Luminous Audio Technology Archimedes Power Amplifier

Designer Michael Bettinger comes up with another solid state component winner

“Are you okay? Did something happen?” asked my audio pal, Colin.

“I’m crestfallen. Life seems to have lost all meaning,” I reply. “I had to pack up and send back those Luminous power amps, and now I don’t feel like listening to music on my system.” 

But of course, one evening a few days later, I was spinning Mellow Waves by Cornelius using my Ampsandsound Zion Monos, and feeling it big time. The Zions, which had become chopped liver only a week prior, were back to tickling my fancy.

It’s funny how that is. I will become obsessed with comparing components to find the most sonically vivid little attributes that light up my cortex. This is so that I can (hopefully) communicate these attributes in a review. Rarely - although it does happen - I review something that sounds so good that it takes on Holy Grail status for me. This is how it was during my time with the phenomenal new amps from Luminous Audio Technology - the Archimedes are that good. 

A Little History (and some tech)

I’ve been a major fan of the products offered by Luminous for a few years now. 

At HiFi shows, I’m drawn to the little companies building bespoke gear purely out of a passion for music reproduction. Finding such gear is a big reason I like attending audio shows. Capitol Audiofest is particularly good in this regard and is where I met Tim Stinson and Mike Bettinger of Luminous Audio Technology about 3 years back (in the Before Times). This resulted in my review of their most excellent Axiom III preamplifier. I was so smitten with the sound of the Axiom III, except for a lack of features that matter mainly to a reviewer, that I considered purchasing it.

At the 2022 Capitol Audiofest, I briefly heard their new offering, the Archimedes power amps, and agreed to a review. Although I couldn't tell for sure because of a lack of familiarity with the speakers Tim used in the Luminous room at CAF, I would swear I heard something special about the presentation of the bright, chimey, high frequencies I heard from the acoustic guitars on a Tom Petty cut we listened to. 

Fast forward almost a year to when I had the new amps at home in my system, once again hearing that special something about Archimedes' reproduction of high frequencies - and that was only the beginning of the fun.

Luminous is a collaboration between Tim and Mike, with Mike being more than just a designer for hire - although he is just that for other companies, most notably at one time but not now, for VPI. 

Y’all remember Ampzilla and Son of Ampzilla, right? Well, Mr. Bettinger’s back story in HiFi involves being with Great American Sound during its heyday - and then afterward by offering repairs and circuit and parts upgrades. The late great James Bongiorno was the G.A.S. figurehead and designer of record for those legendary pieces. Still, Mr. Bettinger must have learned more than a thing or two from Mr. Bongiorno because there is an elegance and classiness to the design and sonics of the Luminous Archimedes amps that is an evolution of James’s later design topology for Sumo Electric Co., primarily the SUMO Power from the mid 1980’s.

Since the pair I received was so early in the first production run, Mike had to send me a pdf of the owner’s manual. I don’t see any reason why I should paraphrase his excellent description of the hows and whys of the amp, so I’ll simply copy and paste a bit of it:

The Archimedes is a 100-watt mono amplifier featuring:

• Balanced speaker drive topology focused on accurately controlling the motion of speakers, most audibly in the low frequencies

• Minimum-loop power supply and output stage layout techniques, providing effortless dynamics and improving complex load capabilities

• Applied PCB circuit layout and routing technologies that enhance low level resolution and circuit stabilities in sensitive differential input and voltage amp stages

• Together these design techniques provide a clean, dynamic, nuanced performance that adapts easily to all types of complex speaker technologies

Design brief:

Starting at the input stage: the Archimedes uses a cascoded JFET-based differential input amplifier, implementing a fully differential voltage amp stage.

The voltage amp stage provides a true four quadrant output signal to the dual Class-A/B output stages. An advantage of this approach is that it guarantees that the circuitry and the music are identically loaded from input to output, thus lowering distortion.

While balanced/bridged output stages are not new, the Archimedes dramatically improves on this technology using a fully discrete, four quadrant input-to-output signal path, as described above. The four power amplifier circuits use a Sziklai configuration, known for its higher current gain and stability.

The pcb layout applies a unique isolated drive circuit approach that minimizes interactions between the four individual drive circuits and power supplies, providing a dramatic improvement in low-level resolution and lowering both THD and IM distortions.

The DC power is routed through wide power plane traces. Providing a low damping factor (before feedback).

Physically the AC power to the amplifier and rectifier/filters are located within two inches of the power transistors, once again improving the headroom and dynamics - no long, high inductance supply wiring as seen in most power amplifiers.

DC power to the input/VA stages is augmented with wide distributed capacitance traces that improve dynamic headroom and stability to the input stage where the music signal is the most fragile.

The Design: Balanced-Drive and ground.

The Archimedes topology has been designed as fully balanced from input to output, with +/- loudspeaker connections of the loudspeaker driven in push-pull fashion by four identical outputs of a perfectly balanced differential amplifier (the four quadrants).

Why is this important? Because the loudspeaker is, electrically, a motor. A speaker designer chooses one form of technology (of the many available) to create motion and sound from the application of power. All motors exhibit electrical characteristics that make the amplifier’s job a lot more difficult than it would appear.

Specifically, the job of the amplifier is manifold. It must supply the power to move the loudspeaker and must absorb the inductive energy reflected to the amplifier by the speaker. Not only does the amplifier need to source power to the speaker, but it must also sink, or absorb the energy generated by the speaker drivers (known as back EMF). Applying power to a speaker causes the speaker to produce an opposing force that fights the drivers’ efforts to move. This reverse power is directed back to the amplifiers output, unless it is absorbed by the power amp it affects the performance of the speaker.

Both single-ended (tube) and symmetrical amplifier designs must rely on the power-supply ground return path to the transformer to complete the signal path through the speaker. Like the shortcomings of the speaker itself, the power transformer center tap provides a less than ideal electrical connection for the speaker negative terminal.

What the Balanced Drive Technology brings to this picture is the ability to control both terminals of the speaker drivers more effectively by locking their motion between a positive amplifier and a negative amplifier, allowing the amplifier to more effectively absorb the reactive power that is being generated by the speakers. 

If you got through this excerpt from the manual, you should have lots of respect for the design, I certainly did. But fancy design briefs and specs don’t tell us much about how a pair of Archimedes (or any component) will sound in situ. I’ll try my best to do just that.

In Use

Each Archimedes is not that heavy or particularly large compared to most other power amps I’ve tested for review. The guts reside in an attractive yet minimalist, silver-finish, rectangular box. A power push-button on the front panel lights when the amp is on. One of the amps sent had a plexiglass, rather than metal, top cover so I could see inside. Hmm. The symmetry of parts and layout indicated a complimentary circuit, but the only input was a natively single-ended RCA plug. After talking to Mr. Bettenger, I now understand that one of the key elements of the Archimedes design is the differential input stage. This part of the circuit is where the unbalanced RCA input is transformed into a symmetrical signal that is sent to 4 separate power sections in a sort of super push-pull arrangement. This, of course, is responsible for keeping speaker drivers in total control by the Archimedes. Having a quad array of balanced/bridged amps removes the unpredictable nature of a loudspeaker's path to ground, which typically is constantly changing due to storing and releasing energy. In addition, the differential input feeding this quad amp array allows different amounts of local feedback to be used in four separate loops. Mike told me although he has taken things quite a bit further in many areas, his original inspiration for this topology comes from the Sumo - The Power, one of James Bongiorno’s post-GAS designs.

Along with the RCA input on the back panel are two pairs of Cardas speaker binding posts, an IEC socket for the power cord, and a modest amount of fins to heat sink the four power transistors. I’m a sucker for simplicity, so I was already enamored of the amps, even before playing music.

During my time with the Luminous amps, my system consisted of:

QLN Prestige Five loudspeakers (on Iso Acoustics pucks), VAC Master Preamplifier with phono option, Ampsandsound Zion Monos, TW Acustic Raven LS turntable, and 10.5” arm fitted with a Dynavector XV-1t - including alignment and an azimuth correction shim from Wally Tools. Innuos Zen Mini streamer using Roon and Qobuz feeding a Forssell Technologies MADA-2a DAC. Cabling was a mixture of Iconoclast and Cardas. Later on, a Pass Labs XP-32 line preamp arrived for review. I mated the excellent Lab 12 Meltos 2 phono pre with the XP-32 when listening to vinyl.

I’ll start by saying that I found the overall sonic signature of the Archimedes amps exceptionally seductive. That is an adjective I usually reserve for vacuum tube gear. The Archimedes were quick and clean but not at the expense of musicality. The midrange and low mids were as full-flavored as any vacuum tube amp I’ve heard.

My regular ride-or-die Ampsandsound Zion monos sounded slow and congested in comparison. This was a big shocker. Over several weeks, I went back and forth from the Zions to the Archimedes. I was astounded by how much more control of the low end was evident with the Luminous amps in the system. Fast transients had more clarity and less textural overhang when using the Archimedes. Imaging, while sounding different than the uber-3D-ness of the Zions, was just as spacious as any tube amp I’ve auditioned in the system. 

The Archimedes amps do this without pulling the pieces of a recording apart. The additional low-end clarity and punch are just what the doctor ordered for the Prestige Fives, which in my listening room tend towards sounding a little under-damped in their low-frequency reproduction. I can’t say the Archimedes had a deeper reach into the lowest octave versus the Zions, but the visceral punch of bass drums and bass instruments was more satisfying when using the Archimedes.

Sometimes, I hear/think in colors. I noticed that vocal sibilance and cymbal crashes had more of a white or even clear quality, as opposed to a darker gray and opaque vibe when not using the Archimedes. 

Sometimes, I start the listening portion of my review process with a mental list of reference recordings, some of which I’ve recorded, mixed, or mastered. As one might surmise, only a small portion of these selections are what I would consider “audiophile” level recordings, but I know ‘em, and I like ‘em. Nothing you would hear at a show, but special to me nonetheless. Which reminds me, does anyone ever listen to “Keith Don’t Go” or London Grammar at home? If I hear the Disturbed cover of “The Sounds Of Silence” at a show, I’m usually headed out the door. To each their own, I guess.

Sounds

Spec’d at 100 watts per channel, I found the Archimedes to be as sure-footed and immune to audible clipping as any 200-1000 watt amp I’ve ever used. Small-scale dynamics were displayed to a very granular degree. Large-scale dynamic contrasts were as explosive as was contained in any given recording. I played some vintage Telarc records like The Cleveland Symphonic Winds conducted by Fennell. Holy bass drum, Batman!

All that punch and detail in the low end is coupled with an expensive-sounding and grain-free perception of high-frequency transients that musically complemented any recording I played. I listened for hours on many nights and mornings before work without my focus on anything but pure musical enjoyment. 

The Bird and The Bee self-titled release on vinyl is one I played a lot. This recording collaboration of Greg Kurstin and Inara George (daughter of the late great Lowel George) is such a treat. Great songs, Inara’s gorgeous and provocative vocals sailing on ear-worm melodies and chord progressions would be enough, but the sound of this record is stunning on its own.

The Luminous Archimedes delivered every detail and nuance with a classy silkiness up top and a controlled pounding on the bottom. I was in heaven.

Of course, I played Kevin Gilbert - Thud in all its AAA glory. This record has been a mainstay for many years in my regular rotation. I love the songs, production, and general analog-ness of the sound of this record. I considered this record to have an excellent sonic presence while also being a bit dark sounding. As my system has improved over the years (especially my turntable/arm/cart setup), I've realized that this record has all the detail my ear loves when played back on a great system.  

The Luminous amps were like a magic piece of the puzzle that allowed all the cuts on Thud to come out of the speakers in a way that was clear and detailed without robbing the mid-bass of a thickness that, for me, is one of the unique sonic attractions about this record. Kevin’s honey-colored vocals on “Goodness Gracious” retained his powerful, over-compressed, and in-your-face presentation - with sibilance being faster and cleaner than I’ve yet to hear. 

Right before I had to send these beauties back, I received a sealed vinyl copy via Discogs of Fiona Apple - When The Pawn… I have streamed this many times, and it’s another one that I love virtually all the songs. The production and mixing are a masterpiece of late-analog, pop. It was not originally issued on vinyl until Vinyl Me Please did their thing. 

This record is sometimes heavily layered but edges right up to the line of being over-produced without going over and sounding too self-indulgent. The Luminous amps once again brought the heat, displaying all the textural-sounding keyboard parts, percussion, and vocal layers to the extent that, yes, I heard new things. No, it was not distracted from the core musical message; it was simply easier to hear all those sometimes buried treasures. Thanks, Fiona, Thanks, Jon Brion. Thanks, Rich Costey. Y’all rule on this one.

Dr. John, Goat Rodeo, Beck, Ray Charles, Death Cab For Cutie, Steely Dan, Linda Ronstadt, Lake Street Drive, Radiohead, Nine Inch Nails, Elvis Costello, scads of Blue Note reissues, D’Angelo, Pat Metheny (of all periods in his vast catalog with The Way Up via Qobuz being a transcendent experience), and a long list of others became a sumptuous treat to listen to with the Archimedes in the system.

So What Do You Really Think?

For starters, anyone looking to change power amps should put the Luminous Audio Technology - Archimedes on their short list of candidates. With an MSRP of $8,900 a pair, it’s not a casual purchase. It’s also not the $39,500 you'll need to come up with for a CH Precision A 1.5.

While I can’t know if it will hit the mark for those who crave vacuum tubes, it’s NOT your typical solid-state offering. 

Until I hear some other solid-state amp that will no doubt be substantially more expensive - most likely a power amp that is designed, voiced, and executed in a similar hi-rez-with-musicality manner, but with price being no concern, I will have to call the Archimedes not only a great value but also the best-sounding 100-watt solid-state amp I know of.