TECHNICALDESCRIPTION
©CyrusAudioLtdJun2014 8 Cyrus6DAC,Cyrus8DACservicemanualIssue1
NOTE:‐Referencenumbersinthetextarefortheleftchannel.
AnalogueinputselectionandTapeMonitor
The input and tape monitor selection is via an electronic audio selector switch (IC101). The
switch is a 7 way 2 pole switch followed by a buffer (IC103) which then feeds audio to the
volumecontrolsectionofthecircuit.
The Zone 2/Tape output is separately selected via a second electronic switch (IC102). The
signal from the Zone 2/Tape selector is then sent to the Zone 2/Tape output via the buffer
IC104.
Digitalinputs
In addition to the six analogue inputs described above, the amplifiers include a digital input
switcher and a two channel D/A Converter to enable connection of an additional five digital
inputs,fourofwhicharestereoSPDIFformatandoneUSB.
Digital input selection is performed by an 8:1 input multiplexer in a Digital Input Receiver
(IC701). The DIR is clocked by a 24.576MHz reference clock. The input sample rate is
determined by comparing the incoming frequency to the reference clock. The frequency is
then read by the system microcontroller on the front panel PCB, and displayed on the front
panelLCDdisplay.
TheoutputfromthemultiplexedSPDIFinputsignalisthensynchronisedbyaninternalPLLand
decodedtoI
2
S(a3‐wiredigitalaudioformat)byIC701.
The USB input is decoded by IC601. This enables the amplifier to play music from a PC or
similar, but is not suitable for connecting Flash drives or the like. When a USB device is
connected, the power supply for IC601 is powered via T601. When there is no USB master
device connected to the USB type socket, the power supply for IC601 is powered down,
stoppingtheclockforIC601.Whenenabled,andwithaUSBaudiosignalconnected,IC601will
re‐format theaudio signalto IEC958/SPDIFformat whichis routedto IC701, the digital input
switch.
TheI
2
SaudiodatafromtheinputswitchIC701isfedtoIC801,astereoD/AConverter.TheD/A
Converterconvertsthedigitalaudiointoan analogue output.Thisisamplifiedandfilteredby
IC802 before being passed to the DIG inputof IC101(the inputswitch on themain analogue
amplifierPCB)viaCON100.
ThedigitalaudiosignalsfromIC801arealsofedtotheQxDACupgradeconnectorCON902.Ifa
QxupgradeDACisfittedtoaCyrus8DAC,aflexfoilcableisfittedbetweenCON902andtheQx
DAC PCB to connect digital audio and power etc to the Qx DAC. The audio output of the Qx
DACisconnectedtoCON100onthemainPCB.Inthisconfiguration,theaudiooutputcableof
theDigitalInputmoduleisconnectedtoaspareconnectorCON905.
Thepowerforthe digitalinputPCBissuppliedfromaseparatelowvoltagewindingofthemain
powertransformer.Thisisthenrectifiedandsubregulatedtoanumberofindividualsupplies,
one3.3Vandtwo5.0V.Therectifiedandunregulatedsupplyisalsopasseddirectlytothemain
analogue amplifier PCB to providepower forthe LCDbacklight. The 15V power
supplies for
theanaloguepostDACfilterareprovidedfromthemainanalogueamplifierPCB.
WhentheamplifierissettostandbythepowertothewholedigitalinputPCBisremoved.
IfadigitalinputisnotselectedforlisteningonthemainamplifierorinZone2,the
digitalPCB
will be held in reset to eliminate digital noise interference coupling to the main analogue
inputs.
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