L10, M10, P10 and now C10…

The second big change is architectural. The CH head units, despite their dual mono circuitry, have always followed a linear layout, with inputs on one end and outputs on the other. In the case of the C10 audio box, that’s all change. Instead of a linear topology, it adopts mirror image architecture, with central inputs flanked on either side by the left and right channel DACs/outputs. That might not sound like that big a change, but its real significance will become apparent in a moment.

The best 4×4 by far?

Next up, the DACs themselves. In one sense these are an evolution of the DACs found in the C1.2: they use the same R2R chips, the same fully differential topology and run a development of the same, DSP-based, PEtER spline-filter algorithm. But their actual architecture and operational mode is entirely different. The DACs in the C10 employ a phase arrayed arrangement with four DACs for each leg of each channel – for a total of 16 DACs, given the differential topology – operating in a sequential series to create what CH are referring to as a DSQ Phase Array DAC. What does that actually mean? As the over-sampled data stream arrives from the DSP, the first sample is passed to the first DAC in the array, the second to the second DAC and so on. With four DACs in the array, the first DAC receives the first, fifth and ninth samples, the second DAC gets the second, sixth and tenth samples, etc, etc, ad infinitum.

Inner face of the DAC board, with four DAC chips in a vertical array. There’s four more on the outer face, arranged in reverse order.

In purely physical, component count terms, that doubles the number of DAC chips in the C10 compared to the C1.2’s eight. But in processing terms it raises the sample rate from the 16x Fs (705.6/768 kHz) in the C1.2, to 64x Fs (2.8224/3.072MHz) in the C10.

Obviously sorting, sequencing the samples and routing each to the correct device has demanded a significant revision to the operational software and considerable attention to clock accuracy and implementation. That task has been eased to some extent by switching to a 3rd order Sallen-Key Bessel low-pass filter (as opposed to the combined first and second order filters used in the C1.2) resulting in a significant reduction in propagation delay: the difference between 20Hz and 20kHz, measured in nanoseconds in the C1.2, is now less than two femtoseconds.

Although the really big changes in approach and engineering are to be found in the audio box, don’t overlook the significance of the power supply. Unlike the supplies found on previous 10 Series products, like the L10 and P10, with their twin, captive umbilicals, the C10’s supply has four, removable umbilicals, with separate feeds for left and right DACs, the digital/control circuitry and the clock. The grounding topology routes the digital ground to earth, the DACs (independently) to the left and right signal grounds and keeps the clock independent, with its own ground.

Stepping up…

The significance of the removable umbilicals and separated power/grounding ‘zones’ becomes obvious once you start thinking in terms of the C10 Mono. In the case of the C1.2, going Mono, involves buying a pair of additional chassis into which you transplant the left and right DACs, feeding them from the central head unit (essential to receive the incoming digital signals). You can then round out your C1.2 Mono DAC by adding up to three X1 power supplies, for a six-box D-to-A solution.