Parasound HCA-3500 power amplifier

Just in case you didn't know this when you bought the Parasound HCA-3500, it says on the cover of the owner's manual: "Designed in California, USA by John Curl." Described as an "audio design legend," an appellation with which he seems quite uncomfortable, John Curl has certainly been around the audio business longer than most. He's been employed by or has consulted for some of the biggest names in consumer and professional audio—including Harman/Kardon, Ampex, and Mark Levinson—and was the designer of at least two classic products: the Mark Levinson JC-2 preamplifier and his own Vendetta Research phono stage, still considered by many people to be the best phono stage ever built.


In recent years, Curl has been a consultant to Parasound, and was responsible for the revision of the Parasound HCA-2200 amplifier to Mark II status, which took it from an initial negative review in Stereophile to a Follow-Up that described it as a product that "succeeds in spades" (Vol.17 No.3). In discussing the HCA-3500, Curl is refreshingly candid and hype-free, saying that the Parasound's parts are of good quality, but not at the cost-no-object level, and admits that the amp's build quality does not rival those of Krell or Mark Levinson. He sees himself as a conservative designer, concerned with evolutionary improvement and attention to detail rather than "revolutionary" circuit topology.

Description and design
The HCA-3500's build quality may not be quite in the Krell/Levinson league, but it's hard to see how it could be better at the price. The look is more pro/industrial than audio jewelry, with an impression of solidity and toughness. This big, hefty amplifier has handles fore and aft and weighs nearly 100 lbs. Its aluminum chassis is much thicker and less resonant than that of the similarly priced Rotel RB-1090 (reviewed elsewhere in this issue). The XLR balanced input jacks are Neutriks, with two sets of gold-plated RCAs for noninverting and inverting operation, and two pairs of gold-plated 5-way binding posts of the plastic-knobbed variety. There are separate IEC AC jacks for each channel (two 12-gauge power cords are included) with two power switches, emphasizing the HCA-3500's dual-monophonic operation. Each channel has its own power supply, based on a 1.4kVA toroidal transformer and featuring 97,600µF capacitance, edging out the Rotel's 1.25kVA/88,000µF. The filter capacitors are low-ESR types, with multiple polystyrene-film bypass capacitors. The circuit boards are double-sided glass epoxy.

The HCA-3500 is a high-bias class-A/AB design, maintaining class-A operation up to 15W into 8 ohms. The circuit is direct-coupled, with no inductors or capacitors in the signal path, and features a DC servo with a 0.5Hz rolloff. The input stages are class-A, with matched J-FET pairs; the high-voltage driver stage uses hand-picked MOSFETs, and the output stage has eight complementary pairs of 15 amp/60MHz transistors per channel. Proprietary Music Activated Bias circuitry enables full bias only when music is playing. After music has stopped playing for about a minute, bias is reduced to a trickle, thus minimizing power consumption and heat.

Although the HCA-3500 includes balanced inputs, it's not an internally balanced design. There are multiple protection circuits that guard against DC at the amplifier's input, speaker impedance overload, excessive temperature buildup, and possible internal malfunction. Front-panel Left and Right channel-status indicators turn from green to red if there's a problem; the protection circuits normally reset when the fault condition is remedied.

Tracking down noise caused by ground loops in an audio system is often a tricky business. You can have a system that's perfectly quiet, and then you add a new component, and all of a sudden there's buzz/hum.

This was the case when the Parasound HCA-3500 was introduced to my system. The HCA-3500 driven by the CAT SL-1 Ultimate preamplifier resulted in what sounded like AC noise—low enough in level to be masked by music most of the time, but audible from the listening seat between CD tracks. (Mechanical hum from the transformers was exceptionally low.) The system was dead quiet with the CAT driving the Rotel RB-1090 or the Bryston 9B-ST. I tried all the usual remedies—checking connections, lifting/reconnecting AC grounds, plugging components into the same outlet/different outlets, changing interconnects—to no avail. The noise was still present when I plugged the PS Audio Ultralink Two digital processor directly into the HCA-3500, which might be taken to indicate that the problem was with the amplifier.


But when I used the Parasound AVC-2500 surround processor/preamp, the system was quiet. I eventually concluded that the problem was not due to any one component, but to the interaction between components. At this point I thought of getting hold of another high-end preamplifier, but that would have meant spending more time getting accustomed to the sound of the system with the new preamp—assuming that it did not interact negatively with the HCA-3500.

The solution came courtesy of Bryston vice president James Tanner and Bryston design engineer Stuart Taylor (the "ST" of the Bryston 9B-ST, 7B-ST, etc.). I gave James a call because I remembered that I had had a similar problem in my home-theater system, involving an early sample of the 9B-ST and a surround processor. That time, the problem was solved by Bryston modifying the amplifier's internal grounding arrangement. Would they help a rival amplifier manufacturer deal with a grounding problem?

Yes, indeed! With a spirit of cooperation that should be a model for the industry, Stuart Taylor told Parasound technical ace Andy Murray about the exact changes made to the Bryston 9B-ST that eliminated the AC noise they had encountered in some applications. Andy sent me another sample of the HCA-3500, modified as per Stuart's suggestions, and, like magic, the AC noise was gone. The amplifier also sounded a bit smoother. With this problem out of the way, I could start listening again in earnest. All comments in the review about the HCA-3500's sound refer to the second, modified sample. I'm told that all current and future production of the HCA-3500 incorporates the modified grounding scheme.

Tom Norton had used a Parasound HCA-3500 as a subwoofer amplifier to drive the Whise Profunder 624 subwoofer (reviewed in the July/August 1999 Stereophile Guide to Home Theater), and he reported that the amplifier performed exceptionally well in this role. Indeed, the HCA-3500's attribute that I found most impressive was its ability to extract bass from the speakers. With the HCA-3500 in the system, the low-frequency response of my Dunlavy SC-IV/As was about as good as I've heard: deep, tight, and powerful.

In this area, the HCA-3500's performance was clearly superior to that of the Rotel RB-1090, and seemed to essentially match the Bryston 7B-ST ($5000/pair), the previous bass champion in my system. (That is, if memory serves. I no longer had the Brystons around for direct comparison.) Heard without reference to the Parasound, the Rotel's bass was actually pretty good, but as driven by the Parasound, the Dunlavys seemed to go lower, with better control. The bass drum in the intro to "Dein ist mein ganzes Herz," on Thomas Hampson's new operetta CD (EMI 5 56758 2), sounded a bit mushy and diffuse with the Rotel, but acquired a more solid foundation and better focus when played through the Parasound. The SC-IV/A is a fairly difficult load in the bass, its impedance dropping below 4 ohms, so the HCA-3500's ability to drive this load so effectively is a testament to its excellent current capability.

Although the HCA-3500 could earn its keep as a subwoofer amp, it was certainly no one-trick pony. Performance through the rest of the frequency range, while not as outstanding as the bottom end, was never less than creditable, particularly when price is considered. The sound was wide-ranging, dynamic, detailed, and had much of the finesse that I associate with multi-$k amplifiers. The HCA-3500 provided tons of detail, and had exceptional delineation of depth information. Dynamics were outstanding, the sound of the speakers driven by the Parasound amplifier having a high "startle factor," and cranking up the volume resulted in the sound just getting louder, with no sense of dynamic compression at high levels. The Rotel RB-1090, which has a slightly higher rated power output, sounded a bit compressed at levels that the Parasound took in stride.

However, I should note that the volume levels I'm talking about were very high; I would not want to listen at such levels for more than a few minutes. At a more sensible volume, the HCA-3500 showed its dynamic capability by effectively communicating the music's ebb and flow (what some call "microdynamics").

The HCA-3500's tonal balance was generally quite neutral, the amplifier imposing little of its own sonic personality on the music—which is as it should be. When I listened to the Parasound on its own, without direct comparison to other amplifiers, I had a hard time identifying a sonic character that I could ascribe to the HCA-3500 rather than to some other component in the system.

However, over time, and with numerous comparisons between the HCA-3500 and the Rotel RB-1090, I came to feel that the Parasound had a slightly forward sound, with a bit more upper-midrange/treble grain. These characteristics showed up as a somewhat etched quality on voices, massed strings, and the upper harmonics of trumpets, making the sound ever so slightly fatiguing over time.

Although I believe that, on a comparative basis, these differences are real, they must be interpreted in a system context. The Dunlavy SC-IV/A is one of the world's most accurate reproducers of music, but I wouldn't describe its sound as inherently sweet or forgiving. If there is any kind of upper-midrange or treble hardness in the system, or indeed in the recording itself, the SC-IV/A will certainly tell you about it. The HCA-3500 would be a better match with a speaker that has a more forgiving tonal balance, such as the Aerial Acoustics 7B, which I reviewed in Stereophile in July 1999 (Vol.22 No.7).

Cost-conscious audiophiles often complain about how high-end audio seems to be dominated by products with prices that could provide a substantial down payment on a house. I think they have a point. However, what tends to get overlooked is the fact that there are also some outstandingly good buys on the market; correcting for inflation, you can get much more for your money today than you could even 10 years ago.

The Parasound HCA-3500 is a case in point. Priced at what, in a high-end context, is a very reasonable level, the HCA-3500 offers performance that in many ways approaches that of the cost-no-object blockbuster amps. The HCA-3500 scores well by almost all of the criteria important to sound reproduction, especially bass and dynamics, falling behind the competing Rotel RB-1090 only in the purity and sweetness of its upper midrange and treble. Given my priorities, the balance of virtues presented by the Rotel is closer to what I want from an amplifier, but this does not prevent me from appreciating all that the Parasound has to offer. In the right system, with speakers and other associated equipment that lean toward the sweet side of neutral, the Parasound HCA-3500 is capable of topnotch performance and represents outstanding value.

Parasound Products
950 Battery Street
San Francisco, CA 94111
(800) 822-8802