I²S. "We all know that I²S can simplify a design. When not in use but installed, our MQA option board already bypasses in the absence of MQA data. That creates an almost straight line from streamer to R2R modules. This was true for Morpheus and remains unchanged. Without an external I²S standard, each company has its own approach. Some adopt the 3V logic level, others 5 volts. Some use balanced signals, others single-ended. Then we have different connectors like UTP/RJ45, HDMI or separate lines for data, clock, master clock and left/right frames. Still we won't know what pins correspond to each line. Our approach was to make this rock solid. We decided on unshielded twisted-pair or UTP cable with its specific 100Ω impedance so both our transmitter and receiver share that impedance. The transmitter then must be able to drive it across long cable with relatively high voltage since due to the receiver's impedance only half that level is available to the receiver. With our implementation we can send I²S across 30 meters with no jitter or distortion. And I mean at least 30 meters which was our only available length in the lab. I don't imagine practice will exceed this length."

Optional MQA plug-in board.

"I²S is very risky non-standard business. Morpheus and its Father are DC coupled. When they power up with no digital data, the DACs create a random output. It might be the maximum 3V on each output pin but that will be different each time the machine fires up. If you're lucky, it might be zero. We of course use muting relays but as long as no digital data presents to the modules, random voltage is present at all times. With DC-coupled amplifiers like your Kinki EX-B7 monos, this triggers their DC protection. Back to the standard inputs of USB, coax, AES/EBU and optical, when you select those, the S/PDIF receiver or USB module generate so-called 'digital zeros'. When driving the R2R modules, these zeros set the analog outputs to 0V. Even when these inputs don't see signal, they still generate zeros. This reset happens during our muting period. With Morpheus, selecting I²S first switches in the S/PDIF receiver so that digital zeros enforce a zero-volt output. Afterwards the circuit sets itself to the chosen I²S input."

"Another risk of I²S is arriving from a streamer and for some reason the digital cable disconnects. Now the last sample which the DAC saw will maintain the output at its voltage. There's no data change so no clock can fill the R2R modules with new data. Again this can trigger protection circuits inside DC-coupled ancillaries. To avoid these issues, I use a so-called data watchdog circuit on the motherboard. When selecting I²S before data is available or when not in use, an I²S simulator activates to present the R2R modules with digital zeros."

Improvise. Adapt. Overcome. Morpheus and his father as digital marines. So far the battle was over PCB layout and I²S challenges. Other skirmishes next.

Sonnet Morpheus

"Daddy's home!" By mid May, Father of Morpheus certainly was on his way. "Here are some photos. The board is still green because it's a prototype which shall occupy my time for a few more weeks. Compared to Morpheus, the toroidal 30VA transformer here has twice the power. While Morpheus uses ~8 watts, this will consume about twice that. The Traco part is an experiment to split analog and digital domains completely."