Mark Levinson No.30.6 Reference D/A processor
In particular, the '30.5 introduced the concept of a FIFO (First-In, First-Out) buffer to high-end digital separates in order to minimize the effect of interface jitter. The input data are fed into a RAM buffer several thousand samples long, then clocked out with crystal-controlled oscillator precision. To avoid the buffer either emptying or overflowing, with resultant glitches in the sound, the master-clock crystal oscillator was locked to one of 256 rates closest to the long-term average clock rate of the incoming data, which Madrigal calls "intelligent operation."
The No.30.5 revision was supposed to incorporate HDCD decoding, but the delayed release of the Pacific Microsonics PMD-100 chip mandated using a conventional digital filter chip from NPC. But when the PMD-100 became available, Madrigal's design team introduced an HDCD upgrade kit for the No.30.5, consisting of the HDCD chip mounted on a small header board to replace the NPC chip, and a firmware change. This version was reviewed in the April 1995 Stereophile (Vol.18 No.5), with Robert Harley commenting on the "startling increase in soundstage transparency, image specificity, and the ability to keep individual lines separate."
I bought the 1992 review sample of the No.30, and have since purchased and performed both the ".5" upgrades myself, thus confirming the validity of Madrigal's "Reference" philosophy. Five years later, it is time for the ".6." Unlike earlier upgrades, this one has to be done by the factory.
Yes, the chassis layout remains the same, as does the separate PLS-330 power supply, the eight digital inputs, the buffered digital output, the comms port, the intelligent FIFO, and the balanced and unbalanced outputs. But for the first time since 1992, the upgrade involves replacing the D/A converters in the unit's twin towers. The original UltraAnalog DACs have been replaced by new 24-bit DAC modules designed and built by Madrigal. (UltraAnalog is now owned by Wadia.) These are genuine R-2R ladder DACs, compared with the delta-sigma (1-bit) DACs used by many other 24-bit processors, and are hand-adjusted in manufacture, using a precision Vishay trim resistor, a microscope, and a computer test setup. The new analog boards are made from Arlon 25N, the same low-dielectric-loss material used in Madrigal's other Reference and "S" components.
Both the input receiver and the digital processing board are new. With a throughput capacity of greater than 10 megabits/s, the former can now handle any data rate likely to be encountered from the DVD medium. It handles up to 24/96 data but—most important—is reprogrammable to cope with new data formats. The processing board uses four SHARC 21061 DSP chips, which have a 32-bit data path (plus an 8-bit mantissa) for greater arithmetical precision, to implement both a conventional digital filter and the HDCD decoding filter. The exact filter algorithms were chosen after extensive listening tests. The FIFO buffer now locks exactly to the long-term average clock rate of the incoming data, and Madrigal claims a master-clock stability more than 2500 times that of the No.30.5—just four parts per billion compared with 1.5 part per million. In addition, the FIFO now comes after the digital filtering, so that the data are fed to the DACs with the lowest-possible word-clock jitter.
Finally, as well as offering ML's usual comms port and a RS232 data port for future software upgrades, the No.30.6 has the hardware and connectors for PHASTLink multiroom operation. (The actual PHASTLink controller is a dealer-installable option.) Due to different chassis requirements, PHASTLink is not available on upgraded No.30.5s.
A new No.30.6 costs $16,950. The cost of the upgrade from a No.30 or '30.5 costs $4995 including a new "30.6" front panel, or $4495 without. Contact your dealer to book upgrade time at the factory.
Against the No.30.5: All comparisons were performed with levels matched to within 0.1dB at 1kHz, using the No.32's input gain-offset function. The '.6 was 0.7dB louder than the '.5, something to watch out for in direct comparisons.
On the excellent James Taylor Live at the Beacon Theater DVD-Video (Columbia Music Video CVD 50171), which has stereo 24-bit linear-PCM tracks recorded at 48kHz in addition to the Dolby Digital surround track, the No.30.6 had a slightly more forward upper-midrange presentation, with more high-frequency air apparent. More important for me, the older processor's rather thickened lower midrange and bass region were usefully leaned-out, with more subjective LF extension apparent. When bass player Jimmy Johnson (better known to audiophiles as Flim of Flim & the BB's) plunges down to the low-B string of his Alembic instrument on Beacon Theater, the No.30.5 sounded a little too fat and "puddingy," whereas on the '30.6 it merely sounded deep, deep, deep.