Emerging from your shipping box regardless will be a 43 x 43 x 9.3cm black aluminium casing. The plain front has a power switch at the left, an input selector duo at right and left from center an input indicator with a numeric blue LCD. Over at the business end there's the right output bay at left (RCA, XLR and ACSS); S/PDIF on BNC and RCA, Toslink, an option bay for HDMI, RJ45 for I²S and USB 3.0 in the middle; and at the right the left output socketry cluster. Mr. Qinghua specifies an S/N ratio of >120dB and output impedance of < 5Ω for RCA and XLR. Max output voltage is 2.5/5V RCA/XLR and 2mA+2mA for the current-domain ACSS. Bandwidth is 20Hz–100kHz with THD of <0.0005% across the audible band. USB and I²S accept up to 32bit/384kHz. S/PDIF is limited to 24/192. USB will also receive up to DSD256/11.2MHz. I²S can process DSD512.

This DAC uses a proprietary digital filter simply called DSP-1 written to an Altera Cyclone IV processor. This FPGA performs all the oversampling calculations and is responsible for the processing of DSD. The R2R 7 is thus two DACs in one. DSD is not converted to PCM but processed as DSD all the way. Whilst on the subject of PCM, there is always the question how a ladder DAC can reach 24-bit resolution which requires 2*24 possible output levels. Each level is 1/16th/millionth of the total range to demand that resistors be matched to 0.00001% tolerance. Such resistors don't exist; not now or ever. The very best to market are of 0.01% precision to require a trick to bridge the gap. Enter an FPGA, in this case no fewer than four Xilinx complex logic programmable devices. Their task is to switch the resistors in parallel not series.

At each tick of the ultra-precise temperature-controlled clocks, these processors will finish a complete output cycle whereas a serial approach would require more cycles to complete the same task. In short, with the help of these digital processors, there's full control over the analog ladders whose resistor tolerance is compensated for true 24-bit resolution. But there are still more CLPD on board. There's one for each input channel where it acts as S/PDIF receiver and jitter killer by reclocking the signal before handing it over to the central Altera Cyclone FPGA which is the platform for the x 2, 4 and 8 oversampling. Yes, there are no fewer than 11 programmable controllers in the R2R 7. And if one does not want to oversample to prefer pure NOS mode, the processor offers four different variants of non-oversampling. Really.

Once the signal is analog, it is buffered in a transistor-based output stage where our earlier LampizatOr encounter had championed tubes. This output stage is DC coupled and uses old-fashioned through-hole parts by way of single-ended FET in two parallel stages biased in class A. A quartet of op-amps handles DC servo to avoid coupling capacitors. The power supplies include three oversized transformers for the left and right analog plus the digital section. To complete the picture, the interior is compartmentalized into three bays with 5mm thick aluminium separators to avoid EM interference. So much for theory.

To get practical and clock that vital extra burn-in, we reached for our PS Audio PerfectWave CD/DVD transport and used a Crystal Cable interconnect to the Audio-gd DAC. With the transport on repeat, we played in silence for a good two weeks while doing other business. Occasionally we checked into some CDs like the incredibly dynamic Drums & Bells by Brad Dutz and Chris Wabich. For this we connected the R2R 7 with unbalanced Nanotec interconnects to our Music First passive preamp which fed Trafomatic Kaivalya EL84 monos with equivalent cables. From there Franck Tchang custom biwire loudspeaker cables ran into our 109dB sensitive Avantgarde Duo Omega horns with their additional Taket Bat-pure super tweeters. From the woofers of the Duo Omegas we connected Nanotec loudspeaker cable to our two Zu Submission MkII subwoofers. Quite a litany of gear but the results can be excellent. Throughout the burn-in period, we noticed changes in tonality. The recommendation for extensive break-in is no mere recommendation. It is mandatory.