Legend Audio Design Starlet integrated amplifier Measurements part 2
Fig.3 Legend Starlet, THD+noise (%) vs frequency at (from top to bottom at 4kHz): 4W into 2 ohms, 2.83V into simulated loudspeaker load, 2W into 4 ohms, and 1W into 8 ohms.
Spectral analysis of a high-level, low-frequency tone (fig.4) reveals that the second harmonic is the highest in level, with then a regularly decreasing series of higher distortion harmonics. AC supply components can also be seen at 60Hz and its odd harmonics—the former actually lies at -50dB (0.3%), which is pretty poor engineering. (I tried all manner of grounding arrangements to reduce the level of hum, to no avail.) Higher in frequency and at lower signal levels, the distortion shifts in favor of the third harmonic (fig.5). But at high levels, the second again becomes predominant (fig.6). (Note also in this graph the AC-supply-induced sidebands around each of the signal's spectral components.)
Fig.4 Legend Starlet, volume control at 2:00, spectrum of 50Hz sinewave, DC-1kHz, at 14W into 8 ohms (linear frequency scale).
Fig.5 Legend Starlet, 1kHz waveform at 2W into 8 ohms (top), distortion and noise waveform with fundamental notched out (bottom, not to scale).
Fig.6 Legend Starlet, volume control at 2:00, spectrum of 1kHz sinewave, DC-22kHz, at 14W into 8 ohms (linear frequency scale).