground to chassis, connect the XLR-connector’s shell lug to pin 1. In the
interest of safety never disconnect the earth pin on the AC power cord.
For all units that are FCC-approved (radio interference), there is an AC mains filter. This filter needs the
chassis ground for reference, otherwise a current loop is formed via the signal ground.
Use the balanced inputs to avoid hum and interference.
5.5 POWER CONSUMPTION
There are three ways to define the power/current consumption of a power amplifier:
First
, the peak current draw at full output power. Under this condition the power amplifier will trip
the mains breaker within 30 seconds and the amplifier will operate for less than 2 minutes before
thermally limiting. During this time, the temperature of the power supply will be stabilized at a
temperature that will have no effect on the insulation rating of the AC line cord.
It is more useful to state the
current draw
for different loads and output power levels. The current
draw is stated in Amperes (rms) and this figure corresponds to the value of the mains fuse required.
Table 3: LA15a Current Draw @ 4 ohms
Operating Condition
Current Draw in Amperes (rms)
Idle state (no load)
2.8 A (rms)
1/8 of full power (- 9 dB)
12 A (rms)
1/3 of full power (-5 dB)
18 A (rms)
Full power (0 dB) at 1 kHz, 1% THD
32 A (rms)
