Linn Classik CD receiver Measurements: CD Section

Sidebar 2: Measurements: CD Section

Fed a full-scale CD sinewave, the Linn Classik power amplifier clipped with its volume control set at "81" out of a possible 100 settings, this equivalent to an attenuation of 13dB for external sources. All measurements of the CD section were therefore done at the Preamplifier Out jacks with the volume set at "80," at which value the level was 814mV. This suggests that outboard amplifiers used with the Classik need a higher-than-usual sensitivity. The preamp outputs didn't invert signal polarity, and had a source impedance of 146 ohms over most of the audioband, this rising to 583 ohms at 20kHz.

The CD transport tracked gaps in the data spiral of up to 1.25mm in length without dropouts, which is excellent. The two pairs of traces in fig.1 show the CD frequency response at -12dBFS, with (bottom pair) and without (top) pre-emphasis. As is usual with British audio components, the extreme lows are rolled off, reaching -0.5dB at 21Hz and -3dB at 8Hz. There is a broad 0.2dB rise in the top two audio octaves with a pre-emphasized signal, possibly audible as a very slight brightness but more likely as added detail. Without pre-emphasis, the top octave rises by a negligible 0.1dB at 20kHz. Channel separation (not shown) was excellent in the midrange and below, but decreased above 1kHz with increasing frequency to reach a still good 70dB at 20kHz (R-L). The L-R crosstalk was a little worse, reaching -66dB at 20kHz.

Fig.1 Linn Classik, frequency response at -12dBFS with (top) and without (bottom) pre-emphasis (right channel dashed, 0.5dB/vertical div.).

Fig.2 shows a 1/3-octave spectral analysis of the preamp outputs while the CD section decoded data representing a dithered 1kHz tone at -90dBFS. The 1kHz tone actually lies at -85dB, suggesting 5dB of positive amplitude error at this level. The noise floor is higher than I usual find for CD players, with AC components visible at 60Hz and 180Hz, and what is probably a spurious tone can be seen at 400Hz.

Fig.2 Linn Classik, 1/3-octave spectrum of dithered 1kHz tone at -90dBFS, with noise and spuriae, 16-bit data (right channel dashed).

Extending the measurement bandwidth to 200kHz and decoding data representing a 1LSB DC offset gave the spectrum shown in fig.3. Again, some AC power-supply components are visible, as are some higher-frequency spuriae. (I thought at first that the circuitry was picking up some radiated hash from the computer monitor, so I turned it off for this and the preceding measurement.)

Fig.3 Linn Classik, 1/3-octave spectrum of -1LSB, with noise and spuriae, 16-bit data (right channel dashed).