Addon H-MCU is designed to help use H-DAC in projects where I use microcontroller for selecting input and filter settings. It makes it possible to switch input and DAC filter with external remote signals.
Addon H-Filter is a simple filter and output addon for H-DAC with a possibility for a potentiometer to transform H-DAC into a preamplifier. In contrast with other designs of mine, it has been designed with through-hole components to allow easy experimentations with opamps and passive components. It offers high performance with low BOM cost and easy solderability.
H-PreAmp is an addon board for H-DAC, transforming the fixed-output DAC into a very high quality preamplifier with integrated headphone amplifier. H-DAC and H-PreAmp together provide single-ended (RCA) and balanced (XLR) outputs as well as headphone amplifier.
This post arose as a consequence of testing the USB-input of H-DAC. Its PCM2707C-circuit is capable of “only” 48 kHz / 16-bit audio so I was not expecting superb measurement results but was still amazed how bad they actually were. This is purely a technical inspection but the differences are significant so I can easily imagine some golden ears can spot the difference.
Addon BalOut is a small addon board to be stacked on H-DAC to add balanced XLR outputs. It works along with the unbalanced RCA outputs on H-DAC and audio performance is high enough not to be the limiting factor of the H-DAC system.
Following performance figures have been measured in Addon BalOut module:
H-DAC is a high-performance 192 kHz / 24-bit capable DAC board with TI PCM1794A DAC. The board has two coaxial S/PDIF, two Toslink, and one I2S input that can be either on-board 48 kHz / 16-bit USB receiver or an external I2S-device. Input selection and settings are controlled with jumper links that can be replaced by mechanical switches or microcontroller addon board.
Basically in all of my PCM1794A measurements I have seen something strange going on in the distortion figures between left and right channels. Right channel is constantly weaker but the results are very consistent between measurements, parts, and even different opamp models, while left channel shows better performance but the results are very inconsistent.
I will show few examples from different measurements. To be honest, I still do not know what is the root cause of these variations. While I was expecting my design and PCB to be the guilty one, I have seen the behaviour between different component and even different PCBs, it is inevitable that I start pointing my finger at the PCM1794A itself. But before drawing the final conclusion, I will still create a very simple and symmetric test board. However, now I will just present the results I have gathered so far.
