Zesto Leto Ultra II line preamplifier
What sort of audiophile are you?
I think of myself as a critical listener, perhaps a purist, definitely an enthusiast, of music and audio, who enjoys both the journey and the nuts and bolts. I like my hi-fi direct, simple, and personal. Also, I guess I’m a little bit old-school: tube-driven amplifiers with point-to-point wiring; vinyl, preferably early pressings; spun with belt-drive or idler-drive turntables. I listen to digital audio, tooand when I do, I prefer nonoversampling DACs. I like high-efficiency, high-sensitivity floorstanding loudspeakers and prefer them horn-loaded.
Lately, I’ve reviewed conventional class-AB solid-state integrated amplifiers and overachieving low-sensitivity bookshelf speakers, finding them thoroughly enjoyable. My first Stereophile review was of a fantastic class-D power amplifier: the Spec RPA-W7EX Real-Sound. I can listen to lots of different kinds of things, and with pleasurebut give me a choice and I’ll always come back to this preferred kit. I’m flexible, but my preferences are my preferences.
I believe in careful system setup, but I’m not a tweaker exactly: I’ll try most things, but I try not to stress over their use. Interconnect cables and power cords make a difference (footnote 1)of course they dobut I don’t like interconnects so heavy and stiff that they lift my preamp off its moorings. I believe in the efficacy of equipment supports and platforms, too, but I try to avoid treacherous, steel-pointed isolation cones that gash holes in feet and floors, and they don’t need to be expensive to be effective. I swear by Ikea’s Aptitlig bamboo chopping boards under amps and BXI Anti Vibration Isolation Pads under floorstanding loudspeakers, to tame the resonances of my 19th century suspended wood floors. I built a DIY stand for my Kuzma Stabi R turntable with 10 cinderblocks, eight 2×4s, and a really big Ikea board.
I don’t go in for Tice clocks or photos in freezers. I avoid wacky accessories that make civilians think we audiophiles are off our rockers. As I wrote above: I like my audio direct and simple and human-scale.
Zesto Audio president and co-founder George Counnas seems to share my audiophile worldview, at least partly. With his wife, industrial designer Carolyn Counnas, George Counnasa former musician, recording engineer, producer, and military-contractor employeehas brought to market several well-regarded tube-driven preamplifiers, phono stages, and power amplifiers, some of them reviewed in Stereophile, including the original Leto, a predecessor of the product I’m reviewing, which was evaluated by Bob Reina in 2014.
All Zesto Audio products bear a common trait that I appreciate: a certain simplicity, nothing wasted, everything is thought through, everything serving a purpose. No Zesto Audio component I’m familiar with follows that pattern better than the Leto Ultra II preamplifier ($10,900).
Wrapped in a 16-gauge, zinc-plated steel enclosure, which is said to “help isolate the electronic ‘chatter’ from nearby equipment,” the Leto Ultra II preamplifier includes some uncommon functions and control options: separate left- and right-channel ground-lift switches and a mono switch, which is said to help with troubleshooting but is also good for listening. It automatically mutes when powered on or off, “preventing any pops which could damage your speakers or surprise the hell out of you,” according to the website copy. A three-position gain dial3dB, 6dB, and 9dballows various sources to be gain-matched so that you don’t get a big surprise when you switch sources.
The Leto’s control dials employ concave sides, ensuring solid finger grip. Most unusual is a six-position “Presence” control, which “adjusts the harmonic balance in the mid and high frequencies allowing you to dial back what you may consider to be too bright, edgy or aggressive.” The Presence control, Counnas writes on the Zesto website, “was born out of my frustration after finding some of my favorite recordings became unlistenable the more resolved my system became, regardless of the source.”
The Leto Ultra II is curvaceous and good-looking, reflecting industrial designer Carolyn Counnas’s aesthetic: droplet-shaped stainless steel and clear anodized aluminum sections of the preamplifier’s façade, and a curved, mirror-finish transformer cover modeled after the graceful lines of a grand piano. Nothing here resembles a plain black box.
Measuring 17″ wide × 12″ deep × 5″ high and weighing 28lb, the class-A, zero-feedback Leto Ultra II comes with two JJ ECC82/12AU7s and two JJ ECC832/12DW7 tubes, the latter replacing a pair of 12AX7s in the previous version.
“All 12-series tubes have two active amplifiers,” Counnas explained by email. “A ECC82-12AU7 tube has two identical triodes. In a ECC832-12DW7, one triode is a ECC83-12AX7 and one ECC82-12AU7 in the same glass envelope. Otherwise, to achieve the same results the amp would need one ECC83-12AX7 and two ECC82-12AU7s per channel. In my opinion, the less circuits the music goes through, the less affected and purer the sound.”
The big change from the previous Leto Ultra is in the power supply, which has been upgraded to what Zesto calls its Energy Source Power (ESP) supply. (The review unit was upgraded just after the review period started.) This upgrade replaces the earlier IE power transformers with two toroidal transformers: separate supplies for high and low voltage, both capable of more current than the previous supply. High voltage supply was increased from 250V to 300V, providing more headroom and dynamic range. The amp’s maximum output level before clipping increased, which Counnas says provides “more punch.” The upgraded power supply yields “significantly less noise because it does a better job of concentrating the magnetic field,” Counnas explained. It is also said to be “more resilient to power surges.”
A small, nine-button plastic remote handles input, volume, “Presence,” mute, mono, and gain. All functions can be adjusted either from the remote or from the preamp’s front-panel controls.
Those front-panel controls are three silver dials marked Volume, Presence, and Input, with a power rocker around the corner on the chassis’s right side. LEDs indicate the current setting of the Presence control, input, and the gain setting of the current input. The Presence control doubles as a mono switch; the Input selector also mutes.
What is a Presence control? It’s a tone control, but it’s not the usual kind. “Presence is designed to gently reduce unwanted mid and high frequencies in 5 steps,” Counnas continued in the email. “Each step changes the frequency that it starts working with, 1 the highest and 5 the lowest.” The larger the number, the greater the effect.
Around back are six pairs of recessed inputs: three single-ended (RCA) and three balanced (XLR). These are followed by four pairs of recessed output connectors: two single-ended (RCA), two balanced (XLR). Separate left- and right-channel ground toggle switches are followed by a pushbutton for gain adjustment and an IEC connector.
Zesto says that every unit has received “50 hours factory burn-in on all circuits and vacuum tubes,” but that “this Vacuum Tube Preamp can take 200 hours to break in.” I found the Leto Ultra II required at least another week of almost continuous play to reach peak performance. The informative Leto Ultra II manual suggests thereafter allowing “at least 10 to 30 minutes for tubes to warm up to get the best performance from the preamp.”
Footnote 1: As for me, I find conventional audio systems to be, well, quieter without speaker cables and interconnects. The same goes for power cords.Editor
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3138 Calle Estepa
Thousand Oaks, CA 91360
Jim Austin September 2021
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