In terms of technology, Prism goes with an ARM Cortex digital processor, but relies heavily on Prism Sound’s own circuit architecture and reclocking stages. The last is the deliciously named CleverClox hybrid phase-locked loop to act as clock recovery taken from either local or S/PDIF input. This gives a ±50ppm local clock accuracy and a greater than 60dB/decade above 100Hz jitter rejection. This is a balanced set of specifications; as good as it gets without essentially hand-built, tight component matching that demands an order of magnitude more expense, which results in potentially tiny overall improvements. In other words, the Callia sits right on the cusp of the Law of Diminishing Returns as it applies to digital audio.
Although the Callia is a fully digital preamp with no analogue inputs. There are both single-ended RCA and balanced XLR stereo outputs, and these are variable output and controlled from the larger of the two front panel knobs (a resistive-feel potentiometer with a ring of blue LEDs to denote actual volume level). This can also be set to fixed output on that four-switch DIP panel on the rear of the Callia. This is more of a desktop digital ‘hub’ than direct replacement to an existing preamplifier, in part because of the absence of a remote option.Prism Sound went for a high-current, low-impedance headphone amp, with a series of rear mounted DIP switches on the rear panel to match the impedance of your headphones. The options are relatively limited here; less than 32 ohms, between 32 and 50 ohms, or greater than 50 ohms. Three of the four positions on the DIP switch panel mute the main output when a pair of headphones are connected, although one option allows both to play simultaneously, each with its own volume control. This DIP panel also supports legacy and current settings for DSD headroom (or line-up level) for all outputs. It’s worth a quick aside into the packaging and documentation supplied with the Callia because it shows up just how far a lot of domestic audio needs to come. The Prism Sound arrives in a well-made black with blue contrast clamshell box, the kind of thing you might expect a really highend shirt to arrive in. Inside is stiff black foam with cut-outs for the Callia, a chunky USB and power cord, a printed quick-start guide, and a neat aluminium screw-top USB stick that contains the PDF of the full manual and the requisite drivers for Windows computers. The quick-start guide is relatively basic, but will get you up and running. The PDF manual is comprehensive, not only in terms of installation and set-up, but in specifications and the explanations behind those specifications, and even a whistle-stoptour of Prism Sound’s general audio ethos, which is refreshingly down-to-earth.