Technology behind the design of the Isis
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.
The analogue section employs two Burr Brown PCM1794 digital to analogue converters, running in a parallel dual mono mode, driving a high performance discrete class A current to voltage amplifier.
This combination generates an exceptionally wide dynamic range, low distortion, and linear signal. This drives an enhanced discrete Class A output amplifier. The circuit is fully balanced from the digital to analogue converters to the balanced analogue XLR outputs.
The analogue stage has its own dedicated 50VA mains transformer which ensures galvanic isolation between the digital and analogue sections of the player. You will find 10 separate power supply regulators are used in the analogue circuit and each individual amplifier stage has its own dedicated low noise voltage reference.
The digital section is blue printed and selected, with major improvements to the mechanism, optical amplifier, DSP core, PLL, master clock & motor power supplies. Another 10 separate power supply regulators are used in the digital circuit.
The motor, user interface processor & display also have their own power supply. The digital stage also has its own 50VA transformer again ensuring galvanic isolation. The mechanism is graded and matched to the servo circuits, to ensure the servo and optical amplifiers are working at their optimum point, improving error correction and playability.
The headroom of the optical amplifier has been improved by 10% by increasing the voltage in the power supply.
This revolutionary player has been five years in design. Rega, together with its design partners have pioneered a highly advanced servo controller that uses the latest signal processing techniques to ensure that the raw data that is recovered from the disc is of the very highest quality. Because our fully digital servo can use highly advanced algorithms, the laser spot is kept in the optimum position for data recovery in terms of focus, size and tracking.
Extra Error Correction
Previous chip-sets always made compromises on error correction. Formerly it was possible to have good jog resistance or better musical performance.
The Rega chip-set allows optimum musical performance and optimised jog /vibration resistance.
Super-stable phase lock loop
The entire IC is clocked via a very special PLL of our own design. This allows better CD data recovery as well as a big improvement in the quality of the data delivered to the DAC.
Low noise digital design
In the design of our CPU IC, we went to great lengths to ensure that the data and address bus noise was kept to an absolute minimum. This ensures the ground and signal connections to the DAC are as 'clean' as is possible.
Allowing direct connection to a laptop or PC via a USB A-B lead to stream internet radio, MP3 or WMA files directly from your computer via the high quality Isis internal DAC.
The USB input uses an isolated double-clocked USB interface, which permits the digital to analogue stage to be used with a computer USB interface and its own regulated power supply.
The USB benefits once again from galvanic isolation from the main circuitry of the Isis player which eliminates the flow of earth currents between the CD and host computer, and eliminate computer power supply noise.
The Isis will analyse each disc on an individual basis. During the initialising period (rather like the engine management system on a modern car which optimises the engine settings to temperature, fuel quality etc.), the Isis will adjust itself to each disc in order to give optimal trouble free reading.
For this reason the Isis will often play discs with marks or scratches that other players cannot read.