Hi. It might be that the chip is damaged. The cs4398 chip is quite fragile when used without any output stage.
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about 5 years ago
My CS4398 dac is very noisy. One channel is ok (a lot more noise then other dacs, but that is probably a characteristic the CS4398). The other channel is very noisy. I can hear a pulsating noise.
I use it with differential output. I wanted to use it with digital volume control, but that's not possible. Too much noise. I now use it with a voltage divider between DAC and amp (U-pad R1=10k, R2=2.7K). So the impedance the DAC sees should be high enough.