VAC Master Preamplifier/Signature 200iQ Pre & Power Amplifier Lab Report

Lab Report

VAC's Signature 200iQ is a hot number in terms of performance and temperature! In practice, hotspots of 85oC were measured on the top surface of the perforated grille above the KT88s, so adequate ventilation is essential. These KT88s are given no quarter, all four tubes achieving a mighty 145W/8ohm and 205W/4ohm in mono mode via the 4-8ohm tap (or a lower 145W/4ohm via the 2-4ohm tap). There's some headroom for increased dynamic output too [see Graph 1], with 151W/8ohm and 235W/4ohm sourced via the 4-8ohm tap, and 232W/2ohm and 210W/1ohm available via the 2-4ohm tap (or 140W via the 1-2ohm tap). The response is also affected by choice of tap. Also, as expected, distortion increases at very low and high frequencies [see Graph 2], from 0.016%/1kHz to 0.05%/20Hz and 0.035%/20kHz (re. 0dBW), and with level from 0.016%/1W to 0.063%/10W and 0.21%/100W (re. 1kHz) – all comfortably below the level of most contemporary loudspeakers.

The great 'strength' of the Signature 200iQ is its combination of +24dB gain (balanced in) with a very wide 94dB A-wtd S/N ratio (re. 0dBW) – a quality it shares with the equally 'low noise' +9dB gain/98dB S/N ratio (re. 0dBV) achieved by the partnering Master Preamplifier. The latter shares a similar broad-spectrum spread of distortion harmonics with the 200iQ, although these are higher at low frequencies (0.7%/20Hz) before decreasing with increasing frequency to just 0.011%/20kHz [black trace, Graph 2]. The response is usefully extended, rolling gently away below 100Hz to –0.7dB/20Hz (and –2.9dB/5Hz) while reaching out to ±0.0dB/20kHz and –3.6dB/100kHz. PM


Dyn. output vs. THD into 8ohm (4-8ohm tap, black), 4ohm (4-8ohm tap, red; 2-4ohm tap, pink), 2ohm (2-4ohm tap, blue) and 1ohm (2-4ohm tap, green; 1-2ohm tap, br. green). Max. current is 14.4A


THD vs. freq. for Master preamp (0dBV output, black) vs. Sig. 200iQ amp (1W/8ohm, pink; 10W, red)

Continuous power (<1% THD, 8/4ohm) 145W / 205W (4-8ohm tap)
Dynamic power (<1% THD, 8/4/2/1ohm) 151W / 235W / 232W / 210W
Output imp. (20Hz–20kHz, pre/power) 45ohm / 0.76–0.78ohm
Freq. resp. (20Hz–100kHz, pre/power) –0.7 to –3.6dB / +0.7 to –0.4dB
Input sensitivity (for 0dBV/0dBW) 358mV (pre) / 178mV (power)
A-wtd S/N ratio (re. 0dBV/0dBW) 98.2dB (pre) / 93.9dB (power)
Distortion (20Hz-20kHz, 1V/10W) 0.011–0.68%/0.056–0.15%
Power consumption (idle/rated o/p) 240W/345W (94W, preamp)
Dimensions (WHD, Pre/Power) 457x109x368/457x222x439mm
Prices £28,000 (pre +£12,000 phono)/£14,500 (power each)

Valve Amplification Company, Inc.
Florida, USA
Supplied by: Signature Audio Systems, UK
07738 007776