Integrated Amplifiers

Based on appearances alone it might be tempting to compare the K-300i with Krell's earlier S-300i [HFN Feb '09] but, in fact, it has much more in common with the Duo series [HFN Oct '14]. Specifically, the K-300i is free of the S-300i's odd-order harmonics while distortion increases with level (0.0016-0.014% over the specified 150W range at 1kHz) rather than decreasing – an atypical scenario – as in the S model. The frequency response is both flatter and more extended with ±1dB limits of <1Hz-95kHz (vs. 4Hz-60kHz for the S-300i), the output impedance is reduced by a factor of four to just 0.018-0.030ohm (20Hz-20kHz) and, most impressive of all, noise is suppressed to the point of achieving an A-wtd S/N ratio of 95.5dB (re. 0dBW).

Power output exceeds the 150W/300W spec. at 2x208W/8ohm and 2x370W/4ohm, with 230W and 450W into 8/4ohm under dynamic conditions. However, despite the potential of that massive toroid, power into low 2 and 1ohm loads is protected at 480W and 288W [see Graph 1, below].

The optional digital board is based on the ESS ES9028 DAC, implemented here with its minimum phase digital filter, free of pre-ringing and offering a 75dB stopband rejection. The A-wtd S/N is some way behind what is achievable with this DAC at 101dB (re. 0dBFs, preamp output at 2V) but jitter is very low at <15psec with all 48kHz-192kHz sample rates. Distortion falls to as low as 0.0002% at 1kHz and 0.001% at 20kHz (re. –10dBFs) and – important from a subjective standpoint – is otherwise very consistent with frequency [see Graph 2, below]. The frequency responses reach out to –0.67dB/45kHz and –2.1dB/90kHz with 96kHz and 192kHz files, respectively. PM