White noise problem

[stef23]

Hi everyone,
I've realized my first audio DAC, but I have a problem:
when the S/PDIF input of the CS8416 is unplugged I hear some white noise on the headphone even if I mute the dac chip (PCM1781). If I plug in the S/PDIF cable, the noise disappears, and the dac works perfectly.
How can I remove this noise?
Thank you!

 

[wwenze]

Grounding issues?

See if you just touch the outer connector of the spdif cable to the outer connect of the RCA socket does that remove the noise.

Do you hear that noise if your input is connected, but mains power cut off?

 

[stef23]

If I touch the outer connector the noise doesn't disappear. I have the same problem also with the Toslink input (I've used the GP1FAV31RK0F receiver).
If I cut off the main power the noise disappear. It appears only if the signal is not present, because if I connect the Toslink cable to my pc, the DAC works perfectly ( and I don't hear the noise ). When the pc is turned off the noise still appears.

 

[wwenze]

How loud is the noise? Noise from invalid signal should be pretty loud if unmuted.

Either a) muting circuit not working b) muting circuit not attenuating enough c) digital noise leaking onto power supply d) some kind of interaction between a muted output pin and your load. The output may be internally shunted to somewhere like the rails or ground for example. More info on the system would be nice.