1 - TOP PCB

The TOP PCB is mounted on the TEAC CD-5010A CD mechanism. This mechanism is CD ROM based, which has been developed by TEAC specifically for audio applications. The staff at R&D Audio Analogue has contributed to the development of this component by performing the mechanical tests. In the CD-5010A the spin speed has been chosen to decrease the mechanical vibration to make the reading procedure stronger and reduce the jitter too. On the TOP PCB there are: the control digital circuits, their power supplies and the following analogue parts: Input selection, Volume control, DAC section, Vacuum tube Preamplifier, MonoOut section and the respective power supplies. On this board there is also the tuner module connector on which the power supply, the control signals and the audio signals are carried. The analogue and control digital circuits have been designed to be partitioned as much as possible to avoid any undesired interference between the parts. The digital and analogue grounds are obviously separated and even the control signals are transferred from the controller to the analogue parts via optoisolators. The analogue and digital grounds are separately brought to the single unit Earth point via a resistor as to reduce earth noise problems and earth interference.

2 - System Control – Digital Power Supplies

The entire unit is controlled by a microcontroller based architecture where a Bus structure has been added because of the large number of control signals required. To have the best isolation between the analogue and digital parts, optoisolators are used to carry the control signals to the analogue parts. The microcontroller has been placed into the centre of the board to reduce the overall track distances in any direction (especially for the CD Mechanism control signals) and in such a way reduce the probabilities of irradiation and interference. The digital power supply is made from a dedicated secondary stage and all the digital power supply is placed as far as possible from the lowest level sensitive analogue parts.

3 - Vacuum tube preamplifier section

The preamplifier circuit is based on the Rossini CD Player Rev2.0 vacuum tube output stage that has performed very well thanks to its electrical characteristics and audio musicality. The circuit has been designed by the Audio Analogue R&D office to emphisize the sound properties of the vacuum tube and to take advantage of the solid state technology. The vacuum tube is the first phase in an inedited DC coupled low feedback three stage structure. The amount of feedback has been choosen not only on the basis of measurements but also on the basis of listening tests too. What we have tried to do is strike a balance between the vacuum tube “coloring” and solid state “cleanliness”. To use this circuit as Enigma’s preamplifier section we have modified it to increase the maximum allowed input signal voltage and the bandwidth. The preamp section with its low output resistence directly drive the power amp stage.

4 - Anodic power supplies

The vacuum tube preamp stage that we have used is not based on a differential input so the noise on the anodic supply is not reduced by the circuit itself. That is why we have worked on the anodic power supply to make it as clean as possible. The voltage for the anodic power supply is obtained by a high voltage dedicated secondary and then regulated with a voltage regulator made of discrete components. The regulator output is then filtered by a RC filter with a very low time constant (less then 1.24!). At the end no interference between 100Hz is visible on the pre output frequency spectrum. The voltage supplies of the two channels are also separately bypassed to enlarge the listening stage.

5 - Input selection, Volume control, MonoOut section, Phones Out Secion

These parts are all realized with SMD components to take advantage of all available space and reduce the Track’s length. Every Integrated power supply has been bypassed using high quality capacitors for high frequency efficient bypassing (see the “distributed” high quality “Red” Wima Capacitors on the board…). The volume control is bufferless for the best sound transparency. We have used low noise and low distortion input selector circuits. All the signals to different sections have been arranged to eliminate any loading effects between the stages. These parts have their power supply coming from a separated secondary stage which is used also to implement the Tuner module supply and the preregulated DAC section Power supplies.

6 - Dac section

The new DAC PCB use a Burr Brown 24-bit, 192KHz, Enhanced multi level Delta Sigma DAC and a low jitter recovered system clock (50pS!), 96KHz, 24 bit Receiver also from Burr Brown. The DAC Section is realized on a separated board to avoid any unwanted interference due to high frequency digital signals. The power supplies for the receiver and the DAC are taken from the regulated voltages of the TOP PCB and are stabilized “in loco” on the DAC PCB with a dedicated voltage regulator for each power supply. We have used a really high level performance overall conversion circuit, in fact we have reached a THD + N (with a 20Hz-20KHz noise filter) of less than 0.003% for a 0dB digital pure sinewave track.

7 - Tuner Module

The Tuner Module used is a Sanyo technogy based one with electronic tuning and a AM/FM PLL Frequency Synthesizer capable of matching all the AM and FM frequency range used in the various countries. The tuner Module is shielded and keep separated to all the other parts of the unit, the audio signals are low pass filtered as they arrive on the TOP PCB to block every radiofrequency component.

8 - Power Amp Supply and Power Amp

On the bottom PCB placed in the rear part of the unit there are the power amps and their power supply. The power amplifier stages are based on the National Semiconductors integrated component LM3886 which has been used in a lot of audiophile quality audio equipment (such as the Jeff Rowland Concentra Integrated Amplifier). That component is a very reliable one with a lot of inner integrated protections which work with no interference to the sound quality. The LM3886 is protected against over-current and short-circuits and has two different temperature protection systems, one based on the average temperature and the other sensing the immediate temperature. The frequency response of the power stage has been matched with the Preamplifier circuit so we have added a lot of capacitance to supply a good charge reserve and have the correct low frequency response while we have increased the high frequency band limit to not damage the high frequency performance of the preamplifier. The reserve capacitors have been placed close to the power stages for a more efficient charge exchange. There are as much as 15000µF on either the positive or negative power supply for a total of 30000µF, just for the power stages! The control signals from the TOP PCB to the Power stages as for the TOP PCB are passed through optoisolators to leave the analogue and digital grounds separated.