All devices like chips and clocks which are involved in the digital signal rely on DC power which should be stable. Minor instabilities in delivery voltages and their effects on the workings of their parts are yet another jitter source. That's before we consider the digital cables and their connectors themselves whose bandwidth, geometry, impedance and material junctions can introduce reflections and more jitter. In fact, it's perfectly fair to state that at any point of conversion, signal to signal, format to format, interface to interface, there hides an opportunity for jitter to creep in. Qualia Physic to the rescue whose S922 sdr purports to clean up the signal as close to the DAC as feasible. For those who still spin physical media, even non state-of-the-art transports of lower costs remain useful when a heavy investment into any end-of-life luxury transport can be replaced by a more budget version that's instead tricked out with our Portuguese add-on; if the latter delivered. The packages we received contained the S922 SDR reclocker and matching S521 power supply with fixed umbilical cord to connect to the reclocker. Besides courtesy gloves to prevent finger prints, one of the boxes also contained a male XLR to female RCA adaptor. This was no run-of-the-mill plug but one which contained an impedance matcher to convert AES/EBU's 110Ω to the 75Ω standard for coaxial S/PDIF cables.


The first setup we meant to try was the PS Audio PWT as transport. In lieu of connecting its HDMI-carried I²S output into the matching DirectStream DAC's input, we looped the preclocker into the AES/EBU output. The DAC connected to it via AES/EBU. After selecting the correct input on the DAC's touch screen, we waited in anticipation of a nice clean sound. Too bad for us as there was no sound. Moreover, the DAC's display did not indicate any signal lock. After checking all cables, still nada. To learn whether the source or DAC had broken, we connected the transport straight to the DAC without reclocker. Sound. Had the reclocker died in transit? Now we took the clean-bill-of-health transport to our Devialet Premier with Soltanus ESL system downstairs. Here things worked instantly. A quick with/without reclocker session made clear that the Portuguese not only lived and breathed but had a not-to-be-missed effect even in this somewhat gawky setup. We'd gone for the Devialet because at that time we didn't yet have a female AES/EBU-to-RCA adaptor on hand. The NuWave DSD DAC only accepts coax.


Now what? We presented Joao of Qualia physic with our gift of the pesky problem. At the same time we also contacted Paul McGowan and Ted Smith over at PS Audio to ask their opinion on probable cause. Ted suggested checking for an offset between reclocker and DirectStream grounds. Joao concurred about this being a plausible scenario since the DSD DAC lacks a digital input transformer. Joao also mentioned that he had both PS Audio DSD DACs at his disposal and was about to perform various tests including the ground offset check. When results from the tests in Portugal came in, we learnt that with Joao's Panasonic DAT SV-3800 --> reclocker --> DirectStream DAC chain, the DAC recognized the signal in consumer/coax but not in professional AES/EBU mode. Moreover, when the DAT recorder connected directly via XLR or RCA , the situation was the same. In a test with a music server, the situation reversed with the reclocker in place. In both possible direct feeds, either connection was recognized.


Chasing the bug, Joao analyzed the digital signal and concluded that probable cause was the 28th bit of the S/PDIF code. This validity bit has high and low setting. When set to hi, the receiver is triggered to discard the signal. As it turned out, Joao's Panasonic outputs in low mode via XLR, in high via coax. The culprit had been identified. But Joao ran more tests with an Oppo BDP 105 --> CH Precision C1 DAC and an Aurender S10 --> TAD D600 DAC. With all permutations, there now was signal recognition. Joao's final solution was to add a jumper to the reclocker to bridge the validity bit for both modes. Now we were asked to return our loaner so he could install the mod accordingly.