"HagDac" Analog-to-Digital Converter (discontinued)
The HagDac is a high performance daughtercard designed for the Chime USB DAC. It is optimized to operate solely at redbook CD sample rates. A digital filter provides 8x synchronous oversampling to 352.8k, which is then reclocked into the multibit R2R converters (PCM1704) using a custom low-jitter VCXO PLL circuit. A passive 3rd order Bessel filter provides I-V conversion.
This design was done entirely as if each signal were analog. Every digital line is filtered and tuned for lowest noise and crosstalk. Careful use of power and ground planes, surface mount components, and liberal supply decoupling make for a very quiet and tuneful sonic presentation.