To the audiophile, Prism Sound might not be the first name that trips off the tongue when it comes to high-quality digital audio coming out of the Cambridgeshire countryside. But, if you are in the studio, broadcast, or even audio test equipment world, this specialist from the tiny village of Stretham is a name to be reckoned with. This year, Prism Sound crossed the audio Rubicon and has made its first domestic product, the Callia DAC with built in headphone amplifier and preamp.
Essentially the Prism Sound Callia uses the form factor, some of the ergonomics and much of the digital nous of Prism’s Lyra USB interface; in the process gaining domestic inputs and outputs, but losing an A/D converter. Callia also supports RCA and Toslink S/PDIF, and the RCA input can be used in a professional capacity as it supports AES3-ID. In terms of formats, the Audio Class 2.0 USB input supports DSD over DoP to DSD128, and PCM to 32‑bit word lengths and 384kHz sampling rates. However, sampling frequencies beyond 192kHz are passed through a high-performance decimation filter, so hunting down 32/384 files isn’t important in this case. S/PDIF supports PCM up to 24‑bit word lengths, with multiples of 44.1kHz and 48kHz sampling rates up to 192kHz, and DSD64 within a DoP frame.
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.
The interesting thing is there are so many studios using Prism Sound encoders, decoders, SADiE workstations, ProTools interfaces, and mastering devices that many of your recordings already have at least one device from the brand somewhere inthe recording chain. The Callia, goes the argument, is made by the company that knows precisely how music sounds in the studio, and that knowledge extends to the home. There is an obvious temptation to opt for recordings made through
Prism Sound encoders, but in fact that’s almost self-limiting, because people may make the assumption that there is some special link from encoder to decoder. This is simply not the case, so there is no special sifting of the music collection to find recordings that use Prism Sound equipment. However, it’s actually hard to find a modern recording that doesn’t use some form of Prism Sound electronics somewhere in the mix. So, the chances are some of the albums I played featured the company’s electronics somewhere.
This is genuine studio-grade equipment brought home. Callia is no rosetinted canter through your musical collection; it very much tells it like it is. And it’s surprising how many people – when faced with this kind of stark honesty – find themselves wanting something a little less honest. In particular, it seems some would like a sound with more warmth and a little more veiling. Personally though, the unvarnished truth is attractive, even if it comes with less magic glitter sprinkles. And the Prism Sound Callia is good at the unvarnished truth. This DAC gives an insight into the recording itself. You will hear into the mix, discovering the precision of panning, the amount of reverb, the position of microphones… and the limitations to that insight are more to do with the precision of the source and the quality of loudspeakers than the DAC itself. Callia is exceptionally detailed, with extremely precise leading edges. I seem to be on a loose drummer trip at the moment, but listening to thedifference between Ringo Starr’s playing on ‘All My Loving’ [With The Beatles, Parlophone 2009 Mono remaster] and Meg White playing ‘Seven Nation Army’ [Elephant, XL] is extremely easy to follow through the Callia – both have an ability to ‘occupy’ the record, but where Starr’s seemingly-effortless ‘windscreen wiper’ hi-hat is actually swampy and unique, White’s sloppy pounding away at the drum kit is easy to spot.
Moving away from the drum kit, the same complete honesty applies throughout. You get an appraisal of the musician’s and engineer’s art from the Callia, without grace or favour. The sound of an instrument is the sound of that instrument without embellishment or subtraction, and that is a heady wine once you get used to it.
The headphone amplifier stage is very well ‘sorted’ too. You do need to take some time to experiment with the DIP switch block at the rear of the DAC to get the best from the Callia. I found in two cases, the recommended guidelines perfectly suited the headphone used, but in another a more conservative setting was called for. I’m fairly certain this is more down to the vagaries of headphone designers being editorial with the facts about their output load than variability on the Callia’s part, because when set to work with a specific headphone, it works perfectly. In fact, the adjustment of the DIP switches acts more like a headphone volume limiter than a tonal adjustment (unless you are trying to use 300Ω headphones with a sub-32Ω setting). Get this wrong and it might get loud!
There’s a lot to like here. OK, so if you want your electronics to ‘pretty up’ your music, the Prism Sound Callia isn’t for you. Instead, this is one of the most honest DACs you’ll hear. It’s an outstanding and powerful headphone amplifier, too, even if its lack of line level inputs, balance adjustment, and remote control probably limit its real-world practicality as a domestic preamplifier. That’s said, if you want a digital hub connected via long XLR leads to your active loudspeakers, the Callia and a laptop at arm’s length could be all you even need for your musical requirements. An honest, solid, and extremely accurate recommendation.
Type: Digital to analogue converter with preamp and headphone amplifier functions:
Inputs: coaxial RCA and Toslink S/PDIF inputs (AES3‑ID on coaxial input), Class 2.0 Audio USB type B input
Outputs: ¼” TRS headphone jack (on front), RCA pseudobalanced or XLR balanced stereo outputs (on rear), fixed or variable depending on settings
Input selection: auto or manual, LED indication in both cases
PCM word length: 16bit-32bit
Sampling frequencies: 44.1-192kHz (384kHz supported through USB, but fed through decimation filter)
DSD precision: DSD64 through S/PDIF, DSD128 through USB (DSD128 also fed through decimation filter)
Headphone impedance ranges: < 32Ω, 32Ω-50Ω, >50Ω
THD+N: 0.0005%, -0.1dBFS
Dynamic range: 115dB (line), 113dB (headphone), -60dBFS
Local clock accuracy: ±50ppm
Jitter rejection: 60dB/decade above 100dB
Dimensions (W×H×D): 28.5×5×24.2cm
Manufactured by: Prism Media Products Ltd
Tel: +44(0)1353 648888
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