Outboard DACs

Based on the converter technology first seen in its 'Power DAC' [HFN Apr '08] MSB's gold-anodised 'Prime DAC' modules (pictured below) employ precision-matched resistor ladder networks to convert 'bits' into sequential steps of current. In an R-2R DAC the LSB (Least Significant Bit) is represented by the smallest current source, with each subsequent 'bit' twice the output of the last (a ratio of 1:65,536 over 16-bits). Burr-Brown's Sign Magnitude DACs were the most famous commercial example of this technique, employing two R-2R ladder networks with resistors laser-trimmed to achieve a claimed 19-bit accuracy. A pair would handle positive and negative-going signals, respectively, with a notional 20-bit resolution.

Fast forward to today and inside each Prime DAC module is a fully discrete ladder DAC architecture – designed, manufactured and trimmed by MSB's engineers. The partnering digital filter – executed in DSP and FPGA chips – is customised for each sample rate from 44.1kHz to 768kHz. Hence the slightly different HF extension of 96kHz and 192kHz responses [black and red traces, inset Graph]. MSB eschews short minimum phase and other filters in favour of a linear phase type with a very long tap, and ripple length. PM