Linn Classik CD receiver Measurements: Amplifier Section part 2

To capture the actual distortion waveform, I had to operate the amplifier at high power levels. Fig.12 shows the result at 73W into 4 ohms: the subjectively benign second harmonic is predominant, though some higher-order harmonics are also present. One odd characteristic was that as the amplifier approached clipping, some spikes started to appear in the distortion waveform (fig.13) and increased in level with time, suggesting a power supply operating with little margin. (The THD level in this measurement was 0.022%.) The Classik will not be an amplifier you turn to for sustained high-power party music, I suspect.

Fig.12 Linn Classik, 1kHz waveform at 73W into 4 ohms (top), distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.13 Linn Classik, 1kHz waveform at 56.5W into 8 ohms (top), distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.14 shows the spectrum of the Linn's output while operating at around 2/3 the clipping power into 4 ohms. Again, the second harmonic is the highest in level, though the third through eighth harmonics can be seen between -90dB and -100dB. Note the spectral lines at 120Hz and 240Hz, which again suggest a power supply that is being asked to work hard. Driven just below the clipping point with a mix of 19kHz and 20kHz tones, the Classik's output spectrum (not shown) showed a 1kHz difference tone at a lowish -75dB, as well as second-order products at 18kHz and 21kHz at the same level.

Fig.14 Linn Classik, spectrum of 50Hz sinewave, DC-1kHz, at 57W into 4 ohms (linear frequency scale).

Conservatively specified at 75Wpc into 4 ohms (15.75dBW), the Linn proved capable of delivering more continuous power, even with both channels driven (fig.15). Into 4 ohms, 84W were available at the usual 1% THD+N clip point (16.25dBW), with 50W measured into 8 ohms (17dBW). Only into 2 ohms under continuous drive did the Classik stumble, with just 23W available (7.6dBW).

Fig.15 Linn Classik, distortion (%) vs continuous output power into (from bottom to top at 2kHz): 8 ohms, 4 ohms, and 2 ohms (both channels driven).

With a low-duty-cycle 1kHz toneburst, which more closely resembles a real music signal, the Linn Classik belied its tiny size by pumping out 80.4W into 8 ohms (fig.16, black trace), 131.8W into 4 ohms (red), 164.2W into 2 ohms (blue), and falling back into 1 ohm with only 47.1W available (green). The 2 ohm delivery is equivalent to an RMS output current of 9.05A, which is very respectable.