Hegel DAC

New from the Norwegian Hegel company at RMAF was the HD11 D/A processor ($1200), which features a 32-bit TI DAC but also a unique impedance-optimizing circuit on one of its coaxial S/PDIF inputs. Single-ended digital audio connections are specified to be 75 ohm transmission lines, explained Hegel's Anders Eitzeid, but not all all datalinks conform to that specification. (The RCA plug is a major source of the impedance mismatch even when the cable itself has a characteristic impedance of 75 ohms.) The impedance mismatch creates reflections that corrupt the integrity of the RF datastream, increasing jitter.

Using Totem Forest speakers driven by Hegel's H70 integrated amplifier ($2000) and with the HD11 supplied data from the Hegel CDP2 transport ($2650) via the well-regarded Nordost S/PDIF cable, Anders convincingly demonstrated the sonic improvement offered by the impedance-matching circuit by switching between the DAC's digital inputs. (To keep price down, the new circuit operates only on one of the two coaxial inputs.) To my surprise, the improvement was mainly in the low frequencies, which I conjecture is due to the elimination of the random LF jitter components that you can often see as "skirts" around tones in my jitter measurements for Stereophile.