Making CDs Sound Better Than You Ever Thought Possible
The Parasound CD 1 is the result of a collaboration between Parasound and Holm Acoustics in Denmark. The CD 1 demonstrates that CDs can sound significantly better than anyone has imagined possible. The potential of the 16-bit CD format is fully realized for the first time in the CD 1.
The Parasound CD 1 demonstrates a new method for playing Compact Discs. To begin with, it employs a CD ROM drive instead of a conventional CD drive. The CD ROM drive is connected to a passively cooled Intel ITX computer. It uses the Linux operating system kernel and Holm's proprietary software that improves the reading of CD disc data. The CD ROM drive is set to run at four times the speed of a conventional CD player drive in order to accumulate a vast amount of data quickly. Because the CD spins at four times the normal speed, the CD 1 has the advantage of being able to read sections of a disc as many times as needed to significantly reduce read errors.
Advanced Technique for CD Data Analysis
The CD 1 reads a CD multiple times before committing data to an enormous memory buffer stored in RAM. Every data sector is initially read twice and the two reads are compared. When the two reads match, it is because no bit errors were detected and that is accumulated in the buffer memory. When the two reads do not match it is because an error has been detected. That sector is then read repeatedly until good data is obtained.
This sophisticated process almost always results in error-free data. When interpolation techniques are needed they are confined to the single small bad fragment, thereby minimizing their negative sonic side effects.
The bit-perfect, jitter-free information goes next to an asynchronous USB interface. The flow of this information is controlled directly by a separate ultra-high-precision clock that is totally independent from the CD ROM drive clock and whose frequency is absolutely stable.
Analog Devices AD1853 DAC IC
The CD 1 uses a single AD1853 DAC in stereo mode, rather than a separate DAC for each channel. The choice of a single DAC was not budgetary, but rather because a single DAC is inherently free of any inter-DAC delays. The delay between multiple DACs working in parallel can measure up to 10 nanoseconds (10,000 picoseconds), introducing minute amounts of delay into the signal chain. But the jitter on the CD 1's Master Clock to the DAC chip is below 10 picoseconds RMS. To achieve this outstanding DAC clocking performance, even the smallest part-to-part timing discrepancy must be avoided.
Onboard the AD1853 the CD's 44.1 kHz data is converted to 352.8 kHz by 8x upsampling. The upsampling process minimizes the staircase step size of the output current from the audio DAC to achieve the smoothest possible DAC raw output without any related aliasing. This is particularly important because large current source changes that exceed the slew rate of the analog op-amps that are downstream will cause them to generate distortion that impairs audible performance.
Advanced Analog Technology
The quality of the CD 1 analog section is as important as its digital section. Designing an extremely accurate, stable, and linear digital section is a pointless exercise if the analog section does not have the very lowest possible noise to avoid degrading the purity of the decoded signal. It is for this reason that the CD 1 utilizes National Semiconductor LME49990 op amps exclusively in its analog section. The LME49990 is designed specifically for ultra-high end audio applications.
Premium Analog Output Stage
The conditioned analog signal is buffered with yet another pair of LME49990 op amps for the XLR balanced output connectors. The positive leg of each XLR also drives the same channel's analog RCA output jack, so the RCA and XLR outputs cannot be used at the same time. The CD 1 uses Neutrik XLR connectors for the balanced outputs and gold-plated Vampire RCA jacks for the unbalanced outputs. These parts were selected for the high purity of their base metals, sonic superiority and quality of construction. Parasound uses these same connectors in its Halo JC 1, JC 2, and JC 3.
Discrete Analog Option
The Discrete-Op amp button on the CD 1's front panel gives you the option of listening to the analog outputs directly from the LME49990 op amps or via discrete transistor output stages. The discrete output stage is a modernized version of the discrete output stage used in the vintage Parasound DAC-2000 that UltraAnalog designed for Parasound. It uses discrete transistors in a Darlington configuration that operates in the feedback loops of the LME49990s so that the specs for THD and noise are as low as the op amps alone. The discrete circuit subtly changes the sonic character of the CD 1, and fortunately there is no 'wrong' choice.
Multi-Stage Power Supplies and Voltage Regulators
The Parasound CD 1 uses one high current switch mode power supply for its CD ROM drive and Intel computer and a second standby switch mode standby power supply which consumes a mere 0.5w in standby. A separate linear power supply is provided for the analog section, because its characteristics are superior for analog reproduction and appropriate for the CD 1's analog circuit.
The CD 1 has 12 separate point-of-load power supply voltage regulators. Each regulator is assigned to convert voltage downward and maintain it precisely for its assigned analog or digital subsection. 10 voltage regulators are used in the DAC-analog output section alone, and one regulator is used for the S/PDIF digital links. The USB power is filtered by a dedicated regulator for the clock's crystal oscillator. Each power rail is carried on its own isolated power plane. Low voltage DC currents from the analog section's power supply are further noise-shaped by multiple levels of power regulation.
Heavy Shielding Isolates Every Function
The interior of the CD 1 has a network of massive aluminum partitions that isolate each function and circuit from other functions. The analog power supply and its R-core power transformer are each shielded in separate compartments to isolate and shield them from high frequency electromagnetic emissions from the switch mode power supplies, the Intel computer's processor and clock, and the CD ROM drive. Every effort has been made to supply pristine B+ and B- rails so the analog section can achieve its full sonic potential.
The digital input stage and DAC-Analog output stage are also enclosed behind thick aluminum shield partitions so that emissions from the power supplies, Intel computer and CD ROM drive cannot detract from their performance. These shield partitions also add mass and rigidity to the CD 1 chassis, making it virtually immune to the effects of external vibrations.
Outputs, But No DAC Inputs for External Sources
The CD 1 has unbalanced RCA and balanced XLR analog outputs, plus optical, coaxial, and BNC digital outputs. There are no digital inputs, however. The CD 1 design and construction is optimized for near-perfect reproduction of the 44.1 kHz data in Red Book CDs. Adding DAC inputs to accommodate other digital sources would involve far more than simply adding digital input connectors and a selector switch. For the CD 1 to provide comparable levels of performance for CDs and external digital sources would have greatly increased its complexity and selling price.