VAC Renaissance Signature Mk.II preamplifier Measurements part 2

Fig.8 shows the spectrum of a balanced 50Hz sinewave signal at 2V, about the maximum level the preamp will be required to deliver to the partnering power amplifier. Odd-order harmonics typical of transformer saturation are evident, with the third harmonic visible just below -50dB (0.3%)—but so are even-order harmonics. The second harmonic, for example, lies at -54dB (0.2%). As anticipated from the THD curves, the distortion spectrum at higher frequencies (fig.9) is significantly cleaner. Though the third harmonic is still the highest in level, it now lies at almost -70dB (0.03%).

Fig.8 VAC Renaissance Signature Mk.II, balanced line stage, spectrum of 50Hz sinewave, DC-1kHz, at 2V into 100k ohms (linear frequency scale).

Fig.9 VAC Renaissance Signature Mk.II, balanced line stage, spectrum of 1kHz sinewave, DC-20kHz, at 2V into 100k ohms (linear frequency scale).

The Renaissance Signature's behavior when handling the demanding equal-level mix of 19kHz and 20kHz tones varied significantly, depending on whether it was driven in full balanced or unbalanced modes. In balanced mode, even when driving 3V into a 600 ohm load (fig.10), the primary intermodulation distortion products lay at close to -80dB or below. However, in unbalanced mode (fig.11), the IM products rose in level even when the measurement conditions were relaxed to 2V and 100k ohms.

Fig.10 VAC Renaissance Signature Mk.II, balanced line stage, HF intermodulation spectrum, DC-24kHz, 19+20kHz at 3V into 600 ohms (linear frequency scale).

Fig.11 VAC Renaissance Signature Mk.II, unbalanced line stage, HF intermodulation spectrum, DC-24kHz, 19+20kHz at 2V into 100k ohms (linear frequency scale).

Finally, fig.12 shows how the THD+noise percentage in the preamp's balanced output varies with the output level of a 1kHz signal driven into 100k ohms and 600 ohms. If we define clipping as 1% THD, the VAC preamp doesn't clip until it reaches 6.7V into 100k ohms and 5.3V into 600 ohms, both figures well above the level the preamp will be required to deliver into almost any power amplifier.

Fig.12 VAC Renaissance Signature Mk.II, balanced line stage, distortion (%) vs output voltage into 100k ohms (bottom and right) and 600 ohms (top and left).

All in all, I was somewhat disappointed in the VAC preamp's measured performance, considering its $17,000 price and what Brian Damkroger reports to be its superb sound quality. There is also nothing in its measured behavior to indicate why BD felt it to sound a little softened at both frequency extremes.—John Atkinson

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VAC
1731 Northgate Boulevard
Sarasota, FL 34234
(941) 359-2066
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