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VAC Amps Sigma 170i
The new VAC Sigma 170i is the world’s first integrated amplifier with the patented iQ Continuous Intelligent Automatic Bias System. The iQ System holds the true idle point of the output tubes perfectly steady under all conditions, increasing detail & dynamics, lowering distortion & noise, prolonging tube life, and protecting the amplifier. Integrated amplifiers are a great lifestyle choice, and VAC lets you have all of the benefits of tubes without the worry.
With optional MM/MC phono and balanced inputs, the 85 watt/channel Sigma 170i is ready to be the heart of your high end musical experience.
Features include:
- Pure vacuum tube audio circuitry
- 85 watts/channel into 4, 8, and 16 ohm speakers
- Cinema bypass mode for tie in to home theater
- Remote control
- True Class A triode tube line stage
- Pure analogue volume control
- Four inputs
- Optional MM/MC phono with adjustable MC loading
- Optional balanced input
- Optional perforated tube cage (required for CE countries)
- Fascia available in black or silver metal flake paint
- Hard chrome knobs and iQ display bar
- Gold Lion KT88 output tubes
- Premium Cardas RCA & speaker connectors
- Hand made in the United States by VAC
The Special Edition version uses the Statement Series line input transformers with the balanced option, and incorporates exotic capacitors and resistors in key circuit locations for a larger, more vivid, detailed, and organic presentation
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VAC Amps Sigma 170i
The Sigma 170i is a compact, hand-built integrated that marries tube warmth with surprising authority, delivering a classic valve sound with weighty low end, detailed mids and airy treble. Reviewers including Ken Kessler and Hi‑Fi Choice highlight its expansive soundstage, vocal clarity and dynamic punch that often outpaces the quoted 85W/channel rating. Performance features such as the iQ Continuous Automatic Bias System, multiple speaker taps and an optional MM/MC phono module make it flexible for vinyl and multi-speaker setups. Build quality is premium — hand-rubbed finishes, heavy construction and optional protective cage underline a luxury fit and finish. Ideal for listeners seeking tube character without sacrificing slam or scale, the Sigma 170i is presented as a compelling, well‑equipped integrated for serious music systems.
Pros
- Big, convincing dynamics and apparent power that exceed its 85W/ch rating, allowing it to drive a wide range of speakers confidently.
- Exceptionally natural midrange and vocal definition with a spacious, well-defined soundstage that works across speakers and genres.
- Robust build and thoughtful features — hand-built construction, iQ bias monitoring, multiple speaker taps and an optional MM/MC phono module for vinyl lovers.
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Cons
- High entry cost and expensive optional extras (balanced input, phono module, protective cage) increase the overall outlay.
- Remote control is very limited (mute and motorised volume only), which may disappoint users expecting broader system control.
Sound Quality
91/100
Dynamics
90/100
Despite being a KT88 tube design rated at 85W/ch, reviewers repeatedly note strong dynamic authority: 'laughed at everything I could throw at it', 'ensured that every dynamic moment was treated with respect', and 'seemed more powerful than its rating suggests.' These comments justify an excellent dynamics score for a high-power tube integrated amp.
Soundstage Imaging
92/100
Reviewers highlight expansive staging and excellent imaging: 'sense of space and air', 'recreation of a concert hall', and consistently defined vocal elements across different speakers. Multiple sources describe a convincing, large-scale presentation that defies the listening room constraints.
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Build Quality
90/100
Hand-built, heavy construction and carefully considered details are emphasized ('built by hand and meant to last at least one lifetime', 'luxurious, and all its details are well-considered'). Optional protective glass/metal cage and premium finishes further support a strong build-quality rating.
Features Connectivity
91/100
Well-equipped for an integrated tube amp: four line inputs plus cinema bypass, optional balanced XLR input, optional MM/MC phono module with loading options, speaker taps for 4/8/16ohm, preamp outputs, and a motorised volume remote. The optional extras (balanced input, MM/MC, cage) add capability and flexibility, yielding a high features score.
Value for Money
89/100
Reviewers acknowledge the Sigma 170i as luxurious and well-made ('There is value here', 'not inexpensive, but it is luxurious'), while also noting a substantial asking price and costly options (reviews reference ~£10k base and ~£3.7k of options). Overall sentiment is that the amp justifies its premium for buyers in this segment but is not described as a bargain.
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