Wadia Digital 830 CD player Measurements part 2
Fig.4 Wadia 830, right-channel departure from linearity (2dB/vertical div.).
Fig.5 Wadia 830, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit data.
The 830's distortion levels were low and, as can be seen in fig.6, of low order, with the third harmonic predominating. This spectrum was taken from the unbalanced input; the smattering of higher-order harmonics present at the -100dB level was absent from the balanced outputs. High-frequency intermodulation products were also low in level (fig.7), and while the DigiMaster filter does allow some reflection of the fundamental tones from the sample rate and its harmonics, these are still below -80dB (0.01%).
Fig.6 Wadia 830, spectrum, DC-1kHz, 50Hz at 0dBFS, 100k ohm load (linear frequency scale, 20dB/vertical div.).
Fig.7 Wadia 830, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 0dBFS, 100k ohm load (linear frequency scale, 20dB/vertical div.).
Fig.8 Wadia 830, high-resolution jitter spectrum of analog output signal (11kHz at -6dBFS with LSB toggled at 229Hz). Center frequency of trace, 11kHz; frequency range, &$177;3.5kHz.
Fig.8 shows a high-resolution spectrum of the Wadia's unbalanced output while the player decodes data representing a high-level 11kHz tone accompanied by the LSB toggling on and off at a 229Hz rate, an optimal signal for detecting the presence of jitter. The Miller Audio Research Analyzer, with which this spectrum was calculated, examines the FFT-derived spectrum for symmetrical pairs of sidebands, which it then labels. The 830's absolute jitter level was very low, at 144.7 picoseconds (peak-peak), while its clock error was zero! The sidebands marked with red numbers in fig.8 are 229Hz and its harmonics, and are obviously data-related. The sidebands marked with purple numbers are either due to power-supply modulation or lie at very low frequencies. But whatever their source, all the sidebands are very low in level.—John Atkinson