Solid State Power Amp Reviews

For some, it takes the likes of Scheherazade to seduce; for me, simple sound will suffice. But not just any sound. If I'm going to enter into a relationship with an audio component, I want it to last.

I don't know anyone who, having heard the JMF Audio system at AXPONA 2023—the HQS 6002 dual-mono power amplifier ($40,000; footnote 1) and PRS 1.5 dual-mono line stage preamplifier ($36,000) with Harbeth M40.3 XD speakers—did not rave about the sound. In my show report, I credited the system, assembled by Fidelis Distribution and Audio Skies, with delivering "some of the finestsounding music" I heard at the show. "This is the perfect sound for mellow music," I proclaimed. "Bliss."

Only the need to write umpteen show reports in a short span prevented me from saying more. Completely won over and hoping that JMF Audio's amplifiers would sound as good with my Wilson Audio Alexia V loudspeakers as they did with Harbeth 40.3 XDs, this serial reviewer of mono amps immediately asked Michael Vamos of Audio Skies, the US distributor of JMF Audio, if he (I) could review a pair of JMF monoblocks. The $77,000/pair JMF HQS 7001, which, according to the specifications, output 300Wpc into 8 ohms, 500Wpc into 4 ohms, and 850Wpc into 2 ohms, were the best JMF Audio amplifiers Michael could offer at the time (footnote 2). Given their power and price, they promised a near-ideal comparison with my reference Dan D'Agostino Momentum M400 MxV monoblocks, which cost $79,500/pair and are specified to output 400W into 8 ohms, 800W into 4 ohms, and 1600W into 2 ohms (footnote 3).

Background and technology
JMF Audio's website is among the most informative I've encountered. Its extensive "History" section (footnote 4) tells the company's story, explaining that the late Jean-Marie Fusilier (JMF) founded a company in 1974 to produce systems for industrial, defense, and nuclear-plant applications. Jean-Marie designed his first audio product in 1982 and began delivery as JMF Audio in 1985.

JMF Audio's early adopters included René Zingg's Soundville Studios in Lucerne, Switzerland, and Glenn Meadows's Masterfonics Studios in Nashville. Both studios were designed by Tom Hidley. More recently, Morten Lindberg of Grammy-winning label 2L began using JMF Audio's PCD 302 mains filter and power cords to make his recordings. JMF's consumer distribution was limited to Asia until Vamos's Audio Skies introduced JMF Audio electronics to North America at AXPONA 2022.

"Since the beginning, we have used a large power supply, many bipolar output transistors, high voltage for high headroom and precision, bespoke components, and unusual components such as radio-frequency semiconductors," explained Jean-Marie's son, Laurent Fusilier, at the start of a Zoom chat that Vamos also participated in. Laurent now runs the business with his brother, Arnaud.

JMF Audio's website explains in copious detail how the company's technology is implemented in the HQS 7001. Seeking to sort it all out, I asked Fusilier what he considered most important.

"The amplifiers feature a huge reserve of energy, since the large capacitors are charged to high voltages, and that energy depends on the square of the voltage. Our designs are not based on bridged mode. We make symmetrical linear power amplifiers that include a high-current output stage that drives the load. We believe that the reaction of the speakers and their counterforce is usually underestimated. In our opinion, most designers do not consider this. If the power amp cannot adequately drive this load, you don't have a high-fidelity system."

To ensure that the HQS 7001 meets the ambitious specifications the company touts, even with noisy power, a filtered, hard-wired power cable is included. One filter is inside the plug; the other sits at the entrance to the amplifier. "Our experience is that an ordinary IEC connector is too weak for the task," Fusilier said. "When you have connectors inside the amp, outside the amp, and on the cable, current must run through three different connectors. Connectors are always the weakest link. By hard-wiring the power cable, the weak points are eliminated."

Beyond the power cord, the amps are designed to reject noise. "Our balanced interfaces are hand-calibrated for great interference rejection. This results in a common-mode rejection as high as 100dB, while professional interfaces usually show less than 65dB."

Music, Fusilier emphasized, is not steady state. "This is why we give our amplifiers a huge reservoir of energy. The mains are used to charge the [power supply], which contains high-capacity, bespoke capacitors. When there are transients in the music, we don't rely on the mains. Instead, the necessary energy comes from the capacitors, which are located very close to the output; this produces tremendous instantaneous power. After the transient has been delivered, the capacitors are recharged by the mains.

"The signal path is very short, and the slew rate is high. This prevents any masking effect of the large signals on the small signals. When JMF's newly designed amplifiers were tested in Nashville, the engineers were surprised to measure no delay between input and output at 10kHz. We don't rely on a feedback loop for stability; the amplifiers are stable by design. Solid state designs normally require the addition of inductance between the output transistors and the output terminals, for stability. We don't use any. The output stages are directly linked to the output terminal through bolts and large-diameter wires; there is no connector."

Vamos: "From day one, over 40 years ago, JMF Audio has only made reference components. They're not trying to hit a price point. They only focus on making them the best. ... Unlike other companies, they spend all their energy, time, money, and research and development trying to create ultimate amplifiers to serve the music."

Apart from the technical concepts, is there an overarching principle to JMF's design? "My father's dream was universality: to play all kinds of music with fullness and faithfulness for the enjoyment of the music lovers in a broad sense," Laurent Fusilier replied. "To us, our setup was not satisfying in the early 2000s. But now I'm proud to say that my father's goal has been reached: Listeners are drawn into music as an art and forget about the technique.

"We perfect our designs mostly by auditioning classical recordings that are usually made with just a few microphones, so the soundstage is true, and the acoustic is natural. This allows us to evaluate the decay and the dynamics. With most other music, except some acoustic jazz, the soundstage is created artificially in a studio. We have found out that when a design sounds truly honest with classical music and jazz, then it works for everything. We have a partnership with Morten Lindberg's 2L, which enables us to offer a sampler of his recordings with each JMF Audio power amplifier."

JMF Audio's analog printed circuit boards feature proprietary 24K gold plating on both sides. JMF considers gold-plating optimal for natural rendering and better reproduction of nuance, so they apply the same process to connectors. In addition to the output terminals for spades and wires, the amplifiers include proprietary, 6mm-diameter JMF Audio connectors. The company says that by volume, 90% or more of the components and parts in JMF Audio products are manufactured by JMF Audio or made to the company's specifications.

Gold-plating calls for proprietary solder, which is applied by hand and requires higher temperatures. "To avoid damage, after soldering one pin we must wait for the component to cool down before continuing," Fusilier said. "It is a lengthy process."

Designs are modular to ensure maintainability and upgradability. Class-AB ensures efficiency; class-A is reserved for smaller signals that convey nuance and reverberation. "The transition from pure class-A operation is defined by the load, but pure class-A operation extends up to approximately 10W into 4 ohms," Fusilier said (footnote 5).

What you see/What I did
The visual design of JMF amps is simple. Product identifiers and lettering are engraved on the HQS 7001's front panel, top left and bottom right, and filled with rose gold. The front panel also contains a stainless steel Power button, topped by a small white LED that illumines when the amplifier is on and a small VU-meter toggle, topped by a small red LED that lights when the VU meter is engaged. Above these buttons reside two vertical rows of small LEDs. The three LEDs in the left row indicate protection status and only light up in cases of overload, DC offset, or excessively high heatsink temperatures. (They never lit up while I used the amps, and the heatsinks never felt hot.) The seven LEDs in the right row indicate input signal magnitude, in increments of three decibels: –15dB, –12dB, –9dB, and so on, up to +3dB. 0dB indicates an input voltage necessary for full output voltage. Even while playing Shostakovich and Mahler symphonies at top volume in my 16' × 20' × 9.4' room, the –12dB LEDs lit only briefly. The top five meter LEDs never lit.

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Footnote 1: HQS is JMF's acronym for "high quality sound."

Footnote 2: JMF Audio's midlevel monoblocks, they sit between the HQS 6002 dual-mono power amplifier and the topline HQS 9001 monoblocks. The HQS 9001 should be available in the US by the time you read this.

Footnote 3: One notable difference between the JMF Audio HQS 7001 and the D'Agostino M400 MxV is that the JMF includes a proprietary hard-wired power cord that the company recommends be plugged either directly into the wall or via a JMF Audio power line filter. Given the cost of the top-level power cables I use, this increases the price differential. But since different power cables sound different, the D'Agostinos offer more opportunities to tune the sound—for a price.

Footnote 4: See jmf-audio.com/history.

Footnote 5: For more information—a lot more—see jmf-audio.com/amphome.