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Version 1.0

January 2003

LA48a

OWNERS MANUAL

Содержание LA48A

Страница 1: ...Version 1 0 January 2003 LA48a OWNERS MANUAL ...

Страница 2: ......

Страница 3: ... 10 5 1 Mounting 10 5 2 Cooling 10 5 3 Operating Voltage 11 5 3 1 Denmark 11 5 3 2 Switzerland 11 5 4 Grounding 11 5 5 Power Consumption 12 5 6 Heat Power Calculation 13 5 7 Gain and Sensitivity 13 6 CONNECTIONS 14 6 1 Input Connections 14 6 1 1 Balanced Inputs 14 6 1 2 Unbalanced Inputs 15 6 2 Connecting Speakers 15 7 OPERATION 16 7 1 Operation Modes 16 7 1 1 Stereo Mode 16 7 1 2 Tandem Mode 17 7...

Страница 4: ... Unbalanced Line Connection 15 Figure 9 Balanced Line with Unbalanced Equipment 15 Figure 10 Loudspeaker Connection Details 15 Figure 11 Reverse Polarity Operation for Channel B 16 Figure 12 Bridged Mono Cabling 17 Figure 13 LA48a Front Panel Detail 18 LIST OF TABLES Table 1 Output Power Ratings and MLS Switch Settings for the LA48a 8 Table 2 MLS Switch Setting Applications 9 Table 3 LA48a Current...

Страница 5: ...ews No user serviceable parts inside Refer servicing to qualified service personnel 2 4 IMPORTANT SAFETY INSTRUCTIONS Before using your amplifier be sure to carefully read these operating instructions and follow the safety suggestions outlined below 1 Keep this manual for future reference 2 Heed all warnings 3 Follow all instructions 4 Do not use this unit near water Do not spill water or other li...

Страница 6: ...emove top or bottom covers Removal of the cover will expose hazardous voltages There are no serviceable parts inside and removal may void the warranty 18 An experienced user shall always supervise the use of professional audio equipment especially if inexperienced adults or minors are using the equipment 2 5 USER RESPONSIBILITY 2 5 1 SPEAKER DAMAGE Your amplifier is very powerful and can be potent...

Страница 7: ...paration between the equipment and receiver Connect the equipment to an outlet on a circuit different from that to which the receiver is connected Check if the affected unit complies with the EMC limits for immunity CE labelled If not address the problem with the manufacturer or supplier of the affected unit All electrical products sold in the EC must be approved for immunity against electromagnet...

Страница 8: ...d to carry the amplifier and the handles also provide protection for the front panel For fixed installation or when rack front covers are too shallow the handles may be removed by unscrewing the retaining bolts behind the front panel 2 Input Level Attenuators These controls are used to alter the signal level entering the amplifier They are calibrated in dB to assist in the setup of active loudspea...

Страница 9: ...hould be used at all times 7 Power Switch Turns the mains power on or off 8 AC Indicator Indicates if AC voltage is present Note this indicator is located electrically in front of the power switch 9 AFS Indicator Indicates if the AFS Automatic Fuse Saver current limiter is activated 3 3 REAR PANEL Figure 2 LA48a Rear Panel 1 Output Speaker Connector The Neutrik Speakon connector may be unfamiliar ...

Страница 10: ...duce output power in excess of 2000 watts Essentially the LA48a amplifier is a power converter and by selecting MLS positions you are allocating a portion of the available 5800 watts power Figure 3 LA48a Rear Panel MLS Switches Table 1 Output Power Ratings and MLS Switch Settings for the LA48a LA48a MLS SWITCH SETTING LOAD CONFIGURATION 5 dB 4 dB 2 dB 0 dB 16 ohms Stereo 2 channel 220 W 260 W 410 ...

Страница 11: ...ot a straight line and therefore shows a reactive load to the amplifier This reactive load produces back energy that can trigger the current protection and as a result produce glitches in the signal The Solution The solution is to use a Constant Power Converter connected between the power supply and the linear power amplifier The Constant Power Converter can produce more current than it takes from...

Страница 12: ...e applications the amplifier should be fixed in the back with a rear support kit L ACOUSTICS part codes APSUP or MC RKSUP The optional accessory MC RKSUP is designed for use with the L ACOUSTICS RK12 amplifier rack Alternatively the amplifier support kit APSUP is a universal rear support kit for any 19 rack since it is adjustable to accommodate varying rack depths Two rear support brackets two amp...

Страница 13: ...he soft or slow start sequence the fans then blow at high speed before going into idle and the two bottom green LED s come on to indicate that the output circuits are receiving the correct rail voltage 5 3 1 DENMARK National deviation concerning installation of the LA48a Danish safety regulations stipulate the use of an 8 A mains fuse Since the LA48a uses an internal primary mains fuse of 15A the ...

Страница 14: ...ll power 0 dB at 1 kHz 1 THD 20 A rms AFS limited Second the maximum expected average current under worst case conditions corresponding to 1 3 full power program material according to the FTC standard At this level the music will be in a state of constant clip and is therefore the highest power level one can obtain without completely obliterating the program material Third the normal operating pow...

Страница 15: ...y volts rms or dBu referred to 0 775Vrms are required at the amplifier input to obtain full output power Since the output power delivered varies with the load impedance 4 ohms is generally taken as the reference For the LA48a full output power into 4 ohms is 2300 W MLS switch 0 dB and standard gain is 32 dB This corresponds to an input sensitivity of 2 4 Vrms or 9 9 dBu For the LA48a the input sen...

Страница 16: ...ELD GROUND Figure 6 TRS plug The input impedance is high enough 20 kOhms balanced to allow daisy chaining or multiple parallel input connections The headroom of the input circuits is also high enough to accept the maximum output level from virtually any low level signal source Balanced signals are less sensitive to AC hum and radio interference The source impedance should be less than 1 kOhms in o...

Страница 17: ...revents from shock hazard The LA48a power amplifier Speakon connectors are wired in the following manner Channel A Channel B Pin 1 Channel A Channel B Pin 1 Channel A Channel B Pin 2 Channel B Pin 2 Channel B For normal two channel operation connect each speaker load across the Channel A B output terminals positive and ground Since the Channel A Speakon is bi wired it is possible to access both ch...

Страница 18: ...t 60 m 180 ft 7 OPERATION 7 1 OPERATION MODES 7 1 1 STEREO MODE In this mode both channels operate independently of each other and the level attenuators on the front panel control the respective channel levels Never connect either Channel A or B output Speakon terminals to ground or in parallel The recommended minimum nominal impedance for stereo operation is 2 ohms per channel Note Concerning Ben...

Страница 19: ...7 1 4 BRIDGED MONO MODE FEATURES Bridged mono mode combines the power of both 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...

Страница 20: ...e old saying amps on last amps off first 7 3 POWERING UP SOFT START 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 and the two bottom green LEDs illuminate to show the amplifier is operational 7 4 INPUT ATTENUATORS The two input level attenuators on the front panel adju...

Страница 21: ...dition the output level has a slow rise time the effect is like turning the gain up slowly Note if the signal is distorted or clipped before it reaches the amplifier the clip limiter cannot detect it and will not be activated Under normal operation clip limiting is inaudible The limiter can be turned On or Off by depressing or pressing the relevant rear panel clip limit switch L ACOUSTICS recommen...

Страница 22: ...2 dB Effectively this is the same as an LA48a being reduced to the power of an LA24a but again not a single user has reported that the AFS has been activated In reality this is much better than the mains breaker blowing and the amplifier being turned off the listener can hardly hear this since only the headroom will be reduced and if the peaks are around 120 to 130 dB 2 dB is not noticeable 8 6 AC...

Страница 23: ...ls or loudspeaker Check also that VHF protection is not activated If it is remove possible high frequency oscillations from the relevant input Fault The amplifier goes into thermal protection when driven at low level Check that nothing causes a short circuit at the amplifier s output e g faulty cabling or a loudspeaker component short circuit in the voice coil Fault The amplifier goes into protect...

Страница 24: ...cts warranted L ACOUSTICS reserves the right to make changes or improvements in design or manufacturing without assuming any obligation to change or improve products previously manufactured This warranty is exclusive and no other warranty is expressed or implied This warranty does not affect your statutory rights International Please contact your supplier for this information as rights and disclai...

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