L-Acoustics LA 24 User manual

Version 2.2
September 1999
LA 24
OWNERS MANUAL

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 1
LA 24
OWNERS MANUAL
Table Of Contents
• INTRODUCTION 2
• UN ACKING 2
• WARNINGS 2
• USER RES ONSIBILITY 3
Speaker damage 3
Speaker output hazard 3
Radio interference 3
• FRONT ANEL 4
• REAR ANEL 5
• INSTALLATION 6
Mounting 6
Cooling 6
Operating voltage 6
Grounding 7
Power con umption 7
Input connection 8
Connecting peaker 10
Load matching (MLS- witche ) 10
• O ERATING MODES 12
Stereo operation 12
Tandem mono 12
Bridged mono 12
Stereo rever e 13
• O ERATION 14
Operating precaution 14
Powering up - Soft tart 14
Input attenuator 14
Gain 14
Indicator 15
• ROTECTION FEATURES 16
Clip limiter 16
Thermal protection 16
VHF protection 16
Short circuit protection 17
AC main voltage protection 17
DC protection 17
• DESIGN FEATURES 18
Cooling 18
Light weight 18
Switch mode power upply (SMPS) 18
MLS™- witche 19
• SAFETY A ROVALS 20
EMC approval 20
Emi ion 20
Immunity 20
EMC-declaration 20
• A ENDIX A 21
Main voltage election 21
• MAINTENANCE 22
• TROUBLESHOOTING 22
• WARRANTY AND DISCLAIMERS 23
General 23
International 23
• TECHNICAL ASSISTANCE 24
International 24
Factory ervice 24

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 2
INTRODUCTION
Thank you for purcha ing the L-ACOUSTICS LA 24 power amplifier. The amplifier you have
cho en i the culmination of many year of re earch and development and make
amplification more controllable in tead of the traditional "boring black box" that you have
become accu tomed to.
Plea e take ome time to read thi manual and familiarize your elf with the advanced feature
of thi amplifier.
• UN ACKING
Carefully open the hipping carton and check for any noticeable damage. Every L-
ACOUSTICS amplifier i te ted and in pected before leaving the factory and hould arrive in
perfect condition. If found to be damaged, notify the hipping company immediately. Only the
con ignee may in titute a claim with the carrier for damage incurred during hipping. Be ure
to ave the carton and packing material for the carrier' in pection. It i al o advi able to ave
the carton and packing material even if the amplifier i undamaged. Should you ever need to
hip the amplifier alway u e the original packing.
• WARNINGS
Read thi before operating your amplifier:
Do not u e the amplifier if the power cord i broken or frayed.
Alway operate the unit with the cha i ground wire connected to the electrical afety earth.
Do not parallel or erie connect an amplifier output with any other amplifier output. Do not
connect the amplifier output to any other voltage ource, uch a a battery, main ource or
power upply, regardle of whether the amplifier i turned on or off.
Do not run the output of any amplifier back into another channel' input.
Do not block the air intake or exhau t port . Do not operate the amplifier near heat
producing device uch a radiator , tove etc.
Do not pill water or other liquid into or on the unit. Do not operate the amplifier if you or
the amplifier are tanding in liquid.
Do not remove top or bottom cover . Removal of the cover will expo e hazardou voltage .
There are no u er erviceable part in ide and removal may void warranty.
Keep thi manual for future reference.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 3
•USER RES ONSIBILITY
Speaker damage
Your amplifier i very powerful and can be potentially dangerou to both loud peaker and
human alike. Loud peaker can be damaged or de troyed by overpowering, e pecially with
the high power available from a bridged amplifier. Alway check the peaker' continuou and
peak power capabilitie .
Even if the gain i reduced by u ing the amplifier' front panel attenuator, it i till po ible to
reach full output power if the input ignal level i high enough.
Speaker output hazard
Power amplifier are capable of producing hazardou output voltage . To avoid electrical
hock, do not touch any expo ed peaker wiring while the amplifier i operating. See page 10
for information concerning proper connection of peaker .
Radio interference
Thi product ha been te ted and complie with the limit of the European Electro Magnetic
Compatibility (EMC) directive. The e limit are de igned to provide rea onable protection
again t harmful interference between electrical equipment. Thi product u e radio frequency
energy and if not u ed or in talled in accordance with the operating in truction may cau e
interference to other equipment uch a radio receiver . There i no guarantee again t
interference even though the amplifier i EMC approved. If the amplifier cau e interference,
the problem can be corrected by following one or more of the following tep :
a) Increa e the proximity between the amplifier and the affected unit.
b) Connect the AC cord of the amplifier to an outlet that i on a different circuit from that
which the affected unit i connected to.
c) If a radio receiver i interfered with (normally amplitude modulation type) reorient the
antenna.
d) Check whether the affected unit complie with the EMC limit for immunity (CE-labelled).
If not, addre the problem with the manufacturer or upplier. All electrical product old
in the EC mu t be approved for immunity again t electromagnetic field , high voltage
fla he , and radio interference.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 4
•FRONT ANEL
Figure 1. Front panel
1. Carry/protection handle
Both handle can be u ed to carry the amplifier and they al o act a protection for the front
panel. If de ired, they can be removed by removing the crew located behind the front panel.
2. Input level attenuators
The e control are u ed to alter the ignal level entering the amplifier. They are calibrated in
dB to help et up active loud peaker y tem or to cut down on unwanted noi e from the
input ignal ( ee page 14).
3. TEM indicator
Thi indicator i lit if the amplifier trie to operate above it maximum operating temperature
(90
o
C). The indicator fir t come on a a warning to either turn down the input level or check
the cooling arrangement after which point the amplifier will mute the input ignal. When the
cooling fan have returned the output heat ink to the normal operating temperature the
input ignal i unmuted.
4. VHF protect indicator
Thi indicator light when high level, high frequency ignal (above 12 kHz at full power) are
pre ent at the output terminal . When thi happen the input ignal i muted and the proce
cycle until the VHF ignal i no longer pre ent ( ee page 16-17).
5. CLI indicator
Thi indicator how when the amplifier output i clipping or limiting. LED dynamic under clip
condition depend on whether the Clip Limiter i engaged or bypa ed ( ee page 16):
•When the clip limiter i engaged, the clip indicator flicker briefly (limiting)
•When the clip limiter i not engaged, the indicator light for a longer period (clipping).
6. Fan grill filter
Two removeable grille with foam filter are located on the front panel to prevent du t from
entering the amplifier.
7. ower switch
Thi i u ed to turn on/off the amplifier ( ee page 14).

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 5
•REAR ANEL
Figure 2. Rear panel
1. Speaker connector
Neutrik NL4FC Speakon Connector . A full de cription of pin a ignment i found in the
operation ection ( ee page 10).
2. MLS™ switches
Minimum Load Select (MLS) witche . U ed to elect the maximum output power ( ee page
10-11).
3. Clip limiter switch
Turn the clip limiter on ( witch depre ed - in po ition) or off ( witch not depre ed - out
po ition) ( ee page 16).
4. Input signal TRS jack
Alternative to u ing XLR for ignal input or for linking input with other amplifier ( ee page
9).
5. Input signal XLR ( ee page 8).
6. hase reverse switch for channel B
For rever ing the input ignal pha e of channel B or u ed in conjunction with the Link Switch
to allow bridged operation ( ee page 12).
7. Link switch
Allow a ingle input to drive both channel imultaneou ly or u ed in conjunction with the
Pha e Rever e Switch to allow bridged operation ( ee page 12).
8. AC line cord
OUT UT CH.B
MLS
Switch
0
-2
-4
-5
dB
Cl ip Limit er
230 V AC 40- 440Hz
ower Consumption: 110 0 W
CH. B C H. AIN UT
LA 24
Clip Limit er
OUT UT CH.A
0
-2
-4
-5
dB
at ent end ing
1/4"
in1
2
3
Slee ve
Tip
Rin g
Gnd
os
Neg
XL R
ower Amplifier
Mad e in the E uropean Commu nity
ML S.
Switch
Mu st be grou nded
1+1+ CH.B+
1- 1- CH.B-
Re moved !
1+1+ CH .A+
1-
1- CH.A-
2+2+ CH .B+
2-
2- CH.B-
S er. N°:
On Of f On
Of f
Mon o Brid ge
Reverse ol. B
Lin k A+B
S ter eo
N ormal ol. B
32 d B Gain
7. 7 dB u I/ Se nsit ivit y

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 6
•INSTALLATION
Mounting
The amplifier i two rack unit high (2U) and will mount in a tandard EIA 19 inch rack.
Amplifier may be tacked directly on top of each other and there i no need for pacing
between unit . If you intend to fill a rack with amplifier , we recommend racking i tarted
from the bottom of the rack. It i al o recommended that rear upport are u ed for
amplifier mounted in the middle of the rack, e pecially if u ed a part of a portable y tem.
Cooling
The LA 24 u e a forced air cooling y tem to maintain a low and even operating
temperature. All L-ACOUSTICS amplifier are fan ventilated and have front to rear cooling
(generally there i u ually cooler air out ide the rack than in ide). Never try to rever e the air
flow ince the Intercooler® need a pre ure chamber between the fan and heat ink and
thi only work for the normal front to rear direction of air flow ( ee De ign Feature on page
18).
Should a heat ink get too hot, it en ing circuit will mute the hot channel. If the power
upply overheat another en ing circuit will mute all output channel until it cool down to a
afe operating temperature.
Make ure that there i an adequate air upply in front of the amplifier and that the rear of the
amplifier ha ufficient pace to allow the exhau t to e cape. If the amplifier i rack mounted,
do not u e cover or door on the front or rear of the rack.
For fixed in tallation with a central cooling y tem (u ually found in fixed in tallation with a
dedicated rack room) it may be nece ary to calculate the maximum heat emi ion. Refer to
the ection on Power Con umption on page 7.
Operating voltage
A label ju t below the main cable on the rear of the amplifier indicate the AC main voltage
that your amplifier i configured for. Connect the power cable only to the AC ource referred
to on thi label. The warranty will not cover damage cau ed by connecting to the wrong type
of AC main .
L-ACOUSTICS witch mode amplifier u e primary witching, i.e. the main i rectified
directly before the tran former, which mean that the power upply i in en itive to the main
frequency and will operate from DC to 400 Hz.
The amplifier i upplied with an approved European AC line connector. If thi connector i
not appropriate for your country, it can be cut off and wired to a uitable connector in the
following way :
BROWN LIVE
BLUE NEUTRAL
GREEN/YELLOW EARTH

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 7
Once the AC connector i connected to a uitable AC upply, the amplifier can be tarted by
pre ing the AC power witch. When you power up the amplifier it take a couple of econd
to check it circuit (thi i known a the " oft tart" or " low tart" equence), the fan then
blow at high peed before going into "idle" and the 2 bottom green LED’ come on to how
the output circuit are receiving the correct rail voltage.
Grounding
There i no ground lift witch or terminal on thi amplifier. The ignal ground i alway floating
via a re i tor to cha i and the grounding y tem i automatic. If a potential above 0.6 V
pre ent it elf between ignal ground and cha i ground, a hort circuit i introduced between
the two, thereby enabling electrical protection. If a unit in the y tem i faulty, it main fu e
will blow due to thi automatic ground y tem.
If you want to tie the ignal ground to cha i , connect the XLR-connector’ hell lug to pin 1.
In the intere t of afety never di connect the earth pin on the AC cord.
For all unit that are EMC approved for radio interference there i an AC main filter. Thi
filter need the cha i ground for reference, otherwi e a current loop i formed via the ignal
ground.
U e the balanced input to avoid hum and interference.
ower consumption
There are three way to determine the power/current con umption of the amplifier:
Fir t, the peak current draw at full output power. Under thi condition the power will
trip the wall breaker within 30 econd and the amplifier will operate for le than 2 minute
before thermally limiting. During thi time, the temperature of the power upply will be
tabilized at a temperature that will have no effect on the in ulation rating of the AC line cord.
Secondly, the maximum expected average current under wor t ca e program material i
1/3 of full power according to the FTC tandard. At thi level the mu ic will be in a tate of
con tant clip and thi i therefore the highe t power level one can obtain without completely
obliterating the program.
Finally, the "normal operating power", a mea ured according to afety tandard IEC 65
and u ed by a majority of afety agencie . The normal operating power i mea ured u ing pink
noi e, with an average output power equal to 1/8 of full power. One eighth of the total
power i a loud a you can play mu ic while making ome attempt to avoid obviou clipping.
It al o corre pond to a headroom of 9 dB, which i very low for audio program.
For 2 ohm operation, the AFS-protection of the amplifier circuit will not permit long term
current draw and the component temperature ri e will tabilize well below the rating.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 8
MAXIMUM OUT UT OWER
MAINS IN UT OWER
Load # of Ch ower Full ower 1/3 ower 1/8 ower Idle
(watt )
( ine wave)
( ee note 1)
( ee note 2)
8 ohm
2X
1000
2900
1200
600
130
4 ohm 2X 1400 4300 1700 900 130
2 ohm
2X
1400
6000
2200
1100
130
note 1
Mean power with mu ic a program ource (amplifier driven to clip level)
note 2
Normal mu ic power with 9 dB headroom (IEC tandard power rating)
Table 1
The current draw can be calculated by dividing the main input power by the main voltage.
We recommend you de ign your power di tribution y tem to en ure ufficient current for at
lea t 1/8 power operation and to upgrade ervice to meet 1/3 power requirement for heavy
duty demand like di co etc.
The heat power can be calculated according to the following example:
Con ider a headroom of at lea t 9 dB and a 4 ohm load on an amplifier producing 1400 watt
per channel. The 1/8 power per channel i then: 1400 / 8 = 175 watt ; total output: 2 x 175
= 350 watt .
The power con umption according to Table 1 i 900 watt .
The heat power produced i the difference between the power con umption and output
power :
900 - 350 = 550 watt per amplifier.
Input connections
XLR Input connector are balanced and wired according to IEC 268 (pin 2 hot):
PIN 1 GROUND/SHIELD
PIN 2 HOT (+ve)
PIN 3 COLD (-ve)
Figure 3. XLR input connector pinout
There are al o TRS jack for linking etc. They are wired a follow :
TIP HOT (+ve)
RING COLD (-ve)
SLEEVE GROUND/SHIELD
Figure 4. TRS phone plug

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 9
The input impedance i high enough (20 kohm balanced) to allow ”dai y-chaining” or multiple
parallel input connection . To dai y chain, u e the TRS jack provided on each channel. The
input circuit have high enough headroom to accept the maximum output level from virtually
any low level ignal ource.
Figure 5. Rear panel connectors
Do not use XLR and TRS jacks on the same channel simultaneously for mixing or for
other purposes.
Figure 6. Balanced line
To connect an unbalanced ource, tie pin 3 (ring on TRS jack) to the hield of the connector.
If you leave one pin di connected, you will lo e 6 dB in gain.
Figure . Unbalanced line connection
A more optimal method for handling unbalanced ource i hown in Figure 8. Thi i imilar
to the connection for balanced line , except pin 3 i tied to the hield at the ource ide
in tead. The hum and noi e rejection for the cable i equivalent to that for a balanced line. To
minimize hum, alway u e balanced input whenever po ible.
Figure 8. Balanced line with unbalanced equipment

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 10
Connecting speakers
Speaker connection are made via the two Neutrik NL4FC Speakon connector (1).
Speakon are wired in the following manner:
Channel A Channel B
in +1 Channel A+ Channel B+
in 

1 Channel A

 Channel B


in +2 Channel B+
in 

2 Channel B


Speakon Connector Pin Out Diagram
Never connect either output terminal to ground or to another output or input
terminal (see warning on page 2).
For normal two-channel operation, connect each peaker load acro the output terminal
(po itive and ground). ay attention to speaker polarity: loudspeakers connected out
of polarity degrade sound quality and may be damaged as a consequence.
Keep the peaker cable wire a hort a po ible and u e good quality tranded peaker
cable. Do not u e hielded wire, uch a microphone or guitar cable. Remember that the
peaker cable rob the power of the amplifier by increa ing the load impedance and
introducing re i tive power lo e , o called I
2
R lo e .
Load matching (MLS-switches)
Minimum Load Select (MLS) witche are located on the rear panel. The MLS witche
provide load matching capability o that you can drive the LA 24 into 2 ohm without
increa ed heat lo e .
Plea e refer to Table 2 to determine the power delivered into a pecific load for variou MLS
witch etting .
A you can ee from Table 2 the LA 24 can produce in exce of 1000 watt into any
impedance between 1.5 and 8 ohm . The fixed po ition hown in Table 2 guarantee 1000
watt but higher power can be achieved utili ing higher MLS
TM
po ition when connected to
lower peaker impedance .

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 11
L-ACOUSTICS LA 24 OWER MATRIX
MLS SWITCH SETTING
LOAD CONFIGURATION -5 dB -4 dB -2 dB 0 dB
16 ohm Stereo (2 channel) 160 W 180 W 340 W 520 W
8 ohm Stereo (2 channel) 300 W 350 W 650 W 1000 W
4 ohm Stereo (2 channel) 570 W 680 W 1100 W 1400 W
2 ohm Stereo (2 channel) 1040 W 1200 W 1200 W 1400 W
16 ohm Mono Bridged 600 W 700 W 1300 W 2000 W
8 ohm Mono Bridged 1140 W 1360 W 2200 W 2800 W
4 ohm Mono Bridged 2080 W 2400 W 2400 W 2800 W
Power in watt (EIA 1 kHz, 1% THD)
Table 2.
Figure 10. MLS switches on rear panel
MLS
TM
po ition can be et differently for each channel and a variety of combination can be
elected to uit different application ( ee Table 3).
Channel
Impedance
MLS
Power
Comments
A
8
-2 dB
650W
Power
B
8
-2 dB
650W
reduction
A
4
0 dB
1400W
High peak
B
4
0 dB
1400W
power
A
8
0 dB
1000W
Power
B 2 -4 dB 1200W matching
A
8
-2 dB
650W
Power
B
4
0 dB
1400W
sharing
Table 3.
The way to find the be t MLS
TM
po ition for your application i by experimentation. The
amplifier i very well protected (even down to 0.3 ohm ) but when time i of the e ence,
tick to the fixed po ition .
The thing to remember with the LA 24 that it i a power converter and when you elect
MLS
TM
po ition you are allocating a portion of the total power available.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 12
•O ERATING MODES
Stereo operation
For tereo (dual channel) operation, leave the Link and Pha e rever e witche in the
undepre ed po ition (OUT). Both channel operate independently of each other and their
individual level attenuator control their re pective level .
Never connect either output terminal to ground or in parallel. The recommended
minimum nominal impedance, for tereo or tandem operation, i 2 ohm per channel.
Tandem mono
For tandem (dual channel- ingle input) operation, depre the Link witch (IN po ition). Both
channel are now driven by the ame ignal which can be applied at either input connector.
The output connection i the ame a for tereo mode and both level attenuator are active,
allowing you to et different level for each channel. You can u e either of the two TRS
connector for linking the ignal to other amplifier (dai ychaining). Do not use the
remaining XLR and TRS connectors for mixing or other purposes. Never connect
either output terminal to ground or in parallel.
Bridged mono
To bridge the amplifier, depre the Link Switch (7) and Pha e Rever e Switch (6). Both
channel are then driven by a ingle ignal which can be applied at either input A or B. You can
u e any remaining input connector for linking etc. Do not u e the remaining XLR and TRS a
input jack imultaneou ly for mixing or other purpo e .
Connect the speaker leads to pin +1 on the Channel A Speakon (positive speaker
terminal) and pin +1 on the Channel B Speakon (negative speaker negative).
Alternatively, connect the positive speaker terminal to +1 and the negative speaker
terminal to +2 of the Channel A Speakon. Do not connect either of the -1
(negative) pins of the Speakons. Do not connect speakers to channel A or B in the
normal manner in bridged mode, as this can cause serious damage.
The recommended minimum nominal impedance for bridged mono i 4 ohm (equivalent to
driving both channel at 2 ohm ). Driving bridged load of le than 4 ohm may cau e
thermal overload.
Figure 11. Bridged mono connection
For bridged mono operation, both level attenuator mu t be in the ame po ition. We
recommend you leave them in the 0 dB (fully open) po ition.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 13
Stereo reverse
Thi mode i imilar to the Tandem mono mode except that by operating channel A and B in
oppo ite polarity the energy torage in the power upply i more efficient. Thi mean that
the amplifier can deliver up to 10% more power than in tandem mono mode (a ignificant
advantage for ignal below 100 Hz uch a ub ba etc).
For tereo rever e operation, depre the Pha e rever e witch o that Channel B i pha e
rever ed. To compen ate, connect pin +1 on the Channel B Speakon to the speaker's
negative terminal and pin -1 on Channel B to the speaker's positive terminal.
Alternatively, connect pin +2 on the channel A Speakon to the negative speaker
terminal and pin –2 on Channel A to the positive speaker terminal.
Figure 12. Stereo reverse mode
Channel A output i connected a in the normal tereo mode.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 14
•O ERATION
Operating precautions
•Make ure that the power witch i off before making any input or output connection or
operating the witche on rear panel. See page 6-7 regarding in tallation.
•Make ure that the AC main i correct and i the ame a what i printed on the rear
panel of the amplifier. See page 6 regarding operating voltage and power con umption.
•Make ure that the witche on the rear panel related to operating mode , clip limiter ,
and MLS™ are et in the correct po ition. See page 12 (operating mode ), page 16 (clip
limiter ) and page 10-11 (MLS witche ) for further information.
•It i alway a good idea to turn down the gain control before powering up in order to
prevent peaker damage if there i a high ignal level at the input.
owering up - Soft start
When you power up the amplifier it take a few econd to check it circuit (thi i known a
the " oft tart" or " low tart" equence), the fan blow at high peed before going into "idle"
then the two bottom green LED’ come on to how that the output circuit are receiving the
correct rail voltage.
Input attenuators
The two input level attenuator on the front panel alter the ignal level for their re pective
amplifier channel in all mode . They are calibrated in dB to help in etting up active
loud peaker y tem or for cutting down unwanted noi e from the input ignal. In bridged
mode, both control mu t be in the ame po ition o that the peaker load will be hared
equally between the channel .
Gain
The LA 24 i configured for 32 dB gain a tandard. Mo t profe ional mixing con ole operate
at a nominal level of +4dBu therefore 32 dB gain give you plenty of fader movement.
INPUT SENSITIVITY
GAIN Vrm dBV dBu
32 dB 1.88 5.5 7.7

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 15
Indicators
The two bottom green ”ON” LED indicate that the output circuit are receiving the correct
rail voltage.
The ”-25 dB” LED glow when the output ignal i greater than -25 dB (0 dB i referenced to
the full output power a elected u ing MLS witche ). The e LED al o act a ignal pre ent
indicator .
The re t of the green LED form a bar for output level from -20 dB to -5 dB.
The CLI indicator how when the amplifier output i clipping or limiting. Clip indicator
LED dynamic under clipping condition depend on whether the clip limiter i engaged.
•When the clip limiter i engaged, the clip indicator flicker briefly (limiting)
•When the clip limiter i not engaged the clip indicator light for a longer period (clipping)
The remaining yellow LED indicate if any protection circuit are activate. The e are
de cribed below.
Figure 13. Front indicators

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 16
•ROTECTION FEATURES
Each L-ACOUSTICS amplifier ha many advanced protection feature that will protect both
the amplifier and the peaker connected to it hould a fault condition ari e. All protection
circuit are independent and under normal u e the e feature are inaudible. When the
amplifier come out of a protect condition, the output level ha a low ri e time - the effect i
like turning the gain up lowly.
Clip limiter
The clip limiter i included to prevent dangerou ly clipped ignal from reaching the peaker
and damaging it. Limiting circuitry work by monitoring the output and comparing the
di tortion produced between the input and output of the amplifier. If the di tortion exceed
1%THD for any rea on (voltage or current clipping), the limiter reduce the input ignal
proportionally. Note that if the ignal i di torted or clipped before it reache the amplifier,
the clip limiter will not be activated.
Under normal operation, clip limiting i inaudible. The limiter can be turned On or Off by
depre ing the clip limit witch (2).
Clip Limiter ON = witch depre ed (IN po ition)
Clip Limiter OFF = witch not depre ed (OUT po ition)
L-ACOUSTICS recommend leaving the clip limiter witched "on" (button depre ed) at all
time .
Thermal protection
When the amplifier i driven very hard into low impedance , the cooling fan go into high
peed. If the condition that cau e thi continue, the TEMP indicator( ) will light a an
indication that the amplifier will oon thermal out.
After five econd the amplifier will go into thermal protect, muting the input ignal. After 15-
20 econd the amplifier will cool the Intercooler
®
and the cycle will begin again.
Thermal protection tart when the Intercooler
®
reache a temperature above 90
0
C.
VHF protection
When a ignal of more than 12kHz at full output power i pre ent at the output connector
for more than five econd , the VHF protection circuit mute the input ignal and the VHF
LED will light. Thi i a u eful feature ince there are currently no commercially available
compre ion driver that can take 1000 watt of continuou power at 12 kHz!! Thi circuit i
inaudible under normal u e, however it can be turned off.
If the VHF protection is required to be turned off, e.g., for studio monitors, please consult the
factory, as this is a non-user ad ustment.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 17
Short circuit protection
All L-ACOUSTICS amplifier are completely hort circuit protected. The protection circuit
permit very high peak current , but till hold the output device within their afe operation
area. If a hort circuit i maintained, the channel affected will eventually go into thermal
protection and the cycle will repeat.
AC mains voltage protection
If the AC main voltage i out ide the 20% range of allowed operation voltage (over or under
voltage), the power upply will hut it elf down. When the main voltage i above the
minimum tart voltage and below it maximum operating voltage the amplifier will re tart
again.
It take a couple of econd for the amplifier to check it circuit (thi i known a the " oft
tart" or " low tart" equence), then the gain will lowly and gradually be rai ed back to
normal and the fan then blow at high peed before going into "idle". The two green ”ON”
LED indicate when the power upply i operating properly.
DC protection
There are two type of DC protection:
Fu e on the upply branche of each channel (thi i an IEC 65 requirement) and Crowbar
type protection that hort the output. Both of the e circuit come into effect once a DC
level of 10 volt or more i detected on either channel.

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 18
•DESIGN FEATURES
Cooling
L-ACOUSTICS amplifiers run very cool due to a patented heat ink device called the
Intercooler
TM
. Fir t, bipolar output device are mounted directly on a copper heat ink
thereby avoiding thermal lo e normally found when u ing mica wa her . The heat ink i
then mounted horizontally in front of a pre ure chamber where the air flow i con tant along
the entire length of the heat ink due to a horizontal pre ure chamber that i created in front
of it (by compari on, for a conventional tunnel de ign the end of the heat ink oppo ite the fan
invariably get hotter than that directly in front of the fan). When cool air in the pre ure
chamber hit the geometric fin of the Intercooler
TM
, turbulence i produced thereby
enabling efficient cooling.
Light weight
The LA 24 ha an excellent power to weight ratio, (280 W/Kg) making it one of the mo t
powerful 2U amplifier available. The light weight i achieved not only through u e of the
witch mode power upply - the Intercooler
TM
and 9 piece anodized alloy cha i al o
contribute greatly, making rear rack upport unnece ary in many application .
Switch mode power supply (SM S)
Switch mode power upplie are the modern olution to the problem of ize and weight.
However, early example of SMPS u ed for power amplification in audio application were
le than impre ive and literally adopted the type of upply found in many computer today.
The L-ACOUSTICS SMPS i different in that it i regulated. How i thi achieved?
In contra t to other de ign that u e pu h pull converter we have managed to produce a
SMPS that ha the ame characteri tic a a conventional power upply. We have avoided the
pitfall of pu h-pull converter by eliminating the need for limiting on the econdary ide of the
witch tran former. Thi i achieved by u ing en e winding and injecting a magnetic pul e
from the AC line during a pul e time egment which i eparate from the output charge
current pul e.
2
1
3
0
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25 30 35 40 45 50
Current [A]
Voltage [V]
Figure 14. Current-voltage characteristic of different power supply topologies .
1) Conventional power supply shows voltage drop due to internal resistance
2) Regulated power supply used by L-ACOUSTICS
3) Unregulated switch mode power supply with current limiting

L-ACOUSTICS LA 24 MANUAL Version 2.2 17/11/08 19
While the SMPS might ound complex it i actually very traight forward and ha high
reliability. The net performance re ult i good ba and fa t tran ient re pon e. Becau e the
upply i regulated, the LA 24 will produce the ame power output even if the AC line voltage
fall by up to 20% ! Efficiency i al o a ured, and in the ca e of the LA 24 thi i e pecially
apparent - it power upply draw only 4 kW while producing 2 x 1400 W. For a conventional
amplifier, typically only 2 x 650 W would be produced and nearly 3 kW wa ted a heat.
Traditional PSU can al o behave erratically at certain frequencie - particularly at low
frequencie under clip condition where their output impedance ri e . Thi produce
uncontrollable peaker cone movement and under the e condition clip tate are more
audible for the ca e of conventional PSU .
By compari on, the L-ACOUSTICS SMPS produce it rated power output at all frequencie
regardle of peaker demand and AC line condition .
MLS™-switches
Thank to the regulated SMPS, the maximum power available from the output tage can be
adju ted without increa ed heat di ipation or efficiency lo . Thi allow u er to match the
output power to the loud peaker load impedance.
The LED bargraph i al o adju ted to give a correct reading relative to the elected output
power. Becau e the amount of power delivered into a load i dictated by it impedance (at 2
ohm you u e the lea t voltage but require the mo t current), you can cheat with the MLS
witche thereby enabling power in exce of the normal power rating.