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Audio by Van Alstine FET Valve CF Preamplifier

Audio by Van Alstine FET Valve CF Preamplifier

There is good news for all of us glass-audio aficionados: Audio by Van Alstine (AVA) now offers an all-tube version of its linestage preamp. I don’t know about you, but I find the model name a bit confusing, so for the record let me make clear that this is not a FET Valve hybrid. The new linestage does indeed feature an all-tube signal path, relegating MOSFETs to the role of power supply voltage regulators. The basic circuit is rather straightforward: two cascaded gain stages (12AT7 dual triode) followed by a 12AU7 dual triode connected in parallel and configured as a cathode-follower buffer. Frank Van Alstine tells me that this circuit was initially evaluated as far back as 2004 and was put on the back burner because it failed to provide the performance boost he was looking for back then.

In the intervening years, AVA developed a unique method of powering tube stages, which provides a separate high-voltage power supply for each individual plate. The improvement in musicality and transparency was apparently so dramatic that Frank decided recently to revisit the all-tube linestage project with, I might add, spectacular results. The new tube linestage design includes six regulated power supplies, two for each 12AT7 tube section and one for each of the 12AU7 tubes. Adjustable high-voltage regulators are used as a reference for the power supplies, replacing much noisier zener diodes. In addition, capacitor and resistor values have been tweaked and 1k-ohm grid-stopper resistors added for each tube. All capacitors in the signal path are now polypropylene types. A new PCB motherboard houses all active gain stages and power supplies, with room for an optional phonostage. And as an added bonus, the cost to build is less than before, which is reflected in a lower retail price ($2099). Other features are unchanged. There are six line-level inputs, a tape input, a tape/CD-recorder output, dual line-level outputs, a low-gain switch, and a high/low filter to tame aggressive source material. A headphone amplifier is standard, though I did not test it. Remote volume control is a $299 option. Other options include a phonostage ($249 mm, $299 mc) and buffered tape outputs ($149).

Possibly this design’s major takeaway is that there’s still plenty of magic to be found in plain vanilla circuit topology. Series-regulated push-pull (SRPP) and Mu-follower stages have been quite popular in recent years, and each topology has its adherents. Differences in tube operating points and tube types make it difficult to reach a definitive conclusion about which is better, though I would concede that when mated with a plain vanilla power supply the more exotic totem pole circuits have the advantage. However, the sophisticated power supply deployed by AVA makes all the difference. This was the approach used by Audio Research in its highly successful SP3a preamplifier. In fact, Audio Research revolutionized the high-end scene in the 1970s, riding the paradigm of power-supply regulation to market supremacy.

Audio by Van Alstine FET Valve CF Preamplifier

I should mention that a bit of negative global feedback (NFB) is taken from the buffer stage and returned to the cathode of the first gain stage. For those of you who are NFB phobic or wary of cathode-follower stages, I would simply ask you to give the FET Valve a serious audition. You’ll be surprised by its dynamic prowess. To be sure, it’s a bit unusual to deploy NFB in what is truly a single-ended Class A voltage amplifier. One consequence is a reduced distortion spectrum and hence less euphonic residuals. It’s not difficult to imagine that someone in search of aural thrills might actually be attracted to a tube preamp precisely because of a particular euphonic sonic signature. Pervasive tube warmth that blankets the midrange irrespective of the program material falls in this category, and has proven to be a siren call for many tube-o-philes. The FET Valve is far from being a euphonic linestage. It does not imbue the presentation with any tubey coloration. And its frequency response is sufficiently wideband to avoid softening transients and overly liquefying harmonic textures. So if you’re in the market for a linestage that loudly communicates its tube lineage then look somewhere else. In addition, the tonal balance is quite neutral and lacks the overly lush lower midrange that some vintage tube preamps bring to the table.

If you were to ask me what I dislike the most about new-production 9-pin miniature preamp tubes, it would have to be their grainy harmonic textures. That has been a chronic complaint of mine for years, as the differences in textural smoothness between vintage and new-production types can be rather dramatic. Kudos to the audio guru who phrased it as follows: “I’ll take a decent amplifier with the finest tubes any day over the finest amplifier with mediocre tubes.” And that’s audio verity you can take to the bank. It should therefore not come as a surprise that it didn’t take me too long to replace the stock JJ Electronic tubes. Now let me make it perfectly clear that I don’t fault AVA, or any other manufacturer for that matter, for shipping product with new-production tubes—it would be insane to try to do otherwise.

When you are dependent on a steady supply of tubes, there is no rational alternative other than purchasing lots of new stock tubes. But for the end user there are other options, and in my experience it’s pretty easy to locate a few primo vintage preamp tubes at boutique prices. I settled on two of my favorite brands: Philips Miniwatt 12AU7 and Mullard M8162/CV4024 for the 12AT7. More accurately, I tried these lovely tubes first and so had no good reason to go any further.

 

This vintage tube complement totally civilized harmonic textures to the point that the FET Valve performed brilliantly even when coupled with ultra-high-end power amps such as the Lamm Audio M1.2 Reference monoblocks. In this context it was able to generate a believable sense of space with plenty of soundstage depth. In particular, soundstage transparency was simply spectacular with absolutely no discernible veiling. The upper octaves were airy and nuanced and excelled at resolution of brushed cymbals. There are many tube preamps out there that give the impression of enhanced detail by virtue of an overly bright presentation. No worries here. There was always plenty of low-level detail in evidence, but it emerged naturally from the music’s fabric. The bass range was both well defined and sensitive to dynamic gradations. In a nutshell, this combo, a “David and Goliath” mismatch price-wise, was able to boogie with rhythmic conviction.

Enter Pete Millett’s R120 SET amplifier, which is light years removed from the technology of the Lamm Audio monoblocks. There are only about 2 watts on tap, but the first watt, the one that sets the stage, is simply superb. The music’s ebb and flow is totally relaxed and effortless while musical textures are beautifully layered and richly colored. The FET Valve did little to alter the R120’s intrinsic sonics. In fact, with every power amp substitution I could identify the character of the amp without any editorial interference from the preamp.

My review sample was outfitted with the moving-coil cartridge option and factory set to a nominal input impedance of 200 ohms. Note that the phono input is assigned to the first line-level input. I understand that AVA is working on a small stand-alone version of the internal phonostage, with about a $399 price tag.

That would represent pretty impressive pricing since it is said to include nearly $100 worth of semiconductors. The phonostage is based around the Burr-Brown OPA627, a well-regarded FET op-amp, and uses passive RIAA EQ. This high-speed precision op-amp is known for sounding slightly dark and a bit warm in the midrange, though it clearly lacks the effusive warmth of tubes. In my listening tests it went head up against the much more expensive Pass Labs XP30 phonostage, yet another “David and Goliath” matchup. I’m pleased to report that the FET Valve held its ground pretty well. There was plenty of detail to hear, and in this regard, I didn’t feel it was lacking relative to the XP30. Transient speed and control were also excellent. On the debit side I noted a slight reduction in soundstage spaciousness while tonal colors were a bit darker than the real thing and not as fully saturated. Overall, I’m inclined to rank the phonostage as a 7.5 on a scale of 1 to 10, relative to the XP30.

If you’re tired of putting up with the worst excesses of vintage tube sound, then you’ve come to the right place. The FET Valve represents modern tube sound at its best. Its twin virtues, really a happy blend of neutrality and accuracy, guarantee that it will not dominate the personality of your audio system. It responds well to vintage tube substitutions, and so configured, it is without a doubt the best sounding AVA preamp I’ve auditioned to date. And by extension, I’m inclined to accept that it is likely the best affordable full-function preamp money can buy. Consider it as a mandatory audition for anyone with a budget under $6k.

SPECS & PRICING

Inputs/outputs: Five line inputs, one headphone input, two tape inputs; two tape and two RCA main outputs Gain: 20 dB
Noise: <1mV broadband (line or phono circuit)
Input impedance: 47k ohms
Output impedance: 600 ohms
Dimensions: 17″ x 12″ x 3.5″
Weight: 17 lbs.
Price: $2099
Options: MM phonostage $249; MC phonostage $299; remote control $299; buffered tape output $149

AUDIO BY VAN ALSTINE, INC.
2665 Brittany Lane
Woodbury, MN 55125
(651) 330-9871
avahifi.com

Associated Equipment
Basszilla Platinum Edition Mk2 DIY loudspeaker; Lamm Audio M1.2 Reference monoblock amplifiers, Coincident Speaker Technology Dynamo 34SE and Pete Millett R120 SET amplifiers; Apple Mac BookPro running Sonic Studio’s Amarra Version 2.6 software, EAR DACute and AYON Stealth DACs; Sony XA-5400 SACD player with ModWright Truth modification; Kuzma Reference turntable; Kuzma Stogi Reference 313 VTA tonearm; Clearaudio da Vinci V2 phono cartridge; Pass Labs XP-25 phono stage; FMS Nexus-2, Wire World, and Kimber KCAG interconnects; Acoustic Zen Hologram II speaker cable; Sound Application power line conditioners

Tags: AUDIO BY VAN ALSTINE FEATURED

By Dick Olsher

Although educated as a nuclear engineer at the University of Florida, I spent most of my career, 30 years to be exact, employed as a radiation physicist at the Los Alamos National Laboratory, from which I retired in 2008.

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