I took Herb’s reviews into consideration as I went browsing for a ability amplifier to enhance my Sugden LA-4 preamplifier. The $10,000 LKV PWR+ ranked leading on my checklist. I set in a ask for to LKV Research’s majordomo, Bill Hutchins, who dispatched the substantial, 50lb PWR+ to my Greenwich Village flat for analysis.
I enjoyed the New Hampshiremade, 200Wpc (8 ohms) amplifier it became my good state/course-D reference electric power amplifier (footnote 1). The PWR+ presented an extravagant soundstage, bold dynamics, and distinct, pure audio, with easy, exemplary microdynamics and microdetail.
When I spied the shoebox-dimension LKV Analysis PWR-3 electric power amplifier ($3350) at Capitol Audiofest 2021, I wondered, Could this new class-D amp provide a stable chunk of the sonic finesse of the PWR+ amp at a third of its value?
Design and style
The PWR-3, like the PWR+, is a “sound state stereo electric power amplifier with Purifi (footnote 2) Audio’s 1ET400A course-D electric power amplifier modules,” Hutchins wrote to me in an e mail. The PWR-3 is a great deal lesser, while: Its aluminum circumstance stands just 3.5″ substantial, 17″ broad, 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 enter impedance is 200k ohms single-finished there are no balanced inputs.
With the PWR-3, Hutchins needed “to carry to a a great deal lower retail price tag the important properties that make the PWR+ audio as good as it does.”
Hutchins stated that his structure tactic in the PWR+ and PWR-3 brings together “course-A, zero-responses voltage-achieve circuitry applied in a differential configuration with tightly matched JFETs” with two Bruno Putzeysdesigned course-D modules. “Jointly, these circuits remedy a challenge that has bedeviled designers of feedback amplifiers for several yrs: the reduction of performance of adverse suggestions in the upper octaves of the audio spectrum. This reduction degrades substantial-frequency sound.”
Hutchins elaborated even more on his use of detrimental comments. “In an amplifier using loop negative suggestions, the amplifier’s contribution (or absence thereof) to the character of its sound is decided largely by the characteristics of the opinions loop,” he wrote. “Especially, that loop controls (a) the quantity and variety of distortion you hear, (b) the amplifier’s output impedance, (c) the amplifier’s output get, and (d) the variations in frequency response established by amp/speaker interactions.”
When open up-loop get is elevated, I figured out, open-loop distortion rises. “At the higher frequencies, where feed-back weakens,” Hutchins wrote, “the distortion will get started to re-emerge, which can result in a pronounced hardening and sterility of the sound. Also, the outcomes of amp/speaker interactions on frequency response and equilibrium develop into fewer predictable and likely problematic.”
“Right until very lately,” Hutchins wrote, “there was only a person option to this challenge: Prevent damaging feedback. But accomplishing so negates the distortion cancellation and impedance reduction that feed-back offers at reduce frequencies. Audio engineer Bruno Putzeys,” of Purifi, “designed a solution by devising a opinions loop that maintains high, very powerful amounts of negative suggestions up to the major of the audio spectrum. Absent is the sterility of significant-frequency seem. I use this remedy in my Veros PWR+ and PWR-3 amplifiers.
“For the voltage-achieve circuitry,” he ongoing, “I use my have, zero-feed-back circuit, [which] delivers lifelike sound [thanks to] careful style and component matching, employing differential (well balanced) circuitry, thoroughly hand-matched, low-noise JFETs, folded-cascode voltage biasing, present-day-source handle, really significant headroom, and comprehensive regulation and filtering of the minimal-degree electric power rails. For the substantial-latest output phase, I use Putzeys’s Purifi 1ET400A module, which implements his breakthrough,” explained higher than. “These comprise the critical things that develop the seem of the PWR+.
“In developing the PWR-3, I removed as considerably [hardware] as feasible,” Hutchins continued, “but stored these two crucial elementsPutzeys modules and my zero-comments circuitand [thereby] preserved the audio character of the PWR+ at a considerably decrease selling price.
“Putzeys’s groundbreaking do the job delivers an intricate, thoroughly calculated feedback loop that … maintains significant open-loop attain and substantial, rather regular suggestions throughout the audio spectrum with out producing oscillation. [In the PWR+ and PWR-3], this loop generates an output stage that sends the signal from my LKV-developed JFET circuitry to the speakers devoid of incorporating or subtracting (virtually) just about anything.”
Hutchins employed the same Purifi class-D modules in both the PWR+ and PWR-3. In the PWR-3, they are driven by a Hypex Switch Mode Electricity Source (SMPS), changing three heavy, costly toroidal transformers and some other circuitry identified in the PWR+. Accommodating the change-method energy supply necessary “working at reduce rail voltages” other charge-chopping actions integrated “drastically lessening filtering and regulation of minimal-level ability … and [having] all circuitry on one PCB rather than 4, [as] in the PWR+,” Hutchins instructed me.
In addition to undertaking absent with people toroidal transformers of the PWR+, Hutchins removed more than half the electrolytic capacitors located in the PWR+’s energy provide. Also absent are the balanced inputs, two high-top quality switches, the illuminated entrance panel energy swap, and 16 high priced, reduced-noise rectifier diodes.
Absolutely, stripping away all these high-excellent components from the layout would degrade the seem.
“I was not absolutely sure I could use a [switching power supply] and nevertheless get the significant amount of general performance I demand,” Hutchins wrote. “Superior-frequency switching noise does absolutely nothing very good for audio circuits.” When he started out performing on the new structure, that is what he noticed. “At first, switching sounds was leaking into the voltage-obtain circuit, wherever it showed up as sounds and, to some extent, distortion. But trial and error, very careful tweaking of inner shielding, cable routing, and ingredient positioning solved the problem.”
The PWR+ and PWR-3 both of those use JFET-centered circuits for voltage acquire and for the driver circuitry that feeds the Purifi modules. The PWR+ has 72 hand-matched JFETs the PWR-3, 40. But there are a lot of similarities concerning Hutchins’s offspring, and numerous shared parts: JFETs, PNP and NPN transistors, 1% steel film resistors, significant-high-quality film and electrolytic capacitors, purple LEDs (utilized as voltage resources), many switches, and voltage regulators.
Footnote 1: The Shindo Haut Brion remains my tube reference.
Footnote 2: Purifi is a Danish audio firm developing amplifiers, amplifier modules, and transducers. It was established in 2014 by audio engineer Bruno Putzeys and immediate-switching pioneer Lars Risbo.