Rega’s now legendary head electronics engineer Terry Bateman spent 10 years researching the concept of a CD player using valves in the output amplifier. Valves have been widely used in musical instrument and recording amplification from the 1950s to the present day, therefore it made great sense to develop a valve based CD player to match that of the signal chain found in such applications.
This approach kept the circuit straightforward. This is mainly because musical instrument amplification is not excessively hindered by some of the folklore surrounding certain aspects of valve audio design. He took the approach of combining the technical and sonic attributes of valves in a differential instrumentation amplifier circuit driven from differential output DAC with a passive LC filter.
The valve Isis shares the same digital and USB sections as found in the solid state version, however, the analogue stage is valve based with passive filtering. This stage uses two military specification triple mica 5814A (ECC82/12AU7) triodes being driven by the revolutionary Wolfson WM8741 ultra high performance digital to analogue converter.
The output buffer and transformer driver stage uses two ECC88 (6DJ8/6922) triodes. This, like its solid-state stablemate, is of an unorthodox design. The design goal with this player was to keep away from the normal design approach of “let’s run it through a valve to make it sound warm”, but take advantage of industrial valve circuits to make an articulate and competent valve based CD player. Careful choice has been made for every component in the digital and the analogue signal path to ensure the integrity of the signal.
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 utilize custom Rega K-Power smoothing capacitors, and fast diodes have been used throughout in power supply rectification.
The Isis uses enhanced and optimized control code for the control of the CD processor and user display; this will speed up the initialization process by means of a tighter control interface between the user micro and CD processor.