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I received review samples of Esoteric’s Grandioso K1 SACD/CD player and DAC ($31,000 USD) and G1 master clock generator ($26,000) at the same time. Figuring that not everyone would plunk down $57,000 all at once, I first reviewed the Grandioso K1 alone. Now it’s the Grandioso G1’s turn.

No stranger to master clocks, for some time now I’ve been using Stanford Research’s PERF10 Rubidium clock (from $3495). In my review of the PERF10, in December 2015, I concluded that it was one of the biggest audiophile bargains I’d heard. In fact, Esoteric uses the PERF10’s rubidium oscillator, the PRS10, in its G-01, G-01X, and Grandioso G1 clocks.

I know what you’re thinking. But I found, in reviewing the PERF10, that despite sharing the same oscillator, the PERF10’s sound couldn’t compete with that of the 6.5-times-as-expensive G-01 ($23,000), now replaced by the G-01X ($20,000). As I wrote then:

The use of an extremely accurate oscillator, while a great start, does not necessarily make for a state-of-the-art audio clock. When you shell out extra for a high-end clock, you get top-notch hardware [and] design features. . . . Indeed, when the G-01 was in my listening room, it produced transient reproduction, soundstaging, focus, and . . . timbres that were all superior to and more realistic than what the PERF10 could provide.


Of course, the G1 is a member of Esoteric’s statement line, the Grandioso models, which have quickly gained reputations for cutting-edge performance and features. In light of my experience with the G-01, I was eager to find out what the G1 could do. As they say in the clock business, time would tell.

“One can expect an agreement between philosophers sooner than between clocks.”
-- Seneca, in Claudius the God and His Wife Messalina, by Robert Graves

A digital word clock generates a reference pulse that is used to synchronize digital playback devices. In particular, digital-to-analog converters use such a pulse to transform a stepped binary digital code into a continuous analog waveform, activating the digital-to-analog converter a fixed number of times per second -- 44,100, 48,000, 96,000, etc. -- a figure also called the sample rate. The more evenly spaced the sampling pulses, the more accurate the process of converting digital signals to analog.

Most digital components have an internal clock, the heart of which is typically a voltage-controlled crystal quartz oscillator (VCXO). Run direct current (DC) through quartz and it generates a pulse, because the mineral is piezoelectric; that is, it vibrates when charged. However, even minor variations in load, temperature, and voltage can cause quartz to experience frequency shifts; i.e., jitter. Think of your typical quartz clock or watch, whose piezoelectric vibrations may be accurate to within several minutes per year.

For higher performance, an external master clock can be used to generate a reference pulse. External master clocks are often “atomic”; i.e., they contain an oscillator whose workings are based on the electron state transitions of a chemical element (e.g., cesium, rubidium) or compound (e.g., ammonia). In essence, the resonant frequencies of those transitions, which are mostly in the microwave frequencies (300MHz-300GHz), constitute the clock’s “pendulum.”

Atomic clocks are used where the need for accurate signal data is acute, as in broadcasting, electrical power grids, GPS navigation, medical and emergency operations, laboratories, financial services, telecom, aerospace, and the military. Atomic clocks are used by the National Institute of Standards and Technology to calculate the official time standards for the United States.

For years, the most accurate atomic clocks used cesium oscillators, which are accurate to within one second every 300 million years, which is more stable than the earth’s rotation. This has necessitated the occasional insertion, in the calendar of Coordinated Universal Time, of a “leap second,” which allows the clocks to be synchronized to the earth’s actual daily rotation on its axis, aka the mean solar day, and thus the length of the year as well.

Scientists have recently developed atomic optical clocks that are even more accurate than clocks using substances that resonate within the microwave region. These clocks measure ions that resonate in the visible portion of the electromagnetic spectrum -- at frequencies about 100,000 times higher than that of such substances. Although atomic optical clocks theoretically lose less than one second in 15 billion years, the approximate age of the universe, we won’t be using one for audio any time soon. Such clocks are so complex that they frequently crash, and are typically run for only a few weeks per year, to be used as a standard by which to set the less accurate but more durable atomic microwave clocks.

Of course the science of time does not stand still. One scientist has recently built an optical clock with a strontium quantum gas oscillator that is so precise that it is theoretically accurate to within one second over 90 billion years.

High-end audio devices demand accuracy nowhere near one second every 90 billion years. Nor, as indicated, is such accuracy practically achievable. Atomic audio clocks therefore generally feature rubidium oscillators. However, rubidium spontaneously ignites when exposed to air. It also violently reacts with water, bursting into flames and forming caustic hydroxides that cause tissue necrosis -- death -- on contact with the skin. Rubidium must therefore be kept in mineral oil, or in an atmosphere of inert gas.

Rubidium clocks go the gas route. As stated on Sanford Research's website, commercial rubidium clocks operate by:

disciplining a crystal oscillator to the hyperfine transition at 6.834,682,612GHz in rubidium. The amount of light from a rubidium discharge lamp that reaches a photodetector through a resonance cell will drop by about 0.1% when the rubidium vapor in the resonance cell is exposed to microwave power near the transition frequency. The crystal oscillator is stabilized to the rubidium transition by detecting the light dip while sweeping an RF frequency synthesizer (referenced to the crystal) through the transition frequency.

While the above explanation may be difficult for most audiophiles to understand, the upshot is that the accuracy of a rubidium clock is governed by the natural resonance of rubidium atoms.

According to Esoteric’s brochure, the Grandioso G1 uses an American-made rubidium oscillator of extremely high precision that is accurate to ±0.00005 part per million (ppm), also expressible as ±0.05 part per billion (ppb). That oscillator is, of course, the Stanford Research PRS10. To give a frame of reference, the quartz-crystal oscillator in the G-02X master clock is accurate to ±0.01ppm. The quartz-crystal oscillators in Esoteric’s high-end CD players are accurate to ±0.5ppm -- that is, 50 times less accurate. Finally, the quartz-crystal oscillators used in typical CD players are accurate to ±10 to ±50ppm, the latter figure being 5000 times less accurate than ±0.01ppm.


Such accuracy does not come cheap. The PRS10 is more expensive than any other component part used by Esoteric, including the tank-like, high-precision VRDS SACD/CD transport. Like all atomic oscillators, the PRS10 is sensitive to vibrations and to electromagnetic and radio-frequency interference (EMI and RFI). Esoteric has therefore adopted several measures to protect it and the G1’s other sensitive internal components from such contaminants. The G1’s case, extremely heavy and rigid, is constructed of high-grade aluminum. Moreover, the case’s bottom panel has a dual-layer structure comprising two thick plates of steel. The G1’s internal components, including the PRS10, are affixed to different plates to minimize the inter-chassis transfer of vibrations.

For reasons unrelated to vibration control, the PRS10 is loosely mounted on one of these plates with a 0.8mm gap between screws and plate, to allow the oscillator to move more freely. This, Esoteric says, provides a very open sound.

The G1’s pulse signal is output by four newly designed Wide Range Clock Buffer Amplifiers, each with its own power-supply regulator. These amps have high-speed transistors that provide excellent high-frequency performance.

The Grandioso G1’s power supply is newly designed to maximize the performance of the buffer amps. A large, toroidal (i.e., donut-shaped) transformer is used as the main transformer, and an El-frame core transformer for digital control. A series of capacitors is used in the power supply as a filter circuit. These types of filters remove the 50 or 60Hz ripple signals (i.e., noise) found on the AC line. Also, high-quality Schottky barrier diodes are used for rapid response.

The G1’s internal wiring is custom-made, high-quality coaxial, and MIL-compliant with gold-plated SMA and milled brass BNC connectors, each developed for the secure transmission of high-frequency signals.

The best way to tour the G1’s exterior is to start at the rear panel. First on that panel are four 10MHz BNC output terminals, each of which has a toggle switch allowing that output to: 1) operate in a new Adaptive Zero Ground mode; 2) operate in Normal mode; or 3) be turned off. According to Esoteric, Adaptive Zero Ground actively drives the output’s ground-signal voltage to its target of zero, thus reducing jitter caused by variations in such voltage.


Next on the G1’s rear panel is a BNC input connector that accepts a 10MHz or 1pps reference pulse from an external Global Positioning System (GPS) satellite receiver. The GPS is a navigation system maintained by the U.S. Department of Defense and comprising at least 24 satellites. GPS works in any weather conditions, virtually anywhere in the world, 24 hours a day, with no subscription fees or other charges. When used with an optional GPS receiver, the G1’s rubidium oscillator synchronizes with a rubidium or cesium GPS clock.

I got excited about the GPS feature, only to discover that Esoteric doesn’t necessarily recommend its use. According to them, a satellite pulse creates a different but not necessarily better sound than that of the G1’s internal rubidium oscillator. Further, Esoteric says that while some customers prefer the satellite sound, few suitable GPS receivers are available other than some used ex-military ones. Note, too, that a GPS antenna would likely have to be installed on the roof of your house, and if it’s between two other, taller buildings, the GPS signal will be unavailable.

Third on the G1’s rear panel is a switch that activates a Preheat mode, which provides uninterrupted power to the PRS10. For those who don’t want to keep their digital gear turned on 24/7, this mode greatly reduces warmup time, and is claimed to allow the G1 to almost immediately operate at full sound quality. It also extends the oscillator’s life by eliminating its exposure to power surges that occur during the turn-on process.


Last on the rear panel are a brightness control for the blue front-panel display, a ground connector, and an IEC power inlet.

The G1’s thick, gorgeous, aluminum faceplate is very clean. Most prominent are its large, swooping, beautifully machined curves, one of which conceals a bow-shaped LED that bathes in blue light the faceplate’s lower half, including the large central power button, which is flush with the surface. This member of Esoteric’s Grandioso family is one of the most elegant and beautiful audio components out there.

Also on the faceplate are blue LED signal Lock and power indicators, and a set of bicolor 10MHz output indicators: blue for Normal mode, green for Adaptive Zero Ground mode, and unlit for off.

Like all Grandioso components, the G1 has patented, vibration-reducing, pinpoint steel feet that screw into the bottom plate. Unlike most stock feet, these are extremely solid, beautifully crafted, and feature a sophisticated multi-part design.

Most commercial atomic clocks are small and featherweight -- the Stanford Research PERF10 weighs ten pounds and is about 10” deep. By contrast, the G1 weighs a hefty 51 pounds and measures 17 5/8”W x 5 1/4”H x 17 3/4”D. During the early planning stages, Esoteric considered building a rubidium clock into the Grandioso K1, but decided against it because the resulting player would be too large and costly.

Esoteric offers a one-year limited warranty for the G1, to which Integra, the US distributor, adds two years for units sold here. As I’ve argued in the past, in light of Esoteric’s reputation for overbuilding its products and what it charges for them, it would be nice to see something closer to five years.

“One luminary clock against the sky
proclaimed the time was neither wrong nor right.”

-- Robert Frost, “Acquainted with the Night,” from West-Running Brook

Like any Esoteric component, the Grandioso G1 came exceptionally well packaged in a heavy cardboard cocoon that was itself triple-boxed. Because the Stanford PRS10 is designed to rest loosely within the G1, it must be secured prior to shipping. This is accomplished with three transit screws, tightened or loosened through the G1’s bottom plate. The screws must be removed during setup, and reinserted when shipped again.

The G1 connects to an external digital device -- in this case, Esoteric’s Grandioso K1 -- via a BNC coaxial cable. Most audiophile coax cables have an impedance of 75 ohms; a few are 50 ohms. A coax of either impedance can be used for the vast majority of audio applications, and Esoteric states that, in a length less than 3m, either will work very well with the G1. For my listening, I used a Synergistic Research Galileo UEF 75-ohm BNC cable and an Atmosphere Level 3 power cord.


Knowing how sensitive the PRS10 and audio gear in general are to vibrations, I felt very comfortable placing the G1 on Symposium Acoustics’ Osiris Stealth Ultimate equipment rack. One thing this rack is designed to do is quickly drain vibrations from the component to ground, so that sensitive internal parts such as the Stanford’s oscillator can perform at their peak.

The G1’s multi-part feet are surprisingly effective for their stock pedigree. However, I got even better results with two aftermarket feet, Synergistic Research’s MIG 2.0 and Symposium’s RollerBlock Series 2+. If you use aftermarket footers with the G1, be sure to unscrew and remove the G1’s stock footers. The latter lock only when bearing the component’s weight. If left unlocked and dangling from the G1, they’ll vibrate, which should be avoided.

I used two of the G1’s 10MHz outputs, one for the K1 and the other for experimenting with Synergistic Research’s Active Ground Block. As discussed below, I switched between the G1’s Adaptive Zero Ground and Normal modes for each of these outputs. Finally, I turned off the two unused outputs, on the assumption that this would better reduce stray EMI and RFI than the shorting caps that adorn my other components’ unused connectors.

I didn’t use the oscillator’s Preheat mode, though I greatly appreciate its intent. First, I’m not so sure that turning off any of the G1’s circuitry is a good idea. Things like output devices, capacitors, and resistors all need extended periods of time to achieve their peak operating condition. Second, even with Preheat activated, turning off the G1 caused the K1’s to rapidly flash “CLOCK!,” which was annoying.

“Time can be a greedy thing -- sometimes it steals the details for itself.”
-- Khaled Hosseini, The Kite Runner

It’s no secret that a high-quality, external digital clock can allow a digital front-end, whether comprising one box or many, to better resolve low-level detail and reproduce music that is better timed, and thus less grating and fatiguing. That was certainly the case when I connected the Grandioso G1 to the Grandioso K1, which itself is capable of exceptional accuracy and sonic fluency. Nor were the improvements subtle.

I listened to Variations on “The Last Rose of Summer,” by Heinrich Wilhelm Ernst (1814-1865), as performed by violinist Midori and pianist Robert McDonald on Midori’s Live at Carnegie Hall (16-bit/44kHz FLAC, Sony Classical). With the Grandioso G1, Midori’s terse, rapid pizzicati were more finely drawn, and their improved transients better contrasted with her beautiful bowed passages, which were now much more flowing and rhythmic.

With Schubert’s contrapuntal Impromptu in E-flat, D.899 No.2, in the recording by pianist Alfred Brendel (CD, Philips 411 040-2), the G1 removed a layer of distortion and digital harshness from top notes, revealing more beautiful and detailed inner crystalline structures, which made them more precise and penetrating. Bottom notes were now more palpable and musical.


Equally persuasive was what the G1 did with other high-frequency percussion instruments. In Harold Farberman and the All Star Percussion Ensemble’s recording of Bizet’s Carmen Fantasy, a brief (1:28) excerpt from which is found on the DXD sampler Top 12 in Gold Plus: Music that Resounds in Life (CD, FIM GS DXD 001), bells and xylophones had never sounded so clean or high-pitched, or their decays so delicate and long. Lower-pitched percussion transients were much more quick and taut.

The G1 moved even the masterful K1 into a realm of musical beauty, precision, and elegance that is, by all accounts, impossible for a one-box player to achieve alone.

But what many audiophiles don’t realize is that an external clock such as the G1 can also better resolve crucial aural information that more accurately and concretely places singers and instruments on the soundstage, more fully portrays instrumental tone and texture, and better reveals a recording venue’s acoustical characteristics.

When I played Ensemble Viriditas’s performance of “A Virgin Most Pure,” from the compilation Fidelio Reference 2: Festival Son & Image 2007 (CD, Fidelio FACD910), three rows of instruments snapped into place as never before. Now sounding much more solidly three-dimensional were a harp at rear center, a middle row of singers flanked by a recorder at left and a violin at right, and a violinist at front center.

Same thing with “Surrender,” from Tom Petty & the Heartbreakers’ The Live Anthology (four CDs, Reprise 512765), recorded at a 1983 show at California’s Irvine Meadows. Introducing the song, Petty announces that he’s never recorded it. At that point, Stan Lynch, the Heartbreakers’ drummer, shouts, “That’s not true! It was never recorded well!” With the G1, it was now clearer that Lynch’s waggish retort emanated from a position significantly behind Petty. And when the music begins, the images of the band’s instruments and voices were much more airy and focused, with much more of the feel of a live concert due to increased reverberation.

Speaking of reverberation, in the long bowed notes that cap several of the works on the Midori recital, the G1 unearthed previously buried vibrato and hall reflections, which strengthened the notes and made overtones more audible. Yet despite this heightened pitch saturation, the notes were more detailed, and it was now more apparent that the intensity of the high-frequency harmonics on open strings deteriorated more rapidly than those in the middle and lower registers.

Removing the Grandioso G1 from the signal chain caused Midori’s violin to lose these newfound tonal qualities and sound somewhat threadbare and monochromatic in the upper frequencies -- a remarkable achievement, given the Grandioso K1’s already extraordinary ability to reveal overtones.

Toronto’s Massey Hall is known for having an extremely warm, “living-room” sound for a 2752-seat concert venue. With Neil Young’s Live at Massey Hall 1971 (16/44.1 FLAC, Reprise/WEA), the G1 greatly benefited my system’s ability to parse direct from reflected sounds as Young’s voice and guitar, and noises from the audience, rebounded off surfaces (perhaps the sidewalls and balcony façades) that had never sounded closer. As a result, this recording had never seemed so intimate, or Massey more present.

With other recordings, the G1 revealed very different acoustics. Beginning in the 16th century, liturgical choral music was often composed for specific spaces, whether a small church or a large cathedral. The latter was certainly the case with the music on Benedicta: Marian Chant from Norcia, recorded by the Monks of Norcia (CD, De Montfort Music 002315302). These Benedictine monks, average age 33, are known for making sacred music and great beer at their Monastery of St. Benedict, near the saint’s original home in Nursia, in the Italian province of Perugia.

With the Grandioso G1 activated, the monks’ melodic chants sounded much more tranquil and serene, even gorgeously haunting. Further, I had a much better impression of the monastery’s large interior from its long reverberation times, particularly evident in the lower frequencies. This created a much fuller, richer sound, and my greater envelopment by that sound, than with the Grandioso K1 alone. In fact, the reverberations were now so fully revealed that they often seemed to never fully end before being eclipsed by the next verse.


Hearing Benedicta through the Grandiosos drove home why slow-paced, unamplified music such as Gregorian chant and organ solos are really the only types of music that work well in a large church with an extremely lively acoustic. But it also served as another striking example of the G1’s ability to seemingly transport a listener -- this one -- to the recording venue.

As my final task, I tested the G1’s Adaptive Zero Ground output mode, which sometimes seemed to improve the degrees of clarity, focus, and detail. The orchestral bells in the Carmen Fantasy sounded slightly more shimmering, crystalline, and incisive, shedding extremely fine vestiges of glare that I’d have sworn were never there in the first place. The horn in “Pastime Paradise,” from Jen Chapin’s Revisions: The Songs of Stevie Wonder (SACD/CD, Chesky SACD 347), seemed a bit more detailed and textured. The differences were slight, causing me to run more A/B comparisons than I care to remember. However, I generally preferred the G1’s sound with Adaptive Zero Ground engaged. I imagine it’s possible that your mileage may vary, based on the quality of the AC current in your listening room.

“All clocks break, and what breaks them is Time.”
-- Marty Rubin

Spend some time with the Esoteric Grandioso G1 master clock generator and you’ll likely never go back. It not only uncovers in recordings of music levels of detail, precision, and tonal richness previously unsuspected, it also reveals aspects of performances, including those of the recording venue itself, that are missed by less accurate digital pendulums. It also serves as yet another lesson from Esoteric that the state of the art of digital music reproduction is breathtaking. Highly recommended.

. . . Howard Kneller

Associated Equipment

  • Amplifier -- Esoteric A-03
  • Preamplifier -- Esoteric Grandioso C1
  • Sources -- Desktop PC with JCAT USB Card and JCAT USB Isolator running Windows 10, JPlay; Esoteric K-01X SACD/CD player; Stanford Research PERF10 rubidium clock
  • Other electronics -- JL Audio CR-1 active subwoofer crossover
  • Speakers -- YG Acoustics Kipod II Signature
  • Subwoofers -- JL  Audio Fathom v2 (2)
  • Interconnects -- Synergistic Research Galileo UEF
  • Digital links -- JPlay JCAT USB, Synergistic Research Galileo LE USB
  • Speaker cables -- Synergistic Research Galileo UEF
  • Power cords -- Synergistic Research Galileo UEF and Atmosphere Level 3
  • Power conditioners and distribution -- Synergistic Research PowerCell 12 UEF SE and QLS power strips
  • Isolation devices -- Symposium Acoustics: Osiris Ultimate and Standard Racks, Segue Platform, RollerBlock Series 2+ supports. Synergistic Research: MIG 2.0s, Silent Running Audio VR fp Isobase, Tranquility Bases.
  • Room treatments and correction -- Synergistic Research: Acoustic Art System, Atmosphere XL, FEQ, HFT.
  • Misc. -- Mad Scientist Black Discus Audio System Enhancer, WA-Quantum Quantum-Sound-Animator, Hi Fidelity MC-0.5 Magnetic Wave Guides, f.oq damping tape; Synergistic Research: Active Grounding Block, Black fuses

Esoteric Grandioso G1 Master Clock Generator
Price: $26,000 USD.
Warranty: Three years parts and labor.

Esoteric USA
18 Park Way
Upper Saddle River, NJ 07458
Phone: (201) 818-9200

Website: www.esoteric-usa.com