Acurus DIA 100 integrated amplifier
By Corey Greenberg   •   November, 1993 Stereophile should start a "Personals" section in the back of the mag—maybe stick 'em in with the classifieds:

SWF ANALOG FETISHIST looking for a few good LPs. Send photo to P.O. Box 433, Indianapolis, IN.
MWM WITH TUBES seeks same for hot days and hotter nights. Reply to P.O. Box 12, Los Alamos, NM.

I mean, wouldn't that be great? Not only could we all hook up with that Special Someone a helluva lot easier than hanging around hi-fi huts with red hankies protruding from our back pockets, but we could also send messages to the manufacturers telling them what we really want in terms of hi-fi gear. And after trying to assemble a butt-kickin' Real World system of affordable audio components, I know what message I wanna send:

FRUSTRATED SWDTVHIVNWC REVIEWER looking for a pre/power amplifier combo under a thousand clams that delivers true high-end sound. Must kick butt—no fats, druggies, or 30W British integrateds need apply.

To be sure, there are several sub-thou British integrateds out there that offer excellent entry-level sound quality. I love the little $795 Creek 4140S2, for instance—I had one through here a while back and was really impressed by how downright satisfying it sounded, even when surrounded by much more expensive gear. And the Creek's got a terrific switchable MC/MM phono stage to boot—one that alone is worth the entire price of the 4140S2.

But there's one thing the sub-thou British integrateds like the Creek have in common—they don't really KICK ARSE, me lad. Usually rated around 40W, they have enough power to drive a fairly sensitive pair of loudspeakers to comfortable levels, but ask 'em to kick out the jams and they just spit up their Marmite. That might not bother some budget-minded Britophile over there listening to Morrissey purring on a pair of pipspeaks, but this lad needs a bit more steam to press his knickers.

At 100Wpc, the Acurus DIA 100 integrated amplifier has some serious steam. And at five clams shy of a kilobuck, I was eager to throw on my knickers and see what kind of steam it could spew!

Technobabble
The Acurus DIA 100 is one of those one-of-a-kind products that makes you wonder why it's one-of-a-kind. Rather than marry—like most of the sub–$1000 integrateds on the market—a cost-compromised, op-amp–based active line-stage to a similarly cost-compromised power amplifier, the DIA 100 combines a purely passive preamp and a high-gain power amplifier under the same roof.

"So WHAT!," you may not-so-politely exclaim. "Passive preamps have been around for YEARS!! You're just another tax-and-spend Democrat!! Tippycanoe and Tyler too!! CANCEL MY SUBSCRIPTION!!"

However, there are several interesting advantages to combining a passive preamp and a power amplifier in the same chassis. Since the DIA 100's passive preamp is linked internally to its power-amp section, you don't have to factor in the cost of a high-quality pair of interconnects, as you have to do with separate units. And because the DIA 100's power-amp section has around 20dB more gain than most separate amps, it makes up nicely for the lack of gain in the passive preamp. Depending on the sensitivity of the amplifier and speakers, many systems can't achieve realistic volume levels when using passive preamps. I have this problem with my own buffered passive preamp, which is also gainless—with some amps and sources, the system won't play very loudly, even with the volume control cranked all the way up.

But most importantly, the DIA 100's integrated design avoids perhaps the penultimate pandemic passive preamp pitfall. Because of a passive preamp's highish output impedance—usually around 1–2k ohms, depending on the position of the volume control—many high-end cables are high enough in capacitance that they can roll off the highs, making the system sound muffled and slow. The DIA 100 sidesteps this problem by linking its passive preamp section to the power amp with a short length of high-quality, low-capacitance cable, thereby ensuring that whatever HF rolloff that results will be well above the audible range.

Description
The Acurus DIA 100 integrated amp is a handsome, clean-looking piece of hi-fi. Sticking out from the thick, black, brushed-metal faceplate are four rounded knobs—for Volume, Balance, Listen, and Record selection. Both the Listen and Record switches allow the user to select among six identical line-level inputs, labeled CD, D/A, Tuner, Aux, Tape 1, and Tape 2. I'd like to see one of the inputs relabeled Phono Stage, but then I'd also like to see the cast of "Melrose Place" die at the hands of a confused loner. The rear panel houses the usual rows of gold-plated RCA jacks and a pair of sturdy five-way speaker binding posts per channel, as well as a nondetachable AC power cord.

Internally, the DIA 100's build quality is excellent, with a compact circuit layout and high-quality parts throughout. The volume and balance pots are both sourced from Noble, while both the Listen and Record switches feature silver-to-silver contacts. Because the DIA 100's passive preamp section uses pcb-mounted RCA jack assemblies and routes all audio signals over circuit-board traces, there's a distinct lack of the kind of eight-lane–highway wire clutter found in even the best passive preamps. Both the volume and balance pots are located within 1" of the RCA jacks, their knobs connected to the pot shafts by long extension rods that span the depth of the chassis. Thus, internal wiring is further kept to a minimum.

The DIA 100's power-amp section is said to be identical in topology to Acurus's own $995 A250 200Wpc stereo amp, although the DIA 100 is rated a bit lower: 100W into 8 ohms, 150W into 4 ohms. A single power supply feeds both of the amplifier's channels, with a good-sized toroidal power transformer and rectifier bridge smoothed by a pair of 18,000µF/70V reservoir capacitors. Two pairs each of Toshiba bipolar output devices are employed in the DIA 100's output stage, which is connected directly to the speaker posts without a series output inductor. While I was impressed by the overall build quality and design, one aspect of the DIA 100's circuit bothered me. The audio signal taken from the passive preamp section is AC-coupled at the power amp's input with a small 10µF/35V electrolytic capacitor in parallel with a 0.1µF Wima metalized polyester film cap. I was surprised to see these fairly low-grade caps in series with the audio signal, considering the DIA 100's high-end ambitions. Perhaps designer Mike Kusiak had a good reason to AC-couple the DIA 100 with these caps, but it's pretty rare nowadays to encounter a signal source with appreciable levels of DC offset. Mondial might have saved some money and possibly improved the sound by leaving these coupling caps out of the design.

Sound
In trying to find the best-sounding entry-level electronics on the market, I've been wading through some pretty rough-sounding waters. What I've had to face is that there just isn't anything in the sub–$1000 range that approaches the kind of sound quality of the gear I have in my He-Man rig. I've been listening to cheap preamps that add so much grit and congestion to the sound that I don't want to listen to music anymore. I've been listening to cheap amplifiers that either sounded so hard and hashy that I couldn't take it, or so softened and mellow that I felt like pulling a Rip van Winkle.