Интегральные усилители — VAC Sigma 170i

VAC's Sigma 170i is a two-channel tube integrated amplifier from the Valve Amplification Company, founded in 1990 in Sarasota, Florida, by Kevin Hayes and his father Channing W. Hayes. It is hand-made in the USA and appears on the maker's integrated amplifier page as its only current model in that category. The US price was USD 10,000, with USD 800 extra for the balanced input, USD 1,500 for the phono stage and USD 1,400 for an optional cage of glass and machined aluminium. A later US price of USD 10,900 has also been quoted.

Key specs that matter

Output is 85 W per channel into 4, 8 or 16 ohm, taken from separate loudspeaker taps for 2 to 4, 4 to 8 and 8 to 16 ohm loads. Power bandwidth is 13 Hz to 70 kHz. The tube complement is four Gold Lion KT88 output tubes, two per channel in a push-pull ultralinear stage, plus five 12AU7A and one 12AX7A, with two more 12AX7A added when the phono option is fitted. There are four line inputs and a Cinema Bypass input, with the optional balanced XLR input on Input 4 and the optional MM and MC phono stage on Input 1, plus a preamplifier output. The phono stage gives 37 dB of gain for MM and 57 dB for MC, adjustable MC loading, RIAA accuracy within 0.2 dB and residual noise of 3 mV at the output. The amplifier measures 457 mm wide, 203 mm high and 440 mm deep and weighs 32 kg. Mains versions exist for 100, 120, 220 and 230 or 240 V.

Engineering and use context

The central feature is the patented iQ Continuous Intelligent Automatic Bias System, based on a 2014 US patent held by Kevin Hayes. It holds the idle current of each output tube steady regardless of the signal, which VAC says lowers distortion and noise, lengthens tube life and protects the amplifier if a tube fails, so the owner does not need to adjust bias by hand. The line stage is a true class A triode circuit and the volume control is purely analogue, operated by a remote that also handles mute. Cinema Bypass lets a home theatre processor use the amplifier for the front channels. Connectors for RCA and loudspeaker cables come from Cardas. The fascia is finished in black or silver metallic lacquer with chrome knobs, and an iQ display bar. The warranty covers two years for parts and labour, excluding tubes.

Pairing

The three sets of taps let the owner pick the transformer winding closest to the speaker's rated load, so both high-impedance designs and low-impedance speakers of moderate to high sensitivity are both covered.

Alternatives

The VAC Sigma 160i is an earlier integrated model with four KT88 tubes and 2 to 4 and 4 to 8 ohm outputs.