Musical Fidelity Nu-Vista 300 power amplifier Measurements
Before being measured, the big Musical Fidelity amplifier was warmed up for an hour driving a 1kHz sinewave at 1/3 power into 8 ohms. This will maximally stress a solid-state amplifier with a class-B output stage; after the 60 minutes of operation the amplifier's heatsinks were too hot to keep my hand on, implying a temperature of well above 60 degrees C.
The Nu-Vista didn't invert polarity, and its input impedance was a highish 64k ohms. The voltage gain into 8 ohms was 30dB, about 3dB higher than normal for a typical American amplifier, with a 0.08dB mismatch between channels. DC offset was low at 19mV (right) and 23mV (left), and the output impedance was 0.08 ohms/0.04 ohms, left/right, respectively, across most of the audio band. While these figures rose to 0.13 ohms/0.09 ohms at 20kHz, the Nu-Vista 300's source impedance is still low enough that any response variation due to the effect of the speaker's impedance modulus will be minimal.
This can be seen in fig.1, the slightly wavy trace being the amplifier's response into our simulated loudspeaker load. The response into an 8 ohm resistive load was down by about 0.2dB at 20kHz, with the -3dB point above 100kHz. The rolloff was a little greater into 4 ohms, but still negligible in the audio band. As expected, the waveform of a 10kHz squarewave (fig.2) was excellent, though a hint of well-damped overshoot can just be made out. The shape of a 1kHz squarewave (not shown) was textbook-perfect, though again with just a hint of overshoot. Channel separation (fig.3) was asymmetrical, with R-L crosstalk much lower than in the other direction, where the smooth rise with frequency indicates capacitive coupling from the left channel to the right. Nevertheless, the channel separation is more than adequate.
Fig.1 Musical Fidelity Nu-Vista 300, frequency response at (from top to bottom at 1kHz): 2.828V into simulated loudspeaker load, 8 ohms, and 4 ohms (1dB/vertical div., right channel dashed).
Fig.2 Musical Fidelity Nu-Vista 300, small-signal 10kHz squarewave into 8 ohms.
Fig.3 Musical Fidelity Nu-Vista 300, channel separation vs frequency (10dB/vertical div., right channel dashed).