One important design goal was to take the current output, with no internal amplification within the D to A converter, and convert this to an analogue voltage, using discrete class A operational amplifiers and filters.
This circuit can then be optimised for sonic performance. (With most CD players the use of standard operational integrated circuits locks you into the sound of those particular integrated circuits, thus narrowing the scope for improvement). The class A current to voltage conversion amplifier, evolved out of the development of the first stage of the Rega Ios MC amplifier.
It shares identical demands of low noise, high drive capability and gain bandwidth required of the voltage to current amplifier. Careful choice has been made for every component in the digital and the analogue signal path to ensure the integrity of the signal.
The analogue and digital sections are bonded together using a substantial ground plane. It was found during the development of the player that adoption of RF ground plane techniques aided the sonic quality and therefore was included in the final design.
Careful design of the PCB's ensures isolation of not just the digital and analogue sections, but also the motor, display and user interface processor. All sonically critical electrolytic capacitors have been by-passed with polypropylene or polyester film capacitors. In addition to this, large value electrolytic capacitors have also been by-passed with audio grade electrolytic capacitors.
Power supply impedances in the digital to analogue converter are kept very low by the use of solid polymer capacitors. All power supplies utilise custom Rega K-Power smoothing capacitors, along with fast diodes which have been used throughout in power supply rectification.
The Isis uses enhanced and optimised control code for the control of the CD processor and user display.This speeds up the initialisation process by means of a tighter control interface between the user micro and CD processor.