LKV Veros PWR+ power amplifier

As much as I admire Belgian amplifier designer Bruno Putzeys's accomplishments, I have harbored some misgivings about class-D amplifier sound. I do not believe it represents the future of perfectionist audio. Despite the fact that today's active loudspeakers depend entirely on class-D's free horsepower, light weight, and low-temperature operation, I think it sounds vacant compared to class-A. Class-D's primary engineering virtues are its extreme power-to-weight ratio and power-efficiency, as well as its high damping factor. Class-D's chief audiophile virtue is its uncanny transparency, especially in the six lowest octaves, ie, below 1.3kHz. When I listen to good class-D (with a fat, stable linear power supply), I feel like I am gazing into a clear, glass-smooth pond. I can see all the way to the bottom. But (sigh) there are no fish in the pond.

As you already know, I am the Prince of Serendip. For this month I discovered, almost by accident, a power amplifier that puts live fish (and tadpoles and turtles) into a class-D amplifier pond.

The amp I've stumbled on is LKV Research's $10,000 Veros PWR+ stereo amplifier. I first experienced it at Capital Audiofest 2019, where the sound in the LKV room—with the Sonner Audio Legato Unum loudspeakers—struck a remarkable balance between analytical and romantic. I knew something unusually good must be causing that. After a long audition, I told LKV Research's chief-of-everything, Bill Hutchins, that I thought his Veros PWR+ amp sounded more class-A than class-D and asked, may I please review it?

Description
I went to the LKV Research website and clicked Products, then "Veros PWR+ Power Amplifier." The first words I read were: "The Most Musically Accurate Power Amplifier Output Stage Available." I stopped, read it again, then smirked at the expression "musically accurate." I am pretty sure the author is trying to celebrate the fact that LKV Research founder Bill Hutchins uses Purifi Audio's 1ET400A class-D power amplifier modules, designed by Bruno Putzeys. Further down the webpage, the author states that in the Veros PWR+, the 1ET400A modules are driven by a voltage amplifier stage consisting of differential pairs of matched JFETS operated in class-A with no feedback and current-source biasing.

The Veros PWR+ stereo power amplifier is specified to deliver 200Wpc into 8 ohms, 400Wpc into 4 ohms, and 220Wpc into 2 ohms, the maximum power assessed at 1% THD.

A little farther down, the author explains that the Veros PWR+ is equipped with a linear power supply energized by three toroidal power transformers. A 1kVA mains transformer, weighing over 12lb, provides abundant current to the class-D output stage. A second, smaller toroid powers a "floating" +15V DC source that feeds the driver circuitry in the Purifi module. A third toroid "feeds the class-A input/gain/driver stages." All that heavy coiled wire is bolted inside a thick aluminum chassis. The Veros PWR+ weighs 50lb.

820lkv.bac

The chassis front is plain, with only the LKV logo and an illuminated power button. The rear is nondescript, with an IEC power socket, a screw-in fuse holder, a pair of WBT binding posts, a pair of single-ended RCA inputs, a pair of balanced XLR inputs, and a pair of minitoggles for switching between balanced and single-ended operation. The Veros PWR+ is hand-built by Bill Hutchins in North Conway, New Hampshire.

Setup
At first, I positioned the Veros PWR+ amplifier on the suspended hardwood floor in front of my equipment rack and connected it to my Magnepan .7 panel speakers with Cardas Clear Cygnus loudspeaker cable. I hooked it up to my Rogue Audio RP-7 preamp with Cardas Clear Cygnus interconnect. Straight out of the box, the LKV amp sounded fast, liquid, warm, and inviting, just as I remembered it from Capital Audiofest.

The next day, between music tracks, in the midst of pandemic-shutdown silence, I noticed a faint Lutron-dimmer– type buzz that seemed to be emanating from the LKV's chassis. Checking first for hum, I put my ears to the speaker panels and heard only silence. When I examined the chassis with my stethoscope, I realized the sound was originating from behind the front panel, where the 1kVA transformer is bolted. I presumed the buzz was caused by the natural magnetostriction of the transformer coils being amplified by the amp's chassis and the diaphragm of my 1920s wood floor.

Seeking a quick cure, I placed the Veros PWR+ on a Harmonic Resolution Systems M3X-1719-AMG GR LF isolation platform, whereupon the buzz was reduced to a point of serene inaudibility. With the LKV amp on the HRS platform, the sound of music recordings became noticeably purer, with sharper focus. A few days later, on a whim, I switched from the LKV-supplied generic power cord to an AudioQuest Tornado cord, which added bass punch, presence, sharper focus, and more silent silence.

Eriks Ešenvalds's Translations (24/96 FLAC Naxos/Qobuz) is a high–dynamic-range recording with extended passages of extreme quiet. The added silence and clarity produced by these two (not-inexpensive) audiophile "accessories" increased my ability to observe, in a relaxed, focused manner, the nuanced inner workings of the Ethan Sperry–conducted Portland State Chamber Choir (footnote 1).

Listening
John Atkinson knew, as he was recording it, that this Eriks Ešenvalds Translations album would rev me up and engage me on a multitude of levels. He knew I'd recognize the nature poet in Eriks Ešenvalds's compositions. And of course he knows how I relish the sound of choirs in sacred spaces and their vibrating masses of air. He knew how much I enjoyed his previous recording with Erick Lichte (producer) and Ethan Sperry conducting the Portland State Chamber Choir on Eriks Ešenvalds's The Doors of Heaven (24/88.2 FLAC Naxos/Qobuz).

820lkv.1

From the Qobuz liner notes: "The Oregon Poet Laureate Paulann Petersen, whose poetry is set on the first two tracks of Translations, stated: 'Art is translation. Art translates mystery for us without destroying that mystery.'" On this recording, "translates mystery without destroying that mystery" describes very well the serene, humanist spirit conductor Ethan Sperry elicited from his choir as well as the spatial acuity of Atkinson's six-microphone recording. Everyone involved with the Translations project apparently demonstrated proper respect for choral sound, church chapel sound, and the intensity of Ešenvalds's art. That respect makes this Naxos recording a gift to the ear and a sacred inspiration.

The LKV Research Veros PWR+, powering the Magnepan.7 quasi-ribbon panels, exposed all the delicate volumes of activated reverberant air that are held by this transcendent recording. Average class-D amps could never convey the full dreaminess of this type of choral poetic. Why not? Too much information would be missing in the upper octaves. But the class-D LKV amp played equally rich and atmosphere-soaked through the entire audio band. It did atmospheric dreamy like class-A does atmospheric dreamy. Surprising and impressive.

Bye-bye Portland, hello Brazil
The berimbau is a single-string percussion instrument that migrated from Africa to Brazil. It is fashioned from a meter-long stick, hollowed-out gourd, and a steel string, frequently one salvaged from the belting inside an automobile tire. Holding the gourd against his belly, the berimbau player strikes the metal string with a small stick called a baqueta while adjusting the wire's pitch with a stone in his other hand. The berimbau's sound is delicate—all buzz, snap, and resonance. Like a harmonica or jaw harp, the berimbau radiates full-spectrum harmonics, filling my listening room with buzzing, animated aural textures.


Footnote 1: All the observations below were made with the Veros PWR+ on the above-mentioned HRS platform and the generic, LKV-supplied power cord.
COMPANY INFO
LKV Research
19 Randall Farm Rd.
North Conway, NH 03860
(603) 730-7400
ARTICLE CONTENTS

COMMENTS
Bogolu Haranath's picture

May be HR could also review the new PS Audio Stellar M1200 mono-blocks, hybrid tube/class-D amps, $6.000/pair :-) ........

dashendorf's picture

Class D suffers from power pumping. The cure is for the left and right channels TO SHARE the power supply. In other words, beautiful dual monoblocks are SUBOPTIMAL! Yes, heresy, but it is what it is.

Bogolu Haranath's picture

PS Audio another class-D mono-blocks, Stellar M700 are Stereophile Class-A rated ....... Bel Canto class-D mono-blocks, REF 600M and Black system are Stereophile Class-A rated :-) .......

a.wayne's picture

How is sharing the same supply gonna improve “ power pumping “ or is it pimping ..? :)

Ric Schultz's picture

How about a 3000 watt power supply for each channel.....choice of discrete input amp, Air core inductor on Purifi module....and tons of other tweaks.....including binding post bypass system. However, the air core coil is what is really something new. All class D amps till now used ferrite core inductors.....You would never use a ferrite core inductor in a xover of a speaker for the midrange and tweeter......this is common knowledge...it would wreck the sound. How come all class D amps have a ferrite core inductor on the output?.....for practical reasons....not sonic ones. Read more here:

http://tweakaudio.com/EVS-2/Purifi_amp_mods.html

I was reviewed July 1990 in Stereophile Mag. by Robert Harley.....my shunt attenuators were class A rated for 7 years.....so I bean around the block.

Bogolu Haranath's picture

The new NAD M33 uses Purifi modules ...... I don't know whether NAD uses 'ferrite core' inductors or not :-) ........

Several class-D, stereo and mono-block amps are in the Stereophile Class-A list :-) .......

Bogolu Haranath's picture

Objectivists are Apollonian and subjectivists are Dionysian :-) .......

Lars Bo's picture

Maybe they're really both "subjectivists"? That's my understanding.

As an aesthetic pattern of "an accent" to sound and musicality, Apollonian and Dionysian "accents" both seem to clash with an objectivist-ideology of no "personality" in sound, verifiable by numbers, and, I gather, if so, musical honesty.

In any event, I applaud Herb for using these concepts (thanks, Herb).

Bogolu Haranath's picture

There is an interesting article, recently published in TAS about objectivism vs subjectivism (point/counterpoint) :-) ........

Ortofan's picture

... one of the amps from Nord Acoustics which also use the Purifi 1ET400A modules.
https://www.nordacoustics.co.uk/purifi1et400aamplifiers
Their prices seems to be on the order of one-fourth of the price of this amp.

Is it Nextel binding posts, or should it be WBT nextgen binding posts?
http://www.wbtusa.com/pages/binding_posts.html
http://www.wbtusa.com/pages/0703cu.html
http://www.wbtusa.com/pages/0703ag.html
Isn't Nextel that faux suede finish once used on various speakers?

Is the predominance of third harmonic distortion an artifact of the Purifi amp module itself or is it generated by the input/gain/driver stage that LKV adds?

Bogolu Haranath's picture

Third harmonic distortion almost similar to Krell K-300i? :-) ........

Bogolu Haranath's picture

One more ..... Similar to PS Audio Stellar M700? :-) ......

Bogolu Haranath's picture

One more again ...... Similar to Classe Delta monos? :-) .......

BillNH's picture

The distortion is, as JA observed, very low. The third order character is an intended characteristic of the LKV line level circuitry we have spent 8 years perfecting through seemingly endless listening and measuring sessions and innumerable circuit modifications. That circuitry is, I believe, largely responsible for the character of the sound Herb appears to have liked and found to be somewhat class A-like. The Purifi module does its job (principally current amplification) without adding or subtracting (almost) anything at all to or from the signal it is sent. It is simply the best, most accurate way I know of to get the signal from the line level circuitry to the speaker with the appropriately high level of power.

[[Bill Hutchins is chief designer at LKV Research--Editor]]

Thanks for adding that. I was about to do so.

Ortofan's picture

... LKV line level (input) circuitry, did you ever consider a design that might have its distortion characteristics dominated by the second harmonic, rather than the third?

If so, what made you choose the version with predominantly third harmonic distortion?
Or, if not, why not?

For that matter, and given that you're using the Purifi amp modules, why not develop a line/input stage with as little distortion as possible?
Would that approach result in an amplifier whose sound quality was somehow less "musically accurate"?

BillNH's picture

Yes, in developing the design for the phono/line level circuitry used in most of our designs, including the PWR+, we considered, tested and listened (almost to the point of distraction) to numerous circuits and topologies, including some that produce predominantly second order harmonic distortion. There were several goals we wanted to achieve, including very low noise, very low distortion (harmonic and slewing induced) throughout the whole audio frequency range (20-20KHz), natural sounding detail and dynamics. And, beyond everything else, we wanted reproduced sound that was as close to the sound of real voices and instruments as possible. Ultimately the circuit that gave us the best balance (at least to my ears) of these somewhat conflicting goals was a class A folded cascode, differential (balanced) amplification topology executed with hand-matched jfets, stiff current sources and no loop feedback (local or overall). As I you know, the 3rd order harmonic distortion is characteristic of the differential amplification. I hope this answers your question.

Bogolu Haranath's picture

JA1 compares the sound quality of JC1+ with Classe Delta monos, in his review of Classe Delta ...... JA1 says JC1+ has more 'tube like' sound quality ....... JC1+ has 2nd harmonic distortion and Delta monos have 3rd harmonic distortion :-) .......

Bogolu Haranath's picture

Seems like KR also likes the sound of 2nd harmonic distortion in the Parasound A21+ ....... Surprise, surprise, even the mighty Benchmark AHB2 has mild 3rd harmonic distortion :-) ........

dashendorf's picture

Ortofan's questions are very appropriate. The extra cost in the PWR+ versus other systems using Purifi or Hypex or ICE modules is due to using Class A, zero-feedback, matched components in the input circuits and using custom linear power supplies.

LKV's competitors are the 20 k$ & 30 k$ amplifiers, not the 2.5 to 3 k$ amps which use switch-mode power supplies and off-the-shelf input circuits.

Audiophiles generally seek the best quality and adjust for cost. The words "best value" are tricky. Best value? How about your phone connected to a pair of self-powered speakers? Claiming that other companies offer better value creates snickers from non-audiophiles (most of your friends and my friends): "3 k$ for an amp? What a moron. 10 k$? Yikes."

Bill Hutchins in an audiophile. He would claim: "The PWR+ offers BETTER quality at a LOWER cost than dual-mono blocks."

As for binding posts, Bill is an electronic designer primarily. He didn't hear the alleged differences. I do know that when a customer asks for WBT, for a small-charge he's installed them. Not a real issue.

Ortofan's picture

... various configurations, including mono-block, stereo with a single power supply and dual-mono stereo.
https://www.nordacoustics.co.uk/purifi1et400aamplifiers

Also, they offer a choice of input stage op-amps, including a discrete class-A version.
https://www.nordacoustics.co.uk/upopampchoice

dashendorf's picture

I know of many Class D amps. I know of $130 models that are good. LKV Research doesn't use opamps (many internal feedback loops), but does use differential Class A circuits and zero-feedback. Read the review. The sound is natural. LKV thinks of the PWR+ as Class A+D. The 1ET400 provides excellent output circuitry, LKV addresses other issues. Great sound results.

Bogolu Haranath's picture

As an industry veteran said it, 'the increasing importance of smaller differences' :-) ........

Ortofan's picture

... in the input/driver stage is somehow detrimental, do you hold that same position regarding the use of feedback in the Purifi power amp module?

dashendorf's picture

Ortofan, Again, a great question. The output stage requires a great deal of feedback - speakers are very physical and current demands are high. Getting the signal from a source to the output stage at the correct level while minimizing noise and distortion is the value of AZF Circuits, but the output stage is an entirely different animal.

Bogolu Haranath's picture

One could probably get the same results by using tubes in the input stage ...... See, Rogue Audio Sphinx V3 tube/class-D integrated amp measurements :-) ........

dashendorf's picture

Dear Bogolu,

Bill expects CLASS A tube amps to use Class D output. Obviously Rogue is. LKV expects the future of audiophile amps to Class A+D. LKV wasn't the first Class A+D, but Bill would believe he offers the best Class A input circuit. People can debate that. It's fun being an audiophile.

The second issue is adopting the Purifi 1ET400. It's quite simply the best Class D output. Not much debate.

Bogolu Haranath's picture

By using the Rogue RP-7 tube pre-amp, HR is getting some of that tube sound anyway :-) ........

Ortofan's picture

... whose circuitry does not employ any feedback?

dashendorf's picture

The Class A signal circuits in Bill Hutchins's designs employ zero-feedback which requires matched components. He believes this helps minimize a SOURCE of distortion. Many agree.

Ortofan's picture

... misunderstood.

What source(s) - such as a pre-amplifier , digital or analog disc player, tuner, recorder or streamer - are you connecting to this power amplifier whose circuitry does not already employ any feedback?

Or, are you possibly suggesting that the circuitry in this amplifier somehow reduces the distortion in signals from devices that are connected to its input?

In regard to the comment that "many agree", who are these "many"?
What quantity of these amplifiers has been built and sold?
Where would one go to audition this amplifier?

tonykaz's picture

Sound Engineers like Bob Katz, who is a real world perfectionist, favors Class D amplification.

Class D has had a successful future for some time already.

Personally, I love and admire Tubes from Russia despite them being fragile and having a rather short Half-life. Outstanding Solid State devices can seemingly last forever ( according to Nelson Pass ).

Tony in Venice

Ortofan's picture

... whatever happened to the Komuro 845 tube amplifiers?

Herb Reichert's picture

Komuro is an old friend
I gave those PP 845 monos back so he could sell them

He is still building triode amps at the leading edge of what is possible.

hr

Ortofan's picture

... the Icon Audio MB845 MkII Mono, which is a push-pull 845 type tube power amp:
https://iconaudio.com/mb845-mkii-super-845-mono-blocks-mb845-mkii-m-

Alternatively, there is their Stereo 845 push-pull integrated amp:
https://iconaudio.com/stereo-845-integrated-845-pp-amplifier-stereo-845pp

Bogolu Haranath's picture

May be HR could also include the new Harbeth P3ESR XD speakers in the short list of products to review :-) .........

dashendorf's picture

tonykaz. Bill Hutchins has had a c-j tube power amp for decades. Loves it, but wanted to do better. He had to wait for a great Class D.

On the other hand, Class A amplification at low power with highly sensitive speakers remains wonderful. See: https://lkvresearch.substack.com/p/power-amplifier-choices

tonykaz's picture

Low power with sensitive transducers is glorious.

I'm rather niche in my agreement with your statements.

I have felt the immenseness of powerful amplifications and tri-amping capable transducer systems, like being used in large theatres for iMax type installations.

One of my finest Music Systems fits in my shirt pocket and plays beautifully on any park-bench, Gulf Coast Beach, Air Travel seating. ( even during 20 mile bicycle rides )

Tony in Venice

Bogolu Haranath's picture

Please don't steal any mail-boxes, while during those bicycle rides ...... Just kidding ...... Just kidding :-) .....

a.wayne's picture

Hello ,

Maybe you can offer an explanation as to why Class D is so squarewave adverse , how is this instability overcome in music operation and as it should be audible is this possibly the class D sound most have an issue with ..?

Regards

tonykaz's picture

I can't offer any sort of design insights.

Personally, I'm at the point of embracing these efficient designs but not at the point of debating their limitations which seem rather minor.

There are a wide range of Analog lover's complaints.

Functionally, music reproduction advancements ( my opinion ) enable improved access to the dopamine that great music triggers the release of. We no longer need to sit square in front of a well tuned record playing set of planer loudspeakers and Class A tube gear.

How do Square-waves fit into our needs ?, I think I'm missing something from your question.

Philosophically considering, I suspect that electronic design and development is now in accelerated modes. I keep feeling that this next Decade will transition us to....??? . I recall being at RMAF2011 and having the feeling that the Audio Industry was mostly unrecognisable compared to the Audio Industry I participated in the 1980s with this last 10 years bringing amazing advancements i.e. iPhone11 ( for example ).

Fortunately, a person can still own and enjoy a beautiful traditional Tube based, VPI Koetsu Audio System and a state of the Art shirt-pocket traveling High End Audio System w/SD memory of zillions of music. All that wonderful Audio Research & Conrad-Johnson gear is still out there and widely available on eBay.

Wishing you well,

Tony in Venice

tonykaz's picture

Once again, this reviewer paints beautiful pictures.

I can see how a used book store will have a curious youth browsing (in the year 2075 ) this issue of Stereophile, stumbling across and reading this review taking him back to Mr.HR's Bunker Listening room and reliving this review experience.

Mr.HR creates amazingly wonderful art.

Thank You!

Tony in Venice

Kursun's picture

Herb,
When you gaze at the pond and feel something is missing, it is distortion that is missing. The horrible crossover distortion that class AB amplifiers produce...

Class D is only second compared to Class A

JHL's picture

...a random commenter has graciously delivered the kernel of wisdom and insight our motley reviewer's ears and decades of acute experience had missed.

Why thank you random internet commenter. You have saved audio from hearing and indeed from ourselves.

michelesurdi's picture

stereophile is reviewing diy products now?

AaronGarrett's picture

The amp under review and the Bel Canto use different Class D modules. Isn't the difference in sound more likely due to the difference in the modules -- the newer Purifi module being touted by Putzey as much superior to the NCore -- than its particular, expensive implementation in this amp? But maybe that is what Herb is suggesting. Anyway thanks for the tip on the Nana Vasconcelos record! Great music! And the beautifully written review.

dashendorf's picture

AaronGarrett, you hit one of the main reasons:

  • Purifi provides better linearity above 15 kHz than competitors.
  • Linear Power Supply designed to prevent power pumping
  • Class A, Zero Feedback Differential Input Circuits
  • Matched components

There are many great designers. Bruno Putzeys may be the best. Bill Hutchins has leveraged Bruno's genius better than others.

thethanimal's picture

I thought a manufacturer was required to maintain a minimum number of distributors in order to be reviewed in Stereophile? Was this policy change in step with PS Audio’s change in business model? Regardless, it’s a change for the better in the age of internet direct sales. With this policy now changed I can’t think of a better product for Herb to review than the Decware Super Zen Triode SE84UFO, maybe to go along with those Cube Audio full range drivers he’s loved at audio shows.

Jim Austin's picture

Stereophile has long reviewed products from companies that sell direct, with appropriate return policy, as long as they can demonstrate the ability to provide satisfactory after-sales support.

Jim Austin, Editor
Stereophile

thethanimal's picture

My apologies; I have misunderstood the policy then. But I believe by all accounts Decware meets the criteria you have laid out for a review, and I believe such handmade, point to point wired, single ended tube amplifiers they offer would be right up Herb’s, or the late Art Dudley’s, ally. With much love given to Shindo over the years it’d be interesting to hear how an American competitor (or kindred spirit) would compare.

To the review at hand, an electrical engineer coworker insists to me that FET transistors behave in the same way as tubes; perhaps that’s part of the reason this amplifier (and some Pass-designed solid state amps) tickle Herb’s fancy the way they do. I can only offer up that comment for consideration by others without further detail, having gained only cursory knowledge during my own electronics courses while pursuing a degree in another engineering field.

Herb Reichert's picture

and I am preparing to write about Decware now. . . . stay tuned!

hr

Bogolu Haranath's picture

If and when HR gets a pair of floor-standing multi-driver speakers, he could review the Rogue Audio Apollo Dark mono-block amps :-) ......

Bogolu Haranath's picture

May be HR could review the Rogue Audio DragoN, tube/class-D hybrid power amp ($4,000), and compare it with the LKV PWR+ :-) ........

JRT's picture

The listed specifications seem to have an error in the units of measure, "Input impedance: 200 ohms (single-ended), 400 ohms (balanced)."

I suspect that those values should be 0.2 megohms and 0.4 megohms, or equivalent impedance in other units of measure. No?

John Atkinson's picture
JRT wrote:
The listed specifications seem to have an error in the units of measure, "Input impedance: 200 ohms (single-ended), 400 ohms (balanced)."

You are right. I have corrected the input impedances on the Specifications page.

John Atkinson
Technical Editor, Stereophile

Glotz's picture

If I had the dosh, I'd check it out fer sure.

The Denafrips reviews were stellar as well. I want to check out their line more in depth. The Ares 2 looks like an excellent value and might prevent my purchase of a Benchmark DAC3B.

BillNH's picture

I should have said that I am the designer of the Veros PWR+.

Bogolu Haranath's picture

Mr.Bill Hutchins could consider a 5, 7, 9 and 11 multi-channel class-D amp :-) ......

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