April2018

ProiDSD–TheFront

TechNotes

PROIDSD–THEEASYGOINGPERSPECTIVE

THEENCLOSUREANDFRONTPANELINTRODUCTIONOurlatestandgreatestDAC–theProiDSD–isjustaroundthecorner.We’vealreadytackledseveraltechnicalmattersrelatedtothisdevice,andallthesearetobefoundvialinksinthefirstpostofthisthread:

• https://www.head-fi.org/threads/ifi-audio-pro-idsd-the-official-thread.869144/

Inshort,we’veexplainedinourregularfashionwhythisproductisveryunique.Sincethere’sstill some time left to the official launch of our upcoming flagship DAC,we thoughtwe’ddescribe in a less techyandmoreeasygoing,newbie-friendlywaywhatourPro iDSD is allabout.Firststopistheenclosureandthefront.

THEPROIDSD–WHATISITEXACTLY?Thismachine, in short, is aDAC, also knownas a d/a converter andquite commonly as asource. This means that its main purpose is to receive a digital signal either via cable orwirelessly,convertittoitsanalogueformandthenpassitontodevicessuchasa

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preamplifier,astereopoweramplifier,apairofmonoamplifiers,aheadphoneamplifierordirectlytovariousheadphones.Yes,allthesedevicesoperateintheanaloguedomain,whichleadsusontothisstatement:

• TheProiDSDwon’tpassdigitalsignalstoadifferentDACandyes,thisisonpurpose

TheProiDSDwasprimarilybuiltasahighqualitydigitaltoanalogconverterandthisishowitshouldbeused.It’salreadyfunctionpackedasitisand-insteadofmakingitoperableasanS/PDIFconverter-ourgoalwastousethespacenormallyreservedforthisinamoreusefulway.Basically,usingtheProiDSDtofeedasimilardevicewithadigitalsignalisabigwasteofitspotential.

THEENCLOSURENow,wehaveallthatoutoftheway,let’sfocusontheProiDSD’senclosure.ThismachineisthesamesizeastheiFiaudioProiCANandbothproductslookverysimilar.Theenclosureismade out of aircraft grade aluminium and itsmain purpose is to dissipate heat from thedevicesinsideastheywillgethotwhenpoweredon.Inordertofurtherimproveonthis,thechassishasmanyventingholesonitssidesandontop.ThesealigninapleasantlyroundedshapewithamagnifyingglasswithapairoffabulousvintageJANGE5670valvesunderneath.(Quicknote–theseclassactvalvesarenowreservedONLYforourProseriesproductsbutthat’sanotherstory).Anyway,wereckonthattheProserieschassislooksverycool.

THEFRONTPANEL–LEDDIODEANDSTANDBY/POWERSWITCHLet’sstartwiththeupperleftcorner.There’stheiFiPrologobasedonaLEDdiode.OncethePro iDSD is poweredon, this lights upwithoneof four different colours. Each indicates adifferentoperationalstatus:

• Green:warmingup• White:solid-statemode• Orange:tubemode• Red:protectionmode

Movingon,there’sasmall,flatbuttoninthelowerleftcorner.Thisturnstheproductonorputsitinstandbymodeifyouarenotshuttingitdowncompletely.

THEFRONTPANEL–INPUTSELECTORLet’snowgoabittotheright.Alargeandendlesslyrotatingaluminiumknobisnextinline.Ithandlesseveraljobswithitsmainonebeingdigitalinputselection.Youcancyclethroughthefollowingoptions:

• Ethernet/WiFi/HardDisk/MicroSDHC(NetworkBridge/Streamer)• HostUSB• Coaxial/OpticalDigitalInput

April2018

ProiDSD–TheFront

TechNotes

• XLRDigitalInput• BNCDigitalInput

Therearealsotwoadditionaladjustmentoptionsavailableviatheinputselector:

• Brightness(adjustableviaathreesecondpress)• Polarity(adjustableviaalongpress)

THEFRONTPANEL–DIGITALFILTERSELECTORThesmallerknoblocatedabittotherightfromtheinputselectoristhedigitalfilterselector.Itenabletwothings.The first feature (available via pressing the digital filter selector) is our proprietary DSDremastering.Youcanchoosewhetheryou’dliketohaveyourmusic:

• Normal–whereDSDsignalsarepasseddirectlytotheDAC.ForPCMyoumaychoosebetweenasetofdigitalfiltersorbit-perfect,unprocessedPCM

• UpconvertedtoDSD512• UpconvertedtoDSD1024

Thesecondfeatureallowsyoutocyclethroughthesefivedifferentfiltersontheflyviatherotaryaction:

1. 'Bit-Perfect'-Nodigitalfilteringisapplied,onetap12. 'Bit-Perfect+'-Nodigitalfilteringisapplied,onetap,SINCroll-off@HFiscorrected23. 'MinimumPhase'-Minimumfiltering,nopre-ringing,minimumpostringing,32taps34. 'Apodising'-Modestfiltering,nopre-ringing,modestpostringing,128taps45. 'Transient Aligned' -Max filtering,max pre-ringing,maximum post-ringing, 16,384

taps5

Pleasethinkofthesefiltersasdifferentflavours.Eachtradesofffrequencyresponseflatness,transient response and suppression of ultrasonic images in a different way. There is no“perfect”filteroption,suchathingisnotpossible,soselectthefilterthatoffertherightsetofcompromisesforyou.

1) Bit-Perfect is equivalent towhathasbeen called “non-oversampling”, “zero-oversampling”, “filterless” etc. Thisoffers the best impulse response but loses high frequency extension. There is no pre- or post-ringing with animpulseandultrasonic imagesareminimallysuppressed.Thisfilterproducesasoundthat ishighlymusicalwithprecisebutsometimesalittlelimitedimagingandseemstoslightlylackdetailandair.

2) Bit-Perfect+ is AMR’s take on “non-oversampling” and uses a tailored analogue filter to correct the systemresponsesodetailandairarerestored.UntilnowthisoperationwasexclusivetoAMRproducts,theiDSDProis

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the first iFi product to include it. There is nopre-orpost-ringingwith an impulsebut a slight alterationof theimpulseshapeandultrasonic imagesareminimallysuppressed. Itproducesasoundthat isnatural,organicandwithaprecise,focusedsoundstageandthecorrectHFdetailandair.

3) Minimum Phase – Over the years a number of researchers and brands (Ayre’s Charles Hansen, the Luxman“Fluance”filtercometomind)havechampionedveryminimalisticfilterswithminimalringing.InmanywaysthesefiltersareanexcellentcompromisebetweenBitperfectsystemsandthosewithmorecomplexfiltersandhaveaverysimilarsoundcharacteristic.Thereisnopre-ringingandpost-ringingwithanimpulseisminimal,whilehigherorderultrasonicimagesaresuppressedtoagreaterdegreethanBitperfect.Thesoundproducedisquitenatural,organicandwithaprecise,focusedsoundstageandthecorrectHFdetailandair.

4) Apodising – Apodising Filters are relatively new and based on the work of acoustic researcher Peter Cravenpublished in 2004 and championed by Bob Stewart (ofMeridian&MQA) and aim to correct some of impulsedistortionduringrecording.Thisfilteralsoavoidspre-ringingbutintroducesmoreimpulsedistortioninanattemptto “override” the impulse response of the recoding system and suppresses all but the first ultrasonic imagestrongly.Thesoundproducedisfairlynatural,withaslightlyde-focusedandenlargedsoundstageandcorrectHFdetailandair.

5) TransientAligned–Thisfilterisbasedonthetheorythatifaninfinitenumberoftapsfilterwasusedtheresponseofthesystemwouldconformtoatheoretical,mathematical idearesponseandischampionedamongothersbyChord’s Rob Watts. This filter maximizes pre- and post-ringing on impulses – in fact the whole time domainresponseofthisfilterforCD-Audiotakesatotalof0.37seconds.Suppressionofultrasonicimagesismaximal.Thesoundproducedisdistinct,withanenlargedsoundstageandverysmoothhighfrequencies.

We’vealreadycovered indetailhowourproprietarydigital filteringworks inthePro iDSD.Pleasetakealookhere:

• https://www.head-fi.org/threads/ifi-audio-pro-idsd-discussion-thread.702376/page-127

What’simportantisthattheProiDSDisequippedwithaFPGAchipthatrunsoniFiaudio’scustom firmware and is responsible for all filters and remasters listed above. It’s worthnotingthatinthisDAC,theseoperationsarehardwarebased.

THEFRONTPANEL–OUTPUTSECTIONMODEOneofthemostuniquefeaturesofourProiCANisitscomplexoutputstagebasedonbothtransistorsANDvalves.We’vedevelopedittogiveyoutheultimateheadphoneamplifierandan exceptionally flexible product, which will work with headphones of every soundcharacteristicthereis.Ourgoalwastocreateamachinethatwouldbe‘liked’byeverypairofheadphones,IEMsandCIEMsoutthere.Westronglybelievewe’vecrackedit.ThistechwasjusttoogoodtobelockedawayafterweuseditintheProiCANso,wegaveitanother whirl in the Pro iDSD. The output stage of this DAC consists of three differentcircuitrieswhichdeliverdifferentoutcomessoundwise.Youcancyclethroughtheseoutputstagemodes:

1. ‘Solid-State' - a purely solid-state J-FETs based circuit of fully-discrete Class Atopology.

2. 'Tube' - the J-FET circuitry is switched to an all-valve Class A section based on 2xGE5670tubes.

April2018

ProiDSD–TheFront

TechNotes

3. 'Tube+' - reduces available negative feedback to aminimum.As a result, a greateramountofthetubesnaturalharmonicdistortionisproduced(evenorderharmonicsdominate).

Toggling between these threemodes can be donewithout shutting the Pro iDSD off, butthere’sashortpauseasthecircuitryswitchesover.

THEFRONTPANEL–OLEDDISPLAYWebelievethataproductaspackedwithfunctionalitiesastheProiDSDdeservestohaveabrilliant looking, readable, nicely embedded display. OLED was the only answer. Such adisplayprovidesatrueblackcolourandlooksgreat.ItspurposeistoprovideyouwithallthekeyplaybackinfoyouneedwhenusingtheProiDSD.

• Operationmode(PCM/DSD)• Currentsamplerate(44kHz,45MHzetc.)• Bitperfect/filteringmode• Basesamplerate• Currentlyusedinput

THEFRONTPANEL–HEADPHONEOUTPUTSANDGAINSECTIONEven though thePro iDSD isaaboveallelseaDAC ,wewanted tomake itasversatileaspossibleand,inordertodoso,webuiltinasophisticatedheadphoneamplifier.Thiscircuitryisunderstandablybestedonlyby thePro iCAN,ourTOTLstandaloneheadphoneamplifier.Andthere’saverygoodreasonwhythisisthecase.ThecircuitryforboththeProiCANandProIDSDisactuallybasedonclassicstudiocircuitry.Itconsists of tubes given the hybrid treatment with solid state parts to give them a higheroutputcurrent.Thistopologymakesforanexcellentlineorheadphonedriver.ThiscircuitisactuallyVERYSIMPLEandminimizesthenumberofactivestagesandpartsinthesignalpath.Inshort,awin-winscenario.ThemaindifferencesbetweentheProiCANandtheProiDSDinthisregardisthattheProiCANhastwiceasmanyoutputdevices,isbiaseddeeplytowardsclassAasitisoptimisedasaheadphoneamplifierforallheadphones.Meanwhile,thesamecircuitryintheProiDSDisoptimizedasalinedriver,buthasenoughoutputcurrenttodriveheadphones.Itsoutputpowerisreducedintheprocessandthebiasis much less towards class A. As a result, the Pro iDSD is not optimised as a headphoneamplifier,yetitwillstilldrivemostheadphoneswell.In thePro iDSDyouhaveseveralheadphoneoutputs tochoose from.Single-ended6.3mmoutismandatoryindevicesofthiscaliber.Thissocket isalsocomplimentedbyone3.5mm(both SEandS-Balanced, just like the sameoutput inournano iDSDBlack Label) andone

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fullybalanced2.5mmTRRSoutput.Thesetwoaretobefoundrightbelowthe6.3mmout.Tocompletethepicture,anadjustablegainswitchistheretoo.Itallowsyoutoboostthesignalby9and18dBorleaveitindefaultmode(0dBgain).

THEFRONTPANEL–VOLUMECONTROLThealuminiumvolumeknoblocatedneartherightedgeofProiDSD’sfrontpanelislargeandveryeasytouse.OurPro iCANusestheverysameoneand itdoesthe jobnicely!Whyfixsomethingthat’snotbroken?ThePro iDSDvolumeknobcanbeoperatedbyhandorbyasmall remotecontrol (includedwith theproduct).And lastly, in thebottomrightcornerofourflagshipDAC,you’llseeasmallblackscreenwithaninfraredreceiver.Noguessingwhatthat’sfor!As per usualwith iFi audio products, the volume control should be around the 12 o'clockpositionduringnormal listening levels. Inorder tohave themhigher,youcan increase thegainviasmallnearbyknob.Forfurtherinformation,pleasecontact:VictoriaPickles,Marketspress@ifi-audio.com+44(0)1704227204