April 2020

World Premiere Review!
Monoprice Monolith Liquid Gold X Headphone Amplifier
Return Of The King: Monoprice and Alex Cavalli resurrect the legendary Liquid Gold.
Review By Dave Hanson

  The Cavalli Liquid Gold holds legendary status within the personal audio community. I remember when I first entered into the hobby the Liquid Gold felt like the very definition of ultra-high-end unobtanium. Among many within the hobby, it was considered the king of headphone amplifiers. My first encounter with the Liquid Gold was at Rocky Mountain Audio Fest in 2015. I remember vividly how it gave headphones a tremendous sense of body, a level of holographic imaging and transparency I had never heard before. I later got an extended audition with it when Cavalli asked me to write some impressions of the Liquid Gold, Glass and Crimson for the community before what turned out to be their final production run in 2016.

In a private setting, the Liquid Gold was even more impressive. I noted, at the time, that its soundscape didn't seem to have any outer edges – the instruments just floated in a wide-open space with an unbelievable sense of transparency. I'd never heard anything like it. It was the absolute definition of the oft-overused audiophile term "holographic." Now, more than two years since Cavalli Audio closed its doors, founder Alex Cavalli has teamed with Monoprice to resurrect the design of this legendary amp with the Monoprice Monolith Liquid Gold X ($999).

This version is a bit different from the original, however, sporting a much smaller design and an onboard DAC. The Gold X doesn't quite sport the same unbelievable power as the original either, but with 3.9 Watts into a 50 Ohm load, it has plenty of power to drive any headphone, including the notoriously difficult HiFiMAN HE-6se. Like the original, the Liquid Gold X is a fully differential balanced solid-state amplifier. All of the circuit topology and component values are identical to the original Liquid Gold. When it comes to inputs and outputs, things vary slightly. While the original sported a four-pin balanced output and two 6.35mm outputs that could double as three-pin balanced outputs, the Gold X has been paired down to a single four-pin balanced output and a single 6.35mm unbalanced output.

In the back, the Gold X offers a variety of connections: a set of dual three-pin balanced inputs, a set of unbalanced RCA inputs, a USB digital input, a S/PDIF coaxial digital input, and a TosLink optical digital input. One button on the front selects between balanced, unbalanced, and digital; while another selects between the three digital input options. A third button on the front toggles between low and high gain and the fourth button engages the power.

On the back, there is also a switch to engage automatic shutoff, which will power down the amplifier after it idles for about four hours or so without use. Like many other Cavalli designs, the amplifier has a phase splitter in the signal path from the single-ended input, allowing any of the five input options to output in full balanced mode from the four-pin output. Also, like many other Cavalli designs, the amplifier runs a startup sequence, which takes maybe half a minute or so to complete. Once the startup sequence is done, the power light changes from red to white and you're ready to rock and roll.

While the amplifier runs just a tiny bit little warm, it's nothing compared to the original Liquid Gold, which could get pretty toasty. By touch, I would say the Liquid Gold X runs just a few degrees cooler than its sister amp, the Liquid Platinum. Certainly not warm enough to radiate in any noticeable way.

But enough about the design. Let's get into the part everyone is waiting for, the sound.

The Analog Section
The first thing you notice when you plug into the Liquid Gold X is the silent abyss of the background. Like the Platinum, the Gold X's power supply has been moved off-board to a switch-mode power supply, which, no doubt helps its incredibly low noise floor. It is phenomenally quiet for an amplifier with this level of power. I was even able to drive IEMs off of it, without much in the way of noise, until the pot was well past listenable volume. The only catch there is there's not a lot of actual volume play with sensitive IEMs. This amp was designed with full-size headphones in mind.

With full-size headphones, I found I had a little bit more flexibility on the volume pot than on the Liquid Platinum, which is pretty hot with a higher voltage balanced source. The Gold has just a touch more play, it seems, aided by the presence of two gain setting options. While the Platinum offers 5x gain, the Gold offers 4x and 6x, so there's slightly more flexibility overall. If we're talking about volume position in terms of a clock (8 o'clock position versus 9 o'clock position, etc.), I'd say the difference in low gain versus the Platinum's volume pot is about 30 to 45 minutes of extra flexibility in the low volumes.

It's not a ton, but it does give you more wiggle room overall. It would have been nice if the 4x gain was even lower, but I found it to be perfectly functional for the 300 Ohm headphones and planars that got the lion's share of listening time with it. These are the same headphones I would have chosen to pair with an original Liquid Gold, anyway. The sound itself is signature Cavalli. There is a slight bit of extra meat and warmth in the lower midrange down through the midbass, giving it the sweet, tubey sound made famous by the original Liquid Gold. Like the original, it's also sweet and non-aggressive through the upper midrange and treble. It's a very inviting, characteristically "chill" sound – one that's extremely well-suited to long listening sessions.

The soundscape is a good size in terms of both width and depth, but even more impressive is the razor-sharp imaging. Sound locations are extremely dialed in, which is an area that always impressed me about the original Liquid Gold. If pressed, I would guess that it doesn't throw quite as large of a stage as the original Gold, but I don't have one here to compare, so I'll leave that up to the forums to figure out.

Digging deeper into the sound signature of the Gold X, I'd say the mids are the star of the show here, and if you're the type of person who likes a little tubey bloom, but doesn't want to get caught in the endless cycle of tube rolling, I'd venture to say, this might be your best bet under $1000. Nothing from the amp ever feels strained or fatiguing, it's just pleasant and musical through and through.

Comparing against the Monoprice Monolith Liquid Platinum with the classic hard-to-drive choice, the HiFiMAN HE-6se, showcased the differences between the amplifiers quite clearly. Given the popularity of the Liquid Platinum, this likely offers the best lens into many aspects of the Liquid Gold X's sound. Listening to "Piggy (Nothing Can Stop Me Now" from Nine Inch Nails' classic The Downward Spiral revealed several spots where the Gold X surpassed the Platinum. The most noticeable difference came in terms of the bass delivery. With the Gold X, each kick drum landed with a thunderous blast that rattled my eardrums. Switching back to the Platinum, the kick drum registered with a modest "thwack", registering only a fraction of the power.

Another difference I found was the depth layering. As the keyboard enters in the second verse, the Gold X places it at a pinpoint distance behind the other instruments, creating a real sense of magic. The Platinum's placement is much hazier and generally flattened, in comparison. The same sounds are present, but their definition and placement just comes off as a little sloppy when put in direct comparison against the Gold X.

The third and most obvious difference in comparing the two with the demanding HE-6se shows in the upper midrange and treble, where the Gold X always keeps a firm grip of control. The Platinum comes off as thinner, splashier and uncontrolled, pitted against the Gold X's iron grip. This, combined with the greater impact and presence on the low end, causes the Gold X to come off as a bit warmer overall. But if one dives just a little bit deeper and analyzes the sound, the reality is, the Gold X is in much firmer command of the driver, delivering a more even and accurate response.

Switching over to the easier-to-drive 300 Ohm ZMF Verité Closed, the differences become far less pronounced. The easiest way to compare here would be to say the Gold X more or less sounds like a Liquid Platinum with a really sweet set of tubes. Pitted against the Platinum with an early 1960's set of Harleen-manufactured Dario Miniwatt 188CC's, the amplifiers finished in a dead heat. That being said, a pair of cherry 6922-equivalent tubes (CCA, 188CC, etc.) plus the price of their Platinum could very well run you nearly as much or more than a Liquid Gold X. Given the additional digital inputs, extra gain flexibility, additional driving power and extra refinement with more challenging headphones – simply buying a Liquid Gold X seems like a more practical alternative, rather than trying to incrementally upgrade to the same level through tube rolling.

The Digital Section
The DAC is a solid and convenient addition to the total package of the Monoprice Monolith Liquid Gold X. While it didn't quite reach the level of the Chord Hugo 2 that I primarily used to independently test the analog section, that DAC sells for 2.5X the price of the Liquid Gold X ($2,495 versus $999), so it's not a very fair comparison. The Hugo 2 had greater clarity, deeper resolution, a more open stage and a richer, more analog sound overall, in terms of the DAC. In terms of driving headphones directly, I'd probably prefer the Gold X's extra bit of personality and musicality for most headphones as opposed to the Hugo 2's somewhat dry direct-driving delivery.

Comparing against the excellent FiiO M15 ($1299), which is also here for review, with the Gold X registering much closer. Both feature an AKM chipset – 4493 for the Gold X and 4499EQ for the M15. The sound of both DACs through the Gold X's amplifier section was nearly indistinguishable, though I felt the FiiO M15 had a very, very slight edge in the deepest resolution in the individual notes. Drums just came off as a hair more organic through the M15. Could I pick this out in a blind test? Probably not. Given how close they are, it was more or less a wash, which is to say the Gold X's built-in DAC is pretty good overall.

All things considered, I feel that the DAC is a great addition, particularly for the convenience factor. But just like you'd expect from a similarly-priced integrated amplifier, the DAC section can certainly be bested with a good standalone device. Some listeners may find a standalone DAC to be a proposition of diminishing returns, given the agreeable sounding and high-quality DAC integrated here. Others may find they want to push the Gold X to the farthest edges of its capabilities. The fact that you have a choice in the matter is a win.

Final Thoughts
The Monoprice Monolith Liquid Gold X is simply a fantastic piece, top to bottom. It sounds great, drives anything, and can serve as either an all-in-one or a badass amplifier to anchor your system. Is it a mandatory upgrade for owners of the Liquid Platinum? That's hard to say. It is a slightly better amplifier overall. If you're looking for more out of the Platinum and are reluctant to jump into the rabbit hole of tube rolling, then I'd say yes. The Gold X will push you just past the edges of what tube rolling can offer with the Platinum. Also, if you're using the Platinum with an entry-to-mid level DAC, the all-in-one capability should provide you with a nice upgrade across the board.

If you're not a Platinum owner, or you're getting into Cavalli gear for the first time, I would say that this is a great piece that exemplifies the tubey and musical Cavalli sound signature. With a drier or more neutral type of headphone, like the Sennheiser HD800, this can take your musical enjoyment up several notches, as your tunes gain a bit more natural warmth and body without losing their pinpoint accuracy.

Overall, this is an excellent all-around piece and a phenomenal value sitting just under $1000. If you have the opportunity to hear one, it's a must audition.

Additional Equipment Used During This Review
Sennheiser HD800
HiFiMAN HE-6se
MrSpeakers AEON Flow Open
ZMF Auteur
ZMF Verité
ZMF Verité Closed
Campfire Cascade
Campfire Andromeda
Campfire Vega
FiiO M15
Wells Audio Milo Headphone Amplifier
Glenn OTL Tube Amplifier
Monoprice Monolith Liquid Platinum
Chord Hugo 2
DanaCable Lazuli Headphone Cables
DanaCable Onyx Interconnects
Audioquest Big Sur Interconnects
DanaCable Trustream USB Cable
Wireworld Starlight 7 USB Cable
PS Audio Duet Power Conditioner
Roon
Tidal Hi-Fi

Specifications
Type: Type: Fully Differential Balanced Solid State Stereo Headphone Amplifier
Frequency Response: 5Hz to 60kHz (+/-0.05dB)
Rated Output Balanced: 6.2 Watts @ 33 Ohm, 3.9W @ 50 Ohm, and 0.82W @ 300 Ohm
Rate Output Single-Ended: 1.8 Watts @ 33 Ohm, 1.1W @ 50 Ohm, and 0.23W @ 300 Ohm
Output Impedance: 0.13 Ohm balanced, 0.17 Ohm unbalanced
Noise Floor: -103dB (47 Ohm load, balanced output, low gain)
Crosstalk: -88dB
THD+N: 0.0012% balanced and 0.0023% unbalanced @ 1kHz
Dimensions: 8.75" x 8.5" x 2.0" (WxDxH)
Weight: 3.2 lbs.
SMPS: 36V 1.5A
Price: $999

Company Information
Monoprice, Inc. 
11701 6th Street
Rancho Cucamonga, CA 91730

Voice: (877) 271-2592
Website: www.Monoprice.com