1 - Digital Input

The S/PDIF signal is taken from the Cd Mechanism. We have used a CD ROM mechanism specifically developed for the audio application (We even contributed to the design for the firmware test part and for the mechanical stability tests). In fact the maximum speed has been reduced compared to the standard CD ROM mechanisms, and the reading procedure has been made more “Jitterless” and sturdy. To avoid any interference from ground returns we have isolated the S/PDIF CD mechanism output from the main board by a transformer. The SPDIF signal is then send to the DA conversion PCB.

2 - Digital Analog Conversion Section

The circuits performing the digital to analog conversion are placed on a board physically separated from the main board. That’s to avoid any interference on the analog signals due to the return currents of the digital parts of the DAC and transceiver. On the board there are: the transceiver, the DAC and all their frameworks including their power supply voltage regulators and capacitors. The voltage for the “DAC board” is obtained by a dedicated secondary of the transformer and a dedicated voltage regulator. The regulated voltage is then filtered by a RC filter. Then that voltage is used to produce the voltages for the transceiver and DAC by two voltage regulators. The components on the “DAC board “ are predominantly SMD reducing the length of traces carrying high frequency signals to avoid irradiation effects. From the “conversion board” the voltage DAC output is sent to the main board.

3 - Output Stage

The output stage is an original circuit designed by the Audio Analogue R&D office to emphisize the sound propertyes of the vacuum tube and to take vantage of the solid state technology. It is an inedited DC coupled low feedback three stage structure where the vacuum tube is the first one. The amount of feedback has been choosen not only on the base of measurements but on the base of listening tests too. What we have tried to do is a balance of the vacuum tube “coloring” and DAC “cleanliness”. The output stage’s gain is such that we have 1.9Vrms output for a 0dBV track.

4 - Anodic Power supply

The output stage used is not based on a differential input so the noise on the anodic supply is not reduced by the circuit. That’s why we have worked on the anodic power supply to make it as clean as possible. The voltage for the anodic power supply is obtained by a high voltage dedicated secondary and then regulated with a discrete components voltage regulator. The regulator output is then filtered by a RC filter with a very low time constant (less then 1.24).