CROWN-PSA-2-维修操作说明书手册-7-of-7-psa2servicemanual7of7

The gain stage is constructed with UIB whose output iswill allow the compressor to restrain the output power ofrouted to the low-pass filter using U3C.The low passthe unit to protect fragile drivers,etc.filter is standard as a 3-pole Butterworth type of 15K Hz.It also may be readily reconfigured.The input and outputShould stereo tracking of the compressors be desired theof the LP filter are routed to SW10l for selection of thetest points TP5 and TP6 may be shorted together.Thisdesired signal.The output of SW10l is then input to thewill cause the compressors to compress equally despitelimiter-compressor.which channel may have initiated the gain reduction.The limiter -compressor is constructed with deliberatelyIf the action of the compressors is undesirable in anrestricted compression range.Compressors with largeapplication,the OTA's U4 and U5 or comparators U6gain compression capability often exacerbate feedback inmay be removed from their sockets to prevent allsystems where the gain is increased only to be reduced bycompression.the compressor action.Should the input be reduced theWhen making a hurried hook-up of a sound system it isgain will suddenly appear as the compressor recovers andoften handy to know if the amplifier is attached to thefeedback will result.loudspeakers that it is to drive,i.e.,no open or shortedThe compressor is not a part of the circuit function until aspeaker cables.To make this test easier,the PSA-2 has acontrol signal biases on U4.U4 is what is known as anbuilt in tone generator which provides inpulses at a 50Hzoperational transconductance amplifier or OTA.Such arate.As such the spectrum will excite tweeters or woofersdevice converts a small input voltage into an outputwith a signal that has very little power yet is quitecurrent which is proportional to the control currentdistinctive and audible.injected into pin 5.When Q100 is off,R117 acts to assureThe generator is constructed with UID which excitesthat no leakage current will enable any amount ofboth signal channels with a pulse shaped by CI incompression.When Q100 is on,the current in R118 turnsconjunction with RIII and R211.UID is wired as anon U4 which becomes an additional feedback loop inastable which has sufficient regeneration to oscillate onlyparallel with R112 and decreases the net stage gainwhen SWI is closed.proportional to the current in R112.The input signal toU4 is provided by the divider R114 and R113.Since theI.PSA-2/PSA-2X DisplayOTA has an offset voltage like any other op-amp,thismust be offset by a small DC voltage from R115 andThe display of the PSA-2 is a combined set of indicatorsRI16,the offset adjustment.Failure to null this errorto show the state of the output stage supplies,powerwould result in thumping of the compressor as it changedapplied to the control supply,signal on the outputs andgain.CIII is used to decouple any DC from the module.outputs overloaded (IOC).The output is then routed to the jack switch in J21.If anAmber LED D1,powered b