PRISM SOUND Callia DAC/preamp
An all-digital DAC and preamp which sounded so good, we felt like dancing.
Its name means ‘beautiful voice’, which we reckon is a pretty good way to describe the talents of this all-digital DAC and preamp.
In the decades since the digital revolution in audio, the digital-to-analogue converter has become a vital link in the hi-fi chain. DACs first arrived as standalone units for upgrading CD players, graduating to a full role once file-based replay became a thing, so that an offboard unit was required to turn the potentially hideous noise from computers into high-quality audio. Today most amplifiers have built-in digital inputs and DACs within. But for the best possible quality, a separate DAC is still very much the way to go.
These converters are reversing the digitisation performed in the recording studio, where analogue microphones are digitised at a high level for mixing and mastering (unless the studio in question is one of the few analogue hold-outs, in which case the ADC may be held until the final point of mixdown).
So there’s a good argument that companies involved in studio equipment may be able to deliver useful products in the consumer DAC space, since they know what goes on at the start of the chain.
UK digital specialist Prism Sound is once such company, a relative newcomer to the audiophile arena, but an old hand in the professional audio sphere, having been founded back in 1987 by Graham Boswell and Ian Dennis, electronics engineers who had just left Neve, where they’d developed the legendary world-first commercial audio mixing console using DSP. According to Boswell, Prism Sound was founded “with the aim of making digital conversion good enough for the most demanding listener”, and all their products are designed and manufactured at the HQ in Cambridgeshire, England.
So much better than ‘good enough’ were Prism Sound’s first DACs and ADCs, in particular the ADC-1, that they became popular in recording studios around the world. When Prism Sound developed the world’s first AES/EBU interface analyser (the DSA-1), it became the standard tool for broadcasters around the world, including the BBC, NHK, NBC, CBS, ABC and CCTV.
Equipment
The choice of Greek name here is a good one (Greek names are something of a theme for the naming of Prism Sound products), given it translates as ‘beautiful voice’, or just ‘very beautiful’. And Prism Sound’s Callia DAC does indeed look — and more importantly sounds — rather beautiful. It is quite small, just 285 × 242 × 50mm
including feet, and correspondingly light at 2.1kg. The front panel is simple, and both clearly and beautifully laid-out.
The large knob is the volume control for the line outputs, of which there are two — unbalanced (via gold-plated RCA terminals) and balanced (via gold-plated XLR terminals). It’s surrounded by a ring of blue LEDs that illuminate to give a visual representation of volume setting.
While a DAC doesn’t need a volume control if playing into a standard amplifier, this provision means the Callia can be used directly into a power amplifier, if required, operating as a pre-amplifier as well as DAC. There are limitations there — the first being that all your source components need to be digital, because the Callia has no analogue inputs (perhaps because simply passing them through isn’t possible with the digitally implemented volume control). And even in the digital sphere you’re limited to three digital inputs — USB, coaxial digital and optical digital. But if that does suit you, then the Callia might provide a considerable bonus in terms of system simplicity.
The USB input handles PCM up to 352.8k and 384kHz at up to 32 bits, as well as DSD64 and DSD128. The coaxial and optical digital inputs handle PCM to 176.4k and 192kHz at up to 24 bits, as well as DSD64. Mac users using the USB input are good to go ‘out of the box’ but Windows users with anything less than the latest Windows 10 updates will need to install a driver to send high-res audio to the Callia. This software is handily included on a USB stick (much better than a disc!) supplied with the Callia, together with the Callia’s User Manual (written by Ian Dennis himself), as well as software that will enable you to perform firmware upgrades yourself as they become available. A printed ‘Quick Start’ guide is also included, should you be in a hurry.
The smaller rotary control to the right of the volume control is a second control for the 6.35mm headphone jack on the front panel. Inserting a headphone plug into this socket mutes the analogue line outputs, which may be against your desires, but there are DIP switches on the rear panel with which you can defeat this muting. Other DIP switches very usefully allow you to optimise the Callia’s low-impedance headphone amplifier to perfectly match your headphones, with one setting for phones with a nominal impedance of below 32 ohms, another for phones with nominal impedances of between 32 and 50 ohms, and another for high-impedance headphones above 50 ohms.
When setting the DIP switches you do need to be careful not to move DIP-1 inadvertently, because it disables the front-panel volume control causing the Callia to deliver its maximum output voltage at the output terminals. But you might choose that option if playing the Callia into a full integrated amp or preamp.
DIP-2 switches DSD headroom between 0dB and +3.1dB (the latter position is used to prevent ‘hot’ DSD streams from clipping).
Input switching is managed automatically, with the Callia automatically detecting an active digital input and switching to it, after which it ‘locks’ into position and shows the format of the data stream on the front panel, using the LEDs immediately to the left of the volume control. If you don’t want auto-switching, you can switch the circuit off, after which manual switching is accomplished by brief presses of the power on/ standby button at the far right of the front panel. (A longer press puts the Callia into standby mode.) This same button, used in conjunction with the main volume control, also allows you to vary the brightness of the front-panel LEDs.
Internally, Prism Sound does most of its processing using in-house algorithms, via a Spartan-6 FPGA and 32-bit ARM Cortex microcontroller along with Prism Sound’s own clocking circuitry, which it calls a ‘CleverClox’. This is a hybrid phase-locked loop that locks the Callia’s clock to the selected SPDIF source with better than ±50ppm local clock accuracy, resulting in ultra-low jitter, claimed to deliver >60dB/decade above 100Hz jitter rejection. Although some Cirrus Logic CS4398 DACs are on the PCB, Prism Sound reportedly uses only their final switched-capacitor stage.
Performance
Once I had installed the Callia and started to use it, my first thought was that either I would to have develop stronger fingers, or that the Callia’s volume control would loosen-up after continued use, because out-of-the-box, it’s quite stiff to turn, whereas the headphone volume control, on the other hand, was quite easy to turn, though with a slightly ‘raspy’ action. The Callia does not come with a remote control, Prism Sound likely expecting it to be used as a ‘desktop’ unit, in which case the user would always be within arm’s reach.
The very first album we played through the Callia proved to be jaw-dropping on two fronts. For a start, it was made immediately obvious that the Callia ‘tells it like it is’ and provides super-precise digital-to-analogue conversion. Yet it wasn’t a ‘digital’ sound, a possible pointer that that whatever filtering Prism Sound is using, it
“It’s a level of music playback that makes you feel like dancing as much as critical listening...”
isn’t a standard ‘brick-wall’ filter. The result was a ‘cleanness’ to the sound that was as revealing as it was involving.
The second jaw-dropping event was the sound we were hearing from the disc, a 1958 live recording of Harry Belafonte in Carnegie Hall. It would appear that the engineer (Bob Simpson) just set up a few microphones, and didn’t mess with levels or equalisation. Amazingly, it then seems that no-one ‘mastered’ the tape before its transfer to CD. The result is a recording that is amongst the best and most realistic available, and there is sheer pleasure in hearing how live recordings should be made, even before you appreciate the stunning musicianship from both Belafonte and his backing musicians. It’s a level of music playback that makes you feel like dancing as much as critical listening.
After the smoothness of Belafonte, the grim grit of The Peep Tempel’s latest CD ‘Joy’ was a jolt back to modern reality, but what a jolt. There’s story-telling here (via spoken word), and more story-telling (yep, spoken word again), but also a musical bacchanalia. Beautifully recorded, too, as just a few seconds listening to Neuroplasticity will prove (and will show where the album title originated). If you’re looking for a track to show off your subwoofer’s prowess, you could do worse than spin the CD’s lead track Kalgoorlie, which is bass and grunge pierced by ear-shredding, stabbing guitar.
All of which was revealed exactly by the Callia, whose own performance sunk us deep into the trio’s performance, while at the same time almost contradictorily revealing the precision of Anna Laverty’s superb engineering. But not an album for the faint-hearted, so listen at your own risk…
Trialled with the even-more testing fare of a 70-piece symphony orchestra, the Callia once more showed its ability to reveal the ‘weave’ of the music while at the same time uniting the threads into a glorious tapestry of sound. No, not classical, but ‘Live in Columbia’ by The Alan Parsons Project. The only problem is that when you hear, say, I Wouldn’t Want to Be Like You, you’re going to want to hear the whole of the album that gave it life (‘I, Robot’), and the same would be true of the tracks Turn of a Friendly Card and Eye in the Sky.
No matter what type of digital music we played through the Callia, from CD quality up to DSD, the backgrounds seemed totally silent, and thankfully always a truly ‘musical’ silence, not the ‘digital black’ that some DACs deliver when there’s no music playing or, worse, ‘between the notes’. When listening to the Callia, any silences — however short or long — merely served as pauses in the cause of the music to separate either individual notes, musical phrases or tracks. And when listening to solo instruments played at a live venue, you could hear the ‘acoustic’ of the venue itself… though also, sometimes — alas! — traffic noises from outside that venue! Such is the revealing nature of the Callia DAC.
The Callia’s headphone output, incidentally, is awesome. It drove all the headphones to hand to their maximum level without any audible distortion while also delivering outstandingly transparent sound. And the dedicated volume control meant we could leave the headphone volume at a preferred level while still adjusting the main volume control to suit the listening situation (with the same scenario operating vice versa, of course!).
Conclusion
The omission of an analogue input may make this more DAC than preamp for most users, but what a DAC! Prism Sound’s foray into the consumer audio market is a tour de force, a genuine state-of-the-art DAC and headphone amplifier at what qualifies as an entry-level price for the technology involved and the quality delivered. Lesley Swan