Wadia 27ix & Wadia 270 transport Page 2
The digital low-pass filter conforms to Wadia's proprietary DigiMaster algorithm and is implemented in a pair of Motorola DSP56004 chips. The filter runs at a 64x oversampling rate. To minimize word-clock jitter, the master clock crystal is mounted very close to the DAC chips. An ST-optical link carries the master clock signal from the DSP board to the rear panel, so that the 270 transport can be slaved to the 27ix master clock. This differentiates the i version from the earlier 27.
The x modification consists of a revised DSP board, which in turn has a revised Xilinx Field-Programmable Gate Array chip to handle 96kHz and 88.2kHz sample rates. I understand the DACs run at the same 64x rate for both low and high sample rates, but the oversampling ratio is halved at the higher rates. Owners of earlier 27s can return the units to the factory for updating, the modification costing $450 plus S&H. In their literature, Wadia states that a similar upgrade will be available to allow the 27 to decode Sony DSD-encoded data from Super Audio CD, and claims that, if and when an encrypted high-sample-rate DVD-Audio data output standard is agreed on, the processor already has the necessary internal real estate and a blank panel on its rear.
For the record, the first x DSP board Wadia installed didn't work at the 96kHz sample rate. The replacement was fine.
Wadia 270 CD transport
This large, heavy transport is physically identical to Wadia's 850 and 860 CD players, but has an upgraded Teac CMK-3.2 VRDS transport mechanism, with vibration-damping material added by Wadia. Two features distinguish it from the pack.
The first is the presence of a digital input as well as the usual array of digital outputs. An ST-optical link allows the 270's data-retrieval clock to be slaved to the DAC master wordclock in the 27i or 27ix. This should drastically reduce interface jitter in the D/A's analog output. When the 270 is used in a conventional manner, its output wordclock is derived from a temperature-compensated crystal oscillator.
Second is the "mode" button on the remote, which operates both the 270 and 27ix. This button steps the 270 through three states of "resolution enhancement": in state A, the 270 outputs data with the word length increased from 16 to 24 bits, using high-pass-filtered dither with a triangular probability function (TPDF); in state B, the TPDF dither is low-pass-filtered; the third setting has the 270 outputting plain-Jane 16-bit data. (It should be noted that if the 270 is used with HDCD-equipped processors, modes A and B will defeat the HDCD decoding.)
The 270's construction echoes that of the 27ix, except that it has a slightly different-colored fluorescent display, and three pushbuttons: play/track advance, stop/eject, and backtrack. Internally, the construction is to the same immaculate standard as the 27ix. The transformer is isolated in its own vibration-absorbing subchamber, the circuitry is shielded, and all the metalwork consists of panels milled and machined from solid stock.