420 Stereo PowerAmplifier
420 User’s Guide Symetrix, Inc. retrieval system,without permission,inwriting,from scanning, recordingorbyanyinformation storageand 420electronic ormechanical,including photocopying, reproduced ortransmittedinanyform orbyanymeans, Under copyrightlaws,nopartofthis manualmaybe with regardtotheperformanceoruse oftheseproducts. a recommendation.Symetrixassumes noresponsibility purposes onlyandconstitutesneitheranendorsementnor Mention ofthird-partyproductsisforinformational Symetrix isaregisteredtrademarkofSymetrix,Inc. ©1999, Symetrix,Inc.Allrightreserved. Subject tochangewithoutnotice. Symetrix partnumber53420-0A00 Rev A.00,25February,1999 Appendix A Chapter 11 Chapter 10 Chapter 9 Chapter 8 Chapter 7 Chapter 6 Chapter 5 Chapter 4 Chapter 3 Chapter 2 Chapter 1 Table ofContents pcfctos20 21 23 19 13 & Bridged-MonoModeSwitch 16 Disassembly Instructions 10 7 Warranty &Service Specifications 3 Troubleshooting Technical Tutorial Applications 1 Using the420 5 420 Basics 2 Front &RearPanelOverview Fast Setup Operator SafetySummary Introduction Email [email protected] Email Mountlake Terrace Mountlake 78-7727 7 (425) ax F 6408 216th St. SW St. 216th 6408 78-7728 7 (425) el T USA 43 980 A W , Chapter 1 Rear panel Front panel Website: Email: Fax: Phone: contact usatthenumbers/addressesbelow.Yourcallsarealwayswelcome. your questionsinside.Shouldyouhaveanycommentsorquestions,pleasedonothesitateto We recommendthatyoureadthismanualcover-to-cover.Youwillfindtheanswerstomostof useful fornear-fieldmonitorapplicationsorheadphonedriverapplications. terminals. Afrontpanelswitchallowsyoutoturnofftherear-panelspeakerterminals,whichis You candriveonepairofphonesfromthefront-paneljack,ormanypairsrear-panel In recordingstudiosandothersimilarapplications,the420makesanidealheadphoneamplifier. tions canusethisfeaturetomixpagingsignalsorandmusicsignals. can usethisfeaturetocheckthemonocompatibilityoftheirsignals.Commercialsoundapplica- The front-panel M amplifier. controls, asa2-channelamplifier,withindependentlevelorsingle-channelmono signal (balancedorunbalanced).The420canbeusedasastereoamplifier,withgangedlevel which accepteitherbalancedorunbalancedsignals.The420producesfulloutputwitha0.5Vinput For convenience,the420isequippedwithboth1/4"TRS(tip-ring-sleeve)andXLRconnectors, bridged modetheminimumloadimpedanceis8ohms. video, andwithheadphones.Instereomode,theminimumloadimpedanceis4ohms,inmono- intended forusewithnear-fieldmonitors,smallspeakersused“radioreference”audio-for- a singlechannelamplifiercapableof40-wattsoutput(mono-bridgedmode).Theis audio systems.The420maybeoperatedasatwochannelamplifierwith20-wattsperchannel,or The Symetrix420isatwo-channelpoweramplifierintendedforuseinprofessionalandcommercial STEREO POWER STEREO AMPLIFIER 420 100 WATTSMAXIMUM www.symetrixaudio.com [email protected] (425) 778-7727 (425) 778-7728 UNITED STATESOFAMERICA SEATTLE WASHINGTON, MANUFACTURED IN CLIP 2 3 1 0 4 GAIN 5 CHANNEL 1 10 6 7 9 8 FUSE FUSE CONTROLS GAIN INDEPENDENT DUAL TRACKING ODE switchmixesthetwoinputstogether.Broadcastandrecordingapplications CLIP 2 CHANNEL 2 37 1 0 4 GAIN 5 10 6 9 8 MODE STEREO MONO HEADPHONES STEREO SLEEVE RING TIP MONITOR TYPICAL INPUTS SLEEVE SPEAKER =GROUND= RING =HIGH(+)= =LOW(-)= ACTIVE MUTED TIP PIN 1 PIN 3 PIN 2 2 3 1 20 WATTSPERCHANNEL8OHMS(CLASS2WIRING) CHANNEL 2 OUTPUTS CHANNEL 1 UNBALANCED/ BALANCED Introduction INPUT 2 BALANCED POWER UNBALANCED/ BALANCED INPUT 1 BALANCED 1 420 N 2 conductor and ground. Aprotectiveground conductors orbetween eitherpowersupply more than250Vrmsbetweenthe powersupply operate fromapowersourcethat doesnotapply Power Source instructions. Install inaccordancewiththe manufacturer’s and followallwarningsinstructions. Please readandkeeptheseinstructions.Heed Important SafetyInstructions Boldface C Warning Caution Note manual. Someparagraphsmayuse Several notationalconventionsareusedinthis Terms polarizedplugsuppliedwiththeunit fully other with the Caution product (i.e.thismanual). instructions intheliteratureaccompanying important operatingandmaintenance(servicing) triangle isintendedtoalerttheuserofpresence persons. Theexclamationpointwithinanequilateral magnitude toconstituteariskofelectricshock the product’senclosurethatmaybeofsufficient presence ofuninsulated“dangerousvoltage”within equilateral triangleisintendedtoalerttheuserof The lightningflashwitharrowheadsymbolwithinan Equipment Markings Operator SafetySummary 420 These are: capitalization areusedtoidentifycertainwords. or o userserviceablepartsinside.Referservicingtoqualifiedservicepersonnel APITALS Il nesetrouveal’interieuraucunepiecepourvantentrereparéel’usager. Warning WARNING: SEE OWNERSMANUAL.VOIRCAHIERD’INSTRUCTIONS.
AVIS:
as aheading.Certaintypefacesand S’adresser aunreparateurcompétent. Strong emphasis. Controls, switchesorothermarkings system. 420 orotherequipmentinyour heeded, maycausedamagetothe Identifies informationthat,ifnot health orthatofothers. ignored, maybehazardoustoyour Identifies informationthat,if on the420’schassis. you tobetterusethe420. supplies extrainformationtohelp extra emphasis.A Identifies informationthatneeds any extensioncord,receptacle,or To preventelectricshock,donotuse Thisproductisintendedto RISK OFELECTRICSHOCK NE PASOUVRIR RISQUE DECHOCELECTRIQUE THIS EQUIPMENTTORAINORMOISTURE ELECTRIC SHOCKDONOTEXPOSE TO REDUCETHERISKOFFIREOR inserted. outlet unlessthebladescanbe CAUTION DO NOTOPEN Note generally Note Note, Note, Caution , . operate normally, orhasbeendropped. been exposedto rainormoisture,doesnot have fallenintotheapparatus, theapparatushas is damaged,liquidhasbeenspilled orobjects way, suchaswhenapowersupply cordorplug required whenthe420hasbeen damagedinany refer allservicingtothefactory. Servicingis serviceable partsinsidethe420. Incaseoffailure, User-serviceable parts only withadampcloth. accessories specifiedbythemanufacturer.Clean covers andpanelsproperlyinstalled.Onlyuse panels. Donotoperatetheproductwithout worse), donotremovetheproductcoversor Stay OutoftheBox unused forlongperiodsoftime. this apparatusduringlightningstormsorwhen (including amplifiers)thatproduceheat.Unplug heat registers,stoves,orotherapparatus install nearanyheatsourcesuchasradiators, mains voltage,orifimproperlyfused.Donot inclement weather,improperorunknownAC explosive atmospheres,inwetlocations, ment underanyofthefollowingconditions: Operating Location value is0.5A,250VAC,slowblowing. slow blowing.For230VACoperation,thecorrect operation, thecorrectvalueis1.0A,250VAC, accepts 5x20mmdiameterfuses.For117VAC the IECACinletconnector.Thefuseholder Proper Fuse they exitfromtheapparatus. convenience receptacles,andthepointwhere walked onorpinched,particularlyatplugs, condition. operating locale.Useonlyacordthatisingood and connectorspecifiedfortheproductyour Proper PowerCord shock. appear tobeinsulated,canrenderanelectric tive parts,includingknobsandcontrolsthatmay ground connectionislost,allaccessibleconduc- Danger fromLossofGround of theobsoleteoutlet. your outlet,consultanelectricianforreplacement your safety.Whentheprovidedplugdoesnotfit grounding prong.Thethirdprongisprovidedfor grounding plughastwobladesandathird safety purposeofthegroundingplug essential forsafeoperation. grounding conductorinthepowercord,is protective groundconnection,bywayofthe before makinganyconnectionstotheproduct.A power cordintoaproperlywiredreceptacle the powercord.Toavoidelectricshock,plug grounded throughthegroundingconductorof Grounding in thepowercord,isessentialforsafeoperation. connection, bywayofthegroundingconductor Protect thepowercord Thechassisofthisproductis Theuseraccessiblefuseisapartof
Do notoperatethisequip- To avoidpersonalinjury(or Use onlythepowercord Therearenouser Do notdefeatthe Chapter 2 Iftheprotective frombeing . The P S M C C Front PanelControl Set thecontrolsandswitchesonfrontrearpanelas follows: Settings Warning Caution the rearofunit. Connect theACinputtoanpowersourceofpropervoltageandfrequency,asmarkedon Figure 3-1.420generichookupdiagram. really onlyintendedtodriveonepairof‘phones. louder) ifyouusethescrewterminalsonrearofunit.Thefront-panelheadphonejackis rear oftheunit.If420isdrivingaheadphonedistributionsystem,you’llgetbetterresults(read the 420’soutputtoloudspeakers(orotherload)usingbarrierstripconnectorlocatedat Connect yourinputsourcetotheeitherXLRconnectorsorTRSphonejacks. Connections section isfastsetup.Refertolaterchaptersforexplanationofthe420’scontrolsandfunctions. Follow theseinstructionstogetyour420up-and-runningasquicklypossible.Theintentofthis Fast Setup Chapter 3 OWER PEAKER HANNEL HANNEL ODE OUTPUTS 20 WATTSPERCHANNEL8OHMS(CLASS2WIRING) M 2G 1G UTE HNE CHANNEL CHANNEL AIN AIN 2 inside thechassis.Referallservicetoqualifiedpersonnel ortothefactory. Lethal voltagesarepresentinsidethechassis.There nouserserviceableparts service toqualifiedpersonnelorthefactory. internal damage.Therearenouserserviceablepartsinsidethechassis.Referall Failure toconnectthe420properACmainsvoltagemaycausefireand/or 1 u/troIpt2Connectbalanced or or balanced Connect In/On Input Out/Active 2 Out/Stereo 2 Input 9:00 o’clock 9:00 o’clock Setting UNBALANCED/ BALANCED INPUT 2 BALANCED 2 3 1 Outputs Rear PanelConnectors UNBALANCED/ BALANCED INPUT 1 BALANCED 2 3 1 unbalanced sourcehere. unbalanced sourcehere. system, orotherload. headphone distribution Connect loudspeakers, Connect Fast Setup 3 420 4 420 C With thesignallevelofsourceatareasonablelevel,increasegain420untileither the balancedinputbufferamplifiersortocauseprecedingunitclip. amplifier intoclipping.Ifthegaincontrolsareturneddownsufficiently,itispossibletoeitherclip as possible.Thisensuressufficientamplifiersensitivitythattheprecedingunitcandrive Generally speaking,thegaincontrolsonapoweramplifiershouldbeoperatedatashighsetting The amplifier’s C listed inthesettingstableonpreviouspagearenowmade.The420shouldpasssignal. The 420’scontrolsandswitchesarenowsetaccordingtotheprecedingsection.Allconnections Initial Setup LIP indicators illuminateortheacousticaloutputofloudspeakersissufficient. LIP indicators shouldnotbeilluminated. Chapter 4 S Monitor M Mode C Channel 2 G C Channel 1 E IndicatesthepresenceofACpower. LED S Power S G G STEREO POWER STEREO AMPLIFIER 420 WITCH PEAKER TEREO LIP LIP AIN AIN AIN ONO LDIndicatestheonsetofclippingatoutput420. LED Indicatestheonsetofclippingatoutput420. LED C /S ONTROLS H M TEREO EADPHONES CLIP 1 UTE 2 4 3 0 GAIN 5 CHANNEL 1 6 10 9 switch In D In switch 7 8 CONTROLS GAIN INDEPENDENT DUAL TRACKING CLIP 2 1 CHANNEL 2 37 4 0 GAIN 5 10 6 information. Turns the420on. O Mutes (disconnects)therear-panel headphones ofanyimpedance,from4ohmsandup. ¼ in.TRSjack.Connectstereoheadphoneshere.Thisjackwilldrive G both inputsofthe420aremixed(ahead In S mode. control byanyothername.Thisisactiveonlyin I Controls thegain,orinputsensitivity,ofchannel2420.Avolume In I both channels.Usethismodeforstereoapplications. both channels.Theinputsarestillseparate,there’sjustonecontrolfor D mode. Refertothe any othername.Thiscontrolisactiveregardlessofthe420’soperating Controls thegain,orinputsensitivity,of420.Avolumecontrolby 9 8 MODE STEREO MONO NDEPENDENT TEREO UAL HEADPHONES STEREO T MONITOR mode,bothchannelsofthe420areseparate.InM RACKING SPEAKER ACTIVE MUTED Front &RearPanelOverview mode, thegaincontrolsforbothchannelsareseparate. mode,thegaincontrolforchannel1sets UAL T RACKING /I UTPUT NDEPENDENT terminals. AIN switchformore controls). POWER NDEPENDENT ONO mode, 5 420 6 420 M I I O F AC P S NPUT NPUT USE ERIAL UTPUTS ONO 100 WATTSMAXIMUM OWER 1XLR-female(pin-2hot)paralleledwithTRSphonejack.Usethisinput XLR-female(pin-2hot)paralleled withTRSphonejack. 1 2 B N RIDGE UMBER UNITED STATESOFAMERICA SEATTLE WASHINGTON, MANUFACTURED IN I NPUT sic Located internally. switch FUSE FUSE for mono-bridgeapplications. minimum loadimpedanceis8-ohms. negative loadconnectiontothechannel2+outputterminal.The positive loadconnectiontothechannel1+outputterminal,connect impedance is4-ohms.Formono-bridgeapplications,connectthe connect theotherloadtochannel2output.Theminimum channel applications,connectoneloadtothe1outputand turned on/offviathefront-panelS #6 screwterminals.Thisistheoutputof420.Theseterminalsmaybe 250V ac,slowblowing(BussmantypeGDC-500ma). 1A, 250VAC,slowblowing(BussmantypeMDL-1)230VAC:0.5A, 1Ampere Slow-blowfuse.Replaceonlywithsametypeoffuse117Vac: Refer torear-panelmarkingforcorrectACsourcevalue. IEC-power connector.ConnectonlytoappropriateACpowersource. [Please sendinthecompletedwarrantycard.] SLEEVE RING TIP TYPICAL INPUTS SLEEVE =GROUND= =HIGH(+)= RING =LOW(-)= TIP PIN 1 PIN 3 PIN 2 2 3 1 20 WATTSPERCHANNEL8OHMS(CLASS2WIRING) CHANNEL 2 PEAKER OUTPUTS CHANNEL 1 M UTE UNBALANCED/ BALANCED switch. Forstereoor2- INPUT 2 BALANCED UNBALANCED/ BALANCED INPUT 1 BALANCED Chapter 5 same ornearly thesame),operatinganamplifier intothelowestpossible impedanceresultsinthe Since outputpowerincreases asloadimpedancedecreases(assumingthatthevoltage remains the rating wouldonlydeliver25watts intoa16-ohmload. scenario anddependsonactual circuitdesign).Thus,anamplifierhavinga50-watt,8-ohm, power diminished poweroutput.As theloadimpedancedoubles,outputpowerhalves(thisis abest-case higher thantheamplifier’srated minimumisharmless.Ofcourse,thereaprice,andthat priceis 4 For solid-stateamplifiers,operatingwithoutanyloadconnected orwithaloadwhoseimpedanceis rating, smokeastheunitself-immolates. 20 load impedancesmeanincreasingcurrent,anduponexceeding theamplifier’smaximumcurrent protection circuitry.Withoutcircuitry,oratleast somesortofcurrentlimiting,lower current limitusuallyresultsinclippingwhichiscausedby theactivationofamplifier’sinternal Reaching anamplifier’svoltagelimitationresultsinclipping. Reachinganamplifier’sinternal 420 Crest Crown Symetrix Make For example: voltage andcurrentthattheamplifiercandelivertoitsload. minimum loadimpedance,combinedwiththeoutputpowerrating,definesmaximumvaluesof resistance mustremainabovesomeminimumvalue:theamplifier’sloadimpedance.The deliver toaload(theloudspeaker).Ifbothvoltageandcurrentarelimited( intimately relatedtotheamplifier’soutputpower,andamountofvoltagecurrentthatitcan Usingsimplealgebra,youcanmanipulatetheseequationstosolveforany What thismeansisthattheimpedanceofaloudspeakerandabilityanamplifiertodriveitare where:E=electromotiveforceinvolts,Rresistanceorimpedanceohms, E = PR E = IR The relationshipsbetweenvolts,amps,impedance,andwattsisstatedasfollows: current thatcanbedeliveredtoanyload. power supplycurrentcapacitycombinedwithamplifiercircuitlimitationsdeterminesthemaximum supply voltagedeterminesthemaximumthatamplifiercandelivertoanyload,and current thattheamplifiercandelivertoload(powerisvoltstimesamps),amplifier’spower All amplifiershavelimitationstotheiroutput.Sinceoutputpowerisdeterminedbythevoltageand Amplifier OutputLimitations require 2.82voltsat0.35ampstodriveitwithaone-wattinput. require significantamountsofpowertomakethemoperate.Thus,an8-ohmloudspeakerwill Why isthisimportant?Onlybecauseloudspeakersarerelativelyinefficientdevices,andassuch, P=IE where:P=powerinwatts,Icurrentamperes(amps),andEelectromotiveforcevolts. current flowofonevoltandampere(amp),or10volts0.1ampere. as theproductofvoltagetimesamperage.Onewattisonewatt,regardlessifitresulta loudspeaker coneorheatupdummyloadresistors).Powerismeasuredinwatts,whichdefined power toitsload.Powerisameasureofenergy,whichtheabilitydowork(likemove What isaPowerAmplifier?Apoweramplifieronecapableofdeliveringsignificantamounts phones inyourstudio?We’lltrytoanswerthesequestions,andmore,thischapter. happens whenyoumono-bridgeanamplifier?DoreallyneedaBIGamplifiertorunhead- remain oneoftheleastunderstood.Whyisminimumloadimpedanceimportant?Whatreally Although poweramplifiersareoneofthebasicbuildingblocksanyaudiosystem,theystill C30I 9 34.35 4 295 DC-300AII 0110 2 1400 8001 Model combination ofknownandunknownvariables. I =currentinamperes,andPpowerwatts. Watts Minimum Load Output (Volts) 52.92 8.94 and theyare 420 Basics 26.45 8.59 2.23 Output (Amps) ), theload 7 420 8 copper litzwirehere(widersoundstage, glowsinthedark,out-of-this-worldhighend,$2x10 We’re notgoingtodebatethe prosandconsofdeuterium-enhanced,99.999+%purity saturnian A WordAboutWire connected inseriesdonotperformthesameasloudspeakers connectedinparallel For multiplespeakers,parallelconnectionispreferableto series connection.Loudspeakers greater (perchannel). multiple speakers(perchannel),ensurethatthecombined impedance ofallspeakersis4ohmsor Considering themodestoutputpowerof420,thereisn’t muchtosayhere.Ifyouaredriving Driving Loudspeakers anything else. ensure thatneitheroftheoutputconnectionscancomeincontactwithground,themselves,or loudspeakers andlivingthings.Ifyouoperateanyamplifierinmono-bridgedmode,takestepsto entire soundsystemtoimmediatelyoscillate,usuallyatfullpower,whichisnothealthyfor should comeincontactwithamicrophone(perhapsviaitsstand...)itisquitepossibleforthe (and lotsoffolksdo),theshellplug,whichisusuallygrounded,notgrounded.Ifplug stereo amplifier.ThismeansthatifyouuseTS(tip-sleeve)phoneplugsforspeakerconnectors Few usersrecognizethefactthatneithersideofloadisgroundedwhenyoumono-bridgea amplifier channelseeingtheequivalentofa4-ohmload. the loadimpedance.An8ohmload,connectedacrosstwoamplifierchannelsresultsineach As farastheamplifierisconcerned,eachchanneldrivesanequivalentloadequaltoone-halfof increases inproportiontothesquareofvoltage). would beiftheloadhadonesidegrounded,whichresultsinfourtimespower(since positively, theotherendswingsnegatively.Thus,voltageacrossloadistwicewhatit tions aloneandinvertingthepolarityofoneamplifierchannelcausesendloadtoswing are driveninthesamedirection;thereisnovoltage connecting theloadacrosstwooutputchannelsdoesn’tworkbecausebothendsof the loadisgrounded)increasesvoltagedevelopedacrossload.Parallelinginputsand Using twoamplifierchannelstodrivebothsidesoftheloadsimultaneously(usually,oneside power intotwicetheimpedance. either fourtimesthepowerofasinglechannelintosameimpedanceortwicesingle-channel Bridging requirestwoamplifierchannelsandformanyamplifiers(butnotthe420)translatesinto Mono-bridged operationisacommonmethodofincreasingthepowerdeliveredtoload. Mono-Bridged Operation mono-bridged mode The minimumloadimpedanceofthe420is4ohmsinstereoordual-monomodeand8 A goodrule-of-thumbisDON’Toperateanyamplifierbelowitsratedminimumloadimpedance. nothing (iftheamplifieriswellprotectedand/orextremelyunderrated)totriggeringsmokealarms. Operating asolid-stateamplifierbelowitsratedminimumloadimpedancecandoanythingfrom minimum loadimpedanceisjustanotherwayofstatinganamplifier’smaximumcurrentoutput. sponds to2.5amps.At0.5ohms,800watts(20Vintoohms)corresponds40amps!The limiting factoristhemaximumcurrentthatamplifiercandeliver.At8ohms,50wattscorre- deliver 800wattsintoa0.5-ohmload.Obviously,youcan’tdothistomost(99%)amplifiers.The volts intoanyloadimpedancewoulddeliver50wattsan8ohmload.Thissameamplifier maximum poweroutput.Takingthistoitsillogicalconclusion,anamplifiercapableofdelivering20 Even foratwenty wattamplifier,yourspeaker wireshouldbereasonably large. Ataminimum,18- meter). Instead,howaboutone paragraph’sworthofcommonsense? 420if youmust,butonlymust. . across theload.Leavingoutputconnec- 1 6 . Doit per loudspeaker’s impedanceisanythingbutresistiveonlycomplicates matters. source impedance,ineffectthedampingfactorseenbyeach speakerisunity.Thefactthata other speakerasitssourceimpedance.Sincedampingfactor istheloadimpedancedividedby has nobearingoreffectontheamplifier’smaximumoutput capability. The settingofanamplifier’sgaincontrolaffectsonlytheamplification factoroftheamplifierand control, aslong ity oftheamplifier.Themaximumpossibleoutputlevelissame,regardlesssetting ity oftheamplifier.Thegaincontrolreducesamplifierorinputsensitiv- This destroysthemyththatreducinggainsettingsomehowreducespoweroutputcapabil- duced viathegaincontrol,canbeovercomebyincreasinginputsignalsameamount. Note thephrase,“Givenaconstantinputsignal.”Thismeansthatgivenamountofloss,intro- signal level,whichamountstochangingtheoutputpower,changesvolume(yes!). Given aconstantinputsignal,varyingthislossvariestheoverallgain,whichoutput signal path. record, thegaincontrolonanamplifierinsertsadjustableamountofloss(attenuation)into The gain/volumecontrolsfoundonamplifiersareanotherobjectofmisunderstanding.Forthe The GreatGainControlMystery to bedrivenfroman8-ohmoutputthatnormallydrivesloudspeakers.” what theyreallymeanis“suitablefor8-ohmoutputs,”or“theseheadphonesaresensitiveenough Now youshouldrealizethatalthoughmostofthese‘phonessay“8ohms”somewhereoranother, many headphones(thatarepopularinstudios)thein-betweenregion. 600 ohmsorhigher,andlowimpedanceisdefinedas200lower.Fortunately,therearen’t impedance andlowimpedance.Forthepurposesofthisdiscussion,highisdefinedas delivered totheheadphones.Therearetwofundamentallydifferenttypesofheadphones:high Usually, whatmostfolkswantisLOUD.ThewayyougetLOUDtoincreasetheamountofpower headphones beforeyoubuythem. To betrulysuccessful(withoutanunlimitedbudget),youneedtoconsiderthesensitivityofyour The scientificmethodstartswithavolumerequirement,andworksbackwardtowardstheamplifier. amplifier. Repeataslongthereismoney. science. Themoneymethodissimple:buyabigamplifier.Ifitisn’tloudenough,bigger Driving headphonesisnogreatfeat.Gettingthemloudcanbeaccomplishedtwoways:moneyand Driving Headphones more importantthewiresizebecomes. copper), sheerphysicalsizeisthewaytofly.Remember:longerlengthofspeakerwire, to minimizethewireresistance.Asidefromusingsilver(whichhashigherconductivitythan want. Thebiggestsinglethingyoucandoforyourloudspeakerswhenpickacablethemis gauge zipcordworksjustfine.Ifyoucan,14-gaugewireisevenbetter.Usegodzilla-cableif 1 When twoloudspeakersareconnectedinseries,eachspeaker “sees”theimpedanceof some signalgetsthrough. 9 420 Using the420 Themono-bridgemodeswitchislocatedinternally (refertoAppendixA). • 10 operation. In S D modes differasfollows: The 420hasseveraldifferentoperatingmodesallowingchangesinhowthe G Operating Modes Connectors Electrical Onerackspace (1.75inches)required,12.5inchesdepth(includingconnector Mechanical Installation Requirements (1.75 inches). the ventholesinamplifier’stopandbottomclearofobstructionsbyatleastonerack-space allow breathingspacebetweeneachamplifier.Singleamplifierinstallationsshouldstrivetokeep The 420maybeinstalledfreestandingorrackmounted.Multipleamplifierinstallationsshould Installation Thefront-panelMONOswitchisaheadofthe two G TheS • TheTRSandXLRconnectorsareparalleledwitheach other. • Thebalancedinputamplifiersareaheadofthe G • • note ofthefollowing: On thefollowingpageyoucanfindblockdiagramfor420.Pleasetakeamomentand Block Diagram you startoutbyusingtheprocedurefoundin“FastSetup.” This sectionisintendedformoreadvancedusers.Ifyouareafirst-timeuser,werecommendthat Todriveboth amplifierchannels withthesameinputsignal. Tomono-sum twounrelatedsignals (likepagingandmusic). • Tomono-sumastereoinput signaltocheckformonocompatibility. • • You canusethemono/stereo switchthreeways: jacks (itspositionhasnoeffect onsignalsatthejacks). the outputleveloftheirrespective G determined bytheinputsignallevels(nottwogaincontrols). Thetwo input channelsaremixedandthemixroutedtobothchannels. Theproportionsofthemixare The M Mono andStereo I 420 The gaincontrolsmaybeoperatedtwodifferentways:D Gain ControlOptions mono operation,andmono-bridgedoperation. NDEPENDENT UAL T ONO RACKING PEAKER /S TEREO TEREO M and C The gainofeachamplifierchanneliscontrolledindependently bytheC C The gainofbothamplifierchannelsiscontrolledsimultaneouslybythe connectors arealsoprovided.TheXLRandTRSparalleled. XLR-3 femaleforinputs.Pin2oftheXLRconnectorsis“Hot.”TRS 230V ACnominal,50Hz,100Wattsmaximum. 117V ACnominal,60Hz,100Wattsmaximum. least oneemptyrack-spaceaboveandbelowtheunitforventilation. allowance). Rearchassissupportrecommendedforroadapplications.Allowat M HANNEL UTE mode,the420operatesastwoindependentamplifiers.In mono mode,thetwo ODE switchdoesnotaffectthefront-panel S HANNEL switch,locatedonthefrontpanel,selectsbetweenmono andstereo 1G AIN 2G control. outputs AIN controls. . The M . The ONO AIN /S controls. TEREO AIN UAL controls. T switchisisolatedfromtheinput RACKING TEREO H andI EADPHONES AIN NDEPENDENT AIN controlsdetermine Chapter 6 controls operate, jack. . These HANNEL 1 CLIP
CHANNEL 1 PRESS GAIN
INPUT 1 BALANCED OFFSET NULL SPEAKER SERVO MUTE (SHOWN MUTED) CHANNEL 1 + OUTPUT CHANNEL 1 INPUT 1 - OUTPUT UNBALANCED/ BALANCED MODE CHANNEL 2 SWITCH OFFSET NULL - OUTPUT (SHOWN STEREO) SERVO CHANNEL 2 + OUTPUT GAIN CONTROLS (4 ohms MINIMUM) DUAL TRACKING CLIP
CHANNEL 2 GAIN INDEPENDENT PRESS 100 ohms STEREO INPUT 2 HEADPHONES BALANCED TIP=CHANNEL 1 RING=CHANNEL 2 100 ohms MONO BRIDGE SWITCH INTERNAL ON PCB (SHOWN AS STEREO)
INPUT 2 UNBALANCED/ BALANCED REV-B
Figure 6-1. Overall block diagram 11 420 12 S functional. Ifyouconnectapairofheadphonestothefrontpanel connection (connectittotheplussideofspeaker).Only C output terminals.Thechannel1plusterminalisthein-phaseornon-inverting In mono-bridgemode,usetheC be removedtoaltertheswitchsetting.ReferAppendixAforsettinginstructions. To avoidinadvertentoperation,themono-bridgeswitchislocatedinternally;topcovermust Anyconnectors usedbetweentheamplifierandspeaker(s)shouldbeinsulatedsothat • Bothsides oftheload(loudspeaker)aredriven.Thereisno“ground”asfar • a single8ohmload.Someimportantthingstoremember: As describedinChapter5,mono-bridgemodeusesbothamplifierchannelstodeliver40wattsinto Mono-Bridge Mode 420 8 ohms. In mono-bridgemode,the420delivers40wattsintoan8ohmload.Theminimumloadimpedanceis will receiveout-of-phasesignals(notharmfultoanythingexceptphaseorpolarityfanatics). together whentheplugisinsertedorwithdrawn). design oftheplugexposesbothconductorsandtwoaremomentarilyshorted other conductor.Ordinaryphoneplugsareespeciallyproblematicinthisapplication(sincethe neither sideoftheconnectorcanaccidentallycontactground,otherconductor,orany loudspeaker isconcerned. HANNEL 1I NPUT , and connect thespeakeracrosstwoplus(+) HANNEL TEREO 1G H EADPHONES AIN control is control jack, they jack, nature oftheline itself,andwhetherornotthere aretransformersorrepeatcoils involved. be necessarytobuild-outtheoutput impedanceoftheunitatsendingend.Thisdepends onthe connections. Attheotherendof theline,youmayneedtoterminatelinewitharesistor. Itmayalso two plusoutputconnections.Tie thegroundfrombalancedlinetoeitherofminusoutput For drivinglonglines,puttheunit intobridgedmonomode.Drivetheline(balanced,ofcourse) fromthe on theremainder. tions thisway,eachtoalevelofapproximately+23.5dBm. Shortinganyoneoutputhasnoeffect Ensure thattheunitisoperatinginbridgedmonomode.You candrive37isolatedoutputconnec- Figure 7-1.Distributionamplifierwiring load. Fordistributionamplifierapplications,refertoFigure7-1. 420 performswell.Inbridgedmonomode,thedeliversatleast+27dBmintoa600ohmbalanced In applicationsrequiringdrivingextremelylonglines,oranlargenumberofoutputs,the No FoolingDistributionAmplifier blood. Use the420todriveboothmonitors,orensurethatheadphonesareloudenoughdraw Broadcast system orsimultaneoustranslationsystem. operate highly-dividedzonepagingsystems.Inachurch,the420candrivewiredhard-of-hearing In commercialsoundinstallations,usethe420tooperatealocalsystemmonitorspeaker,or Commercial Sound (see below). except inverysmallstudios.Youcanalsousethe420todriveyourheadphonedistributionsystem reference speakers.The420probablyisn’tpowerfulenoughtodrivemostnear-fieldmonitors This isprobablytheprimaryusefor420.UseittodriveAuratonesorsmallhome-stereo Recording Studios Here areafewapplicationsthatthe420lendsitselfto. Chapter 7 Applications REV-B 13 420 14 420Figure 7-2.Asimpleheadphonedistributionbox (you’re welcometoaddmore)andinterconnectstheheadphonesystemusingmiccables. boxes sprinkledhitherandyonthroughoutthestudio.Eachboxhasfourheadphonejacksonit Figure 7-2showsatypicaldistributionbox.Instudio,theremightbefourorfiveofthese orchestras orotherlargegroupslive,usingonemix. minimum loadimpedance.Thisprobablyisn’ttooseriousalimitationunlessyouareintorecording impedance guys)onyourheadphoneamplifierbecausesoonerorlateryouarriveattheamp’s Although thelowimpedancephonesgenerallygetlouder,youcan’thangasmany(ashigh Ifyouhavehighimpedancephones,thenneedvoltagecapabilitytomakethemloud. 2. Ifyouhavelowimpedancephones,thenneedhighcurrentcapabilitytomakethemloud. 1. involved inmakingaloudheadphonesystem: The 420isideallysuitedtoheadphonedistributionsystems.Therearetwobasicstrategies Headphone DistributionSystems This translatestoamoderate8ohmpowerrating,like100watts. This translatestoamodest8ohmpowerrating,like20watts. MDR-7506 HD424 Pro 4X K240 Headphones beyond thescopeofthis(short)discussion. You canaddvolumecontrolsandchannelswitchingtotheboxifyouwant,butthosedetailsare impedance. Thetablebelowlistsmaximumquantitiesfortheheadphonesshown. can bedrivenatoncedependsontheheadphoneimpedanceandamplifier’sminimumload the impedanceofheadphonesfoundinyourstudio.Themaximumnumberthat (which occurwheneveryoupluginorunplugasetofphones).Picktheresistorvalueaccordingto and (mostimportantly)protecttheamplifierfromshortedcableschannel-to-channelshorts The resistorsshowninFigure7-2isolatethejacksfromeachother,protectphonessomewhat, Figure 7-3.Amplifierconnectionsforheadphonedistributionsystem remains isolatedfromthesystemground(exceptvia420). connectors aresimplywiredinparallel.Takespecialpainstoensurethatpin1ofthe amplifiers, too).Figure7-3showstheconnectionsneededatamplifierend.Noticethatall connections momentarilyastheyarematedorunmated.Thiscanbeharmfultothe420(mostother the averagestudiothananythingelse.TRSplugsorstereophoneshorttheirtipandring We usemiccablesforthisapplicationbecausethereareusuallymorehangingaround 1141 137 121 138 125 10 212 20 87 134 118 Max SPL 135 122 Maximum # 8Ohmtotalload 21 525 8Ohmtotalload 41 Max SPL 4Ohmtotalload 175 4 Ohmtotalload Maximum # RIGHT(+) LEFT(+) COMMON(-) 321 3 21 AS REQUIRED CONNECTIONS ADDITIONAL RIGHT(+) LEFT(+) REV-A COMMON(-) 15 420 16 420impedance ofthedrivingdevice. so, thentheinputimpedance ofthesucceedinginputmustbeequaltoorgreaterthan the output from modernequipmentthat requires power(batteriesorAC)isaninstanceofthistype ofrating.If their geartosee.Inmostcases, seeingaoutputimpedancefigureof10,000(10K)ohms orhigher equipment. Whattheyreallymeanisthatthistheminimum loadimpedancethattheywouldlike Some manufacturersstatearelativelyhigh-impedancefigure astheoutputimpedanceoftheir the devicethatdrivesit. Always makesurethatadevice’sinputimpedanceishigher thantheoutputsourceimpedanceof following way: The impedancerelationbetweenoutputsandinputsneeds tobeconsidered,butonlyinthe sources. Guitars, high-impedancemicrophones,andmanyelectronic keyboardsdonotqualifyasline-level mately -70to-20dBm.Lineinputsshouldonlyseesignals inthe-10to+24dBm/dBurange. box, oranoutputdesignatedmicrophone-leveloutput.Electrically, thisisintherangeofapproxi- ratio. Thus,microphoneinputsshouldonlyseesignalsoriginatingfromamicrophone,direct(DI) Signal levelisveryimportant.Mismatchcauseseitherlossofheadroomorsignal-to-noise between anoutput(signalsource)andtheinputthatitconnectstoreceiver). So, whatisreallyimportant?Signallevel,and(toamuchlesserdegree),theimpedancerelation impedance (orhigh-impedance).Thesameappliesto1/4-inchjacks. presence of3-pinXLRconnectorsshouldnotbeconstruedtomeanthattheinputoroutputislow- are sometimesusedforloudspeakers,whichanythingbuthigh-impedance.Therefore,the ance andunbalanced),thisdoesnotpredisposethemtoonlyusage.Afterall,1/4-inchjacks Similarly, although1/4-inchjacksaretypicallyusedforthingslikeguitars(whichhigh-imped- not necessarilyhigh-impedanceandbalancedsignals/linesarelow-impedance. worse thattheyareassociatedwithaparticulartypeofconnector.Notso.Unbalancedsignals Some folksseemtobelievethatbalanced/unbalancedlinesandimpedancesarerelated;oreven RFsystemsarematchedbecausewereallyconcernedwithmaximumpowertransferand • Poweramplifiersarefussybecauseanabnormallylowloadimpedancegenerallymeansavisit • Ancientaudiosystemsoperateat600ohms(or someotherimpedancevalue),andmustbe • but undesirableaswell. systems arevoltagetransmissionandsourceloadmatchingisnotonlyunnecessary, power transfer,whichreachesamaximumwhensourceandloadarematched.Modernaudio only forancientaudiosystems,poweramplifiers,andRF.Technicallyspeaking,thereasonis Over theyears,wehaveallhadimpedancematchingpoundedintoourheads.Thisisimportant fully) clarifyyourunderstandingofthesubject. digging aholeanydeeperthanabsolutelynecessary,weofferthefollowingdiscussionto(hope- In anyaudioequipmentapplication,thequestionof“matching”inevitablycomesup.Without Matching LevelsvsImpedances This sectiondiscussesamultitudeofthings,allrelatedtogettingsignalsinandoutthe420. Technical Tutorial Video signals(composite,baseband,orotherwise)shouldbetreatedlikeRF. with matchingtheimpedanceoftransmissionline(keepsnastythingsfromhappening). speakers connectedtotheamplifierreallyis. to theamphospital.Thus,it’simportantknowwhattotalimpedanceofpile power transfer,hencetheneedforinput/outputmatching. about matching.Theseunitsweredesignedwhenaudiosystemsbasedonmaximum equipment thatusesvacuumtubes,orwasdesignedpriorto1970,youshouldbeconcerned matched, bothattheirinputsandoutputs.Generallyspeaking,ifyouaredealingwith Chapter 8 connection. At the420,high/pluswireconnects topin2,thelow/minus wireconnectstopin3, shield, theseconnecttothesource’s ground;connectthehigh/plussidetosource’s signal tors plustheshield)from sourcetothe420.Atsource,connectlow/minusside tothe To operatethe420fromunbalanced sources,runa2-conductorshieldedcable(that’stwo conduc- anced sources. Figure 8-1(onthenextpage) illustrateshowtoconnectthe420variousbalancedand unbal- Input andOutputConnections output onaphonejack). especially whengoinginandcomingoutthroughdifferent connectortypes(likeinputonanXLR, unimportant. Ifyoursystemisbothbalancedandunbalanced, thenyoumustpayattentiontothis, uses balancedinputsandoutputs,the420thisway,thenpolarityconventionis The 420usestheinternationalstandardpolarityconventionofpin2hot.Therefore,ifyoursystem Polarity Convention large (evenridiculous?)numberofloadssimultaneously. might beuseful,forinstance,ifyouneededano-foolingdistributionamplifiercapableofdriving no problemdrivinghigh-impedanceloads;(the420candrivea600-ohmloadto+27dBm.This ance is4ohmsinstereo/dual-channelmodeand8mono-bridgedmode.Ofcourse,there The 420’soutputisintendedtodriveloudspeakerorheadphoneloads.minimumloadimped- aforementioned impedances. driven fromanysource(balancedorunbalanced)capableofdeliveringatleast-10dBuintothe The 420’sinputimpedanceis10kilohmsbalanced,andunbalanced.inputsmaybe Modernbridgingsystemswhereinputsbridgeandoutputsarelowsourceimpedances Unbalancedsemiprofessionalequipmentapplications. • 600-ohmsystemswhereinputandoutputimpedancesarematched. • • tion. Thisincludes: The 420isdesignedtointerfaceintoalmostanyrecordingstudioorsoundreinforcementapplica- I/O Impedances in semiproormusical-instrument(MI)equipment(-10dBu300millivolts). less thanwideopen.Theunitisquietenoughtooperateatlowersignallevelssuchasthosefound tivity ishighenoughthatthe420canbedriventofulloutputwithinputgaincontrolsset The 420isdesignedaroundstudio/professionallinelevels:+4dBuor1.23volts.inputsensi- Signal Levels Foraudio,impedancematchingisonlyneededforantiqueequipmentandpoweramplifier 2. Matchsignallevelsforbestheadroomandsignal-to-noiseratio. 1. The twofactsthatyouneedtoderivefromthisdiscussionare: drive 4-ohmorhigherimpedances,typicallyloudspeakersheadphones. (that is,begreaterthan10timestheactualsourceimpedance).The420’soutputsareintendedto Symetrix equipmentinputsaredesignedtobridgetheoutputofwhateverdevicedrivesinput (voltage transmissionsystems). times theoutputsourceimpedance)yourlineoutputs. outputs. Inallothercases,ensurethatyourlineinputsbridge(areintherangeof2to200 i leeGround Signal Tip Sleeve Pin 3 1/4"Phone Pin 2 Pin 1 XLR igLow Ring High 17 420 18 match itupwith thedestinationconnectorin rightcolumn.Wireyourcableaccording tothediagrams. in modernaudioequipmentatline ormicrophonelevel.Locatethesourceconnectorinleftcolumn and 420Figure 8-1.Inputandoutputconnector wiring.Thesediagramsrepresentthemajorityofconnectors used connections. Itwillworkbetter. you aredrivingaheadphonesystem(multiplepairsof‘phones),thenusetherearpanelscrew only forheadphones(plugginginaloudspeakerwon’thurtanything,itjustbeveryloud).If phones. Thetipconnectstochannel1andthering2.Thisjackisintended The 1/4inchoutputjackonthefrontpanelisaTRS(tip-ring-sleeve)wiredforstereohead- moved. prevent shortingtheamplifieroutputstogetherwhenheadphoneplugsareinsertedorre- channel (oneinserieswiththeleftchannel,onerightchannel).Theresistors system, ensurethateachheadphonejackhas(atleast)a22-ohm,5-wattresistorinserieswith dual-mono modeand8-ohmsinmonobridgemode.Ifyouaredrivingaheadphonedistribution speakers orheadphonedistributionsystems.Theminimumloadimpedanceis4-ohmsinstereo/ The rear-paneloutputterminals(accept#6spadelugsorbarewires)areintendedtodriveloud- difference betweeneithermethod. works, butismoresusceptibletohumandbuzzthanthepreferredmethod.Therenolevel Figure 8-1convertsthe420’sbalancedinputintoanunbalancedatconnector.This 420’s balancedinput(eventhoughthesourceisunbalanced).Theotheralternativeshownin and theshield(always)connectstopin1.Thisispreferredmethodasitmakesbestuseof PIN 1=GROUND+LOW SLEEVE =GROUND+ RMNNTASOMR(ELECTRONIC) NON-TRANSFORMER FROM SLEEVE =GROUND PIN 3=NOTUSED PIN 1=GROUND TPCLO YERXPRODUCTS) (TYPICAL OFSYMETRIX MALE TRSPLUG TERMINAL STRIP TERMINAL STRIP (-) =NOTUSED MALE TSPLUG PIN 2=HIGH PIN 2=HIGH RING =LOW PIN 3=LOW FEMALE XLR FEMALE XLR FROM UNBALANCEDOUT FROM UNBALANCEDOUT = GROUND = GROUND (+) =HIGH (+) =HIGH TIP =HIGH TIP =HIGH FROM BALANCEDOUT FROM BALANCEDOUT FROM BALANCEDOUT (-) =LOW BALANCED OUTPUT
LOW
1 3 2 1 3 2 RING TIP SLEEVE SLEEVE RING FLOATING BALANCEDOUTPUT RNFRE COUPLEDOR TRANSFORMER TIP TO UNBALANCEDINFROM TO UNBALANCEDIN TO BALANCEDIN TO BALANCEDIN 1 3 2 TO BALANCEDIN SLEEVE =GROUND RING =LOW TIP =HIGH MALE TRSPLUG SLEEVE =GROUND+ TIP =HIGH MALE TSPLUG (-) =LOW (+) =HIGH TERMINAL STRIP SLEEVE =GROUND+ TIP =HIGH MALE TSPLUG = GROUND PIN 3=LOW PIN 2=HIGH PIN 1=GROUND MALE XLR REV-B LOW LOW No outputinbridgemono lw ue Arethespeakerconnectionsshorted? Checkinputsignallevels,andlevelcontrolsettings. Blows fuses (hiss) Noise Checkinputsignal. Isittoohot,orisalreadydistorted? Distortion Checkinputconnectorwiring(refertoFigure8-1). Monobridgeswitchengaged. output in buzz or Hum out-of-phase Outputs Checkcablesandconnections. output No SYMPTOM Troubleshooting Chart Chapter 9 1 current limiting circuitry. The clipLEDsdonotindicate clippingcausedbytheactivationofamplifier’sinternal Are youusingtheC Is thefuseOK? Check outputbypluggingheadphonesintofront-panelheadphonejack. Check forACpowerpresence.PowerLEDon? S the fuseblowsimmediately,callfactory. Disconnect speakers,disconnectinputs,replacefuse,turn uniton.If Is theinputsignalalreadynoisy? Check gainsettingsonupstreamequipment. Is somethingelseclipping? mode or8ohmsinmono-bridgemode. Check outputloading.Shouldbeabove4ohmsinstereo/2-channel Are the C loss intheinputgaincontrols)? source becauseitdoesn’thaveenoughoutputleveltoovercomethe Are theinputgaincontrolsturneddowntoofar(causingclippingin Is thehumorbuzzcomingoutofprecedingunit? components onthe Ground loop.Checkrelatedsystemequipmentgrounding.Areall Is thefront-panel S Are theloudspeakersorheadphonesOK? Is theresignalcomingoutofthesource? Are allofthecablesgood? headphones? Are inputsdrivenbyoutputs,andoutputsdrivingspeakersor PROBABLE CAUSE PEAKER M LIP UTE LEDsindicatingclipping switchout? PEAKER same HANNEL ACground? M 1I UTE NPUTS switchout? ? 1 ? Troubleshooting 19 420 20 The unitshallbeaSymetrixIncorporated model420StereoAmplifier. 120V nominalAC(108to132V)60Hz. The amplifiershallbecapableofoperatingbymeansits ownbuilt-inpowersupplyconnectedto Independent clippingindicatorsshallbeprovidedforeach outputchannel. controls. panel switchshallbeprovidedtosumthetwoinputsignals androutethemtothetwogain front panelswitchshallbeprovidedtomutetherear outputconnections.Anotherfront There shallbea¼"tip-ring-sleevejackmountedonthefront panelforstereoheadphoneoutput.A switch shallallowtheChannel1gaincontroltosimultaneously controlthelevelofbothchannels. The poweramplifiershallbeprotectedfromoutputshort-circuits. AfrontpanelDualTracking greater than95dB.Frequencyresponseshallbe20HztokHz(+0dB,-1dB). THD shallnotbegreaterthan0.04%,@1kHz,wattin8Ohms.Signaltonoiseratio amplifier outputs. shall accommodate+24dBusignalswithoutdistortion.Screwterminalsbeprovidedforpower wiring), and¼"TRSfemale.TheinputcircuitryshallincorporateRFIfilters.balancedinputs The inputsshallbeactivebalancedbridgingdesignsterminatedwith3-pinXLR(AES/IECstandard unit shallalsohaveamono-bridgemodewhichdelivers40wattsintominimumloadof8Ohms. The unitshallbecapableofdelivering20wattsperchannelintoaminimumload4Ohms. It shalloccupyasinglerackspace.(1U) The poweramplifiershallbeacompact,twoinput,output,highperformance,amplifier. Oneperchannel 420 ArchitectsandEngineersSpecifications Indicators Clip 420 Specifications Specifications iiu od4Ohms,stereomode; 100-Ohmsourceimpedance, dBu +21 20 watts RMS, Output Headphone Load Minimum 40wattsRMSintoan8-Ohmload bridged) (mono Output Maximum Maximum Output(stereo/2-channel) Maximum InputLevel Outputs nusInputs Input/Output 420 dB >95 dB 27 >60dB(22kHzbandwidth) <0.04%,@1kHz,wattinto8Ohms 0dBufor20wattsintoan8-Ohmload 20HztokHz(+0,-1dB) THD+Noise Distortion Typical Signal toNoise Maximum Gain Sensitivity Crosstalk Frequency Response (measured at120VAClinevoltage) Performance Data Two, 4Ohmsminimumimpedance,#6screwterminals <0.2%, 20HztokHz,@wattsinto8Ohms BalancedCMRRgreaterthan55dB@1kHz 10 kilohmsLine-LevelBalancedBridging XLR-Female ParalleledwithTRS¼"jacks per channel,intoa4-or8-Ohmload 19V opencircuitwithspeakersoff 8 Ohms,monobridgedmode Size x197.25inches,4.3748.2618.415centimeters (hwd)1.72 Physical In the interest of continuous product improvement, Symetrix, Inc. Symetrix, improvement, product continuous of interest the In 120Vnominal,108to132VAC, Note: 7.6lbs(3.5kg)net,10(4.6kg)shipping Power Requirements Electrical Weight reserves the right to alter, change, or modify these specifications these modify or change, alter, to right the reserves without prior notice. prior without degrees C. The maximumoperatingambienttemperatureis25 Chapter 10 60 Hz,100watts removal ofproductsorsubstitute facilitiesorsupplyhouses. costs andexpensesincurred inconnectionwithlabor,overhead,transportation,installation or revenue, costofcapital,claims ofcustomersforserviceinterruptionsorfailuretosupply, and any incidentalorconsequentialdamagesincludingbut not limitedtodamageforlossof product oranypartthereofwhichgivesrisetotheclaim. InnoeventwillSymetrixbeliablefor resale, repair,replacementoruseofanyproductwillnot exceedthepriceallocableto otherwise arisingoutof,connectedwith,orresultingfrom themanufacture,sale,delivery, The totalliabilityofSymetrixonanyclaim,whetherincontract, tort(includingnegligence)or Limitation ofLiability by applicablelaw. This limitedwarrantygivesthebuyercertainrights.Youmayhaveadditionalrightsprovided information onbehalfofSymetrix. assume anyliabilityormakeadditionalwarrantiesrepresentationregardingthisproduct Symetrix doesnotauthorizeanythirdparty,includingdealerorsalesrepresentative,to date ofpurchase. Warranty RegistrationmustbecompletedandmailedtoSymetrixwithinthirty(30)daysofthe period. to theoriginalpurchaserandanyonewhopurchasesproductwithinspecifiedwarranty This limitedwarranty,withallterms,conditionsanddisclaimerssetforthherein,shallextend purpose. ties, includingbutnotlimitedtowarrantiesofmerchantabilityandfitnessforaparticular ers forpersonal,family,orhouseholduse,Symetrix systems andisnotintendedforotherusage.Withrespecttoproductspurchasedbyconsum- This Symetrixproductisdesignedandmanufacturedforuseinprofessionalstudioaudio buyer's remedieshereunderareSOLELYandexclusivelyasstatedherein. fitness foraparticularpurposeormerchantability.Symetrix'swarrantyobligationand implied orstatutory.Symetrix,Inc.expresslydisclaimsanyIMPLIEDwarranties,including The foregoingwarrantiesareinlieuofallotherwarranties,whetheroral,written,express, freight collect. airfreight atBuyer'sexpense.OutsidetheContinentalUnitedStates,productswillbereturned within theContinentalUnitedStates.AtBuyer'srequestshipmentmaybereturnedvia will bereturnedfreightprepaidbySymetrixviaUnitedParcelService(surface),toanylocation determination ofwarrantycoverageliessolelywithSymetrix.Productsrepairedunder proof oftheoriginaldatepurchase(datedcopyretaildealer'sinvoice).Final warranty claimbeforerepairorreplacementiscarriedout.Symetrixmay,atitsoption,require factory. Symetrixreservestherighttoinspectanyproductswhichmaybesubjectof from Symetrix.BuyerwillprepayallfreightchargestoreturntheproductSymetrix may bereturnedbyBuyeronlyafteraReturnAuthorizationnumber(RA)hasbeenobtained gives Symetrixpromptnoticeofanydefectorfailureandsatisfactoryproofthereof.Products material orworkmanshipwithinone(1)yearfromdateofpurchase,providedthattheBuyer replacing, atSymetrix'soption,thepartorpartsofproductwhichprovedefectivein ship forone(1)year.Symetrix'sobligationsunderthiswarrantywillbelimitedtorepairingor Symetrix, Inc.expresslywarrantsthattheproduct 420 LimitedWarranty Chapter 11 will befreefromdefectsinmaterialandworkman- expressly disclaimsallimpliedwarran- Warranty &Service 21 420 22 420sending theunittoSymetrix. materials, andfreightcharges.Pleaseremember,youmust callforanRAnumberbefore If thewarrantyperiodhaspassed,you'llbebilledforall necessaryparts,labor,packaging Out-of-Warranty Repairs Visa orMastercard). the returnfreight.AllchargeswillbeCODunlessyouhavemadeotherarrangements(prepaid, for bothpartsandlabor.Inanyevent,iftherearechargestherepaircosts,youwillpay to chargeyou.Ofcourse,iftheproblemturnsoutbeoperatorinflicted,you'llhavepay bent ears).Wewon'treturntheunitinanythingbutSymetrixpackagingforwhichwewillhave the cartontoprotectrackears(youwouldn'tbelievehowmanyunitsarereturnedwith with bubble-wrap.PacktheboxfullofStyrofoampeanuts.Besurethereisenoughclearancein yourself afavorbyusinganoversizecarton,wraptheunitinplasticbag,andsurroundit you forpropershippingmaterials.Ifdon'thavethefactorypackagingmaterials,thendo If youchoosetosendusyourproductinsomesortofflimsypackaging,we'llhavecharge charges. We'llprepaythereturn(surface)freight. Just dothesefivethings,andrepairsmadein-warrantywillcostyouonlyone-wayfreight To getyour420repairedunderthetermsofwarranty: In-Warranty Repairs 8AM (800hours)though4:30PM(1630hours),PacificTime. authorization (RA)number.Thetelephonenumberis(425)778-7728,MondaythroughFriday, Before sendinganythingtoSymetrix product ithasmanufacturedforaperiodoffiveyearsfromdatemanufacture. At theSymetrixfactory,willperformin-warrantyorout-of-warrantyserviceonany to obtainservice.IfyouresideintheU.S.thenproceedasfollows: United StatespleasecontactyourlocalSymetrixdealerordistributorforinstructionsonhow If youhavedeterminedthatyour420requiresrepairservicesandlive Servicing the420 .ShiptheunittoSymetrix, WritetheRAnumberonoutsideofbox. 5. 4. Includeyourname,address,daytimetelephonenumber,andabrief Packtheunitinitsoriginalpackagingmaterials. 3. CallusforanRAnumber. 2. 1. We do statement oftheproblem. not acceptfreightcollect , contactourCustomerServiceDepartmentforareturn freight prepaid.
shipments . outside of the of .Replacethetopcover andallfastenerspreviouslyremoved. 5. Depressthe switchplungertoselectmono-bridgemode(plunger remainsIN).Forstereomode, 4. Locatetheswitch,whichissituatednearinputconnectors. 3. Removethe topcoverusingthepreviouslydescribedprocedure. 2. Disconnectthe420fromAC powersource. 1. or resettheswitch,usefollowingprocedure. To preventinadvertentsetting,thebridged-monomodeswitch islocatedinsideofthe420.Toset Bridged-Mono ModeSwitch Liftoutbothprintedcircuitboards,takingcarenottostressthetwovoltageregulators orthe 11. Removetwoscrewslocatedonthechassisbottomthatsecureheatsink. 10. Disconnectthegreensafetygroundwireatchassisscrewterminalbyremovingnut. 9. Removetwo6-32SEMSscrewsthatfastenthepowersupplyPCBtochassis. 8. Removethetwo6-32x1/2inchmachinescrewsthatfastenIECconnectortochassis. 7. Removefour6-32x1/4inchSEMSmachinescrewsfromthemainprintedcircuitboard. 6. Removetheknobsfromfrontpanel.panelandsetitaside. 5. Removeonescrewfromeachofthefourcornersfrontpanelandin 4. Unplugthetwotransformerconnectors(oneforeachprintedcircuitboard). 3. Removethetopcoverusingproceduredescribedpreviously. 2. Ensurethatthe420isdisconnectedfromACpowersource. 1. Circuit BoardRemoval Slidethetopcover1inchtowardsrearofunit,thenliftfree 6. Removetwo6-32flat-headscrewsfromthetopcover. 5. Removeone6-32x1/2inchscrewfromthetop-middleoffrontpanel.Usecautionto 4. Removetwo6-32x1/2inchscrewsfromeachsideofthechassis. 3. Removefour6-32x1/2inchscrewsfromtherear-panel. 2. Ensurethatthe420isdisconnectedfromACpowersource.Disconnectanyinputor 1. Top CoverRemoval Warning Caution Appendix A the switchplungershouldbe OUT. ribbon cablethatjoinsthetwocircuitboards. Ensure thatthiswireisreconnectedwhenreassemblingthe420. bottom-center ofthefrontpanel. chassis. prevent thescrewdriverfromslippingandmarringfrontpanel. speaker cables. unit disconnectedfromallACpower. Lethal voltagesarepresentinsidethechassis.Performallserviceworkwith Refer allservicingtoqualifiedservicepersonnel. operating instructionsportionofthismanualunlessyouarequalifiedtodoso. electric shockdonotperformanyservicingotherthanthatcontainedinthe These servicinginstructionsareforusebyqualifiedpersonnelonly.Toavoid
Disassembly Instructions&Bridged-MonoModeSwitch 23 420 24 420 Website: http://www.symetrixaudio.com Email: [email protected] Mountlake Terrace,WA,98043 Fax: (425)778-7727 Tel: (425)778-7728 6408 216thSt.SW Symetrix, Inc. USA