Lab.gruppen LAB 4000 User Manual

Also see for LAB 4000: Brochure Specifications

Contents

Lab.gruppen LAB 4000 User Manual Manual pdf 10 page image

10This is a useful feature as there are currently nocommercially available compression drivers that cantake 500 watts of power at 10 kHz!! this circuit isinaudible under normal use, however it can be turnedoff.If the VHF protection is required to be turned offi.e. for studio monitors, please consult yoursupplier, as this is a non-user adjustment.Short circuit protectionAll LAB.GRUPPEN amplifiers are completelyshort circuit protected. The protection circuitpermits very high peak currents, but still holds theoutput devices within the safe operation area. If ashort circuit is maintained, the channel affected willeventually go into thermal protection and the cyclewill start again.Adaptive Fuse Saver, AFS tm -limiter;The AFS TM circuit continuously monitors the mainscurrent. If the average mains current is too high for a16 ampere slow blow fuse, as it can be during socalled bench tests, the AFS™-limiter will limit themains current to a safe level. If theAFS-limiter is activated this will be indicated bythe AFS-LED on the front panel. The AFS limiterwill not be activated during normal use, even if themusic will be in the state of constant clip.AC mains voltage protectionIf the AC mains voltage is outside the allowedoperation voltage ( over or under voltage) , thepower supply will shut down itself. When themains voltage is above the minimum start voltageand below its maximum operating voltage theamplifier will restart again.It takes a couple of seconds to check its circuits (thisis known as the "soft start" or "slow start" sequence),the gain will slowly and gradually raised back tonormal, and the fans then blow at high speed beforegoing onto "idle". The two green ”ON” LED’sindicate when then power supply is operatingproperly.D.C. protectionThere are two types of DC protection:Fuses on the supply branches of each channel (this isan IEC 65 requirement).A Crowbar bar protection that shorts the output.Both these circuits come into effect once a DC levelof 10 volts or more is detected on either channel.Design featuresCoolingThe LAB.GRUPPEN amplifier runs very cool dueto a patented heat sink called IntercoolerTM . Theoutput devices (bi-polar) are mounted directly on acopper heat sink thereby avoiding thermal lossesnormally found when using mica washers (the heatsink is mounted horizontally in front of a pressurechamber) The air flow is constant along the wholeheat sink,thanks to a horizontal pressure chamber in front of it,(in a conventional tunnel design the end of the heatsink opposite to the fan invariably gets hotter thanthat directly in front of the fan). When cool air hitsthe geometric fins of the IntercoolerTM, turbulence isproduced thereby enabling efficient cooling.Light weightThe switch mode amplifiers has a very good powerto weight ratio, (480w/Kg) making it one of themost powerful 2u amplifiers available.. The lightweight is achieved not only by the PSU, but theIntercoolerTM and the 9 piece anodized alloy chassiscontribute greatly, rear rack supports are unnecessaryin most applications.Switch mode power supply (SMPS)Switch mode power supplies are the modernsolution to the problems of size and weight.However, early examples of SMPS used in poweramplification were not ground breaking, andliterally adopted the type of supply found in manycomputers today. The LAB.GRUPPEN SMPS isdifferent in that it is regulated. How is thisachieved?In contrast to other designs, that use push pullconverters we have managed to produce a SMPSthat has the same characteristics as a conventionalsupply. We have avoided the pitfalls of push-pullconverters, by eliminating the need for limiting onthe secondary side of the switch transformer. Thisis achieved by using sense windings, injecting amagnetic pulse from the AC- line during a pulsetime segment which is separated from the outputcharge current pulse.Whilst the SMPS may sound complex it is actuallyvery straight forward with high reliability.The net result is good bass and fast response.Because the supply is regulated, the poweramplifier will produce the same power output evenif the AC line falls by more than 20% !Efficiency is also assured, and in the case of theLAB 4000 this is especially apparent ; its powersupply draws only 6 kW and yet it produces 2 x2100 W.

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