With the SPL Diamond, the hifi brand presents us with a DAC derived from its productions for the professional world. It is sure to appeal to the most demanding audiophiles who are fans of digital sources.
This new DAC uses original technological solutions, specific to the brand, to take full advantage of the subtleties offered by hi-res digital audio streams. The most striking of these innovations, which SPL considers to be its benchmark technology, is probably the one called Voltair. It is based on the obvious. In order to faithfully reproduce the most extreme dynamics, the system must be capable of going from a modest output level of a few hundred millivolts to a much higher voltage excursion.
However, most DACs only have a relatively modest voltage supply. Usually of the order of a dozen volts. This inevitably limits the dynamic output voltage. This insurmountable limit can be detrimental to the reproduction of the most intense dynamic peaks.
Voltair technology solves this problem by providing the SPL Diamond’s analogue output stages with a supply voltage of 120 V, divided into +60 V and -60 V with respect to earth. This is four times the supply voltage of operational amplifiers based on integrated circuits. This gives a very wide operating margin before the output signal is clipped due to insufficient supply voltages.
However, while the basic concept of Voltair technology may seem attractive, no integrated circuit or operational amplifier on the market is designed to operate at such high voltages.
Specific op-amps
To overcome this difficulty, SPL has developed its own operational amplifiers, the SPL 120 V Supra. As a result, 120 V technology offers Diamond exceptional specifications and sonic supremacy. On a purely technical level, it is a real asset in terms of dynamic range, signal-to-noise ratio and even safety margin for the electrical excursion of the output signal. The result is an incredible wealth of detail and a perfectly serene, controlled listening experience.
Double filtering
SPL has also worked particularly hard on the filtering of the SPL Diamond. As with any DAC, the analogue output of the digital/analogue conversion chip must be smoothed by a low-pass filter. The Diamond has two such filters. One is dedicated to sources delivering PCM audio streams and the other to DSD streams. Different cut-off frequencies are required for optimum smoothing of the artefacts inherent in digital/analogue conversion. Here again, the low-pass filters fitted to the Diamond use Voltair technology. In this way, the entire analogue signal processing chain benefits from its qualities.
A top-of-the-range chip
The heart of the SPL Diamond is built around a top-of-the-range AKM AK4490 Velvet Sound™ chip, whose reputation is well established. Produced by Asahi Kasei Electronics, this chip converts PCM audio with 32-bit resolution and a sampling rate of up to 768 kHz, equivalent to 16 times the resolution of a CD. The chip can also process DSD 256 streams.
This means the Diamond is ready to handle the most up-to-date high-definition audio streams without a care in the world. Thanks to its particularly advanced processing capabilities, it is able to fully exploit and even enhance the musicality of any recording, expressing the timbres, playing and specific temperament of each instrument. The tiniest micro-information and the slightest subtlety are faithfully reproduced so that they become perceptible, guaranteeing rich, in-depth listening.
A finely tuned clock
Again to optimise the processing of digital streams, the SPL Diamond has a particularly open clock management system. It is capable not only of synchronising to the clock associated with the source stream, but also of using an external reference clock. The Clock switch on the front panel allows you to select either the clock from the incoming stream, in the Source position, or the clock from the signal applied to the Word IN input, in the Word position. This operating mode eliminates any artefacts associated with jitter problems.
Versatile connectivity
In terms of connectivity, the Diamond is equipped with sockets compatible with the highest quality standards. In addition to the traditional coaxial and optical inputs, there is an AES/EBU socket and a USB-B port. Asynchronous, it is dedicated to connecting the DAC to a computer, for example. Its analogue outputs are also available on both RCA and XLR sockets, so you can connect the Diamond to the most advanced components, or even to professional equipment. A set of dip-switches allows these analogue outputs to be set to either a fixed or variable level, controlled by the volume potentiometer on the front panel.
In use
We’re absolute fans of this compact box, and above all of its studio ergonomics, which are representative of a utilitarian product used every day. No frills, just real functionality. The SPL Diamond has a display that constantly shows the type of digital stream being processed and its sampling frequency. There’s also a source selector, and the volume control means it can even be connected directly to power units without the need for a preamplifier. Our tests were equally conclusive with both fixed and variable outputs.
Be warned, though, that the Diamond does get quite hot in daily use. Don’t put anything on its cabinet. And beware of the mains phase: it has a major influence on the sound.
The sound of the SPL Diamond
We began our listening sessions with our basic protocol, i.e. a basic ‘black’ mains cord and the excellent and very inexpensive Viablue NF-A7 RCA interconnect cables (see our test in this issue). The result was immediately straightforward and direct. You feel more like you’re behind a console in a studio than in front of a traditional hi-fi system that tends to embellish the signal.
You feel the music, especially acoustic music, with a physical impression. The bass lines are well articulated, and the impacts are clean and powerful. There’s not the slightest damping or attempt to seduce. This very live listening experience is really enjoyable because it gets straight to the point.
After a few hours, we swapped the Viablue for Absolue Creations TIM-Essentiel, and the power cord for a Furutech G-314 Ag-15 Plus at €200, and we entered a much more subtle, but still lively, world. The feeling of control over the whole bandwidth is very pleasant. Generally speaking, this Diamond doesn’t try to captivate you with overly sophisticated listening that might seem sterile, but with fundamentally balanced and homogeneous reproduction.
The adjective that immediately springs to mind is ‘unfiltered’ in the noblest sense of the word. Here, the electronics are not superimposed on the original message. Not a hint of coloration, quite the contrary. Its avowed aim is to let you experience the vitality and neutrality that your recordings can conceal. In this respect, it’s an undeniable success. A minimalist rock ensemble is brought to life between your two speakers.
The energy of a symphony orchestra is totally unleashed without spilling over in a disorderly fashion. The voices are hyper-realistic in their softness, as well as in their sometimes rocky aspect. And who can do more can do less, which allows the SPL Diamond to be subtle and measured on a string quartet or a soprano voice. It doesn’t favour any particular musical style. On the other hand, it makes a point of never inducing the slightest coloration, even if it can sometimes be pretty and pleasing to the ear. So if you want to have a precise idea of how your records sound, this is the converter for you.
Our conclusion
We were delighted to discover this unusual converter. It’s clear that SPL has drawn its legitimacy from the recording studio, where the notions of seriousness, straightness and dynamics are not taken lightly. With it, we find the very fluid and musical side to which the AKM chip has accustomed us, and the superb dynamic behaviour of the German manufacturer’s proprietary circuits. The cocktail of the two is a real success. But what really adds to the story is the price at which the SPL Diamond is offered. At €2,500, there aren’t many on the market capable of offering such good flow control. A great discovery, then, and a brand to keep an eye on, there’s no doubt about it.
Authors: Estève Fabry and Laurent Thorin
Technical sheet: SPL Diamond
- Origin: Germany
- Price : €2,499
- Dimensions : 278 x 57 x 300 mm
- Weight : 3.15 kg
- Sampling : PCM 32 bits/768 kHz
- Frequency response : 4 Hz to 300 kHz
- Signal-to-noise ratio : 102.3 dB
- Dynamic range : 135 dB
- Crosstalk: 108 dB at 1 kHz
- Total harmonic distortion : 0.001001% Native DSD 256 compatible
