The EVO 400 did wonders for Linear Tube Audio’s ZOTL Ultralinear amp. For the record, it replaced LTA’s microZOTL reference preamplifier in the chain, which had earned my respect in terms of detail resolution and transient speed, basically as an exemplary purveyor of modern tube sound. But, as you might have guessed by now, it lacked convincing tonal weight. The EVO’s twin virtues of Goldilocks-like textural liquidity and tonal conviction saved the day, delivering a much needed infusion of textural fat and richness of tone. The really good news was that it delivered the beef without sacrificing speed and detail. Transients were negotiated with admirable speed and control. Struck cymbals shimmered with plenty of air, and massed string sound was supremely realistic. The treble range was simply sweet and detailed without gratuitous brightness or brashness to interfere with the reproduction of violin overtones or the upper registers of soprano voice. There was not much to complain about at the other frequency extreme. The bass range was reproduced with excellent pitch definition and timing, though bass control did not quite equal that of the much more expensive Lamm L2.1 Reference. Of course, ultimate bass extension would be totally dependent on the associated loudspeaker and matching power amplifier. But know that the EVO 400 can dig as deeply as your system will allow.
In the context of the Fyne Audio F501 loudspeaker, imaging could only be described as spectacular. Image outlines were almost palpable and focused within the confines of a soundstage of remarkable depth and breadth, which was totally untethered from the speakers. Stage dimensionality was a function of the recording and, in particular, took full flight on Calrec Soundfield single point-source microphone recordings. Midrange clarity was such that it allowed each recording’s ambient information to be readily discernible. Given an excellent front end, the EVO proved itself time and again not to be the weak link when it came to low-level detail or spatial resolution. Neither did it impede the program material’s dynamic prowess. Its feel for microdynamic nuances and ability to scale the macrodynamic range from soft to loud captured much of the music’s dramatic content.
My initial concern was that the stock Chinese 12AU7 tube complement might prove to be a weak link in the overall implementation based on first impressions right out of the box. By the way, all of the preamp tubes were measured on my Maximatcher MaxiPreamp II digital tube-tester for gain, transconductance, and noise. All of the stock 12AU7s were low-noise and tightly matched in terms of gain. Eventually, my initial perception of slightly grainy textures dissipated and remained just barely noticeable in the context of solid-state amplification. Lesson learned: The stock tubes take a very long time to break in. So be patient, there should be no urgency to roll-in vintage types as the stock tubes are quite good. But if you’re as curious as I was, start off with the first gain stage tubes (V4 and V5) since they appear to capture about 80% of the sonic changes. I tried both 1950s Raytheon black plate and RCA clear tops for the first gain stage and noted clear improvement in the areas of tonal color saturation and microdynamic contrasts, though I preferred the Raytheon 12AU7 due to its greater textural liquidity. I’m sure that there are many other worthwhile substitutions as there are tons of 12AU7 variants out there, and, no doubt, Kevin Deal would be happy to weigh in on this subject as well.
The balanced connectivity turned out to be a big deal. Driving the Wyred 4 Sound SX-1000R monoblocks, which feature switchable RCA and XLR inputs, I was hugely amazed at how much more refined the XLR connections sounded. Clarity took a big step forward, and anybody with a functioning pair of ears would have had no trouble at all telling the difference. These monoblocks are known to sound better with balanced inputs, but the sonic enhancement in this setting was larger than I had noticed previously. It would appear the output stage cathode followers are quite happy with the balanced output quadfilar transformers.
The EVO 400 is not only PrimaLuna’s best line preamp offering ever, but it also holds its own against ultra-high-end competition. It’s hard to escape the impression that it was designed from the ground up on a power amplifier chassis. It features massive and sophisticated power supplies, high-voltage regulation, exotic passive parts, and, oh yes, tube rectification via a pair of 5AR4s. Miraculously, it manages to combine the virtues of modern tube sound with the tonal heft and timbral realism afforded by vintage tube preamps. If purity of expression and tonal realism are two of your sonic priorities, get ready to embrace the EVO 400. I certainly did. In a nutshell, it’s an insane audio bargain that delivers pure tube magic.
Specs & Pricing
Inputs: 3x RCA, 2x XLR, 1x HT Bypass
Outputs: RCA, XLR, RCA tape out
Tube complement: 2x 5AR4 rectifiers, 6x 12AU7
Frequency response: 10Hz –95kHz, ±1dB
Input sensitivity: 650mV
THD +N: <0.5% at 2V output level
S/N ratio: 93dB
Input impedance: 220k ohms
Output impedance: 256 ohms
Dimensions: 15.2" x 8.1" x 15.9"
Weight: 52.8 lbs.
DUROB AUDIO BV
P.O. Box 109
5250 AC Vlijmen
UPSCALE AUDIO (U.S. Distributor)
2504 Spring Terrace
Upland, CA. 91784
Loudspeakers: Analysis Audio Omega, Russel K. RED 50, Watkins Audio Gen Four Mk II, QUAD ESL-57 by Electrostatic Solutions, Fyne Audio F501, Basszilla Platinum Edition MkII DIY
Power amplifiers: Wyred 4 Sound SX-1000R and VTL Manley reference series 100/200 monoblocks, Linear Tube Audio’s ZOTL Ultralinear, Berning EA-230, Eric Barbour’s SV-572-10 SET
Phono front end: Kuzma Reference turntable; Kuzma Stogi Reference 313 VTA tonearm; Koetsu Rosewood Signature phono cartridge; Jeff Rowland Design Group Coherence phonostage
Digital front end: Audiolab 6000CDT transport; Altmann Attraction, Schiit Audio Yggdrasil, and Soekris 1421 DACs
Cable & interconnects: Museatex Crypton & Tara Labs RSC speaker cable; Acrotec 6N, Wire World, and Kimber KCAG interconnects
Accessories: Sound Application power line conditioners