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Acurus DIA-100 Direct Amplifier - $700 (Langley)
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Cosmetically, the unit is well-preserved, showing only light signs of use.
Made by Mondial Designs, the DIA-100 is celebrated for its clean, dynamic sound and straightforward design. It remains a well-regarded choice among audiophiles who value power, purity, and musicality.
(Acurus = “Accuracy of the U.S.A.” — a name that reflects the brand’s mission of delivering honest, high-fidelity sound.)
The Acurus DIA-100 is a "Direct Input Amplifier," a unique high-fidelity integrated amplifier from the 1990s that combines a high-gain power stage with a purely passive preamplifier section. Manufactured by Mondial Designs, it is highly regarded by audiophiles for its clean, transparent, and authoritative sound, often compared to separate components costing significantly more.
Key Specifications
According to Stereophile and manufacturer documentation, the DIA-100 features:
Power Output: 100 Watts per channel into 8 ohms; 150 Watts per channel into 4 ohms.
Design: Solid-state with a passive control section and a high-current output stage using Toshiba bipolar devices.
Inputs: Six line-level inputs (CD, D/A, Tuner, Aux, Tape 1, Tape 2); notably, it lacks a built-in phono stage.
Dimensions & Weight: 17" W x 5" H x 14" D; weighs approximately 35 lbs.
Damping Factor: Greater than 300, allowing it to drive taxing speaker loads effectively.
Performance and Sound Quality
Sonic Character: Reviewers from Stereophile describe it as "gutsy and upfront" with a slightly bright, forward treble that remains smooth rather than grainy.
Transparency: Because it lacks active circuitry in the preamp stage, the signal remains exceptionally clean. One user on the Polk Audio Forum noted its "sheer strength" and ability to drive speakers to loud levels with focused imaging.
Passive Preamp Trade-off: To compensate for the lack of active gain in the preamp, Acurus designed the power section to be about 20dB more sensitive than standard amplifiers.
Extract from Stereophile Jul 2008 Issue with courtesy
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.
But all it took was ten seconds into the first CD I played through the DIA 100 to realize that this Acurus integrated is not only the best-sounding pre/power combo under a thousand bucks by far, but one of the best values in all of high-end audio, period. After I'd tried countless mid-priced preamps and power amps in my Real World system, mostly to no avail, the DIA 100 immediately took the system up several full notches in sound quality. No joke: This is the best sound I've heard for the bux.
So what does it sound like? "Tube-like" is not a word I'd use to describe the DIA 100—tonally, the Acurus is gutsy and upfront, with a somewhat bright, forward character. The DIA 100's brightness isn't a hardness or graininess in the fashion of most inexpensive electronics, but an emphasis in the low to mid-treble that should be taken into consideration when matching the DIA 100 to the other components in a system. While it was never objectionable to any reasonable degree—in this price range, treble purity is almost nonexistent—the DIA 100's forward treble was its second most noticeable characteristic.
Its most noticeable characteristic was its effortless, butt-kickin' low end! In this respect, the Acurus integrated reminded me of its big brother in Mondial's line, the $1850 Class B–ranked Aragon 4004 Mk.II, which has the most authoritative butt muscle of any amplifier I've tried. The DIA 100 didn't match the Aragon for sheer power and iron-fisted slam, but it utterly annihilated the other similarly priced gear I had on hand. With the system powered by the DIA 100, bass lines had just the right sense of all-out drive and definition—Fred Frith's high-flyin' electric bass lines on Naked City's eponymous 1989 CD (Elektra 79238-2) punched and pulsed through the mix without the typical reticence and/or lack of definition of either the Rotel/Adcom or Rotel/Rotel pre/power combos. The DIA 100 also excelled in pitch definition, allowing the slightest string bends and other electric bass inflections to be heard with far greater ease than with the other inexpensive amplifications.
As the DIA 100 is basically a synergistically designed passive pre/power duo, I built up a simple passive preamp using a Bourns conductive-plastic stereo 10k pot in a small project box and connected it to Adcom's GFA-555 II 200W amplifier ($850) with 1m of Kimber's PBJ interconnect. The duo of the passive preamp and the Adcom sounded much better overall than the less expensive Adcom and Rotel amps and preamps I had on hand, with far less congestion through the midrange and a more authoritative bass range. Even so, I preferred the sound of the DIA 100 to the passive preamp linked to the GFA-555 II. The passive/Adcom duo sounded less transparent overall than the DIA 100, with a more recessed midrange and a shallower soundstage. The DIA 100 came much closer to the sound of my reference rig.
The DIA 100 was also clearly superior to its similarly priced competition in top-to-bottom cleanliness and clarity. Nothing I had on hand that was even remotely close to the DIA 100's price could match its open, transparent sound. It took the $1200 Muse Model 100, mated to Melos's SHA-1 headphone amp/line-stage ($1000) with a $62 pair of Kimber PBJ interconnects, to get a significantly better sound. And this audio assemblage is more than twice the price of the DIA 100.
Compared to the other entry-level electronics I had on hand, the DIA 100's midrange was far smoother, cleaner, and transparent—the vocals on the Fairfield Four's Standing in the Safety Zone CD came across quite cleanly, without the congestion and upper-midrange glare typical of budget electronics. I did detect a very slight bit of veiling through the lower midrange, which mainly gave vocals like the Fairfield Four's a tiny bit of gruffness. However, this slight bit of midrange veiling was much, much less audible than the gross colorations and other sonic shortcomings of the other entry-level gear I tried, and was only apparent when the DIA 100 was directly compared with more expensive components like the Muse Model 100 and the Melos line-stage.
As I said, the DIA 100's trebles sounded relatively clean, but there was a noticeable emphasis in the low to mid-treble that gave the overall sound a not-unwelcome sharpness with the Spica Angeluses. With the NHT SuperZeros, which have a more extended high end, the DIA 100's added brightness wasn't as much of a good thing. Using AudioQuest's Type 4 speaker cable instead of the more extended Kimber 4TC helped smooth out the sound of the DIA 100 when driving the NHTs, especially with brightly balanced CDs such as ex–Fabulous Thunderbirds singer/harpist Kim Wilson's Tiger Man (Antone's ANT 0023, footnote 1). Again, while the DIA 100's high end was slightly emphasized, it did not share the grain, hardness, and spit of its similarly priced competition. Despite its tipped-up treble, the DIA 100's high end was far cleaner and more transparent than anything I've heard in its price range.
The DIA 100 also had it all over the competition in throwing up a credible soundstage. I haven't been able to wring as large or as deep a soundstage from my living-room system as I have from my He-Man rig, but the DIA 100 consistently gave the Real World system a larger, more detailed soundstage than anything else in the rack. I've said it before and I'll say it again: The Roger Waters Amused to Death CD is totally LAME-O when it comes to musical value, but for sheer soundstage size it may be the current champeen. And of all the entry-level gear I had, only the DIA 100 was able to fill the room from sidewall to sidewall with a solid, three-dimensional cloud of illusory sonic imagery. The QSound images beyond the speakers' outer edges were reproduced as distinct images, while details such as the edges of the storm image as it moves from right to left on track 3 were markedly more distinct and focused than with the other electronics, which tended toward a more diffuse, less detailed rendering. Some of the other gear was able to throw up as wide a soundstage, but only the DIA 100 possessed enough image focus to precisely locate each and every detail in the CD's dense, swirling mixes.
There was a downside to the DIA 100's high level of resolution, however. Because it was able to present all the detail without obscuring it with a layer of congestion, the DIA 100 showed up the weaknesses in the various midpriced CD players to a much higher degree than with the other entry-level electronics. JVC's $850 XL-Z1050TN, for instance, enjoyed a pretty wide lead over the $450 Rotel RCD-955AX, which, while a standard-bearer at its price, had a rougher-sounding midrange, a shut-in treble range, and a more forward balance overall. The differences between the two very different-sounding CD players were much more audible with the DIA 100 than with the other electronics I tried in the chain. What this means is that merely plopping the DIA 100 into your budget rig may not be the best thing that ever happened to your system, because it's going to let you hear so much more of what your upstream gear is doing that you might find yourself racing back to your local hi-fi hut to buy a new CD player, cables, etc. And when you hear what a better CD player can do with the DIA 100, you might start to suspect that your ol' reliable speakers have now become the bottleneck of your system.
In other words: Welcome to high-end audio!!
In the court of the he-man king
The DIA 100 proved to be such a worldbeater in its price range in my Real World system that I was curious to hear how it stacked up against the time-tested reference gear in my He-Man rig.
If you've been following my Real World reviews, you know that practically none of this entry-level stuff can compete sonically with the best that's out there—nor can it fairly be expected to. The designer trying to bring in a speaker for $200/pair or an amplifier for $350 just can't begin to compete with one who's free to use better-quality parts, larger power supplies, and bigger bribes to reviewers. (JUST KIDDING! You can build a larger power supply these days for a lot less than you used to.) What the budget-minded designer can and should do, however, is try to balance out the compromises in a budget design so the product does the least harm to the music. In my experience, this is rarely accomplished—while a few products have certainly been liveable-with, none was outstanding enough sonically to make me forget whatever reference component it had displaced.
The DIA 100, however, came the closest to this trick of any entry-level piece of hi-fi gear I've tried. While I could certainly hear what it was doing to the sound of my He-Man rig, it was more than up to the high level of the rest of the system, providing true high-end sound with few real apologies.
How did it fall short? To be sure, there was a level of midrange veiling, a very slight chalkiness that the DIA 100 brought to the system when compared to the $1000 Melos SHA-1 preamp, $1850 Aragon 4004 Mk.II amplifier, and the $350/m/pair of Kimber KCAG interconnect between them. And the residual brightness of the DIA 100 was readily audible over the big NHT 3.3s, although it was less of an annoyance here than with the less expensive NHT speakers and signal sources. Instruments and vocals seemed to be pushed more forward in the soundstage than with the reference gear, although I wonder if that wasn't just the DIA 100's tipped-up balance in the low treble subjectively adding a bit of presence to the sound.
But that was about it. In most other areas of performance, the DIA 100 held its own amazingly well, considering the price differential (footnote 2). Low-end drive and definition remained outstanding. Image focus and soundstaging, while admittedly not up to the reference gear's level, were nonetheless extremely impressive, and unequaled in my experience for anywhere near the DIA 100's price.
Driving Miss Daisy's Thiels
Here's one to tell the grandkids. Midway through the review period, I got a pair of Thiel's new CS3.6es (footnote 3) in my listening room for a few weeks. The Thiels are very fine speakers, but I soon found that none of the amps I had on hand were up to driving them very loudly with any control in the bass—this was before I'd received the iron-fisted Aragon 4004 Mk.II, and before JA's measurements showed that the Thiel pretty much approximates a 2.5 ohm resistor! No wonder all the amps in my stable had such a hard time driving the CS3.6—a speaker with this low of an impedance curve, especially through the bass, can only be driven well by an amplifier with a very low output impedance and the ability to source—as JA would say—a "goodly" amount of current.
The big VTL Deluxe 225 tube amps couldn't drive the Thiels at all, sounding bloated and lifeless. The Muse amps I had on hand—the Muse Model 100 and the new Model 160—weren't able to handle the Thiels either. Even the normally hard-assed Adcom GFA-555 II blew its fuses when asked to drive the CS3.6es to minimum Rock-Approved levels. My old Dynaco Stereo 70 started crying when I came near it, so I didn't even take it off the shelf.
On a whim, I brought the DIA 100 in from the Real World system and hooked it up to the Thiels. Ta-Daaaa! NOW the Thiels came to life! For the week I spent with the Thiels until the Aragon 4004 Mk.II arrived, I left the DIA 100 hooked up to the CS3.6es, and it did a terrific job driving these difficult-load speakers to pretty ungodly levels while sounding firm, clean, and not ruffled in the slightest. For a $995 integrated to sound terrific when driving the easy load of the Spica Angeluses is one thing. But for the DIA 100 to beat out several high-end amplifiers costing between $1200 and $5000 when asked to drive a taxing load like the Thiel CS3.6 is pretty amazing performance.
Summing up
There is no other combination of preamp and amplifier on the market for under $1000 that will come closer to the best sound (available at any price) than the Acurus DIA 100. Clean, musical, and authoritative, it represents extraordinary value for the money. While its brightish but clean low treble will ruthlessly reveal weaknesses in typical budget gear upstream, the DIA 100 is refreshingly free of the kinds of gross coloration and congestion that mar so many affordable electronics. Compared with its similarly priced competitors among separate amps and preamps, the DIA 100 offers a level of sound quality unprecedented in this price range, and earns a solid Class B rating among the integrated amplifiers in Stereophile's "Recommended Components."
If the lack of a phono stage doesn't bother you and you're looking at line-stage/power-amp combos under $3000, the Acurus DIA 100 definitely belongs at the head of your must-audition list. Recommended U-Bet!
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