Hey all, looking for a design/layout review before I send this off for fab. It's a small interface board that takes two symmetrical line-level analog inputs and outputs them as an ADAT optical stream meant to sit between a tube amp / analog gear and an ADAT-capable audio interface.



What it does:

\- 2x symmetrical line inputs via JST connectors (CH1/CH2) (Output from secondary coil of an UTM3510)

\- Each channel buffered through a dual op-amp (TI OPA1637) before hitting the ADC  
(-9.8dB to match with EBU R68)

\- Analog Devices ADAU1978 (quad ADC) digitizes (2-Channel Summing Mode), clocked off a 12.288MHz oscillator (standard ADAT 256fs rate)

\- An ATtiny85 sequences power-up/reset for the ADC and encoder chip and configures the ADC over I2C

\- Digital audio gets level-shifted 3.3V→5V (SN74LVC8T245) into a Coolaudio V1401, which encodes it to the ADAT optical format

\- 5-position DIP switch feeds the V1401's config pins

\- TOSLINK output connector

\- 5V in via screw terminal, on-board 3.3V LDO



Specs:

\- 4-layer, 1.6mm,

\- Stack: Top signal / GND plane / Vcc plane (split into 5V and 3V3 section ) / Bottom signal



What I'd love eyes on:

* Unsure on splitting the 3.3V / 5V VCC plane
* Unsure on powering the ADAU1978's AVDD / DVDD / IOVDD

PCB REVIEW - Line to Adat Converter