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3) Passive Filtering and Discrete Analogue stage
Each d/a converter operates in the 'voltage output mode', giving >119dB dynamic range. All ltering is passive. A
fully-balanced 3rd order capacitor/inductor/capacitor lter is used to remove ultrasonic noise directly after the d/a
conversion rather than active, feedback-based circuits.
Active lters struggle with the amount of ultrasonic noise and RFI they have to handle and at a few 100kHz they
often lose the ability to lter noise at all, which is precisely where a lot of it is present.
Passive CLC circuitry in the Pro iDSD provides the correct ltering well into the MHz region, so that the follow-on
analogue stage is not required to handle ultrasonic noise and RFI originating within the DAC processes.
An all-analogue six-track Japanese Alps potentiometer is to be found directly after DAC and lter stages. It can be
bypassed if volume control is not required.
The actual analogue circuitry is more precisely a line/headphone driver stage. First seen in the Pro iCAN, it's fully
balanced and 100% discrete, direct-coupled (without coupling capacitors) and tube/solid-state user-selectable.
Our design is not just op-amp based discrete but radically different - pure Class A topology. It was inspired by
exceptional sounding, legendary studio equipment.
