Denafrips Pontus II Clicks Or Static?

@whipsaw - You can call it a hardware problem if you want, but IMO, it was (is) a rational approach to solving the problem of jitter reduction of source-clocked digital data.

@jaytor  If it was not a hardware problem, then how would you explain why other manufacturers of higher-end DACs have not encountered such problems? Jitter reduction is essentially a "settled issue", even in much less expensive DACs.

My understanding, though I could be wrong, is that the issue was not reported by users of the Terminator DACs. If that was the case, and it was a software issue, then why would it not have been a simple matter to resolve?

Finally, as you have a technical background, does this Cisco explanation of FIFO overruns not apply here? And if not, can you explain why?

Overruns appear in the output of the show interface Serial 0 command when the serial receiver hardware is unable to hand received data to a hardware buffer because the input rate exceeds the receiver's ability to handle the data. 

This occurs due to a limitation of the hardware. Overruns occur when the internal First In, First Out (FIFO) buffer of the chip is full, but is still tries to handle incoming traffic. The serial controller chip has limited internal FIFO.

@whipsaw - I am making some assumptions here on the exact implementation of Denafrips' designs, since they have never really published a detailed description.

As I understand it, the input data is clocked into the FIFO using the source device's clock (embedded in the SPDIF signal), and clocked out of the FIFO using the DAC's internal clock.

If the clocks are different enough in frequency, eventually the FIFO will overflow (if the source device's clock is faster) or underflow (if the source clock is slower). So, yes, CISCO's explanation is basically correct.

I'm not an expert on modern DAC implementation, but I believe that many DACs (particularly lower priced DACs) use a phase-locked loop to adjust the DAC's clock frequency to match the source clock. They may also use a FIFO so the PLL can be slow responding to minimize jitter. But a PLL will still not be as stable and jitter free as a fixed crystal oscillator (particularly an temperature controlled oscillator).

I suspect the reason that the problem was less common (or non-existent) with the Terminator and T+ is that the clock used in these DACs is higher quality (more accurate) than the clocks used in the lower priced models, and these DACs probably also tend to be used with higher quality sources (which have more accurate clocks). I have not heard that the FIFO implementation is any different, although it's possible that larger FIFOs were used. 

I also suspect that many higher end DACs use a similar approach to Denafrips and just did a better job with the FIFO management (perhaps using the same approach that Denafrips is now using). 

Thanks @jaytor – I appreciate your technical insights. I tend to believe that it was likely a (Denafrips) clock issue, but whatever the exact cause, I hope that the latest firmware has resolved the issue for owners of the affected DACs. 

I had the same issues about a year ago, Alvin had me do a firmware upgrade, that resoled the issues for 90% of the time, a month ago I did the new firmware upgrade, sound was good more detail, started checking left and right plus polarity, when I would Roon and play back was DSD left and right where backwards, through pcm play back it would be just the opposite and phase was off. Alvin replied that I had to change the phase through some programing he gave me, did and I thought problem was resolved, not , I had to go through 8 steps to get the correct I2s config, that also was effectting left and right ch.After all that now the small clicks and static are back. Just sent Alvin an email, had to share.

I have had this issue, but isn't frequent enough in nature to be a problem. At least to me anyway. The noise I get from my Pontus ll is a extremely soft low level pop, which happens maybe twice during a 3 hour listening session. While I would appreciate dead silence, it isn't that offensive to bother me. Pops, clicks, and snaps from vinyl are FAR more annoying than this.