LKV PWR-3 power amplifier

Reviewing LKV Research's Veros PWR+ power amplifier in the September 2020 issue, Senior Contributing Editor Herbert Reichert enthusiastically opined, "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." Herb concluded, "Sound quality and music enjoymentwise, the LKV Research Veros PWR+ amplifier sits on a higher mountain than any other class-D amp I've encountered."

I took Herb's comments into consideration as I went searching for a power amplifier to complement my Sugden LA-4 preamplifier. The $10,000 LKV PWR+ ranked top on my list. I put in a request to LKV Research's majordomo, Bill Hutchins, who dispatched the large, 50lb PWR+ to my Greenwich Village flat for evaluation.

I enjoyed the New Hampshire–made, 200Wpc (8 ohms) amplifier; it became my solid state/class-D reference power amplifier (footnote 1). The PWR+ presented an extravagant soundstage, bold dynamics, and clear, pure sound, with effortless, exemplary microdynamics and microdetail.

When I spied the shoebox-size LKV Research PWR-3 power amplifier ($3350) at Capitol Audiofest 2021, I wondered, Could this new class-D amp deliver a solid chunk of the sonic finesse of the PWR+ amp at a third of its price?

The PWR-3, like the PWR+, is a "solid state stereo power amplifier with Purifi (footnote 2) Audio's 1ET400A class-D power amplifier modules," Hutchins wrote to me in an email. The PWR-3 is much smaller, though: Its aluminum case stands just 3.5" high, 17" wide, and 13" deep. It weighs just 17lb. Its power output is rated at 175Wpc into 8 ohms, 360Wpc into 4 ohms, and 225Wpc into 2 ohms. Voltage gain is specified as 26dB, and input impedance is 200k ohms single-ended; there are no balanced inputs.

With the PWR-3, Hutchins wanted "to bring to a much lower retail price the essential characteristics that make the PWR+ sound as good as it does."


Hutchins explained that his design approach in the PWR+ and PWR-3 combines "class-A, zero-feedback voltage-gain circuitry implemented in a differential configuration with tightly matched JFETs" with two Bruno Putzeys–designed class-D modules. "Together, these circuits solve a problem that has bedeviled designers of feedback amplifiers for many years: the loss of effectiveness of negative feedback in the upper octaves of the audio spectrum. This loss degrades high-frequency sound."

Hutchins elaborated further on his use of negative feedback. "In an amplifier employing loop negative feedback, the amplifier's contribution (or lack thereof) to the character of its sound is determined largely by the characteristics of the feedback loop," he wrote. "Specifically, that loop controls (a) the amount and type of distortion you hear, (b) the amplifier's output impedance, (c) the amplifier's output gain, and (d) the variations in frequency response created by amp/speaker interactions."

When open-loop gain is increased, I learned, open-loop distortion rises. "At the upper frequencies, where feedback weakens," Hutchins wrote, "the distortion will start to re-emerge, which can result in a pronounced hardening and sterility of the sound. Also, the effects of amp/speaker interactions on frequency response and balance become less predictable and potentially problematic."

"Until very recently," Hutchins wrote, "there was only one solution to this problem: Avoid negative feedback. But doing so negates the distortion cancellation and impedance reduction that feedback provides at lower frequencies. Audio engineer Bruno Putzeys," of Purifi, "created a solution by devising a feedback loop that maintains high, very effective levels of negative feedback up to the top of the audio spectrum. Gone is the sterility of high-frequency sound. I use this solution in my Veros PWR+ and PWR-3 amplifiers.


"For the voltage-gain circuitry," he continued, "I use my own, zero-feedback circuit, [which] delivers lifelike sound [thanks to] careful design and component matching, employing differential (balanced) circuitry, carefully hand-matched, low-noise JFETs, folded-cascode voltage biasing, current-source control, very high headroom, and extensive regulation and filtering of the low-level power rails. For the high-current output stage, I use Putzeys's Purifi 1ET400A module, which implements his breakthrough," described above. "These comprise the essential elements that create the sound of the PWR+.

"In designing the PWR-3, I eliminated as much [hardware] as possible," Hutchins continued, "but kept these two essential elements—Putzeys modules and my zero-feedback circuit—and [thereby] preserved the sound character of the PWR+ at a dramatically lower price.

"Putzeys's groundbreaking work provides an intricate, carefully calculated feedback loop that ... maintains high open-loop gain and high, relatively constant feedback throughout the audio spectrum without causing oscillation. [In the PWR+ and PWR-3], this loop creates an output stage that sends the signal from my LKV-designed JFET circuitry to the speakers without adding or subtracting (virtually) anything."

Hutchins used the same Purifi class-D modules in both the PWR+ and PWR-3. In the PWR-3, they are powered by a Hypex Switch Mode Power Supply (SMPS), replacing three heavy, expensive toroidal transformers and some other circuitry found in the PWR+. Accommodating the switch-mode power supply required "operating at lower rail voltages"; other cost-cutting measures included "greatly reducing filtering and regulation of low-level power ... and [having] all circuitry on one PCB rather than four, [as] in the PWR+," Hutchins told me.


In addition to doing away with those toroidal transformers of the PWR+, Hutchins eliminated more than half the electrolytic capacitors found in the PWR+'s power supply. Also gone are the balanced inputs, two high-quality switches, the illuminated front panel power switch, and 16 costly, low-noise rectifier diodes.

Surely, stripping away all those high-quality parts from the design would degrade the sound.

"I wasn't sure I could use a [switching power supply] and still get the high level of performance I demand," Hutchins wrote. "High-frequency switching noise does nothing good for audio circuits." When he started working on the new design, that is what he saw. "Initially, switching noise was leaking into the voltage-gain circuit, where it showed up as noise and, to some extent, distortion. But trial and error, careful tweaking of internal shielding, cable routing, and component positioning solved the problem."

The PWR+ and PWR-3 both use JFET-based circuits for voltage gain and for the driver circuitry that feeds the Purifi modules. The PWR+ has 72 hand-matched JFETs; the PWR-3, 40. But there are many similarities between Hutchins's offspring, and many shared components: JFETs, PNP and NPN transistors, 1% metal film resistors, high-quality film and electrolytic capacitors, red LEDs (used as voltage sources), various switches, and voltage regulators.

Footnote 1: The Shindo Haut Brion remains my tube reference.

Footnote 2: Purifi is a Danish audio firm building amplifiers, amplifier modules, and transducers. It was founded in 2014 by audio engineer Bruno Putzeys and direct-switching pioneer Lars Risbo.

LKV Research
19 Randall Farm Rd.
North Conway, NH 03860
(603) 730-7400

MFK's picture

Thank you for a well written and descriptive review. Did not know about In My Pocket. Wonderful, a keeper!

Jack L's picture


Southwire is the largest building wires supplier in Northern America & supplies all types of wires/cables for the civil/building constructions & to nearly all hardwares stores, e.g. Home Depot, Lowes for electrical jobbers. It got its own copper recycling plant to smelt copper from scraped cables & wires taken from dmolished buildings to make its new wires/cables.

The reason I mention it here is I would NOT use any industrial/building wires for audios. I think the Southwire solid wires used in PWR-3 should be THHN (PVC insulation + nylon outer jacket). Excellent building wires for outdoor use. For audio? sorry not for me !

Beldon also supplies tons #14 loudspeaker wires, better than Southwire building wire, IMO.

Listening is believing

Jack L

PS: Amazon also supplies Belden wires for small runs.

Jack L's picture


Yes, such "leaking' of RFI/EMI can be conductively from the SMPS hard wiring to the amp stages & AIRborne from the SMPS all over inside the amp housing.

It is practically not easy to stop the airborne RFI emiited from a SMPS unless the entire amp section were housed in conductive Faraday cage effectively grounded. I don't see such electromagnetic shielding box inside the amp to protect the amp section !!!

Yes, SMPS can be very compact in size, efficient for constant voltage/current supply & CHEAP to install, but it is a wild RF beast hard to tame.

I would never want any SMPS to be part of my audio amps to save the RF noise problem. That said, the NMH batteries for biasing all the triodes in my design/built power amp are recharged by an OUTboard SMPS. located a few feet fom the amp & is 100% electrially disconnected from the amp whenever the amp is on.

Play a smart RFI game !

Jack L

Archimago's picture

Hmmmm, you seem to be excessively phobic of SMPS.

Got some evidence to show that this is even a problem? Where is this "wild RF beast" that's "hard to tame"?

Jack L's picture


If you know how a SMPS works, you could be more "excessively phobic"" than me.

I did posted this SMPS problems in Stereophile forums a couple times before & apparently you missed reading them.

Again, SMPS is to convert the input AC (50Hz/60Hz) to DC to power any computerized equipment, digital TV & audio equipment, most commonly CD/DVD players & DAC, even audio amps.

It works on a past transistor/chip which switch between low-dissipation, full-on & full-off modes at high switching frequency up to a few MHz. Very high electrical efficiency but generate nasty EMI noise which is required to be duly suppressed in any commercial building application to prevent interferring the digital equipment inside the building.

Any SMPS emits EMI through conduction via hard wiring to the powerline hooked up to it as well as to the electronics inside the same location as in the case of the power amp under this review.

It also transmits RFI noises through the air.

With my wideband powerline & EMI noise digital analyzer, I tested EMI noise on the powerline with CD/DVD players using built-in SMPS plugged in it in several domestic & commercial locations. The digital screen showed EMI noise surges once the CD player was swithced on & none shown once the player was switched off.

This therefore also hinted me to install dedicated powerlines exclusively for analague equipment, e.g. amps, TTs & tape decks etc & exclusively for digital equipment, e.g. Cd/DVD/DAC/digital TV etc.
So no more digital-analoglue 'crosstalks".

For good music, no SMPS for me audios !

Jack L

Jack L's picture



I think the only thing I like this power amp is "gone are the balanaced inputs" - gone are the discrete bipolar junction devices/op-amp chips which built up the differential balaned inputs - better sound !!!

As I said so many times in Sterephile forums before, equal impedance balanced audio transmission is historically for landline telephone transmissions & then for auditoriums/outdoor PA installation & recording studios where miles & miles audio cables are involved.

Technically, any audio cable runs shorter than 100 feet do NOT need balanced transmission. So balanced differential inputs for any home audios are REDUNDANT let alone the undue sound impairment by the balanced circuitry electronics & additional costs ! NOT audio consumers friendly at all.

Listening is believing

Jack L

tabs's picture

The only thing notable about the PWR-3 and PWR+ is how poorly it compares to conventional Purifi 1ET400A builds despite LKV’s exorbitant prices. There is no magic here. He is buying the same Purifi amp module as everyone, but then goes and does things to it that add a bunch of distortion and poor measured performance. Among Stereophile measurements, the $2000 NAD C298 is the obvious pick for an apples to apples comparison since it also uses the same amp module. It mops the floor with even the $10,000 PWR+. This has nothing to do with using a SMPS in the PWR-3! The C298 has a SMPS and it doesn’t have any of the same problems.

The performance of Purifi is undeniable. LKV exists to coddle uninformed people who would otherwise not trust a mass-manufacturered, inexpensive, Class D (shudder the thought!) amp. LKV assembles them in New Hampshire, gives them that mysterious, home-brew audiophile look, and gives them reason to think it’s a special product with meaningful elements of the highly revered Class A topology, and then jacks up the price. Then dummies who intrinsically trust an ugly, unoptimized, $10,000 amp from a company no one’s ever heard of before over a proven groundbreaking $2k unit from NAD buy it and know at least their neighbors will never see another one like it.

Jack L's picture


I would ask the same question too !

Profiteering by "coddling uninformed people" by hook or by crook !

This is a realworld, hang on to yr wallet !

Jack L

JRT's picture

Anyone considering an amplifier utilizing Purifi Eigentakt technology...

Purifi is selling a newer Eigentakt module, 1ET7040SA. Compared to the 1ET400A the 1ET7040SA is capable of delivering higher maximum peak output current (much also depends on cooling/heatsink), 40A rather than 25A. That may be useful in driving loudspeakers exhibiting low load impedance.

There are amplifiers currently available for sale (and for review) which utilize this newer module. For example, VTV is offering a dual mono two channel amplifier (in one shared enclosure) which uses two 1ET7040SA amplifier modules, two Hypex SMPS1200A400 power supplies (which VTV marketing highlights as the same power supplies utilized by Purifi to demonstrate their module), a multitude of choices among different input board options, and various options in chassis connectors for input and ouput, and is currently priced from $1,893.00 to $2,888.00 depending on selected options. They also offer monoblocks at a higher price (for two) due to the two separate enclosures, and those are currently priced from $1,072.00 to $1,619.00, depending on selected options. Notably and disappointingly missing among VTV's input board options is Tom Christiansen's Neurochrome input board, which is well engineered with a goal of high purity, not toward adding a different nonlinear sound characteristic.

I would like to see Stereophile review that VTV amplifier or the similar separate monoblocks and compare the various input boards (so would need to enlist a reviewer capable of swapping those boards, and have VTV's assent). I would also like to see VTV offer the Neurochome input board as one of the options.

Also, Purifi may soon be selling power supplies (not Hypex power supplies), so look for those, and look to see what capacitors are utilized in those (differences in operating life, etc.).

This is not SPAM. I have no financial interest in any of this, have no affiliation with any of those selling these amplifiers and components.