The Design in Details
The Avarice represents a fusion of the finest state-of-the-art design techniques that are a must for any high quality audio product.
The Avarice has one, 75R BNC coaxial input for a standard S/PDIF digital audio input signal. The input is galvanically isolated by a transformer in order to achieve maximum rejection of any received signal interference. The signal is carefully terminated with a view to maximum attenuation of any reflections, and linearly processed. Alternatively, the Avarice can be equipped with one optical input.
The Avarice can receive an input signal of any bit depth, with sampling frequency between 32 and 192 kHz. With the optical input, incoming sampling frequencies are guaranteed to work up to 96 kHz. Higher frequencies require use of high-quality low-loss optical cable. There is a clear indication of the incoming sampling frequency on the front panel, by a four-segment LED bar.
The SPDIF digital signal output is transformer coupled, using a coaxial BNC connector with 75R impedance. The signal passes through a two-step digital re-clocking stage in order to achieve maximum insulation from the noise and interference of the internal signal-processing circuits. The entire output circuit is supplied with power from a separate, discreet low-noise regulator. Thanks to the 4-times upsampling, the output sampling frequency can reach a maximum value of 192kHz. Of course, lower output sampling frequencies can be set. The output bit depth can be set to 16 or 24 bits.
In addition to the carefully designed SPDIF input and output, used to minimise transport jitter, any instability in the signal clock is further attenuated in the downstream digital processing stages. The WM8804 chip , working as a buffered digital PLL circuit, takes care of decoding the incoming SPDIF signal. The chip runs in full software mode, using proprietary PLL parameter settings, optimised separately for every incoming sampling frequency. The clock signal is provided by a highly stable crystal oscillator powered by a separate low noise regulator, together with the PLL section of the receiver. A number of output SPDIF signal modes can be set, to reduce the influence of data jitter. In these modes, intra and inter-frame structure of the S/PDIF protocol is modified in order to clean up the audio band from S/PDIF signaling artifacts.
The qualities of our DSP algorithms have been well described in the section about the Vanity module. The Avarice goes even further in this respect – up to 4 x upsampling is performed in a single filter stage. This is a design feature superior to the cascaded filters used in common DAC chips, where every stage adds more rounding error to the signal.
High quality digital filters are no longer the privilege of luxury CD - DVD players of leading manufacturers - with the Avarice, almost any digital signal source with a low-quality SPDIF output can be significantly improved. Users can easily modify all important signal processing parameters, using switches that are well accessible.
The circuit is meticulously designed, using a 4-layer PCB with spatial arrangement of components, with a view to achieving maximum attenuation of any interference among the functional blocs of the device, and the best ESD and EMC properties. The oversized multi-stage filtering of the power supply is supported by 7 independent linear regulators, of which two are discrete low-noise types. The standard 2.1 mm DC jack enables power supply from various power sources with wide voltage range from 8 to 15V, and at least 1A of current. The circuit board is placed in a deep black-anodized and laser-engraved 120x78x43mm aluminium box.