Cavalli Audio Liquid Glass Hybrid Valve/Solid-State Headphone Amplifier/Preamplifier

Cavalli Audio is a USA-based manufacturer of world-class headphone amplifiers. They are ‘bespoke’ products, since the amps typically allow at least some degree of customization to meet buyers’ requirements. But the underlying qualities that typify all Cavalli designs involve company founder Dr. Alex Cavalli’s commitment to sound quality and to the sort of rigourous and conservative engineering that makes for long-term reliability. Where some designers proudly tout ‘edge of the envelope designs’, Dr. Cavalli rejects the idea of pushing circuit parameters ‘to the edge’ as ill-advised posturing at best and shoddy engineering at the worst. As Dr. Cavalli once said to Hi-Fi+, “if you have to use ultra-exotic parts or stress your circuitry to the limits to get the performance you need, then you probably do not have an adequate design in the first place.”

Cavalli’s first two headphone amplifiers, the Liquid Fire, an amplifier geared for use with conventional (that is, dynamic or planar magnetic driver-equipped) headphones, and the Liquid Lightning, geared specifically for use with electrostatic headphones, have both received considerable critical acclaim (some writers consider the Liquid Fire and Liquid Lightning as true, state-of-the-art designs). But now Cavalli’s third amplifier, called the Liquid Glass ($3,500 in the US, or £2,325 in the UK), has entered production.

Before we start, it might be useful to talk about the nature of the sound Cavalli is pursuing. Cavalli Audio, I would say, does its level best to pursue tonal neutrality, high levels of resolution, and extreme faithfulness to the incoming audio signal. But unlike some competing accuracy-seeking amps, which can at times sound sterile and antiseptic, Cavalli amplifiers strive to capture the unforced, “liquid” character of live music itself, which is why Dr. Cavalli often uses the word “Liquid” in his amplifier names.

Cavalli’s Liquid Glass amplifier, however, offers a fresh take on the case for a ‘neutrality-über-alles’ sound, in that it is a hybrid valve/solid-state amplifier created specifically for those known as ‘tube rollers’ (that is, enthusiasts who experiment with various valve substitutions in search of ever higher levels of sound quality). As Cavalli says, the Liquid Glass “is especially designed to reflect exactly what the tube [valve] does and sounds like.” Accordingly, the Liquid Glass provides a tube-powered front-end section backed by a high-input-impedance (and thus easy-to-drive), ultra high-resolution, ultra-low-noise solid-state output buffer section. In the interest of even greater sonic purity, Cavalli notes that, “there is intentionally no global negative feedback, which is normally used [in other manufacturer’s designs] to reduce THD and increase bandwidth.” But, as the amplifier’s specifications demonstrate, the Liquid Glass delivers exemplary bandwidth and low distortion, even without global negative feedback.

Moreover, the tube section is extremely versatile, providing pairs of both octal (that is, eight-pin) and nonal (that is, nine-pin) valve sockets, with separate user selectable controls for setting valve heater and plate voltages. For my tests I tried sets of 6SN7, 6GU7, 12AU7, CV181, 8416, and 6922 valves, but there are many more types of valves the Liquid Glass can support (see Technical Specifications, below, for a complete list). As a general rule, if a desired valve type fits the Cavalli’s valve sockets (and, Dr. Cavalli advises, “conforms to either 6SN7 or 12AU7 pin-out arrangements…”), then the valve can be made to work in the Liquid Glass. The point is that users can choose from amongst hundreds of types and brands of valves, each offering their own distinctive take on the sonic truth.

Now many amplifiers that claim to pursue sonic truth take what might, tongue-in-cheek, be called the Highlander approach to high-end audio, as if amplifiers were fiercely declaring, “In the end there can be only one (true sound, that is)…” In contrast, Cavalli’s Liquid Glass opens the door to the possibility that while the sound of live music may be a constant there can be many viable paths toward realizing that ideal sound as perceived by critical listeners of varying listening habits, musical tastes, and so forth.

Hi-Fi+ reviews are, of course, supposed to give you some idea of how the product under review actually sounds, which for obvious reasons becomes a tricky proposition with the Liquid Glass. Let me start by saying that the Glass’ solid-state, unity gain buffer stage is exceedingly quiet, offers an exceptional degree of tonal neutrality, excellent transient speed, and pleasing freedom from edge or glare. Importantly, the buffer stage can also drive most any headphone (even very power hungry models), meaning that the buffer stage does virtually all of the heavy lifting in terms of actual power output. As a result, you hear each valve set under nearly ideal circumstances, the valves providing voltage amplification as best they can, while taking responsibility only for powering the Liquid Glass’ easy-to-drive buffer stage.

After considerable comparison listening I identified a handful of valve sets that, for me, yielded the most accurate and neutral presentation overall. My preferences included a Cavalli-supplied set of Electro Harmonix 6SN7s (the default valves that ship with each Liquid Glass), a pair of NOS (new old stock) Sylvania 6SN7s, and a gorgeous set of Shuguang 50 Years Treasure CV181 valves. These were my preferences, but yours might well vary. The beauty of the Liquid Glass is that it invites (and enables) listeners to do their own research and then to choose valves that best fit their own tastes and perceptions of the musical ideal.

For me, the Liquid Glass + 6SN7 pairing gave a great combination of gain, relatively low noise, excellent detail and definition, and a certain desirable quality of top-to-bottom consistency and evenness of timbre that not many other valve sets could match. The Electro Harmonix 6SN7 valves gave a powerful, clean-edged presentation that tended to emphasize the leading edges of transient sounds just a hair (much as certain high-end solid-state amplifiers tend to do). By comparison, the Sylvanias offered slightly less gain than their Electro Harmonix counterparts, with plenty of detail but somewhat less emphasis on transient edges for a sound that was a bit softer, rounder, and more full-bodied than the Electro Harmonix presentation.

By comparison, the Shuguang CV181s offered many of the virtues of the 6SN7 valves, but with even higher gain, a still quite low noise floor, and a certain quality of expansiveness and spaciousness that made the most of low-level reverberant details in the music. The result was a headphone listening experience that, while not quite loudspeaker-like in its presentation, nevertheless pulled the music outside of the listener’s head, allowing the music to fill a giant acoustic space.

In the end, the Liquid Glass is all about giving listeners sonic options. During my listening tests I tried the six valve types cited above and the honest truth is that, through the Liquid Glass, each had certain distinctive sonic benefits to offer, meaning there really was no sonically ‘right’ or ‘wrong’ choice. Like a fair and impartial judge, the amp effortlessly revealed different aspects of the music that one valve type (or brand) might handle better than another. This ability to look honestly and deeply into the mysteries of musical textures, timbres, transient sounds, and dynamics is what makes the Liquid Glass so special and, frankly, so endlessly entertaining.

Let me provide some illustrations to show how the sound of the Liquid Glass played out on real world music. One track I found useful as a bellwether piece of music for purposes of evaluating subtle textures and low-level details was singer Anne Bisson’s inventive cover of Pink Floyd’s ‘Us and Them’, from Bisson’s Portraits and Perfumes [Fidelio CD]. This very well-recorded track can sound good to very good through many different amplifiers, but it also provides extremely delicate textural and transient details that can, through truly great amplifiers, give the track a striking, otherworldly, ‘Alice-through-the-looking-glass’-like presentation that inexorably draws you into an alternate sonic reality.

That alternate reality might best be described as Anne-Bisson-channeling-Edith-Piaf-channeling-Roger-Waters as captured in an incredibly intimate French-Canadian jazz club-like setting. Every small instrumental texture and point of emphasis is heard in almost shocking clarity and detail, as are even the most delicate of inflections from Bisson’s voice. The result, through the Liquid Glass, is a mesmerising presentation that has a nearly dreamlike quality. On an intellectual level, you realise you are hearing more intimate levels of detail than you could or would hear from most live musical events. But on an emotional level, the sound is so sumptuous, so lavish, and so beautiful that you may set considerations of ‘realism’ aside for the moment to simply savour the experience for what it is. At its best, the Liquid Glass can show you beautiful things in recorded music you may never have experienced before and to hear them is to want to hear more.

Another track that shows off the Liquid Glass’ capabilities is ‘Sarasvati’, which is the first movement of Robert Paterson’s nine-part composition The Book of Goddesses [American Modern Recordings CD]. This piece was written for the Maya trio, which consists of flute, harp, and percussion—instruments captured, in the AMR recording, in a mid-sized and highly reverberant acoustic space. Sarasvati is the Hindu goddess of knowledge and for this reason the movement is given a distinct Indian feel, with the harp playing lines reminiscent of those that might be produced by traditional Indian stringed instruments such as the veena. In turn, the trio’s percussionist primarily plays an expressive Indian clay pot drum called a ghattam. Two aspects of the performance caught my attention. First, I was struck by the incredible purity of timbre the Liquid Glass affords—a quality that listeners can of course fine tune and enhance to taste through experimentation with various valve sets. Second, I was impressed by the amp’s clear, surefooted retrieval of reverberant information. The Liquid Glass conveyed layer upon layer of low-level details, in the process vividly conveying the acoustic characteristics of the recording venue. What is more, the amp’s soundstaging was likewise special; rather than leaving music trapped inside the listener’s head, the Liquid Glass cast exceptionally wide, well-detailed sound fields replete with wonderfully precise lateral imaging cues.

I consider the Liquid Glass an exceptional headphone amplifier, though one that may not be for everyone. Listeners who require reassurance that there is only one possible ‘right’ sound may find Cavalli’s Liquid Glass too flexible for its own good. It is, after all, a terrifically open-minded product, which offers as many uniquely beautiful sonic ‘realities; as there are valve sets to audition. But, for listeners who value the musical quest as much as the ultimate destination, the Liquid Glass stands as an open invitation to explore and to savour. It is without a doubt one of the finest hybrid headphone amplifiers yet made, and one that demands an audition from those who seek the best.

Technical Specifications

Type: Hybrid Valve/Solid-State Headphone Amplifier/Preamplifier.
Valve Complement:

• 8-Pin valves: 6SN7, 12SN7, VT231, CV1986, CV1988, B65, B63, ECC32, and CV181.
• 9-Pin valves: 12AU7, ECC82, 5963, 6680, 5814, 12AT7, ECC81, 6DJ8, ECC88, 8416, 6H30, 6189, 6N1EB, 6H23EB, 7730, ECC802, 6CG7, 12BH7, 6FQ7, and 6GU7.

Valve heater voltages: 6.3V (2A) or 12.6V (1A), switch selectable.
Valve plate (or B+) voltages: 200V or 300V (at maximum of 40mA for both valves), switch selectable.
Inputs: Two single-ended stereo (RCA)
Outputs: One variable-level stereo preamp output (RCA), one fixed line level stereo output serving as an output loop for Input 1 (RCA), two headphone outputs (one via 1/4-inch TRS jack, one via 4-pin XLR-type connector). Output is switch selectable between Preamp and Headphone Amp modes.
Gain: Varies with valve type (gain = ½ the mu of the triodes in use).
Power output: Up to 6Wpc @ 50 Ohms
Frequency response: +/-0.1dB, 5Hz –60kHz; +0/-1dB, 3.3Hz – 190kHz; +0/-3dB 3.3Hz – 370kHz.
Distortion + Noise @ 1kHz: 0.035%
THD+Noise @ 1Vrms output; 0.1% @ 2.5Vrms output; 0.5% at 12.75Vrms
Faceplate: Matte silver or “stealth” black.
Dimensions (HxWxD): 11.75 x 40 x 27cm
Weight: 10kg
Price: £2,325

Manufactured by:
Cavalli Audio
Tel: +01 512 413 8765
URL: www.cavalliaudio.com