Linn Classik CD receiver Measurements: Amplifier Section

Sidebar 3: Measurements: Amplifier Section

The Linn Classik was preconditioned by being run at 1/3 full power for an hour, which maximally stresses the output stage. The blue-painted metal chassis was hot, though not so much that I couldn't keep my hand on it. All amplifier measurements were taken with the volume control set to its maximum setting of "100." The control operates in accurate 1dB steps, though a number of settings produced no change in level. Settings of "80," "79," and "78" were all equivalent to an attenuation of 14dB compared to full scale, for example. The unity gain setting is "46," which is 38dB down from the maximum level. With the control set to "100," an input of 100mV at the Aux input produced 7.733V out into 8 ohms, giving a maximum voltage gain of 37.8dB—higher than what would typically be required for normal playback levels.

The amplifier section doesn't invert absolute polarity, and channel separation was only a moderate 54dB across the band. The Classik's input impedance for external line-level source components was a sensible 47k ohms over most of the audioband, this dropping slightly to 42.2k ohms at 20kHz. The output impedance was a moderate 0.114 ohms at 20Hz and 1kHz, rising to 0.125 ohms at 20kHz.

As a result, there is very little modification of the amplifier's frequency response when measured into our standard simulated loudspeaker load (fig.8, top trace at 2kHz). The overall response is sensibly arranged to roll off above and below the audioband, the former slightly rounding off the leading edges of a 10kHz squarewave (fig.9). The 1kHz squarewave (not shown) had an essentially perfect shape.

Fig.8 Linn Classik, frequency response at (from top to bottom at 2kHz): 2.83V into dummy loudspeaker load, 1W into 8 ohms, and 2W into 4 ohms (0.5dB/vertical div.).

Fig.9 Linn Classik, small-signal 10kHz squarewave into 8 ohms.

The treble and bass controls each operate in seven positive and seven negative steps. Their maximum effect is shown in fig.10, where it can be seen that the bass control actually functions as a bandpass boost/cut control, the former presumably compensating for the low-frequency rolloff of Linn's small Tukan speaker.

Fig.10 Linn Classik, effect of treble and bass controls set to their maximum and minimum positions (5dB vertical div., right channel dashed).

The A-weighted signal/noise ratio (ref. 1W/8 ohms) was moderate at 77.2dB, this worsening slightly to 68.6dB with a wideband, unweighted measurement. For small signals, the measured distortion (fig.11) was dominated by noise below 2kHz, though the inevitable rise at higher frequencies and into lower impedances can be seen in this graph.

Fig.11 Linn Classik, THD+noise (%) vs frequency at (from top to bottom at 4kHz): 4W into 2 ohms, 2W into 4 ohms, 2.83V into simulated loudspeaker load, and 1W into 8 ohms (right channel dashed).