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Old 31st May 2013, 09:48 PM   #1
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Default Suggest on my project,PCM1794

Hello,World!
So my thesis is done.It's a PCM 1794 DAC with USB.However,I want to use it for listening too.This is my first digital project.
I'm using latest XMOS for USB->I2S.The PCM1794 is done with active I/V with LM4562 and OPA1612 for LPF.It's a bit like the datasheet schematic,just with lower gain on transimpedance amps.It works alright,and I'm pleased with the sound.It's much more detailed than my modded AP2496,however,I always want more,and 3 of my favorite AD8599 opamps are yet to come.Sound is a bit defocused now.
What else to make it better?I'm powering the analog part with LM317/LM337,7805 for +5V,and some unknown 3.3V regulator for digital.1000uF ouput caps on these.Can you recommend me "cleaner" linear regulators?
How about the DF roll-off?What's your opinion,sharp or slow?

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I know I can't expect optimum performance on this board,but all traces are covered with thick wire and solder,and are as short as possible.I've achieved 120 dB SNR on perfboard with my headphone amp,so why not.


Thanks for reading!

Edit:the PCM1794 accepts and plays 384 kHz?Is this normal?

Last edited by GTrenchev; 31st May 2013 at 11:27 PM.
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Old 2nd June 2013, 02:43 PM   #2
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The PCM1794A digital filter slope selection subjective choice seems to depend much on the implementation of other circuit elements. I use a passive resistor output with my PCM1794A based DAC, and ended up preferring the fast roll-off slope. However, before arriving at this passive output, I had preferred the slow roll-off mode when using an op-amp based output stage.

At any rate, since the PCM1794A features a dedicated hardware input pin enabling real-time toggling of the filter slope, you don't need to settle this question before hand. You can conveniently switch back and forth at your leisure while listening with your own ears.
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Old 5th July 2013, 09:53 PM   #3
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Can you tell me how to remove offset ? 16 mV on one channel and 4 mV on the other. Should I use more accurate resistors on I/F and output filter ?
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Old 13th July 2013, 09:58 PM   #4
jaycee is offline jaycee  United Kingdom
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Those regulators are fine but do not hang such large capacitances on the output pins. This is just unnecessary stress on the regs. The best place for large capacitance is BEFORE the regs, and some small, ie 100uF afterward. Bypass with good 100nF ceramics.

Assuming you do not want to use coupling caps, the best way to remove the DC is a servo.
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