Listening
I've heard VAC amplification at many audio shows and a few dealer events over the last several years. But with few exceptions—one being at the Florida Audio Expo in early 2020, where I heard this very amplifier driving Acora SRB speakers—those have always been demos of VAC "Statement" products deployed in extreme systems (driving, often, Von Schweikert Ultra-series loudspeakers) to great effect.
At times, I'd questioned whether tubes could provide the power needed to control large woofers (footnote 2) and deliver slam in certain genres, including loud rock'n'roll. I've often been surprised how well they did.
This is the first time I've had a VAC product in my listening room.
I did most of my listening with the nominally 8 ohm Acora Acoustics SRB standmount speakers (reviewed in the January issue) connected to the 4–8 ohm tap. As noted there, the 170i iQ proved an excellent partner for these exotic granite two-ways. The 170i iQ fleshed out the Acora's precise images, making them more vivid and corporeal. Vocal passages, particularly a cappella or incidental, were compelling in clarity and convincing in detail. The Fela Kuti track "Fefe Naa Efe," on Afro Beat: Hard African Funk, Afro Jazz and Afrobeat (CD, Blow Recordings BlowCD03), opens with Kuti joking, chuckling, then reciting a proverb. I've heard this intro many times, but here the vivid imaging allowed me to sense Kuti's swaggering presence. Horns and honking saxes sounded huge and liquid; rhythms and grooves rock-steady and powerful.
It just feels right to turn up rock'n'roll, so I did, and when I did, the VAC-driven system sounded ever better.
I spun a few tracks from the White Stripes' Elephant (LP, Third Man Records TMR 200) on the Clearaudio Performance DC Wood turntable with Tracer tonearm and Talisman v2 MC cartridge. According to its liner notes, this double album was recorded, mixed, and mastered with all-vintage, all-analog equipment. The album's grungier, dirtier production came through in all its ragged glory: Jack White's growl and searing squeals from his Airline "JB Hutto" Res-O-Gras guitar never became piercing or shrill, the heavy feedback on the bluesy "Ball and Biscuit" was weighty and convincing, and I could almost feel the air moving through Meg White's kickdrum. It hit harder than expected. Almost paradoxically, the 170i iQ's smooth continuity served rough edges well, and with plenty of detail.
At first, I set the VAC's phono section loading at 200 ohms; later, I switched to 450. (The suggested loading of the Talisman v2 cartridge is 400 ohms.) 450 added substance—and sounded louder—but may have given up a little resolution and crispness, or control.
Even under the weight of heavier fare and higher SPLs, the VAC held up. The Acoras have a neutral to slightly cool character. The 170i iQ's hints of warmth balanced that out while adding body and a feeling of continuity to the music.
There's a lot happening on Big Red Machine (LP, Jagjaguwar JAG335), a collaboration of Bon Iver's Justin Vernon and The National's Aaron Dessner. This album (and act, which shares the name) is filled with some 40 collaborators' worth of musical contributions. The setup with the 170i iQ might not have matched the fleetness of transistors on drum machines, omnichord, OP-1, and other synth beats on complex electronic material, but the quick attacks and driving pulses didn't sound sluggish—or especially tubelike. This folktronica trip contains layered string and choral sections, piano, and more. The quick starts and stops and blips on "Lyla" and "Air Stryp" were fun and exciting.
Later on, as an experiment, I swapped out the Acoras for the MBL 126 Radialstrahler omnidirectional loudspeakers, which have a recommended amplifier power spec of 200Wpc, well above the 170i iQ's 85Wpc. These MBL speakers are a modest (4 ohm nominal) load in impedance terms, but their specified sensitivity is very low, in large part because they distribute energy evenly in the room instead of beaming it straight at the listener.
This setup exceeded my expectations on plenty of music, including a recent release from the British "virtual band" Gorillaz. On Song Machine, Season One: Strange Timez (LP, Parlophone), every track features guest artists, from St. Vincent through Elton John to Beck. Peter Hook, the bass player from Joy Division and New Order, appears on "Aries." He often plays his bass more like a lead guitar, with "hooky" melodic lines. Hook's distinctive bass line was solid and easy to follow through the VAC/MBL combo.
Another standout track, "Désolé," showcases lively vocals from Malian singer Fatoumata Diawara amid a wild hubbub of instrumentation. The MBL/VAC system resolved the subtle expressive details of Diawara's spirited, lilting vocals. Percussion, electronic and acoustic, propelled the track forward with plenty of punch and pop. Violin, viola, and cello also sounded lush, lovely, and liquid. The strings serve as an intriguing counterpoint to the track's steady, funky groove; their timbres seemed true. Each vocalist and instrument was individuated within a spacious soundstage.
All this in spite of the 170i iQ being way below MBL's recommended power specs. I wanted a little more bass extension and tautness, but it sounded delightful.
With the VAC in the system, sustains and decays seemed extended. Anouar Brahem's Le pas du chat noir LP (ECM Records 1792), an intimately recorded trio of Brahem on oud, François Couturier on piano, and Jean-Louis Matinier on accordion, provided some of the most compelling listening I experienced during the review period. The players are close-miked, precisely placed on a 3D soundstage. Scale seemed well approximated, and timbres felt natural. Backgrounds were dark as night. Accordion swells sounded so full and had such long decays that they took on an organ-like presence. The instruments' overlapping long sustains created layers and lush textures. The title cut captivated with intensity and clarity. Modal melodies meandered. The tension in the music, as in the oud strings, was palpable. A winner.
"Miki Dora" by Amen Dunes (44kHz/16-bit Qobuz stream via Roon) is named for a surfer from the '50s and '60s, a world traveler who did time in a US jail and designed the best-selling surfboard of all time even as he decried surfing's increasing commercialization. This mellow indie folk song doesn't have a chorus; instead, its gentle tension builds almost to the end, when a harmonized vocal line gets repeated in an unexpected climax. The repetition feels wavelike, with a sense of bobbing and swaying in an ocean of rhythm. The VAC, paired with this song's slightly lean, lo-fi production, captured well the song's organic vibe.
Conclusion
The VAC Sigma 170i iQ did well across criteria typically associated with tube amps, and more: sweet treble, excellent midrange, musicality, bloom. Timbres were more natural than warm. Bass was substantial, with good definition. The VAC amp seemed more powerful than its rating suggests, and often delivered solid attacks. It's not inexpensive, but it is luxurious, and all its details are well-considered. It was a pleasure to set up and to use. It's built by hand and meant to last at least one lifetime. There is value here.
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COMMENTS
Not hidden by out of focus camera work or Photo manipulation like is common for Chinese Audiophile stuff.
A Quality product made by Loyal Employees at a Fair price.
Is $10,000 a fair price? , the reviewer seems to think so. ( seems pricy to me )
Tony in Venice Florida ( about 25 miles from this outfit )
... by the time you add on the prices of the optional XLR upgrade, the optional phono stage and the optional tube cage.
Would you still choose this VAC amp when, for the same or even lower cost, you could instead have either the combination of a McIntosh C22 preamp and MC275 power amp or the combination of a Luxman CL-38UC preamp and MQ-88UC power amp?
Hello Mr.Ortofan,
I would want or desire this Amp if it's Sound Quality is outright/downright outstanding and I could justify it's price.
I already own liquid gold amplification systems so I'd have to be dazzled enough to reorganise my outstanding to make room for this piece.
but before that:
I'd be taking a close look to see what's holding my gear back that I hadn't noticed and attempt to revise & improve.
I'm impulsive, I might just love these VAC folks and their gear!
Owning a system Made in Sarasota Florida would be spiritually wonderful for me!
Do they have a scatch & dent department?
Tony in Venice Florida
We should be thinking about the price of that unit in comparative terms. Your examples are p100% apt.
Ouch!!!!!!!! "Talk about going back in time of no damping factor"
6.5db frequency response variation in the audible range. And that's with a simple simulated Kantor speaker load. Hate to see what happens into something like some nasty Wilsons or something harder.
"Using our definition of clipping, which is when the output's THD+noise percentage reaches 1%, the amplifier with both channels driven with a 1kHz signal clipped at 11.8Wpc into 8 ohms"
And on the lower taps you'd have less wattage, do they just want to drive things like Klipsch-Horns etc
Cheers George
Yes, lets do Horns!!
Tony in Venice Florida
ps. you make good points, I like reading your thoughts!!!
George,
I thought I'd chime in here, first to say that I really like he collegiality demonstrated in this and quite a few other threads lately. Disagreement is fully compatible with courtesy (not that I'm seeing a ton of disagreement here.
But I'd also like to comment on the content of your post. This is obviously an old-school amplifier with high-quality construction and parts. Choices were made. Output impedance could have been reduced with the judicious use of negative feedback. The designer chose not to go that route, finding that the disadvantages outweighed the advantages--or, to put it more positively, that the SQ advantages of the sound even with the possibility of gross frequency-response variations was so good he left it alone. Those seeking lower output impedance can find it even within the VAC line.
I've heard this amplifier only at shows, in unfamiliar systems, so no opinion I express should be taken too seriously. With an amplifier like this, much care must be taken to matching it with the right loudspeaker; while it's possible that one might get synergy with less-demanding Wilsons, that's a crap-shoot--not an obvious match. If that's your cuppa, probably best look elsewhere. It should however make an excellent match with, eg, a pair of DeVore Orangutans, or Audio Notes, or anything that loves tubes and doesn't care much about high output impedance (or thrives on it). I heard this amp at a show (Tampa?) with the little Acoras, in a small hotel room, and thought the system sounded great.
One more point to make, which I'm sure is already familiar, but I'll put out here anyway: For an amp like this, "clipping" means something quite different than it does for a classic solid state amp. There's no sudden rise in harsh distortion. Here, "clipping" is just a word coupled with a more-or-less arbitrary number.
There's room for more than one model of excellence in the world, is my main point.
My Best to all,
Jim Austin, Editor
Stereophile
I think it is so great that companies will make unique products like this that have such a small niche. To me, some of these rise to the point of being functioning art.
It isn't something I'd ever own but, just like exotic super cars, it is fun reading about and fun to know someone had the passion to build it.
Now, back to listening to my home built 6L6GC single ended tube amp.
... with a sufficiently high output impedance, such that it will result in audible variations in frequency response when connected to a typical speaker, would it not be beneficial to potential customers for them to publish a list of those speakers they have used during the development of that amplifier, and to identify which ones they have found to be relatively more, or less, compatible?
.. because the user has no control over it, other than choosing a matching speaker.
I don't think it's praiseworthy for a manufacturer to describe this as an "85 watt" amplifier when it appears not to meet even 1/2 of its rated specification. Even if you subscribe to the "Julia Child" theory of assembling a stereo system ("a little bit of this, just a dash of that, and voila it all sounds wonderful"), I don't think its fair of the manufacturer not to advise the purchaser that this amp needs to be partnered with speakers that are 90 dB+ efficient and have benign impedance curves or he/she needs to be satisfied with modest loudness levels in a small room. And that goes for dealers, too.
I won't even comment on the price tag, except that it is not axiomatic that expensive parts + expensive labor costs = great sound quality. If it were, I -- an English major -- would be capable of building a great-sounding amplifier.
It would be interesting to compare this amplifier sonically to a properly assembled Dyna Stereo 70/PAS3x combination with fresh capacitors, something I did assemble more than 50 years ago. The Stereo 70 uses EL34 output tubes in ultralinear configuration, not KT 88s. The PAS3x uses a quad of 12ax7s.
the definition of amplifier clipping is simply when the top of a waveform is "clipped" off by the limits of its power supply.
https://www.google.com/search?q=define+amplifier+clipping&hl=en&sxsrf=ALeKk02Ucvbb193qad5LwNe-FpElAJjKjg:1616777397957&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjDo_GTtc7vAhVSUt8KHS90CYkQ_AUoAnoECAEQBA&biw=1920&bih=915
and
https://www.google.com/search?q=define+amplifier+clipping&sxsrf=ALeKk02BI8L246FcYsaTslc_76YjxoSRNQ:1616781755522&source=lnms&tbm=isch&sa=X&ved=2ahUKEwif8N2xxc7vAhV9ElkFHVA_Cx0Q_AUoAnoECAEQBA&biw=1920&bih=915
By this standard EE definition this amplifier probably delivers more watts than shown here. (Even thought 85 watts seems very optimistic for KT88s.)
According to Bob Cordell (Designing Audio Amplifiers pp 516-524)"... amplifier clipping is exacerbated by negative feedback."
Consequently, low-feedback tube amplifiers are said to clip more 'gracefully" than solid-state and 'appear' in practice to deliver more than their rated power.
just saying
herb
Herb,
It's simple enough to define "clipping" from an operational/theoretical point of view. The other perspective is, "what does it look like when you measure it?" That's what I was addressing. If you look at this distortion vs power for this recently published Counterpoint amp review (solid state):
and compare it to the VAC
You see that the first as a kink followed by a more rapid rise. In the VAC, the closest equivalent to that kink happens at, what, 2.8W from the 8-16 ohm tap? This is not a 2.8W amp!
But because of the kink and the fast rise, that same feature does define clipping on the solid state Counterpoint amp. Notice that it hits 1%--JA's usual criterion--just slightly above the power where the kink occurs. For the VAC, in contrast, there is no kink, but the amp hits 1% at roughly four times the power where it starts rising. What's more, there are no sudden changes in the distortion--just a steady rise--up to 50W, where the measurement stops. Gentle clipping!
Not shown here, but if you look at the 4-8 ohm tap measurement--fig.7 in the VAC's measurements section--you can see that it does have an eventual kink--at about 80W--well above 1% distortion. Looked at from this perspective, you could almost say that the clipping point--the kink--is never reached in those higher-impedance-tap measurements!
Best Wishes,
Jim Austin, Editor
Stereophile
... increasing distortion from the VAC amp become audible?
At what power output level does the increasing distortion from the VAC amp become audible?
There's no straightforward answer to this question, as it depends on the nature of the amplifier's harmonic distortion, the kind of music being played, and the impedance and sensitivity of the loudspeakers.
I created tracks on our no-longer-available Test CD 2 - see www.stereophile.com/content/istereophileis-test-cd-2-tracks-20-26, so listeners could test for themselves at what percentage of pure second, third, and seventh harmonic become audible with a 500Hz tone. I find that 0.1% or even 0.03% of seventh harmonic will be audible, due to the fact that the frequency of the distortion is very much higher than 500Hz. However, 1% of second harmonic is only just audible with the pure tone because the distortion is both musically consonant and has a frequency much closer to 500Hz.
All these harmonics will be less audible with music, due to masking, as long as the amplifier is not also creating intermodulation distortion products that will have no harmonic relationship with the music. In that respect, this VAC amplifier performs reasonably well, as its intermodulation distortion at moderate powers is relatively low (fig.13).
John Atkinson
Technical Editor, Stereophile
... is the definition of the old German high fidelity norm DIN 45500.
Cutting through right to the truth!
Gentle clipping IS different than hard clipping. Real world or on paper.
Both amazing posts! Thank you for level-setting and a bit of clarifying.
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