Seems like when Sumo went belly-up they took all all their documentation with them. Anyone have a schematic for this unit or a service manual or something of the like? Mine has a non-functional coax input and I believe the automatic on/off isn't functioning properly either. The unit works via its optical input, so hopefully there's just a broken wire or bad solder joint or something along those lines, but if I could find a schematic to check component values against, well, that'd be awesome.
The digital-to-analog converter (DAC) is a dual-channel Burr-Brown PCM67P, so-called "hybrid" DAC. It gets its name from the fact that the upper 10 bits of the word 18-bit digital are converted to analog by a one-bit resistor ladder converter, and the lower 8 are processed by a 1-bit converter with noise shaping. goes. This hybrid approach theoretically combines both conversion techniques: good low-level linearity from the 1-bit portion, with improved dynamics, and other properties associated with multi-bit converters. Sumo chose PCM67 after listening to a variety of DACs. Theorem is the first product that I have reviewed to use this DAC; It does not seem to have caught on among high-end designers.