USB audio DAC with PCM2704

Posted on Feb 7, 2014

High quality DAC convertor from USB to S/PDIF. I choose PCM2704 circuit, which sent me TI company like sample. Circuit has analog output for headphones and digital S/PDIF output with electrical and optical(TOSLINK) interface. We can use too 3 HID buttons for setting volume and mute. Schematics is almost identical to PCM2704 datasheet. Circuit includes these components: DAC, S/PDIF output and HID

USB audio DAC with PCM2704
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part with three buttons MUTE, VOL+ and VOL-. For USB input is used standard miniUSB connector. Headphone output uses standard 3. 5" stereo jack socket. For signal conversion from TTL level to differential signal is used RS-485 bus transceiver. For optical output is used optical transmitter TOTX173 from Toshiba. First I drill holes for crystal, wires, connectors and buttons. Next I settle intergrated circuit PCM2704, because I need more space for soldering. I put circuit on right place, solder one pin in the corner and next solder all pins on second side with thin tin. Next I solder first side. Effect is, that almost all pins are shorted. Next I must use copper solder wick for draining of tin out. If there are anough colophony that pins automatically unjoin thanks to surface tension. Next I put on the board circuit 75176B, SMD resistors and capacitors. These components I solder that after right position I hold them with nail, small screwdriver or tweezer. One pin I solder with small amount of tin. If the component is on the right place, I solder them on the opposite side and finally on the first side. Next I solder SMD connector, wire junctions and finally all components from a top side. Circuit should work immediately after connection to computer. It is seen as standard USB soundcard. For usual operating systems like Linux or Windows XP are not needed any drivers. It should work too volume settings using buttons. PCB is...

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