Solid State Power Amp Reviews

In December 2023, I took the train from New York to Los Angeles to attend the Los Angeles & Orange County Audiophile Society's 30th annual Gala. I took the trip because it is both stimulating and satisfying to spend an afternoon in the company of more than 200 audiophiles and music lovers; I also wanted to see John Curl presented with the Society's fourth Innovation Award, by George and Carolyn Counnas of Zesto. John was given the award "for his groundbreaking contributions to the field of solid-state audio amplifiers, circuit innovation, mastering recorders and much more."

I first met John more than 40 years ago, at a Consumer Electronics Show in Chicago, where I was blown away by John's intuitive and innovative approach to circuit design. As J. Gordon Holt wrote in his 1988 review of John's Vendetta phono preamplifier, "In the pursuit of audio perfection, Curl little comprehends the meaning of 'compromise.' His designs tend to be truly no-holds-barred, using the best components money can buy to produce the best sound and highest reliability the state of the art allows."

Along with Nelson Pass, Keith Johnson, Dan D'Agostino, and Bob Cordell, all of whom are still with us, and Charley Hansen, Bascom King, and James Bongiorno, who have passed on, John is up there in the pantheon of American designers of solid state amplification products.

After working on video recorder design at Ampex, John Curl designed and built the sound systems for The Grateful Dead's road shows, then designed the legendary Mark Levinson JC-2 preamplifier and the electronics for David Wilson's UltraMaster tape recorder. John Curl met Parasound founder Richard Schram in 1989, and since then Curl has designed all of the Bay Area company's high-power amplifiers as well as consulting on the design of the low-level circuits of many of the company's other components (footnote 1). I enjoyed a beer with John in the Buena Park Hilton's bar after the Gala. I also chatted with Parasound's new owner, David Sheriff, who had acquired the company in December 2022 following Richard Schram's retirement.

The first new product from Parasound under Sheriff's ownership is the subject of this review, the JCA100 Tribute monoblock power amplifier, which is priced at $30,000/pair. The JC in the amplifier's name stands for John Curl; A100 refers to the fact that the output stage is biased into class-A up to the maximum power of 100W into 8 ohms. "Tribute" is indeed intended as a tribute to John Curl's lifetime of achievement.

Only 100 pairs of JCA100 Tributes will be made, each set hand-assembled to order in the United States, Sheriff told me, with a lead time of 4–6 weeks from the placement of the order. Notably, a significant portion of the proceeds goes to Curl. "We are using this as an avenue to 'give back' financially to John in a meaningful way," Sheriff wrote in a follow-up email, adding that Parasound "will also be using substantial portions for scholarship seedings for future repair techs (a dying breed right now, but still much needed)."

The JCA100 Tribute
When I unpacked the amplifiers, I was somewhat surprised that, other than the "97L" and "97R" serial numbers on their front panels (footnote 2), they didn't look any different from the Parasound Halo JC 1+ monoblock that I reviewed in Stereophile's June 2020 issue. (A full description of the JC 1+'s design, components, and construction can be found in that review.) The JCA100 has an identical chassis with substantial heatsinks on the sides, the same controls and connections; it even has a "JC 1+" legend on the rear panel. I asked Sheriff if the new amplifier was based on the older amplifier.

"Correct," he responded. "We intentionally wanted people to understand that this is a limited-run, modified JC1+ tribute edition. Quite a bit of engineering and testing. We will not be offering conversions/upgrades from JC 1+ to JCA100 or JCA100 specifications."

I asked if I would be correct in writing that to manufacture a JCA100, Parasound takes a JC 1+ from its US inventory, modifies it, and replaces the front panel with the new one that has the limited-edition serial number.

"Two JC 1s get modified into the matching set, blueprinted for performance, faceplate/ears/feet swapped." Sheriff said that there will be other tribute products over the next couple of years—a preamp and a phono preamp—which can be supplied to match. "The PRE and PHONO will only be available with the serial number to the purchaser with the same serial on the JCA100s," he wrote.

The new amplifier's specifications indicate that the output stage's bias current has been increased so that the amplifier runs in class- A up to the specified power of 100W into 8 ohms. This power is much lower than the JC 1+'s maximum of 450W into that load. I asked what design decision underlay this reduction in maximum power? Were there other modifications and changes to the circuit?

Darren Myers, Parasound's new Vice President of Research and Development, explained that "the goal of this design was to create an amplifier capable of 100W of class-A operation into 8 ohms. To accomplish this, the voltage rails on the output stage were lowered, reducing the maximum voltage swing into 8 ohms compared to a stock JC 1+. This allows for a manageable amount of power dissipation on the output stage while having adequate quiescent current to achieve the 100W class-A power specification.

"To optimize this class-A operation, there are several internal modifications applied to the circuit, including transformer and component value changes. John Curl worked directly with the Parasound design team for over a year to design and optimize the modification process. John and the entire team at Parasound are so proud of what we've come up with. The outcome is truly something very special."

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Footnote 1: An interview with John Curl can be downloaded from parasound.com/pdfs/JCinterview.pdf.

Footnote 2: Sheriff chose the review samples' serial numbers to reflect the fact that Stereophile's website first saw the light of day in 1997.