VALVE ISIS

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.

Valve version of our reference Isis CDP

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.

KEY FEATURES

Rega’s advanced CD technology
Twin Wolfson DACs
Rega ‘K-Power’ smoothing capacitors
Custom designed reference case
CNC reference remote control

DESIGN

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 un-orthodox 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 PCBs 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, and fast diodes 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 will speed up the initialisation process by means of a tighter control interface between the user micro and CD processor.

TECHNOLOGY

The differential output of the digital to analogue converter drives a valve differential (operational) amplifier, with a very modest amount of feedback to stabilise the operating conditions. The 5814A based differential amplifier, with a solid-state current generator in its tail, takes full advantage of the differential output from the digital to analogue converter. This is followed by a passive Butterworth second-order LC filter. Finally, this signal is buffered using a low anode resistance ECC88 triode to drive the output and balancing transformer.

In design it was felt that unnecessarily high levels of THD would unduly overwhelm the qualities of the digital stage of the Isis. The overall THD is typically 0.06% being prominently even order, where the 2nd harmonic predominates. This will give the sonic dynamics of the valves without dominating the sonic qualities of the digital section.

After many hours of tube rolling, we found the 5814A differential amplifier position was best on the grounds of micro-phonics, reliable operation and sonic qualities. Both the HT & LT power supplies are fully regulated and use the same power supply parts as used in the solid-state Isis. Like the solid-state analogue stage, the Valve Isis has its own dedicated 50 VA mains transformer, ensuring galvanic isolation between the digital and analogue sections of the player.

The Isis has an isolated balanced output, and in keeping with the spirit of the valve circuit topology, we have opted to use a transformer in this position. This balancing transformer is made to the same exacting standards of that found in the Ios MC amplifier.

We hope that you enjoy this product as much as we have enjoyed creating it.

All these features amalgamate to create the supreme level of performance found in the Isis and provide a perfect partner for the Rega Osiris amplifier.

DIGITAL SECTION

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 50 VA 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.

DIGITAL

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.

USB INPUT

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.

DISC ANALYSIS

The valve 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.