As someone who is passionate about music and engineering, designing my own audio equipment is a fun and rewarding process. This digital to analog converter (DAC) design uses some of the best off the shelf components available and results in a world-class listening experience.
A significant amount of has been but into the design of the power supply to ensure that the power rails are extremely low noise. This is accomplished by a capacitance multiplier on the power rails of the AC to DC converters followed by a linear regulation stage.
This design features a USB and optical input to support a wide variety of sources. The digital to analog conversion in accomplished by a Texas Instruments PCM1794 which features one of the highest dynamic range (129dB at 4.5V RMS Stereo) and lowest total harmonic distortions (0.0004%) of any off the shelf DAC ICs available. It is for this reason the PCM1794 was selected. As a point of reference, this is an updated version of the DAC IC used in the Sennheiser HDV820 (PCM1792).
The output stage is designed using ultralow noise precision op amps to achieve an extremely noise signal. The op amps used are the Linear Technology LT1028 which feature a typical voltage noise of only 1.0nV / sqrt(Hz) at 10kHz. This ultralow voltage noise and fast slew rate of of 11V/uS makes the LT1028 and excellent op amp for high quality and responsive audio.
There are two outputs from the DAC that can be used, a balanced differential output and a single-ended output. Having both balanced and unbalanced outputs allows for mode modularity to interface with other equipment. The balanced differential output is also useful to common-mode noise reduction for higher than optimal noise environments.
Future of the project:
The first prototype of the design has been manufactured and tested. From the testing there are a few minor design aspects that need revised before being consumer product ready. The power supply has been revised into a standalone assembly to reduce board size and cost. This was done because the power supply section is relatively simple and only required a two-layer PCB. The remaining design is significantly more complicated and component dense and thus requires a four-layer design. It is for this reason the power-supply was revised as a stand-alone assembly. Additionally, the placement of the connectors need adjusted to better fit into a custom enclosure.
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