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PCM1794A

H-DACObsolete

H-DAC – High performance 192 kHz / 24-bit DAC with addon options

by nihtila
written by nihtila
  • Very high performance; measurement results with coaxial S/PDIF input:
    • Output level: 2.0 Vrms
    • Dynamic range / SNR: 122 dB (A-weighted)
    • THD+N ratio: -103 dB (0 dBFS/1 kHz signal, 48 kHz sample rate)
    • Crosstalk: -128 dB at 1 kHz, -112 dB at 10 kHz
  • Supports S/PDIF, Toslink, USB, and external I2S inputs
  • Unbalanced outputs (RCA) on board, balanced (XLR) addon available
  • Hardware-controlled – no need for microcontroller (but one can be added with addon)
  • Can be powered by AC or DC supply
  • Addon available to transform H-DAC into preamplifier/headphone amp
  • New output stage addons can be easily designed to experiment with components and circuits
  • CS8416 S/PDIF-receiver, PCM1794A DAC, LM4562 opamps (or any SO-8 dual opamp), PCM2707C USB-audio, LM2940/LM2990, TPS73633, TPS79133, and REG103 regulators

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.

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Audio Measurements

PCM1794A left/right channel distortion difference

by nihtila
written by nihtila

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.

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Audio Measurements

PCM1794A output stage opamp measurements: LM4562, NE5532, and OPA2134

by nihtila
written by nihtila
  • LM4562 and NE5532 show almost identical performance in I/V stage, while OPA2134 is 2 dB weaker.
  • LM4562 is the best performer in differential amplifier.
  • The best solution is to use NE5532 in I/V-stage and LM4562 in differential amplifier as it gives almost identical performance to all-LM4562 implementation
  • Differences in distortion are mostly due to odd left/right channel differences of PCM1794A.
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Audio Theory

DAC digital filters and their impact in time and frequency domains

by nihtila
written by nihtila

Many DAC chips and devices using those chip have user selectable options for digital filter response to fine-tune tonal characteristics. I will take PCM1794A used on H-DAC as an example and see what effects these filter types have on impulse and frequency responses. This is just scratching the surface of the topic by briefly introducing some technical effects that can be measured. Tonal characteristics are not discussed here; those are highly subjective and a topic of another post (or debate).

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