Sigma

About the Sigma

The California Audio Labs Sigma is a tubed digital-to-analog converter (DAC) that uses a 12AX7 vacuum tube in its analog output stage to provide a warm, musical sound. It features a straightforward design with no front-panel controls except a single LED indicating digital lock. The unit accepts one coaxial and one TosLink optical digital input and outputs analog audio via RCA jacks. Internally, it uses a Crystal Semiconductor chipset and high-quality Wima capacitors in the analog stage. The power supply includes a large transformer feeding multiple regulated stages, including a high-voltage plate supply for the tube and separate regulation for tube heater, digital, and analog sections. The Sigma is noted for its build quality, simplicity, and low parts count, which allows it to be It has a relay-based mute circuit to prevent noise during tube warm-up and when no digital signal is locked. The DAC is praised for its musicality and timing, though it may not match modern DACs in soundstage depth or resolution. It was originally released in the early 1990s and remains a respected classic tube DAC.