A project log for TOSLINK DAC

Instead of a $10 box from Amazon, go above and beyond

Nick SayerNick Sayer 10/22/2021 at 02:470 Comments

v1.4.1 is back from OSHPark. It's almost perfect, so far as I can tell. There's just one interesting issue. If you remove the optical input, you get a noticeable white noise output. This is despite the MUTE pin being pulled high by the ERR output of the CS8416. This didn't happen with the DIR9001.

Now, when the PLL unlocks, the master clock output is 750 kHz, which results in something like a 2 kHz LRCK, which is far lower than the minimum input to the PCM1793. But damnit, MUTE is pulled high, so none of that should matter. ERR is driving both the error LED and MUTE, and as a result, it's a little bit low - about 2.8 volts or so. But the PCM1793's minimum threshold for high is 2 volts, so it still should be enough.

I guess a workaround for this would be to supply an actual replacement clock to OMCK. In hardware mode, the CS8416 will supply OMCK on RMCK (and will derive BCK and LRCK from it) if it's available. If not, then you get the unlocked PLL clock of 750 kHz.

I don't think I'll bother, though. If I were to do anything more at this point, I might attempt to replace the CS8416 with an alternative, but I don't think I have a great deal of incentive to do so since the PCM1793 itself isn't rated for higher than 200 kHz sample rates, and I certainly have no use for anything higher than that.