I need for my 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 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.